Quantum Physics
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Showing new listings for Friday, 22 November 2024
- [1] arXiv:2411.13643 [pdf, html, other]
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Title: Emergent disorder and sub-ballistic dynamics in quantum simulations of the Ising model using Rydberg atom arraysComments: 5 pages, 4 figuresSubjects: Quantum Physics (quant-ph); Quantum Gases (cond-mat.quant-gas); Statistical Mechanics (cond-mat.stat-mech)
Rydberg atom arrays with Van der Waals interactions provide a controllable path to simulate the locally connected transverse-field Ising model (TFIM), a prototypical model in statistical mechanics. Remotely operating the publicly accessible Aquila Rydberg atom array, we experimentally investigate the physics of TFIM far from equilibrium and uncover significant deviations from the theoretical predictions. Rather than the expected ballistic spread of correlations, the Rydberg simulator exhibits a sub-ballistic spread, along with a logarithmic scaling of entanglement entropy in time - all while the system mostly retains its initial magnetization. By modeling the atom motion in tweezer traps, we trace these effects to an emergent natural disorder in Rydberg atom arrays, which we characterize with a minimal random spin model. We further experimentally explore the different dynamical regimes hosted in the system by varying the lattice spacing and the Rabi frequency. Our findings highlight the crucial role of atom motion in the many-body dynamics of Rydberg atom arrays at the TFIM limit, and propose simple benchmark measurements to test for its presence in future experiments.
- [2] arXiv:2411.13661 [pdf, html, other]
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Title: Non-Bloch self-energy of dissipative interacting fermionsComments: 7+5 pages, 3+1 figuresSubjects: Quantum Physics (quant-ph); Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el); Optics (physics.optics)
The non-Hermitian skin effect describes the phenomenon of exponential localization of single-particle eigenstates near the boundary of the system. We explore its generalization to the many-body regime by investigating interacting fermions in open quantum systems. Therein, the elementary excitations from the ``vacuum'' (steady state) are given by two types of dissipative quasi-particles composed of single-fermion operators. We perturbatively calculate the self-energy of these quasi-particles in the presence of interactions, and utilize the non-Bloch band theory to develop an exact integral formula, which is further simplified by imposing complex momentum conservation. The formula allows calculating the Liouvillian gap modified by interactions with high precision, as demonstrated by comparison to numerical results. Furthermore, our results show that interactions can even enhance the non-reciprocity of fermion hoppings, contrary to the conventional viewpoint from the Pauli exclusion principle. Our formulation provides a quantitative tool for investigating dissipative interacting fermions with non-Hermitian skin effect, and generalizes the Fermi liquid theory to open quantum systems in the context of diagrammatic perturbation theory.
- [3] arXiv:2411.13667 [pdf, html, other]
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Title: Entanglement growth in the dark intervals of a locally monitored free-fermion chainComments: 11 pages, 8 figuresSubjects: Quantum Physics (quant-ph); Disordered Systems and Neural Networks (cond-mat.dis-nn); Statistical Mechanics (cond-mat.stat-mech)
We consider a free fermionic chain with monitoring of the particle density on a single site of the chain and study the entanglement dynamics of quantum jump trajectories. We show that the entanglement entropy grows in time towards a stationary state which display volume law scaling of the entropy, in stark contrast with both the unitary dynamics after a local quench and the no-click limit corresponding to full post-selection. We explain the extensive entanglement growth as a consequence of the peculiar distribution of quantum jumps in time, which display superpoissonian waiting time distribution characterised by a bunching of quantum jumps followed by long dark intervals where no-clicks are detected, akin to the distribution of fluorescence light in a driven atom. We show that the presence of dark intervals is the key feature to explain the effect and that by increasing the number of sites which are monitored the volume law scaling gives away to the Zeno effect and its associated area law.
- [4] arXiv:2411.13669 [pdf, html, other]
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Title: Quantum Algorithm for Vibronic Dynamics: Case Study on Singlet Fission Solar Cell DesignDanial Motlagh, Robert A. Lang, Jorge A. Campos-Gonzalez-Angulo, Tao Zeng, Alan Aspuru-Guzik, Juan Miguel ArrazolaSubjects: Quantum Physics (quant-ph)
Vibronic interactions between nuclear motion and electronic states are critical for the accurate modeling of photochemistry. However, accurate simulations of fully quantum non-adiabatic dynamics are often prohibitively expensive for classical methods beyond small systems. In this work, we present a quantum algorithm based on product formulas for simulating time evolution under a general vibronic Hamiltonian in real space, capable of handling an arbitrary number of electronic states and vibrational modes. We develop the first trotterization scheme for vibronic Hamiltonians beyond two electronic states and introduce an array of optimization techniques for the exponentiation of each fragment in the product formula, resulting in a remarkably low cost of implementation. To demonstrate practical relevance, we outline a proof-of-principle integration of our algorithm into a materials discovery pipeline for designing more efficient singlet fission-based organic solar cells. Based on commutator bounds, we estimate that a $100$ femtosecond evolution using a second-order Trotter product formula of a $4$-state model of an anthracene-fullerene interface requires $117$ qubits and $1.5 \times 10^7$ Toffoli gates in a reduced dimensionality of $11$ modes. In its full dimensionality of $246$ modes, it requires $1065$ qubits and $2.7 \times 10^9$ Toffoli gates.
- [5] arXiv:2411.13712 [pdf, html, other]
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Title: Self-testing quantum randomness expansion on an integrated photonic chipGong Zhang, Ignatius William Primaatmaja, Yue Chen, Si Qi Ng, Hong Jie Ng, Marco Pistoia, Xiao Gong, Koon Tong Goh, Chao Wang, Charles LimComments: 15 Pages, 5 Figures, and 2 TablesSubjects: Quantum Physics (quant-ph)
The power of quantum random number generation is more than just the ability to create truly random numbers$\unicode{x2013}$it can also enable self-testing, which allows the user to verify the implementation integrity of certain critical quantum components with minimal assumptions. In this work, we develop and implement a self-testing quantum random number generator (QRNG) chipset capable of generating 15.33 Mbits of certifiable randomness in each run (an expansion rate of $5.11\times 10^{-4}$ at a repetition rate of 10 Mhz). The chip design is based on a highly loss-and-noise tolerant measurement-device-independent protocol, where random coherent states encoded using quadrature phase shift keying are used to self-test the quantum homodyne detection unit: well-known to be challenging to characterise in practice. Importantly, this proposal opens up the possibility to implement miniaturised self-testing QRNG devices at production scale using standard silicon photonics foundry platforms.
- [6] arXiv:2411.13737 [pdf, html, other]
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Title: Quantum Friction near the Instability ThresholdSubjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
In this work, we develop an analytical framework to understand quantum friction across distinct stability regimes, providing approximate expressions for frictional forces both in the deep stable regime and near the critical threshold of instability. Our primary finding is analytical proof that, near the instability threshold, the quantum friction force diverges logarithmically. This result, verified through numerical simulations, sheds light on the behavior of frictional instabilities as the system approaches criticality.
Our findings offer new insights into the role of instabilities, critical divergence and temperature in frictional dynamics across quantum and classical regimes. - [7] arXiv:2411.13739 [pdf, html, other]
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Title: Conditional t-independent spectral gap for random quantum circuits and implications for t-design depthsComments: 53 pages, 6 figuresSubjects: Quantum Physics (quant-ph); Computational Physics (physics.comp-ph)
A fundamental question is understanding the rate at which random quantum circuits converge to the Haar measure. One quantity which is important in establishing this rate is the spectral gap of a random quantum ensemble. In this work we establish a new bound on the spectral gap of the t-th moment of a one-dimensional brickwork architecture on N qudits. This bound is independent of both t and N, provided t does not exceed the qudit dimension q. We also show that the bound is nearly optimal. The improved spectral gaps gives large improvements to the constant factors in known results on the approximate t-design depths of the 1D brickwork, of generic circuit architectures, and of specially-constructed architectures which scramble in depth O(log N). We moreover show that the spectral gap gives the dominant epsilon-dependence of the t-design depth at small epsilon. Our spectral gap bound is obtained by bounding the N-site 1D brickwork architecture by the spectra of 3-site operators. We then exploit a block-triangular hierarchy and a global symmetry in these operators in order to efficiently bound them. The technical methods used are a qualitatively different approach for bounding spectral gaps and and have little in common with previous techniques.
- [8] arXiv:2411.13742 [pdf, html, other]
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Title: Benchmarking a wide range of optimisers for solving the Fermi-Hubbard model using the variational quantum eigensolverComments: 42 pages, 30 figures. Associated data can be found at this https URLSubjects: Quantum Physics (quant-ph); Machine Learning (cs.LG); Neural and Evolutionary Computing (cs.NE)
We numerically benchmark 30 optimisers on 372 instances of the variational quantum eigensolver for solving the Fermi-Hubbard system with the Hamiltonian variational ansatz. We rank the optimisers with respect to metrics such as final energy achieved and function calls needed to get within a certain tolerance level, and find that the best performing optimisers are variants of gradient descent such as Momentum and ADAM (using finite difference), SPSA, CMAES, and BayesMGD. We also perform gradient analysis and observe that the step size for finite difference has a very significant impact. We also consider using simultaneous perturbation (inspired by SPSA) as a gradient subroutine: here finite difference can lead to a more precise estimate of the ground state but uses more calls, whereas simultaneous perturbation can converge quicker but may be less precise in the later stages. Finally, we also study the quantum natural gradient algorithm: we implement this method for 1-dimensional Fermi-Hubbard systems, and find that whilst it can reach a lower energy with fewer iterations, this improvement is typically lost when taking total function calls into account. Our method involves performing careful hyperparameter sweeping on 4 instances. We present a variety of analysis and figures, detailed optimiser notes, and discuss future directions.
- [9] arXiv:2411.13761 [pdf, html, other]
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Title: Statistical permutation quantifiers in the classical transition of conservative-dissipative systemsComments: 17 pages, 6 figuresSubjects: Quantum Physics (quant-ph)
We study the behavior of a nonlinear semiclassical system using Shannon entropy and two approaches to statistical complexity. These systems involve the interaction between classical variables (representing the environment) and quantum ones. Both conservative and dissipative regimes are explored. To calculate the information metrics, probability distributions are derived from the temporal evolution via the Bandt-Pompe permutation method. Additionally, we describe the classical limit in terms of a motion invariant linked to the uncertainty principle. Our analysis reveals three distinct regions, including a mesoscopic one, along with other notable findings.
- [10] arXiv:2411.13831 [pdf, html, other]
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Title: Characterizing the transition from topology to chaos in a kicked quantum systemComments: 9 pages, 5 figuresSubjects: Quantum Physics (quant-ph)
This work theoretically investigates the transition from topology to chaos in a periodically driven system consisting of a quantum top coupled to a spin-1/2 particle. The system is driven by two alternating interaction kicks per period. For small kick strengths, localized topologically protected bound states exist, and as the kick strengths increase, these states proliferate. However, at large kick strengths they gradually delocalize in stages, eventually becoming random orthonormal vectors as chaos emerges. We identify the delocalization of the bound states as a finite size effect where their proliferation leads to their eventual overlap. This insight allows us to make analytic predictions for the onset and full emergence of chaos which are supported by numerical results of the quasi-energy level spacing ratio and Rényi entropy. A dynamical probe is also proposed to distinguish chaotic from regular behavior.
- [11] arXiv:2411.13863 [pdf, html, other]
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Title: Unusual crosstalk in coincidence measurement searches for quantum degeneracyComments: 6 pages, 4 figuresSubjects: Quantum Physics (quant-ph)
A dip in coincidence peaks for an electron beam is an experimental signature to detect Coulomb repulsion and Pauli pressure. This paper discusses another effect that can produce a similar signature but that does not originate from the properties of the physical system under scrutiny. Instead, the detectors and electronics used to measure those coincidences suffer significantly even from weak crosstalk. A simple model that explains our experimental observations is given. Furthermore we provide an experimental approach to correct for this type of crosstalk.
- [12] arXiv:2411.13905 [pdf, html, other]
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Title: The transfer of Bell nonlocality between two and three-qubit dissipative systems with counter-rotating-wave termsComments: 10 pages, 7 figuresSubjects: Quantum Physics (quant-ph)
We investigate the effect of counter-rotating-wave terms on bell nonlocality (BN) and entanglement for three qubits coupled with a Lorentz-broadened cavity mode at zero temperature for strong and ultrastrong coupling regimes by employing exact numerical hierarchical equations of motion approach (HEOM). Our findings are as follows: (i) the counter-rotating wave terms significantly increase the rate of decoherence in the three-qubit system; (ii) a consistent transfer of Bell nonlocality between the three-qubit state and its subsystem is observed when the interaction between the qubits and the bath is asymmetrical, which provides effective numerical evidence for the monogamy and complementarity of multipartite nonlocality; (iii) the counter-rotating wave terms can enhance genuine tripartite nonlocality in the qubit system; and (iv) these terms do not significantly generate three-party correlations in zero-excitation cases, which differs from previous studies involving two qubits.
- [13] arXiv:2411.13920 [pdf, html, other]
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Title: iHQGAN: A Lightweight Invertible Hybrid Quantum-Classical Generative Adversarial Network for Unsupervised Image-to-Image TranslationXue Yang, Rigui Zhou, ShiZheng Jia, YaoChong Li, Jicheng Yan, ZhengYu Long, Wenyu Guo, Fuhui Xiong, Wenshan XuSubjects: Quantum Physics (quant-ph)
Leveraging quantum computing's intrinsic properties to enhance machine learning has shown promise, with quantum generative adversarial networks (QGANs) demonstrating benefits in data generation. However, the application of QGANs to complex unsupervised image-to-image (I2I) translation remains unexplored. Moreover,classical neural networks often suffer from large parameter spaces, posing challenges for GAN-based I2I methods. Inspired by the fact that unsupervised I2I translation is essentially an approximate reversible problem, we propose a lightweight invertible hybrid quantum-classical unsupervised I2I translation model - iHQGAN, by harnessing the invertibility of quantum computing. Specifically,iHQGAN employs two mutually approximately reversible quantum generators with shared parameters, effectively reducing the parameter scale. To ensure content consistency between generated and source images, each quantum generator is paired with an assisted classical neural network (ACNN), enforcing a unidirectional cycle consistency constraint between them. Simulation experiments were conducted on 19 sub-datasets across three tasks. Qualitative and quantitative assessments indicate that iHQGAN effectively performs unsupervised I2I translation with excellent generalization and can outperform classical methods that use low-complexity CNN-based generators. Additionally, iHQGAN, as with classical reversible methods, reduces the parameter scale of classical irreversible methods via a reversible this http URL study presents the first versatile quantum solution for unsupervised I2I translation, extending QGAN research to more complex image generation scenarios and offering a quantum approach to decrease the parameters of GAN-based unsupervised I2I translation methods.
- [14] arXiv:2411.13943 [pdf, other]
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Title: Independent Optical Frequency Combs Powered 546 km Field Test of Twin-Field Quantum Key DistributionLai Zhou, Jinping Lin, Chengfang Ge, Yuanbin Fan, Zhiliang Yuan, Hao Dong, Yang Liu, Di Ma, Jiu-Peng Chen, Cong Jiang, Xiang-Bin Wang, Li-Xing You, Qiang Zhang, Jian-Wei PanComments: To appear in Physical Review AppliedSubjects: Quantum Physics (quant-ph); Applied Physics (physics.app-ph); Optics (physics.optics)
Owing to its repeater-like rate-loss scaling, twin-field quantum key distribution (TF-QKD) has repeatedly exhibited in laboratory its superiority for secure communication over record fiber lengths. Field trials pose a new set of challenges however, which must be addressed before the technology's roll-out into real-world. Here, we verify in field the viability of using independent optical frequency combs -- installed at sites separated by a straight-line distance of 300~km -- to achieve a versatile TF-QKD setup that has no need for optical frequency dissemination and thus enables an open and network-friendly fiber configuration. Over 546 and 603 km symmetric links, we record a finite-size secure key rate (SKR) of 0.53~bit/s and an asymptotic SKR of 0.12 bit/s, respectively. Of practical importance, the setup is demonstrated to support 44~km fiber asymmetry in the 452 km link. Our work marks an important step towards incorporation of long-haul fiber links into large quantum networks.
- [15] arXiv:2411.13948 [pdf, html, other]
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Title: Quantum key distribution with imperfectly isolated devicesXoel Sixto, Álvaro Navarrete, Margarida Pereira, Guillermo Currás-Lorenzo, Kiyoshi Tamaki, Marcos CurtyComments: 18 pages, 10 figuresSubjects: Quantum Physics (quant-ph)
Most security proofs of quantum key distribution (QKD) assume that there is no unwanted information leakage about the state preparation process. However, this assumption is impossible to guarantee in practice, as QKD systems can leak information to the channel due to device imperfections or the active action of an eavesdropper. Here, we solve this pressing issue by introducing a security proof in the presence of information leakage from all state preparation settings for arguably the most popular QKD scheme, namely the decoy-state BB84 protocol. The proof requires minimal experimental characterization, as only a single parameter related to the isolation of the source needs to be determined, thus providing a clear path for bridging the gap between theory and practice. Moreover, if information about the state of the side channels is available, this can be readily incorporated into the analysis to further improve the resulting performance.
- [16] arXiv:2411.13955 [pdf, html, other]
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Title: A silicon-based ion trap chip protected from semiconductor chargingDaun Chung, Kwangyeul Choi, Woojun Lee, Chiyoon Kim, Hosung Shon, Jeonghyun Park, Beomgeun Cho, Kyungmin Lee, Suhan Kim, Seungwoo Yoo, Eui Hwan Jung, Changhyun Jung, Jiyong Kang, Kyunghye Kim, Roberts Berkis, Tracy Northup, Dong-Il "Dan'' Cho, Taehyun KimSubjects: Quantum Physics (quant-ph)
Silicon-based ion trap chips can benefit from existing advanced fabrication technologies, such as multi-metal layer techniques for two-dimensional architectures and silicon photonics for the integration of on-chip optical components. However, the scalability of these technologies may be compromised by semiconductor charging, where photogenerated charge carriers produce electric potentials that disrupt ion motion. Inspired by recent studies on charge distribution mechanisms in semiconductors, we developed a silicon-based chip with gold coated on all exposed silicon surfaces. This modification significantly stabilized ion motion compared to a chip without such metallic shielding, a result that underscores the detrimental effects of exposed silicon. With the mitigation of background silicon-induced fields to negligible levels, quantum operations such as sideband cooling and two-ion entangling gates, which were previously infeasible with the unshielded chip, can now be implemented.
- [17] arXiv:2411.14037 [pdf, html, other]
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Title: ZAP: Zoned Architecture and Parallelizable Compiler for Field Programmable Atom ArrayComments: 10 pages, 7 figuresSubjects: Quantum Physics (quant-ph)
Neutral atom quantum computing platforms have gained significant attention due to their potential scalability and flexibility in qubit arrangement. In this work, we present a novel zoned architecture for neutral atom quantum compilation, which divides the system into distinct zones: a storage zone and an interaction zone. This architecture optimizes atom placement and interaction scheduling, effectively reducing the operation depth and improving parallelism during compilation. Through a tailored algorithmic approach, we significantly enhance the compilation efficiency and scalability compared to existing methods. Compared to the state-of-the-art Enola platform, our method achieves a 5.4x increase in fidelity when the system need 100 qubits, marking a pivotal advancement in neutral atom quantum computing. Our approach provides a robust framework for future large-scale quantum computations, ensuring both high fidelity and efficient execution.
- [18] arXiv:2411.14043 [pdf, html, other]
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Title: From classical probability densities to quantum states: quantization of Gaussian for arbitrary orderingsComments: 16 Pages, one figureSubjects: Quantum Physics (quant-ph); High Energy Physics - Theory (hep-th); Mathematical Physics (math-ph)
The primary focus of this work is to investigate how the most emblematic classical probability density, namely a Gaussian, can be mapped to a valid quantum states. To explore this issue, we consider a Gaussian whose squared variance depends on a parameter $\lambda$. Specifically, depending on the value of $\lambda$, we study what happens in the classical-quantum correspondence as we change the indeterminacy of the classical particle. Furthermore, finding a correspondence between a classical state and a quantum state is not a trivial task. Quantum observables, described by Hermitian operators, do not generally commute, so a precise ordering must be introduced to resolve this ambiguity. In this work, we study two different arbitrary orderings: the first is an arbitrary ordering of the position and momentum observables; the second, which is the main focus of the present work, is an arbitrary ordering of the annihilation and creation operators. In this latter case, we find the interesting result that even a $\delta$-function, which in general has no quantum correspondence, can be mapped into a valid quantum state for a particular ordering, specifically the antinormal one (all creation operators are to the right of all annihilation operators in the product). This means that the Gaussian probability density corresponds to a valid quantum state, regardless of how localized classical particles are in phase space.
- [19] arXiv:2411.14065 [pdf, html, other]
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Title: Rabi oscillation and fractional population via the bound states in the continuum in a giant atom waveguide QED setupComments: 10 pages, 4 figures, All the comments are welcomedSubjects: Quantum Physics (quant-ph)
We study the dynamics of two giant atoms interacting with a coupled resonator waveguide (CRW) beyond the Markovian approximation. The distinct atomic configurations determine the number of bound states in the continuum (BIC), leading to different dynamical behaviors. Our results show that when the system supports two BICs, Rabi oscillations dominate the dynamics, whereas fractional population dynamics emerge in the presence of a single BIC. The connection between these dynamics and the existence of BICs is further verified by analyzing the photonic distribution in the CRW during time evolution. These findings challenge the conventional notion that the environment always induces dissipation and decoherence. Instead, the bound states in the CRW-emitters coupled system can suppress complete dissipation of the emitters. This work offers an effective approach for controlling dissipative dynamics in open quantum systems.
- [20] arXiv:2411.14074 [pdf, other]
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Title: Super-Extensive Scaling in 1D Spin$-1/2$ $XY-\Gamma(\gamma)$ Chain Quantum BatteryAsad Ali, Samira Elghaayda, Saif Al-Kuwari, M.I. Hussain, M.T. Rahim, H. Kuniyil, C. Seuda, A. El Allati, M. Mansour, S. HaddadiComments: 12 pages, 9 figures. All comments are welcomeSubjects: Quantum Physics (quant-ph)
We investigate the performance of a one-dimensional (1D) spin-$1/2$ Heisenberg $XY-\Gamma(\gamma)$ quantum chain as a working medium for a quantum battery (QB) and analyze both closed and open system scenarios. The closed QB scenario is explored by analytically evaluating ergotropy across different spin-spin couplings, anisotropies in spin interactions, Zeeman field strengths, charging field intensities, $\Gamma$ interactions, and temperature. Results indicate that ergotropy is highly dependent on spin-spin coupling and anisotropy. Under variable parameters, an increase in the spin-spin coupling strength displays quenches and exhibits non-equilibrium trends in ergotropy. After a quench, ergotropy may experience a sharp increase or drop -- suggesting optimal operational conditions for QB performance. In the open QB scenario, we examine spin chains of sizes $2 \leq N \leq 8$ under the influence of dephasing, focusing on the evolution of ergotropy. We study two charging schemes: parallel charging, where spins are non-interacting, and collective charging, involving spin-spin coupling. In the former, increased Zeeman field strength enhances both the peak ergotropy and charging rate, although without any quantum advantage or super-extensive scaling. In the latter, increasing spin-spin coupling might not achieve super-extensive scaling without introducing anisotropy in the spin-spin interaction. Our results suggest that optimal QB performance and a quantum advantage in scaling can be achieved by leveraging anisotropic spin-spin couplings and non-zero $\Gamma$ interactions, allowing for faster charging and higher ergotropy under super-extensive scaling conditions up to $\alpha=1.24$ for the given size of the spin chain.
- [21] arXiv:2411.14076 [pdf, html, other]
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Title: Sample space filling analysis for boson sampling validationSubjects: Quantum Physics (quant-ph)
Achieving a quantum computational advantage regime, and thus providing evidence against the extended Church-Turing thesis, remains one of the key challenges of modern science. Boson sampling seems to be a very promising platform in this regard, but to be confident of attaining the advantage regime, one must provide evidence of operating with a correct boson sampling distribution, rather than with a pathological classically simulatable one. This problem is often called the validation problem, and it poses a major challenge to demonstrating unambiguous quantum advantage. In this work, using the recently proposed wave function network approach, we study the sample space filling behavior with increasing the number of collected samples. We show that due to the intrinsic nature of the boson sampling wave function, its filling behavior can be computationally efficiently distinguished from classically simulated cases. Therefore, we propose a new validation protocol based on the sample space filling analysis and test it for problems of up to $20$ photons injected into a $400$-mode interferometer. Due to its simplicity and computational efficiency, it can be used among other protocols to validate future experiments to provide more convincing results.
- [22] arXiv:2411.14096 [pdf, html, other]
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Title: A Hybrid Qubit Encoding: Splitting Fock Space into Fermionic and Bosonic SubspacesSubjects: Quantum Physics (quant-ph)
Efficient encoding of electronic operators into qubits is essential for quantum chemistry simulations. The majority of methods map single electron states to qubits, effectively handling electron interactions. Alternatively, pairs of electrons can be represented as quasi-particles and encoded into qubits, significantly simplifying calculations. This work presents a hybrid encoding that allows splitting the Fock space into Fermionic and Bosonic subspaces. By leveraging the strengths of both approaches, we provide a flexible framework for optimizing quantum simulations based on molecular characteristics and hardware constraints.
- [23] arXiv:2411.14098 [pdf, html, other]
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Title: Strongly Confined Atomic Excitation Localization in a Weakly-Driven Atom-Waveguide InterfaceComments: 8 figuresSubjects: Quantum Physics (quant-ph)
An atomic array coupled to a photonic crystal waveguide forms a strongly coupled quantum interface, exhibiting various intriguing collective features of quantum dynamics. Here we consider a homogeneous atomic array and theoretically investigate its steady-state distribution when the incident fields drive the atoms from both sides at asymmetric angles. This effectively creates an interface shared by two zones of atoms under different driving angles. This setup introduces a competition between photon-mediated dipole-dipole interactions and the directionality of coupling, while differences of the travelling phases from the incident angles further influence the overall steady-state behavior. Under this asymmetric driving scheme, the presence of strongly confined localization can be identified, where localization can occur either at the interface or at one of edges. Additionally, we examine the size effect on the atomic localization, deriving an empirical formula to predict parameter regimes that favor interfaced localization. We also consider a defect-driving scheme, where a third zone is created by undriven atoms under symmetric travelling phases. This results in strongly confined single-site excitation localization, which can be explained through analytical solutions under the reciprocal coupling. Finally, we propose several methods for precise control of multiple single-site localizations under the defect-driving scheme. Our results provide insights into driven-dissipative quantum systems with nonreciprocal couplings and pave the way for quantum simulation of exotic many-body states relevant to quantum information applications.
- [24] arXiv:2411.14148 [pdf, html, other]
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Title: Generating entangled pairs of vortex photons via induced emissionSubjects: Quantum Physics (quant-ph)
Pairs of entangled vortex photons can promise new prospects of application in quantum computing and cryptography. We investigate the possibility of generating such states via two-level atom emission stimulated by a single photon wave packet with a definite total angular momentum (TAM). The entangled pair produced in this process possesses well-defined mean TAM with the TAM variation being much smaller than $\hbar$. On top of that, the variation exponentially decreases with the increase in TAM of the incident photon. Our model allows one to track the time evolution of the state of the entangled pair. An experimentally feasible scenario is assumed, in which the incident photon interacts with a spatially confined atomic target. We conclude that induced emission can be used as a source of entangled vortex photons with applications in atomic physics experiments, quantum optics, and quantum information sciences.
- [25] arXiv:2411.14204 [pdf, html, other]
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Title: Exact solution for a class of quantum models of interacting bosonsComments: 11 pages, no figuresSubjects: Quantum Physics (quant-ph); Quantum Gases (cond-mat.quant-gas); Mathematical Physics (math-ph); Exactly Solvable and Integrable Systems (nlin.SI)
Quantum models of interacting bosons have wide range of applications, among them the propagation of optical modes in nonlinear media, such as the $k$-photon down conversion. Many of such models are related to nonlinear deformations of finite group algebras, thus, in this sense, they are exactly solvable. Whereas the advanced group-theoretic methods have been developed to study the eigenvalue spectrum of exactly solvable Hamiltonians, in quantum optics the prime interest is not the spectrum of the Hamiltonian, but the evolution of an initial state, such as the generation of optical signal modes by a strong pump mode propagating in a nonlinear medium. I propose a simple and general method of derivation of the solution to such a state evolution problem, applicable to a wide class of quantum models of interacting bosons. For the $k$-photon down conversion model and its generalizations, the solution to the state evolution problem is given in the form of an infinite series expansion in the powers of propagation time with the coefficients defined by a recursion relation with a single polynomial function, unique for each nonlinear model. As an application, I compare the exact solution to the parametric down conversion process with the semiclassical parametric approximation.
- [26] arXiv:2411.14210 [pdf, html, other]
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Title: Post-selected von Neumann Measurement with Superpositions of Orbital-Angular-Momentum Pointer StatesSubjects: Quantum Physics (quant-ph)
We investigated an orbital angular momentum (OAM) pointer within the framework of von Neumann measurements and discovered its significant impact on optimizing superpositions of Gaussian and Laguerre-Gaussian (LG) states. Calculations of the quadrature squeezing, the second-order cross-correlation function, the Wigner function, and the signal-to-noise ratio (SNR) support our findings. Specifically, by carefully selecting the anomalous weak value and the coupling strength between the measured system and the pointer, we demonstrated that the initial Gaussian state transforms into a non-Gaussian state after postselection. This transition highlights the potential of OAM pointers in enhancing the performance of quantum systems by tailoring state properties for specific applications.
- [27] arXiv:2411.14259 [pdf, html, other]
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Title: Addressing the Readout Problem in Quantum Differential Equation Algorithms with Quantum Scientific Machine LearningComments: 5 pages, 4 figuresSubjects: Quantum Physics (quant-ph); Disordered Systems and Neural Networks (cond-mat.dis-nn); Fluid Dynamics (physics.flu-dyn)
Quantum differential equation solvers aim to prepare solutions as $n$-qubit quantum states over a fine grid of $O(2^n)$ points, surpassing the linear scaling of classical solvers. However, unlike classically stored vectors of solutions, the readout of exact quantum states poses a bottleneck due to the complexity of tomography. Here, we show that the readout problem can be addressed with quantum learning tools where we focus on distilling the relevant features. Treating outputs of quantum differential equation solvers as quantum data, we demonstrate that low-dimensional output can be extracted using a measurement operator adapted to detect relevant features. We apply this quantum scientific machine learning approach to classify solutions for shock wave detection and turbulence modeling in scenarios where data samples come directly from quantum differential equation solvers. We show that the basis chosen for performing analysis greatly impacts classification accuracy. Our work opens up the area of research where quantum machine learning for quantum datasets is inherently required.
- [28] arXiv:2411.14274 [pdf, html, other]
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Title: Quantum Vacuum Self-Propulsion and TorqueComments: 11 pages, 12 figures. Paper submitted for Proceedings of the 5th Symposium on the Casimir Effect, Prian, Slovenia, September 2024Subjects: Quantum Physics (quant-ph); High Energy Physics - Theory (hep-th)
This article summarizes our recent efforts to understand spontaneous quantum vacuum forces and torques, which require that a stationary object be out of thermal equilibrium with the blackbody background radiation. We proceed by a systematic expansion in powers of the electric susceptibility. In first order, no spontaneous force can arise, although a torque can appear, but only if the body is composed of nonreciprocal material. In second order, both forces and torques can appear, with ordinary materials, but only if the body is inhomogeneous. In higher orders, this last requirement may be removed. We give a number of examples of bodies displaying second-order spontaneous forces and torques, some of which might be amenable to observation.
- [29] arXiv:2411.14292 [pdf, html, other]
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Title: Hypothesis testing of symmetry in quantum dynamicsComments: 14 pagesSubjects: Quantum Physics (quant-ph); Information Theory (cs.IT)
Symmetry plays a crucial role in quantum physics, dictating the behavior and dynamics of physical systems. In this paper, We develop a hypothesis-testing framework for quantum dynamics symmetry using a limited number of queries to the unknown unitary operation and establish the quantum max-relative entropy lower bound for the type-II error. We construct optimal ancilla-free protocols that achieve optimal type-II error probability for testing time-reversal symmetry (T-symmetry) and diagonal symmetry (Z-symmetry) with limited queries. Contrasting with the advantages of indefinite causal order strategies in various quantum information processing tasks, we show that parallel, adaptive, and indefinite causal order strategies have equal power for our tasks. We establish optimal protocols for T-symmetry testing and Z-symmetry testing for 6 and 5 queries, respectively, from which we infer that the type-II error exhibits a decay rate of $\mathcal{O}(m^{-2})$ with respect to the number of queries $m$. This represents a significant improvement over the basic repetition protocols without using global entanglement, where the error decays at a slower rate of $\mathcal{O}(m^{-1})$.
- [30] arXiv:2411.14304 [pdf, html, other]
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Title: Non-Markovian to Markovian decay in structured environments with correlated disorderMariana O. Monteiro, Nadja K. Bernardes, Eugene M. Broni, Francisco A. B. F. de Moura, Guilherme M. A. AlmeidaComments: 9 pages, 5 figuresSubjects: Quantum Physics (quant-ph)
Manipulating the dynamics of open quantum systems is a crucial requirement for large-scale quantum computers. Finding ways to overcome or extend decoherence times is a challenging task. Already at the level of a single two-level atom, its reduced dynamics with respect to a larger environment can be very complex. Structured environments, for instance, can lead to various regimes other than memoryless Markovian spontaneous emission. Here, we consider an atom coupled to an array of coupled cavities in the presence of on-site correlated disorder. The correlation is long-ranged and associated with the trace of a fractional Brownian motion following a power-law spectrum. With the cavity modes playing the role of the environment, we study the dynamics of the spontaneous emission. We observe a change from non-Markovian to Markovian decay in the presence of disorder by tuning the correlation parameter. This is associated with a localization-delocalization transition involving the field modes. Two dissipative models that effectively reproduce the behavior of the non-Markovianity are discussed. The dissipation dynamics of the atom can thus be used to extract information about the phase of the environment. Our results provide a direction in the engineering of disordered quantum systems to function as controllable reservoirs.
- [31] arXiv:2411.14328 [pdf, html, other]
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Title: An unusual phase transition in a non-Hermitian Su-Schrieffer-Heeger modelSubjects: Quantum Physics (quant-ph); Other Condensed Matter (cond-mat.other)
This article studies a non-Hermitian Su-Schrieffer-Heeger (SSH) model which has periodically staggered Hermitian and non-Hermitian dimers. The changes in topological phases of the considered chiral symmetric model with respect to the introduced non-Hermiticity are studied where we find that the system supports only complex eigenspectra for all values of $u \neq 0$ and it stabilizes only non-trivial insulating phase for higher loss-gain strength. Even if the system acts as a trivial insulator in the Hermitian limit, the increase in loss-gain strength induces phase transition to non-trivial insulating phase through a (gapless) semi-metallic phase. Interesting phenomenon is observed in the case where Hermitian system acts as a non-trivial insulator. In such a situation, the introduced non-Hermiticity neither leaves the non-trivial phase undisturbed nor induces switching to trivial phase. Rather, it shows transition from non-trivial insulating phase to the same where it is mediated by the stabilization of (non-trivial) semi-metallic phase. This unusual transition between the non-trivial insulating phases through non-trivial semi-metallic phase gives rise to a question regarding the topological states of the system under open boundary conditions. So, we analyze the possibility of stable edge states in these two non-trivial insulating phases and check the characteristic difference between them. In addition, we study the nature of topological states in the case of non-trivial gapless (semi-metallic) region.
- [32] arXiv:2411.14357 [pdf, html, other]
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Title: Anomalous transport in U(1)-symmetric quantum circuitsComments: Comments are welcome!Subjects: Quantum Physics (quant-ph); Disordered Systems and Neural Networks (cond-mat.dis-nn)
In this work we investigate discrete-time transport in a generic U(1)-symmetric disordered model tuned across an array of different dynamical regimes. We develop an aggregate quantity, a circular statistical moment, which is a simple function of the magnetization profile and which elegantly captures transport properties of the system. From this quantity we extract transport exponents, revealing behaviors across the phase diagram consistent with localized, diffusive, and - most interestingly for a disordered system - superdiffusive regimes. Investigation of this superdiffusive regime reveals the existence of a prethermal "swappy" regime unique to discrete-time systems in which excitations propagate coherently; even in the presence of strong disorder.
- [33] arXiv:2411.14359 [pdf, html, other]
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Title: Hilbert Subspace ErgodicityComments: 13+6 pages,12+7 figuresSubjects: Quantum Physics (quant-ph)
Ergodicity has been one of the fundamental concepts underpinning our understanding of thermalisation in isolated systems since the first developments in classical statistical mechanics. Recently, a similar notion has been introduced for quantum systems, termed Complete Hilbert Space Ergodicity (CHSE), in which the evolving quantum state explores all of the available Hilbert space. This contrasts with the Eigenstate Thermalisation Hypothesis (ETH), in which thermalisation is formulated via the properties of matrix elements of local operators in the energy eigenbasis. In this work we explore how ETH-violation mechanisms, including quantum many-body scars and Hilbert space fragmentation can affect Complete Hilbert Space Ergodicity. We find that the presence of these mechanisms leads to CHSE in decoupled subspaces, a phenomenon we call Hilbert Subspace Ergodicity, and which represents a protocol for constructing t-designs in subspaces.
- [34] arXiv:2411.14389 [pdf, html, other]
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Title: Unified and Generalized Approach to Entanglement-Assisted Quantum Error CorrectionComments: 38 pages, 1 figureSubjects: Quantum Physics (quant-ph)
We introduce a framework for entanglement-assisted quantum error correcting codes that unifies the three original frameworks for such codes called EAQEC, EAOQEC, and EACQ under a single umbrella. The unification is arrived at by viewing entanglement-assisted codes from the operator algebra quantum error correction perspective, and it is built upon a recently established extension of the stabilizer formalism to that setting. We denote the framework by EAOAQEC, and we prove a general error correction theorem for such codes, derived from the algebraic perspective, that generalizes each of the earlier results. This leads us to a natural notion of distance for such codes, and we derive a number of distance results for subclasses of the codes. We show how EACQ codes form a proper subclass of the entanglement-assisted subspace codes defined by EAOAQEC. We identify and construct new classes of entanglement-assisted subsystem codes and entanglement-assisted hybrid classical-quantum codes that are found outside of the earlier approaches.
- [35] arXiv:2411.14397 [pdf, html, other]
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Title: Discrete Schrodinger equation on graphs: An effective model for branched quantum latticeJournal-ref: EPL 147, 62001 (2024)Subjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
We propose an approach to quantize discrete networks (graphs with discrete edges). We introduce a new exact solution of discrete Schrodinger equation that is used to write the solution for quantum graphs. Formulation of the problem and derivation of secular equation for arbitrary quantum graphs is presented. Application of the approach for the star graph is demonstrated by obtaining eigenfunctions and eigenvalues explicitely. Practical application of the model in conducting polymers and branched molecular chains is discussed.
- [36] arXiv:2411.14412 [pdf, html, other]
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Title: Adversarial Poisoning Attack on Quantum Machine Learning ModelsSubjects: Quantum Physics (quant-ph); Cryptography and Security (cs.CR); Computer Vision and Pattern Recognition (cs.CV)
With the growing interest in Quantum Machine Learning (QML) and the increasing availability of quantum computers through cloud providers, addressing the potential security risks associated with QML has become an urgent priority. One key concern in the QML domain is the threat of data poisoning attacks in the current quantum cloud setting. Adversarial access to training data could severely compromise the integrity and availability of QML models. Classical data poisoning techniques require significant knowledge and training to generate poisoned data, and lack noise resilience, making them ineffective for QML models in the Noisy Intermediate Scale Quantum (NISQ) era. In this work, we first propose a simple yet effective technique to measure intra-class encoder state similarity (ESS) by analyzing the outputs of encoding circuits. Leveraging this approach, we introduce a quantum indiscriminate data poisoning attack, QUID. Through extensive experiments conducted in both noiseless and noisy environments (e.g., IBM\_Brisbane's noise), across various architectures and datasets, QUID achieves up to $92\%$ accuracy degradation in model performance compared to baseline models and up to $75\%$ accuracy degradation compared to random label-flipping. We also tested QUID against state-of-the-art classical defenses, with accuracy degradation still exceeding $50\%$, demonstrating its effectiveness. This work represents the first attempt to reevaluate data poisoning attacks in the context of QML.
- [37] arXiv:2411.14414 [pdf, html, other]
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Title: Quantum illumination advantage in quantum Doppler radarComments: preliminary version of the paperSubjects: Quantum Physics (quant-ph)
A Doppler radar is a device that employs the Doppler effect to estimate the radial velocity of a moving target at a distance. Traditional radars are based on a classical description of the electromagnetic radiation, but in principle their performance can be improved employing entangled quantum probe states. For target detection, i.e. hypothesis testing, a quantum advantage exists even in the high-noise regime appropriate to describe microwave fields, a protocol known as quantum illumination. In this paper, we show a similar advantage also for a quantum Doppler radar operating in presence of thermal noise, whereas so far a quantum advantage was shown in the noiseless scenario or in lidars operating at optical frequencies with negligible thermal noise. Concretely, we quantify the radar performance in terms of the quantum Fisher information, which captures the ultimate precision allowed by quantum mechanics in the asymptotic regime. We compare a classical protocol based on coherent states with a quantum one that uses multimode states obtained from spontaneous parametric downconversion. To ensure a fair comparison we match the signal energy and pulse duration. We show that a 3dB advantage is possible in the regime of small number of signal photons and high thermal noise, even for low transmissivity.
- [38] arXiv:2411.14416 [pdf, html, other]
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Title: QMA vs. QCMA and PseudorandomnessSubjects: Quantum Physics (quant-ph); Computational Complexity (cs.CC)
We study a longstanding question of Aaronson and Kuperberg on whether there exists a classical oracle separating $\mathsf{QMA}$ from $\mathsf{QCMA}$. Settling this question in either direction would yield insight into the power of quantum proofs over classical proofs. We show that such an oracle exists if a certain quantum pseudorandomness conjecture holds. Roughly speaking, the conjecture posits that quantum algorithms cannot, by making few queries, distinguish between the uniform distribution over permutations versus permutations drawn from so-called "dense" distributions.
Our result can be viewed as establishing a "win-win" scenario: \emph{either} there is a classical oracle separation of $\QMA$ from $\QCMA$, \emph{or} there is quantum advantage in distinguishing pseudorandom distributions on permutations.
New submissions (showing 38 of 38 entries)
- [39] arXiv:2411.13605 (cross-list from hep-th) [pdf, html, other]
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Title: Quantum Field Measurements in the Fewster-Verch FrameworkComments: 21 pagesSubjects: High Energy Physics - Theory (hep-th); Mathematical Physics (math-ph); Quantum Physics (quant-ph)
The Fewster-Verch (FV) framework was introduced as a prescription to define local operations within a quantum field theory (QFT) that are free from Sorkin-like causal paradoxes. In this framework the measurement device is modeled via a probe QFT that, after interacting with the target QFT, is subject to an arbitrary local measurement. While the FV framework is rich enough to carry out quantum state tomography, it has two drawbacks. First, it is unclear if the FV framework allows conducting arbitrary local measurements. Second, if the probe field is interpreted as physical and the FV framework as fundamental, then one must demand the probe measurement to be itself implementable within the framework. That would involve a new probe, which should also be subject to an FV measurement, and so on. It is unknown if there exist non-trivial FV measurements for which such an "FV-Heisenberg cut" can be moved arbitrarily far away. In this work, we advance the first problem by proving that measurements of locally smeared fields fit within the FV framework. We solve the second problem by showing that any such field measurement admits a movable FV-Heisenberg cut.
- [40] arXiv:2411.13642 (cross-list from cond-mat.quant-gas) [pdf, html, other]
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Title: Designing Atomtronic Circuits via Superfluid DynamicsComments: 9 pages, 8 figuresSubjects: Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)
We propose to design atomtronic circuits with Bose-Einstein condensates (BECs) in circuit-like traps that are controlled via mobile barriers. Using classical-field simulations, we demonstrate a universal set of logical gates and show how to assemble them into circuits. We first demonstrate an AND gate based on a T-shaped BEC, utilizing a combination of mobile and static barriers. The mobile barriers provide the logical input of the gate, while the static barrier functions as a Josephson junction that generates the AND output of the gate via a density imbalance across the barrier. Next we show how to combine three AND gates into a circuit, with a design composed of two T-shapes and an H-shape. Furthermore, we demonstrate how to use Josephson oscillations to create a NOT gate and combine it with an AND gate, thereby showcasing a universal set of gates and their assembly into circuits.
- [41] arXiv:2411.13645 (cross-list from hep-th) [pdf, other]
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Title: Real-Time Scattering in Ising Field Theory using Matrix Product StatesComments: 16 + 12 pages, many spacetime pictures of scattering processesSubjects: High Energy Physics - Theory (hep-th); Strongly Correlated Electrons (cond-mat.str-el); High Energy Physics - Lattice (hep-lat); Quantum Physics (quant-ph)
We study scattering in Ising Field Theory (IFT) using matrix product states and the time-dependent variational principle. IFT is a one-parameter family of strongly coupled non-integrable quantum field theories in 1+1 dimensions, interpolating between massive free fermion theory and Zamolodchikov's integrable massive $E_8$ theory. Particles in IFT may scatter either elastically or inelastically. In the post-collision wavefunction, particle tracks from all final-state channels occur in superposition; processes of interest can be isolated by projecting the wavefunction onto definite particle sectors, or by evaluating energy density correlation functions. Using numerical simulations we determine the time delay of elastic scattering and the probability of inelastic particle production as a function of collision energy. We also study the mass and width of the lightest resonance near the $E_8$ point in detail. Close to both the free fermion and $E_8$ theories, our results for both elastic and inelastic scattering are in good agreement with expectations from form-factor perturbation theory. Using numerical computations to go beyond the regime accessible by perturbation theory, we find that the high energy behavior of the two-to-two particle scattering probability in IFT is consistent with a conjecture of Zamolodchikov. Our results demonstrate the efficacy of tensor-network methods for simulating the real-time dynamics of strongly coupled quantum field theories in 1+1 dimensions.
- [42] arXiv:2411.13651 (cross-list from cond-mat.str-el) [pdf, html, other]
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Title: Certain BCS wavefunctions are quantum many-body scarsSubjects: Strongly Correlated Electrons (cond-mat.str-el); Statistical Mechanics (cond-mat.stat-mech); Superconductivity (cond-mat.supr-con); High Energy Physics - Theory (hep-th); Quantum Physics (quant-ph)
We provide a method for constructing many-body scar states in fermionic lattice models that incorporate a given type of correlations with one of the states maximizing them over the full Hilbert space. Therefore this state may always be made the ground state by adding such correlations as a "pairing potential" $\delta H_0$ to any Hamiltonian $H=H_0+OT$ supporting group-invariant scars [arXiv:2007.00845]. In case of single-flavour spin-full fermions the ground state is a special case of the BCS wavefunction written in real space and invariant under any site index relabelling. For multi-orbital fermions this state also resembles BCS but includes higher order terms corresponding to "pairing" of more than two fermions. The broad class of eligible Hamiltonians $H$ is well documented [arXiv:2007.00845],[arXiv:2106.10300] and includes many conventional condensed matter interactions. The part of the Hamiltonian $(H_0+\delta H_0)$ that governs the exact dynamics of the scar subspace coincides with the BCS mean-field Hamiltonian. We therefore show that its BCS ground state and the excitations above it are many-body scars that are dynamically decoupled from the rest of the Hilbert space and thereby protected from thermalization. These states are insensitive to a variety of $OT$ Hamiltonian terms that among others include interactions and (spin-orbit) hoppings. Our results point out a connection between the fields of superconductivity and weak ergodicity breaking (many-body scars) and will hopefully encourage further investigations. They also provide the first practical protocol to initialize a fermionic system to a scar state in (a quantum simulator) experiment.
- [43] arXiv:2411.13695 (cross-list from cond-mat.mes-hall) [pdf, other]
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Title: Robust coherent dynamics of homogeneously limited anisotropic excitons in two-dimensional layered ReS2Rup Kumar Chowdhury, Md Samiul Islam, Marie Barthelemy, Nicolas Beyer, Lorry Engel, Jean-Sebastien Pelle, Mircea Rastei, Alberto Barsella, Francois FrasSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Optics (physics.optics); Quantum Physics (quant-ph)
The discovery of in-plane anisotropic excitons in two-dimensional layered semiconductors enables state-of-the-art nanophotonic applications. A fundamental yet unknown parameter of these quasiparticles is the coherence time (T_2 ), which governs the quantum dephasing timescale, over which the coherent superposition of excitons can be maintained and manipulated. Here, we report the direct measurement of T_2 within the sub-picosecond range, along with multiple population decay timescales (T_1 ) at resonance for anisotropic excitons in pristine layered rhenium disulfide (ReS2). We observe a notable weak dependence on layer thickness for T_2 , and a quasi-independence for T_1 . The excitonic coherence in few-layer ReS2 exhibits exceptional robustness against optical density and temperature compared to other two-dimensional semiconductors, enabling quantum features even at room temperature. No photon echo fingerprints were observed in pristine ReS2, highlighting the homogeneous character of the anisotropic excitonic transitions and a particularly low level of disorder in exfoliated flakes. Lastly, our results for mono- to bulk-like ReS2 support a direct gap band structure regardless their layer thickness, addressing the ongoing discussion about its nature.
- [44] arXiv:2411.13882 (cross-list from cond-mat.mes-hall) [pdf, html, other]
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Title: A 2x2 quantum dot array in silicon with fully tuneable pairwise interdot couplingWee Han Lim, Tuomo Tanttu, Tony Youn, Jonathan Yue Huang, Santiago Serrano, Alexandra Dickie, Steve Yianni, Fay E. Hudson, Christopher C. Escott, Chih Hwan Yang, Arne Laucht, Andre Saraiva, Kok Wai Chan, Jesús D. Cifuentes, Andrew S. DzurakComments: 9 pages, 5 figuresSubjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)
Recent advances in semiconductor spin qubits have achieved linear arrays exceeding ten qubits. Moving to two-dimensional (2D) qubit arrays is a critical next step to advance towards fault-tolerant implementations, but it poses substantial fabrication challenges, particularly because enabling control of nearest-neighbor entanglement requires the incorporation of interstitial exchange gates between quantum dots in the qubit architecture. In this work, we present a 2D array of silicon metal-oxide-semiconductor (MOS) quantum dots with tunable interdot coupling between all adjacent dots. The device is characterized at 4.2 K, where we demonstrate the formation and isolation of double-dot and triple-dot configurations. We show control of all nearest-neighbor tunnel couplings spanning up to 30 decades per volt through the interstitial exchange gates and use advanced modeling tools to estimate the exchange interactions that could be realized among qubits in this architecture. These results represent a significant step towards the development of 2D MOS quantum processors compatible with foundry manufacturing techniques.
- [45] arXiv:2411.13910 (cross-list from hep-ph) [pdf, html, other]
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Title: Quantum gravity corrections to the spontaneous excitation of an accelerated atom interacting with a quantum scalar fieldSubjects: High Energy Physics - Phenomenology (hep-ph); General Relativity and Quantum Cosmology (gr-qc); Quantum Physics (quant-ph)
The Generalized Uncertainty Principle (GUP) extends the Heisenberg Uncertainty Principle by suggesting a minimum observable scale that includes the effects of quantum gravity, which is supposed to potentially result in observable effects far below the Planck energy scale, providing us the opportunity to explore the theory of quantum gravity through physical processes at low energy scale. In present work, we study the corrections induced by the GUP to the spontaneous radiation properties of a two-level atom interacting with a real massless scalar quantum field based on the DDC formalism. The GUP alters the correlation function of the scalar field, consequently affecting the radiative properties of atoms. We compute the rate of change in the mean atomic energy for an atom undergoing inertial motion, uniform acceleration, and uniform circular motion. We show that the GUP can enhance the spontaneous emission rate of an excited state atom in inertial motion; however, it does not alter the stability of the ground-state atom in vacuum. For an atom in uniformly accelerated and uniformly circular motion, the GUP can change both its spontaneous emission and spontaneous excitation rates, and the proper acceleration $a$ can significantly amplify the effect of the GUP on the spontaneous transition rates of the atom.
- [46] arXiv:2411.13940 (cross-list from cond-mat.quant-gas) [pdf, html, other]
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Title: Preparation and observation of anomalous counterpropagating edge states in a periodically driven optical Raman latticeComments: 13 pages, 10 figuresSubjects: Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)
Motivated by the recent observation of real-space edge modes with ultracold atoms [Braun et al., Nat. Phys. 20, 1306 (2024)], we investigate the preparation and detection of anomalous counterpropagating edge states -- a defining feature of the anomalous Floquet valley-Hall (AFVH) phase -- in a two-dimensional periodically driven optical Raman lattice. Modeling the atomic cloud with a Gaussian wave packet state, we explore, both analytically and numerically, how the population of edge modes depends on the initial-state parameters. In particular, we reveal that, in addition to the internal spin state, the initial momenta parallel and perpendicular to the boundary play essential roles: they independently control the selective population of edge states across distinct momenta and within separate quasienergy gaps. Furthermore, we examine the wave-packet dynamics of counterpropagating edge states and demonstrate that their characteristic motion is robust against long-range disorder. These results establish a theoretical framework for future experimental explorations of the AFVH phase and topological phenomena associated with its unique edge modes.
- [47] arXiv:2411.14139 (cross-list from math-ph) [pdf, html, other]
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Title: On the Classification of the L\'evy-Leblond SpinorsComments: 8 pages; based on the L. M.'s talk at ISQS28, Prague, July 1-5, 2024; to appear in the ProceedingsSubjects: Mathematical Physics (math-ph); High Energy Physics - Theory (hep-th); Quantum Physics (quant-ph)
The first-order Lévy-Leblond differential equations (LLEs) are the non-relativistic analogous of the Dirac equation: they are the "square roots" of the Schrödinger equation in ($1+d$) dimensions and admit spinor solutions. In this paper we show how to extend to the Lévy-Leblond spinors the real/complex/quaternionic classification of the relativistic spinors (which leads to the notions of Dirac, Weyl, Majorana, Majorana-Weyl, Quaternionic spinors). Besides the free equations, we also consider the presence of potential terms. Applied to a conformal potential, the simplest $(1+1)$-dimensional LLE induces a new differential realization of the $osp(1|2)$ superalgebra in terms of differential operators depending on the time and space coordinates.
- [48] arXiv:2411.14144 (cross-list from cond-mat.supr-con) [pdf, html, other]
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Title: Superconducting $p$-wave pairing effects on one-dimensional non-Hermitian quasicrystals with power law hoppingComments: 11 pages, 6 figuresSubjects: Superconductivity (cond-mat.supr-con); Disordered Systems and Neural Networks (cond-mat.dis-nn); Other Condensed Matter (cond-mat.other); Quantum Physics (quant-ph)
We study the effects of superconducting $p$-wave pairing on the non-Hermitian Aubry-André-Harper model with power-law hopping. For the case of short-range hopping, weak pairing leads to oscillating quasi-Majorana zero modes, turning to edge-localized Majorana zero modes as pairing strength increases. For the case of long-range hopping, we observe the emergence of massive Dirac modes having oscillatory behavior, similar to Majorana modes with weak pairing. The massive Dirac modes localize at the edges as the pairing strength grows. The superconducting pairing spoils the plateaus observed in the fractal dimension of all the energy eigenstates of the Aubry-André-Harper model with power-law hopping. The number of plateaus decreases with the increasing pairing strength for the weak non-Hermiticity in the system. The phase diagram of the system reveals that real and complex energy spectrums correlate differently with the localization properties of the eigenstates depending on the strength of pairing and hopping range.
- [49] arXiv:2411.14261 (cross-list from hep-th) [pdf, html, other]
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Title: On braid statistics versus parastatisticsComments: 11 pages. Based on a plenary talk at ISQS28, Prague, July 1-5, 2024; to appear in the ProceedingsSubjects: High Energy Physics - Theory (hep-th); Statistical Mechanics (cond-mat.stat-mech); Mathematical Physics (math-ph); Quantum Physics (quant-ph)
I report the recent advances in applying (graded) Hopf algebras with braided tensor product in two scenarios: i) paraparticles beyond bosons and fermions living in any space dimensions and transforming under the permutation group; ii) physical models of anyons living in two space-dimensions and transforming under the braid group. In the first scenario simple toy models based on the so-called $2$-bit parastatistics show that, in the multiparticle sector, certain observables can discriminate paraparticles from ordinary bosons/fermions (thus, providing a counterexample to the widespread belief of the "conventionality of parastatistics" argument). In the second scenario the notion of (braided) Majorana qubit is introduced as the simplest building block to implement the Kitaev's proposal of a topological quantum computer which protects from decoherence.
- [50] arXiv:2411.14302 (cross-list from cond-mat.quant-gas) [pdf, html, other]
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Title: Electrodynamics of Vortices in Quasi-2D Scalar Bose-Einstein CondensatesComments: 15 pages, 1 figureSubjects: Quantum Gases (cond-mat.quant-gas); Statistical Mechanics (cond-mat.stat-mech); Mathematical Physics (math-ph); Plasma Physics (physics.plasm-ph); Quantum Physics (quant-ph)
In two spatial dimensions, vortex-vortex interactions approximately vary with the logarithm of the inter-vortex distance, making it possible to describe an ensemble of vortices as a Coulomb gas. We introduce a duality between vortices in a quasi-two-dimensional (quasi-2D) scalar Bose-Einstein condensates (BEC) and effective Maxwell's electrodynamics. Specifically, we address the general scenario of inhomogeneous, time-dependent BEC number density with dissipation or rotation. Starting from the Gross-Pitaevskii equation (GPE), which describes the mean-field dynamics of a quasi-2D scalar BEC without dissipation, we show how to map vortices in a quasi-2D scalar BEC to 2D electrodynamics beyond the point-vortex approximation, even when dissipation is present or in a rotating system. The physical meaning of this duality is discussed.
- [51] arXiv:2411.14307 (cross-list from gr-qc) [pdf, html, other]
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Title: General Relativistic Center-of-Mass Coordinates for Composite Quantum ParticlesComments: 12 pages, 1 figureSubjects: General Relativity and Quantum Cosmology (gr-qc); Quantum Physics (quant-ph)
Recent proposals suggested quantum clock interferometry for tests of the Einstein equivalence principle. However, atom interferometric models often include relativistic effects only in an ad hoc fashion. Here, instead, we start from the multi-particle nature of quantum-delocalizable atoms in curved spacetime and generalize the special-relativistic center of mass (COM) and relative coordinates that have previously been studied for Minkowski spacetime to obtain the light-matter dynamics in curved spacetime. In particular, for a local Schwarzschild observer located at the surface of the Earth using Fermi-Walker coordinates, we find gravitational correction terms for the Poincaré symmetry generators and use them to derive general relativistic COM and relative coordinates. In these coordinates we obtain the Hamiltonian of a fully first-quantized two-particle atom interacting with the electromagnetic field in curved spacetime that naturally incorporates special and general relativistic effects.
- [52] arXiv:2411.14391 (cross-list from math-ph) [pdf, html, other]
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Title: Phase Space Representation of the Density Operator: Bopp Pseudodifferential Calculus and Moyal ProductSubjects: Mathematical Physics (math-ph); Operator Algebras (math.OA); Quantum Physics (quant-ph)
Bopp shifts were introduced in 1956 in the study of statistical interpretations of quantum mechanics. They lead to a phase space view of quantum mechanics closely related to the Moyal star product and its interpretation as a deformation quantization. In the present paper we pursue our study of Bopp quantization by initiated in previous work and apply it to give a new phase space description of the density operator, that is of the mixed states of quantum mechanics.
- [53] arXiv:2411.14406 (cross-list from cond-mat.stat-mech) [pdf, html, other]
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Title: Full counting statistics after quantum quenches as hydrodynamic fluctuationsComments: 6+14 pages, 3 figuresSubjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)
The statistics of fluctuations on large regions of space encodes universal properties of many-body systems. At equilibrium, it is described by thermodynamics. However, away from equilibrium such as after quantum quenches, the fundamental principles are more nebulous. In particular, although exact results have been conjectured in integrable models, a correct understanding of the physics is largely missing. In this letter, we explain these principles, taking the example of the number of particles lying on a large interval in one-dimensional interacting systems. These are based on simple hydrodynamic arguments from the theory of ballistically transported fluctuations, and in particular the Euler-scale transport of long-range correlations. Using these principles, we obtain the full counting statistics (FCS) in terms of thermodynamic and hydrodynamic quantities, whose validity depends on the structure of hydrodynamic modes. In fermionic-statistics interacting integrable models with a continuum of hydrodynamic modes, such as the Lieb-Liniger model for cold atomic gases, the formula reproduces previous conjectures, but is in fact not exact: it gives the correct cumulants up to, including, order 5, while long-range correlations modify higher cumulants. In integrable and non-integrable models with two or less hydrodynamic modes, the formula is expected to give all cumulants.
- [54] arXiv:2411.14408 (cross-list from cond-mat.mtrl-sci) [pdf, html, other]
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Title: Correlated Structural and Optical Characterization of Hexagonal Boron NitrideJordan A. Gusdorff, Pia Bhatia, Trey T. Shin, Alexandra Sofia Uy-Tioco, Benjamin N. Sailors, Rachael N. Keneipp, Marija Drndić, Lee C. BassettComments: 21 pages, 13 figures, 3 tablesSubjects: Materials Science (cond-mat.mtrl-sci); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)
Hexagonal boron nitride (hBN) hosts quantum emitters that exhibit single-photon emission and spin-dependent fluorescence at room temperature. These features make hBN a promising platform for quantum sensing and photonics. Despite many investigations of their optical properties, the emitters' chemical structure remains unclear, as does the role of contamination at surfaces and interfaces in forming the emitters or modifying their properties. We prepare hBN samples that are compatible with both confocoal photoluminescence microscopy (PL) and transmission electron microscopy (TEM), and we use those techniques to investigate correlations between fluorescent emission, flake morphology, and surface residue. We find that the microscopy techniques themselves induce changes in hBN's optical activity and residue mophology: PL measurements induce photobleaching, whereas TEM measurements alter surface residue and emission characteristics. We also study the effects of common treatments $\unicode{x2014}$ annealing and oxygen plasma cleaning $\unicode{x2014}$ on the structure and optical activity of hBN. The results illustrate the power and importance of correlative studies to elucidate aspects of microscopic mechanisms that influence hBN's functionality as a host for quantum emitters and spin defects.
- [55] arXiv:2411.14410 (cross-list from physics.optics) [pdf, html, other]
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Title: Engineering spectro-temporal light states with physics-trained deep learningComments: Welcome to place your commentsSubjects: Optics (physics.optics); Pattern Formation and Solitons (nlin.PS); Classical Physics (physics.class-ph); Quantum Physics (quant-ph)
Frequency synthesis and spectro-temporal control of optical wave packets are central to ultrafast science, with supercontinuum (SC) generation standing as one remarkable example. Through passive manipulation, femtosecond (fs) pulses from nJ-level lasers can be transformed into octave-spanning spectra, supporting few-cycle pulse outputs when coupled with external pulse compressors. While strategies such as machine learning have been applied to control the SC's central wavelength and bandwidth, their success has been limited by the nonlinearities and strong sensitivity to measurement noise. Here, we propose and demonstrate how a physics-trained convolutional neural network (P-CNN) can circumvent such challenges, showing few-fold speedups over the direct approaches. We highlight three key advancements enabled by the P-CNN approach: (i) on-demand control over spectral features of SC, (ii) direct generation of sub-3-cycle pulses from the highly nonlinear fiber, and (iii) the production of high-order solitons, capturing distinct "breather" dynamics in both spectral and temporal domains. This approach heralds a new era of arbitrary spectro-temporal state engineering, with transformative implications for ultrafast and quantum science.
- [56] arXiv:2411.14426 (cross-list from physics.atom-ph) [pdf, html, other]
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Title: Quantum States Imaging of Magnetic Field Contours based on Autler-Townes Effect in Yb AtomsSubjects: Atomic Physics (physics.atom-ph); Quantum Physics (quant-ph)
An inter-combination transition in Yb enables a novel approach for rapidly imaging magnetic field variations with excellent spatial and temporal resolution and accuracy. This quantum imaging magnetometer reveals "dark stripes" that are contours of constant magnetic field visible by eye or capturable by standard cameras. These dark lines result from a combination of Autler-Townes splitting and the spatial Hanle effect in the $^{1}S_{0} - ^{3}P_{1}$ transition of Yb when driven by multiple strong coherent laser fields (carrier and AM/FM modulation sidebands of a single-mode 556 nm laser). We show good agreement between experimental data and our theoretical model for the closed, 4-level Zeeman shifted V-system and demonstrate scalar and vector magnetic fields measurements at video frame rates over spatial dimensions of 5 cm (expandable to $>$ 1 m) with 0.1 mm resolution. Additionally, the $^{1}S_{0} - ^{3}P_{1}$ transition allows for $\sim\mu$s response time and a large dynamic range ($\mu$T to many Ts).
Cross submissions (showing 18 of 18 entries)
- [57] arXiv:2301.02500 (replaced) [pdf, html, other]
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Title: Violation of Diagonal Non-Invasiveness: A Hallmark of Non-Classical Memory EffectsComments: 12 pages, 2 figuresSubjects: Quantum Physics (quant-ph)
An operational (measurement based) scheme that connects measurement invasiveness and the presence of non-classical memory effects in open quantum systems is defined. Its underlying theoretical basis relies on a non-invasive measurability of (memoryless) quantum Markovian dynamics when the corresponding observable is diagonal in the same basis as the system density matrix. In contrast, violation of this property can be related to intrinsic non-classical memory effects. Related conditions for violation of Leggett-Garg inequality due to quantum memory effects emerge from this perspective. The developed approach applies to open quantum dynamics whose time-evolution is derived from a full unitary (microscopic) description, stochastic Hamiltonian dynamics, as well as for a broad class of non-unitary system-environment models (bipartite Lindblad equations).
- [58] arXiv:2301.05666 (replaced) [pdf, html, other]
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Title: Beyond MP2 initialization for unitary coupled cluster quantum circuitsSubjects: Quantum Physics (quant-ph); Strongly Correlated Electrons (cond-mat.str-el); Chemical Physics (physics.chem-ph)
The unitary coupled cluster (UCC) ansatz is a promising tool for achieving high-precision results using the variational quantum eigensolver (VQE) algorithm in the NISQ era. However, results on quantum hardware are thus far very limited and simulations have only accessed small system sizes. We advance the state of the art of UCC simulations by utilizing an efficient sparse wavefunction circuit solver and studying systems up to 64 qubits. Here we report results obtained using this solver that demonstrate the power of the UCC ansatz and address pressing questions about optimal initial parameterizations and circuit construction, among others. Our approach enables meaningful benchmarking of the UCC ansatz, a crucial step in assessing the utility of VQE for achieving quantum advantage.
- [59] arXiv:2308.04422 (replaced) [pdf, html, other]
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Title: Harnessing high-dimensional temporal entanglement using limited interferometric setupsComments: v2: 10+8 Pages, 3 Figures; v1: 6+10 Pages, 2 FiguresJournal-ref: Phys. Rev. Applied 22, 054054 (2024)Subjects: Quantum Physics (quant-ph)
High-dimensional entanglement has shown to have significant advantages in quantum communication. It is available in many degrees of freedom and in particular in the time-domain routinely produced in down-conversion (SPDC). While advantageous in the sense that only a single detector channel is needed locally, it is notoriously hard to analyze, especially in an assumption-free manner that is required for quantum key distribution applications. We develop the first complete analysis of high-dimensional entanglement in the polarization-time-domain and show how to efficiently certify relevant density matrix elements and security parameters for Quantum Key Distribution (QKD). In addition to putting past experiments on rigorous footing, we also develop physical noise models and propose a novel setup that can further enhance the noise resistance of free-space quantum communication.
- [60] arXiv:2308.08491 (replaced) [pdf, html, other]
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Title: Conditional fluctuation theorems and entropy production for monitored quantum systems under imperfect detectionComments: 5 + 12 pages, 3 figures. The two first authors contributed equally to this work. v2: minor changes, figure added, references added. v3: 8 + 5 pages, 3 figures. New distribution of material, expanded discussions, improved presentation, references added and title modified (accepted in PRR)Subjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech)
The thermodynamic behavior of Markovian open quantum systems can be described at the level of fluctuations by using continuous monitoring approaches. However, practical applications require assessing imperfect detection schemes, where the definition of main thermodynamic quantities becomes subtle and universal fluctuation relations are unknown. Here, we fill this gap by deriving a universal fluctuation relation that links thermodynamic entropy production and information-theoretical irreversibility along single trajectories in inefficient monitoring setups. This relation provides as a corollary an irreversibility estimator of dissipation using imperfect detection records that lower bounds the underlying entropy production at the level of visible trajectories. We illustrate our findings with a driven-dissipative two-level system following quantum jump trajectories and discuss the experimental applicability of our results for thermodynamic inference.
- [61] arXiv:2308.16032 (replaced) [pdf, html, other]
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Title: Trade-off between Information Gain and Disturbance in Local Discrimination of Entangled Quantum StatesComments: 5+14 pages, 3 figuresSubjects: Quantum Physics (quant-ph)
We establish an information gain-disturbance trade-off relation in local state discrimination. Our result demonstrates a fundamental limitation of local strategy to discriminate entangled quantum states without disturbance, which becomes more difficult as the entanglement of the states to be discriminated increases. For a set of maximally entangled states, the capability of local strategy is tightly suppressed, as random guessing without measurements saturates the bound provided by the trade-off relation. We also show that the trade-off can be circumvented when local operations are aided by pre-shared entanglement. To simultaneously achieve correct guessing of state and non-disturbance, an entirely different strategy from conventional state discrimination should be adopted to lower the cost of pre-shared entanglement. We explicitly propose an adaptive and non-destructive strategy based on the stabilizer formalism, which shows a strict advantage over conventional teleportation-based approaches in pre-shared entanglement cost for discriminating a set of maximally entangled states. As an application of the trade-off relation, we propose an entanglement certification protocol that is robust against depolarizing noise and generalize it to multipartite scenarios in a quantum network.
- [62] arXiv:2310.01338 (replaced) [pdf, html, other]
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Title: Uncovering measurement-induced entanglement via directional adaptive dynamics and incomplete informationComments: 8+13 pages, 4+9 figuresJournal-ref: Phys. Rev. A 110, L050602 (2024)Subjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
The rich entanglement dynamics and transitions exhibited by monitored quantum systems typically only exist in the conditional state, making observation extremely difficult. In this work we construct a general recipe for mimicking the conditional entanglement dynamics of a monitored system in a corresponding measurement-free dissipative system involving directional interactions between the original system and a set of auxiliary register modes. This mirror setup autonomously implements a measurement-feedforward dynamics that effectively retains a coarse-grained measurement record. We illustrate our ideas in a bosonic system featuring a competition between entangling measurements and local unitary dynamics, and also discuss extensions to qubit systems and truly many-body systems.
- [63] arXiv:2311.04216 (replaced) [pdf, html, other]
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Title: Directly observing replica symmetry breaking in a vector quantum-optical spin glassRonen M. Kroeze, Brendan P. Marsh, David Atri Schuller, Henry S. Hunt, Alexander N. Bourzutschky, Michael Winer, Sarang Gopalakrishnan, Jonathan Keeling, Benjamin L. LevComments: main text 6 pages and 4 figures plus references, supplement 40 pages and 26 figures plus referencesSubjects: Quantum Physics (quant-ph); Disordered Systems and Neural Networks (cond-mat.dis-nn); Quantum Gases (cond-mat.quant-gas); Statistical Mechanics (cond-mat.stat-mech); Atomic Physics (physics.atom-ph)
Spin glasses are quintessential examples of complex matter. Although much about their order remains uncertain, abstract models of them inform, e.g., the classification of combinatorial optimization problems, the magnetic ordering in metals with impurities, and artificial intelligence -- where they form a mathematical basis for neural network computing and brain modeling. We demonstrate the ability of an active quantum gas microscope to realize a spin glass of a novel driven-dissipative and vector form. By microscopically visualizing its glassy spin states, the technique allows us to directly measure replica symmetry breaking and the resulting ultrametric hierarchical structure. Ultrametricity is known to be emergent in models of evolution, protein folding, climate change, and infinite-range equilibrium spin glasses; this work shows it to be directly observable in a physically realized system.
- [64] arXiv:2311.11329 (replaced) [pdf, html, other]
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Title: Matrix manipulations via unitary transformations and ancilla-state measurementsComments: 6 pages, 1 figureJournal-ref: Quantum Information and Computation 24 (13&14), 1099-1109 (2024)Subjects: Quantum Physics (quant-ph)
We propose protocols for calculating inner product, matrix addition and matrix multiplication based on multiqubit Toffoli-type and the simplest one-qubit operations and employ ancilla measurements to remove all garbage of calculations. The depth (runtime) of the addition protocol is $O(1)$ and that of other protocols logarithmically increases with the dimensionality of the considered matrices.
- [65] arXiv:2401.03367 (replaced) [pdf, html, other]
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Title: Entanglement detection length of multipartite quantum statesSubjects: Quantum Physics (quant-ph)
Multipartite entanglement is a valuable resource for quantum technologies. However, detecting this resource can be challenging: for genuine multipartite entanglement, the detection may require global measurements that are hard to implement experimentally. Here we introduce the concept of entanglement detection length, defined as the minimum number of particles that have to be jointly measured in order to detect genuine multipartite entanglement. For symmetric states, we show that the entanglement detection length can be determined by testing separability of the marginal states. For general states, we provide an upper bound on the entanglement detection length based on semidefinite programming. We show that the entanglement detection length is generally smaller than the minimum observable length needed to uniquely determine a multipartite state, and we provide examples achieving the maximum gap between these two quantities.
- [66] arXiv:2401.12213 (replaced) [pdf, html, other]
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Title: Identifying gap-closings in open non-Hermitian systems by Biorthogonal PolarizationComments: typos correctedJournal-ref: J. Appl. Phys. 135, 094402 (2024)Subjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); High Energy Physics - Theory (hep-th); Optics (physics.optics)
We investigate gap-closings in one- and two-dimensional tight-binding models with two bands, containing non-Hermitian hopping terms, and open boundary conditions (OBCs) imposed along one direction. We compare the bulk OBC spectra with the periodic boundary condition (PBC) spectra, pointing out that they do not coincide, which is an intrinsic characteristic of non-Hermitian systems. The non-Hermiticity, thus, results in the failure of the familiar notions of bulk-boundary correspondence found for Hermitian systems. This necessitates the search for topological invariants which can characterize gap-closings in open non-Hermitian systems correctly and unambiguously. We elucidate the behaviour of two possible candidates applicable for one-dimensional slices - (1) the sum of winding numbers for the two bands defined on a generalized Brillouin zone and (2) the biorthogonal polarization (BP). While the former shows jumps/discontinuities for some of the non-Hermitian systems studied here, at points when an edge mode enters the bulk states and becomes delocalized, it does not maintain quantized values in a given topological phase. On the contrary, BP shows jumps at phase transitions, and takes the quantized value of one or zero, which corresponds to whether an actual edge mode exists or whether that mode is delocalized and absorbed within the bulk (not being an edge mode anymore).
- [67] arXiv:2401.16374 (replaced) [pdf, html, other]
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Title: Analytic Model Reveals Local Molecular Polarizability Changes Induced by Collective Strong Coupling in Optical CavitiesSubjects: Quantum Physics (quant-ph); Chemical Physics (physics.chem-ph)
Despite recent numerical evidence, one of the fundamental theoretical mysteries of polaritonic chemistry is how and if collective strong coupling can induce local changes of the electronic structure to modify chemical properties. Here we present non-perturbative analytic results for a model system consisting of an ensemble of $N$ harmonic molecules under vibrational strong coupling (VSC) that alters our present understanding of this fundamental question. By applying the cavity Born-Oppenheimer partitioning on the Pauli-Fierz Hamiltonian in dipole approximation, the dressed many-molecule problem can be solved self-consistently and analytically in the dilute limit. We discover that the electronic molecular polarizabilities are modified even in the case of vanishingly small single-molecule couplings. Consequently, this non-perturbative local polarization mechanism persists even in the large-$N$ limit. In contrast, a perturbative calculation of the polarizabilities leads to a qualitatively erroneous scaling behavior with vanishing effects in the large-$N$ limit. Nevertheless, the exact (self-consistent) polarizabilities can be determined from single-molecule strong coupling simulations instead. Our fundamental theoretical observations demonstrate that hitherto existing collective-scaling arguments are insufficient for polaritonic chemistry and they pave the way for refined single- (or few-) molecule strong-coupling ab-initio simulations of chemical systems under collective strong coupling.
- [68] arXiv:2402.18953 (replaced) [pdf, html, other]
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Title: Noise-Robust Detection of Quantum Phase TransitionsComments: 11 pages, 10 figuresSubjects: Quantum Physics (quant-ph); Materials Science (cond-mat.mtrl-sci); Other Condensed Matter (cond-mat.other); Statistical Mechanics (cond-mat.stat-mech); Computational Physics (physics.comp-ph)
Quantum computing allows for the manipulation of highly correlated states whose properties quickly go beyond the capacity of any classical method to calculate. Thus one natural problem which could lend itself to quantum advantage is the study of ground-states of condensed matter models, and the transitions between them. However, current levels of hardware noise can require extensive application of error-mitigation techniques to achieve reliable computations. In this work, we use several IBM devices to explore a finite-size spin model with multiple `phase-like' regions characterized by distinct ground-state configurations. Using pre-optimized Variational Quantum Eigensolver (VQE) solutions, we demonstrate that in contrast to calculating the energy, where zero-noise extrapolation is required in order to obtain qualitatively accurate yet still unreliable results, calculations of the energy derivative, two-site spin correlation functions, and the fidelity susceptibility yield accurate behavior across multiple regions, even with minimal or no application of error-mitigation approaches. Taken together, these sets of observables could be used to identify level crossings in a simple, noise-robust manner which is agnostic to the method of ground state preparation. This work shows promising potential for near-term application to identifying quantum phase transitions, including avoided crossings and non-adiabatic conical intersections in electronic structure calculations.
- [69] arXiv:2403.14807 (replaced) [pdf, html, other]
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Title: Exact Hidden Markovian Dynamics in Quantum CircuitsComments: 7+11 pages, 2+1 figuresJournal-ref: Phys. Rev. Lett. 133, 170402 (2024)Subjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech); Strongly Correlated Electrons (cond-mat.str-el); Exactly Solvable and Integrable Systems (nlin.SI)
Characterizing nonequilibrium dynamics in quantum many-body systems is a challenging frontier of physics. In this Letter, we systematically construct solvable nonintegrable quantum circuits that exhibit exact hidden Markovian subsystem dynamics. This feature thus enables accurately calculating local observables for arbitrary evolution time. Utilizing the influence matrix method, we show that the influence of the time-evolved global system on a finite subsystem can be analytically described by sequential, time-local quantum channels acting on the subsystem with an ancilla of finite Hilbert space dimension. The realization of exact hidden Markovian property is facilitated by a solvable condition on the underlying two-site gates in the quantum circuit. We further present several concrete examples with varying local Hilbert space dimensions to demonstrate our approach.
- [70] arXiv:2404.10224 (replaced) [pdf, html, other]
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Title: Prethermalization in aperiodically driven classical spin systemsComments: Main Text (6 pages + 3 figures) + Supplementary Material (7 Pages + 11 figures)Subjects: Quantum Physics (quant-ph); Disordered Systems and Neural Networks (cond-mat.dis-nn); Statistical Mechanics (cond-mat.stat-mech); Strongly Correlated Electrons (cond-mat.str-el); Chaotic Dynamics (nlin.CD)
Periodically driven classical many-body systems can host a rich zoo of prethermal dynamical phases. In this work, we extend the paradigm of classical prethermalization to aperiodically driven systems. We establish the existence of a long-lived prethermal regime in spin systems subjected to random multipolar drives (RMDs). We demonstrate that the thermalization time scales as $(1/T)^{2n+2}$, where $n$ is the multipolar order and $T$ is the intrinsic time-scale associated with the drive. In the $n \rightarrow \infty$ limit, the drive becomes quasi-periodic and the thermalization time becomes exponentially long ($\sim \exp(\beta/T)$). We further establish the robustness of prethermalization by demonstrating that these thermalization time scaling laws hold for a wide range of initial state energy densities. Intriguingly, the thermalization process in these classical systems is parametrically slower than their quantum counterparts, thereby highlighting important differences between classical and quantum prethermalization. Finally, we propose a protocol to harness this classical prethermalization to realize time rondeau crystals.
- [71] arXiv:2404.11306 (replaced) [pdf, other]
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Title: Existential Unforgeability in Quantum Authentication From Quantum Physical Unclonable Functions Based on Random von Neumann MeasurementComments: 20 pages, 6 figuresJournal-ref: 2024 IEEE International Symposium on Information Theory (ISIT), Athens, Greece, 2024, pp. 3112-3117Subjects: Quantum Physics (quant-ph)
Physical Unclonable Functions (PUFs) leverage inherent, non-clonable physical randomness to generate unique input-output pairs, serving as secure fingerprints for cryptographic protocols like authentication. Quantum PUFs (QPUFs) extend this concept by using quantum states as input-output pairs, offering advantages over classical PUFs, such as challenge reusability via public channels and eliminating the need for trusted parties due to the no-cloning theorem. Recent work introduced a generalized mathematical framework for QPUFs. It was shown that random unitary QPUFs cannot achieve existential unforgeability against Quantum Polynomial Time (QPT) adversaries. Security was possible only with additional uniform randomness. To avoid the cost of external randomness, we propose a novel measurement-based scheme. Here, the randomness naturally arises from quantum measurements. Additionally, we introduce a second model where the QPUF functions as a nonunitary quantum channel, which guarantees existential unforgeability. These are the first models in the literature to demonstrate a high level of provable security. Finally, we show that the Quantum Phase Estimation (QPE) protocol, applied to a Haar random unitary, serves as an approximate implementation of the second type of QPUF by approximating a von Neumann measurement on the unitary's eigenbasis.
- [72] arXiv:2404.14611 (replaced) [pdf, other]
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Title: Fermionic tensor network methodsQuinten Mortier, Lukas Devos, Lander Burgelman, Bram Vanhecke, Nick Bultinck, Frank Verstraete, Jutho Haegeman, Laurens VanderstraetenComments: 78 pages, 6 figuresSubjects: Quantum Physics (quant-ph); Strongly Correlated Electrons (cond-mat.str-el)
We show how fermionic statistics can be naturally incorporated in tensor networks on arbitrary graphs through the use of graded Hilbert spaces. This formalism allows to use tensor network methods for fermionic lattice systems in a local way, avoiding the need of a Jordan-Wigner transformation or the explicit tracking of leg crossings by swap gates in 2D tensor networks. The graded Hilbert spaces can be readily integrated with other internal and lattice symmetries in tensor networks, and only require minor extensions to an existing tensor network software package. We review and benchmark the fermionic versions of common algorithms for matrix product states and projected entangled-pair states.
- [73] arXiv:2405.00663 (replaced) [pdf, html, other]
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Title: Quantum cryptographic protocols with dual messaging system via 2D alternate quantum walk of a genuine single-photon entangled stateComments: 13 pages (including appendix), two figures and one table, accepted for publication in Journal of Physics A: Mathematical and Theoretical as a letterJournal-ref: Journal of Physics A: Mathematical and Theoretical (2024)Subjects: Quantum Physics (quant-ph); Disordered Systems and Neural Networks (cond-mat.dis-nn); Cryptography and Security (cs.CR); Quantum Algebra (math.QA); Optics (physics.optics)
A single-photon entangled state (or single-particle entangled state (SPES) in general) can offer a more secure way of encoding and processing quantum information than their multi-photon (or multi-particle) counterparts. The SPES generated via a 2D alternate quantum-walk setup from initially separable states can be either 3-way or 2-way entangled. This letter shows that the generated genuine three-way and nonlocal two-way SPES can be used as cryptographic keys to securely encode two distinct messages simultaneously. We detail the message encryption-decryption steps and show the resilience of the 3-way and 2-way SPES-based cryptographic protocols against eavesdropper attacks like intercept-and-resend and man-in-the-middle. We also detail the experimental realization of these protocols using a single photon, with the three degrees of freedom being OAM, path, and polarization. We have proved that the protocols have unconditional security for quantum communication tasks. The ability to simultaneously encode two distinct messages using the generated SPES showcases the versatility and efficiency of the proposed cryptographic protocol. This capability could significantly improve the throughput of quantum communication systems.
- [74] arXiv:2405.03970 (replaced) [pdf, html, other]
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Title: Quantum Circuit Optimisation and MBQC Scheduling with a Pauli Tracking LibraryComments: 12 pages, 4 figuresSubjects: Quantum Physics (quant-ph)
We present a software library for the commutation of Pauli operators through quantum Clifford circuits, which is called Pauli tracking. Tracking Pauli operators allows one to reduce the number of Pauli gates that must be executed on quantum hardware. This is relevant for measurement-based quantum computing and for error-corrected circuits that are implemented through Clifford circuits. Furthermore, we investigate the problem of qubit scheduling in measurement-based quantum computing and how Pauli tracking can be used to capture the constraints on the order of measurements.
- [75] arXiv:2405.04104 (replaced) [pdf, html, other]
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Title: A Multi-Module Silicon-On-Insulator Chip Assembly Containing Quantum Dots and Cryogenic Radio-Frequency Readout ElectronicsComments: This work has been submitted to the IEEE for possible publicationSubjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Quantum processing units will be modules of larger information processing systems containing also digital and analog electronics modules. Silicon-based quantum computing offers the enticing opportunity to manufacture all the modules using the same technology platform. Here, we present a cryogenic multi-module assembly for multiplexed readout of silicon quantum devices where all modules have been fabricated using the same fully-depleted silicon-on-insulator (FDSOI) CMOS process. The assembly is constituted by three chiplets: (i) a low-noise amplifier (LNA), (ii) a single-pole eight-throw switch (SP8T), and (iii) a silicon quantum dot (QD) array. We integrate the chiplets into modules and show respectively, (i) a peak gain over 35dB with a 3dB bandwidth from 709MHz to 827MHz and an average noise temperature of 6.2K (minimum 4.2K), (ii) an insertion loss smaller than 1.1dB and a noise temperature less than 1.1K over the 0-2GHz range, and (iii) single-electron box (SEB) charge sensors. Finally, we combine all modules into a single demonstration showing time-domain radio-frequency multiplexing of two SEBs paving the way to an all-silicon quantum computing system.
- [76] arXiv:2405.11632 (replaced) [pdf, html, other]
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Title: Attention to Quantum ComplexityHyejin Kim, Yiqing Zhou, Yichen Xu, Kaarthik Varma, Amir H. Karamlou, Ilan T. Rosen, Jesse C. Hoke, Chao Wan, Jin Peng Zhou, William D. Oliver, Yuri D. Lensky, Kilian Q. Weinberger, Eun-Ah KimSubjects: Quantum Physics (quant-ph)
The imminent era of error-corrected quantum computing urgently demands robust methods to characterize complex quantum states, even from limited and noisy measurements. We introduce the Quantum Attention Network (QuAN), a versatile classical AI framework leveraging the power of attention mechanisms specifically tailored to address the unique challenges of learning quantum complexity. Inspired by large language models, QuAN treats measurement snapshots as tokens while respecting their permutation invariance. Combined with a novel parameter-efficient mini-set self-attention block (MSSAB), such data structure enables QuAN to access high-order moments of the bit-string distribution and preferentially attend to less noisy snapshots. We rigorously test QuAN across three distinct quantum simulation settings: driven hard-core Bose-Hubbard model, random quantum circuits, and the toric code under coherent and incoherent noise. QuAN directly learns the growth in entanglement and state complexity from experimentally obtained computational basis measurements. In particular, it learns the growth in complexity of random circuit data upon increasing depth from noisy experimental data. Taken to a regime inaccessible by existing theory, QuAN unveils the complete phase diagram for noisy toric code data as a function of both noise types. This breakthrough highlights the transformative potential of using purposefully designed AI-driven solutions to assist quantum hardware.
- [77] arXiv:2406.01511 (replaced) [pdf, html, other]
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Title: Decoupling of External and Internal Dynamics in Driven Two-level SystemsComments: 14 pages, 3 figuresJournal-ref: Phys. Rev. Res. 6, 043153 (2024)Subjects: Quantum Physics (quant-ph)
We show how a laser driven two-level system including quantized external degrees of freedom for each state can be decoupled into a set of oscillator equations acting only on the external degrees of freedom with operator valued damping representing the detuning. We give a way of characterizing the solvability of this family of problems by appealing to a classical oscillator with time-dependent damping. As a consequence of this classification we (a) obtain analytic and representation-free expressions for Rabi oscillations including external degrees of freedom with and without an external linear potential, (b) show that whenever the detuning operator can be diagonalized (analytically or numerically) the problem decomposes into a set of classical equations and (c) we can use the oscillator equations as a perturbative basis to describe Rabi oscillations in weak but otherwise arbitrary external potentials. Moreover, chirping of the driving fields phase emerges naturally as a means of compensating the Ehrenfest/mean-value part of the detuning operator's dynamics while the presence of driving phase noise leads to a stochastic evolution equation of Langevin type. Lastly, our approach is representation free with respect to the external degrees of freedom and as consequence a suitable representation or basis expansion can be chosen a posteriori depending on the desired application at hand.
- [78] arXiv:2406.14968 (replaced) [pdf, html, other]
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Title: A blindness property of the Min-Sum decoding for the toric codeSubjects: Quantum Physics (quant-ph)
Kitaev's toric code is one of the most prominent models for fault-tolerant quantum computation, currently regarded as the leading solution for connectivity constrained quantum technologies. Significant effort has been recently devoted to improving the error correction performance of the toric code under message-passing decoding, a class of low-complexity, iterative decoding algorithms that play a central role in both theory and practice of classical low-density parity-check codes. Here, we provide a theoretical analysis of the toric code under min-sum (MS) decoding, a message-passing decoding algorithm known to solve the maximum-likelihood decoding problem in a localized manner, for codes defined by acyclic graphs. Our analysis reveals an intrinsic limitation of the toric code, which confines the propagation of local information during the message-passing process. We show that if the unsatisfied checks of an error syndrome are at distance greater or equal to 5 from each other, then the MS decoding is locally blind: the qubits in the direct neighborhood of an unsatisfied check are never aware of any other unsatisfied checks, except their direct neighbor. Moreover, we show that degeneracy is not the only cause of decoding failures for errors of weight at least 4, that is, the MS non-degenerate decoding radius is equal to 3, for any toric code of distance greater or equal to 9. Finally, complementing our theoretical analysis, we present a pre-processing method of practical relevance. The proposed method, referred to as stabiliser-blowup, has linear complexity and allows correcting all (degenerate) errors of weight up to 3, providing quadratic improvement in the logical error rate performance, as compared to MS only.
- [79] arXiv:2407.04155 (replaced) [pdf, html, other]
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Title: Evaluation of phase shifts for non-relativistic elastic scattering using quantum computersComments: 17 pages, 15 figures, 4 tablesSubjects: Quantum Physics (quant-ph); Nuclear Theory (nucl-th)
Simulations of scattering processes are essential in understanding the physics of our universe. Computing relevant scattering quantities from ab initio methods is extremely difficult on classical devices because of the substantial computational resources needed. This work reports the development of an algorithm that makes it possible to obtain phase shifts for generic non-relativistic elastic scattering processes on a quantum computer. This algorithm is based on extracting phase shifts from the direct implementation of the real-time evolution. The algorithm is improved by a variational procedure, making it more accurate and resistant to the quantum noise. The reliability of the algorithm is first demonstrated by means of classical numerical simulations for different potentials, and later tested on existing quantum hardware, specifically on IBM quantum processors.
- [80] arXiv:2407.04756 (replaced) [pdf, html, other]
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Title: On Hamiltonian formulations of the Dirac systemComments: Annals of Physics, in press, 35 pages, new section addedSubjects: Quantum Physics (quant-ph); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th); Mathematical Physics (math-ph)
We extend a previously successful discussion of the constrained Schrödinger system through the Dirac--Bergmann algorithm to the case of the Dirac field. In order to follow the analogy, first we discuss the classical Dirac field as a spinorial variable, by introducing properly defined momenta and a suitably modified, factor ordered Poisson bracket. According to the Dirac--Bergmann algorithm two second class Hamiltonian constraints emerge, leading to a factor ordered Dirac bracket on the full phase space. This becomes the Poisson bracket on the reduced phase space in the canonical chart adapted to the shell. The Dirac equation is recovered both as consistency condition on the full phase space and as canonical equation on the reduced phase space. Alternatively, considering the Dirac field as odd Grassmann variable, we present the details of the Dirac--Bergmann algorithm (with either left and righ derivatives acting on Grassmann valued superfunctions and involving a different type of generalized Poisson and Dirac brackets). We propose a recipe for the canonical second quantization of all three versions of the generalized Dirac brackets, yielding the correct fundamental anticommutator.
- [81] arXiv:2407.20916 (replaced) [pdf, html, other]
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Title: Parallel ergotropy: Maximum work extraction via parallel local unitary operationsComments: 20 pages, 3 figures, minor corrections, version submitted to PRASubjects: Quantum Physics (quant-ph)
Maximum quantum work extraction is generally defined in terms of the ergotropy functional, no matter how experimentally complicated is the implementation of the optimal unitary allowing for it, especially in the case of multipartite systems. In this framework, we consider a quantum battery made up of many interacting sub-systems and study the maximum extractable work via concurrent local unitary operations on each subsystem. We call the resulting functional parallel ergotropy. Focusing on the bipartite case, we first observe that parallel ergotropy outperforms work extraction via egoistic strategies, in which the first agent A extracts locally on its part the maximum available work and the second agent B, subsequently, extracts what is left on the other part. For the agents, this showcases the need of cooperating for an overall benefit. Secondly, from the informational point of view, we observe that the parallel capacity of a state can detect entanglement and compare it with the statistical entanglement witness that exploits fluctuations of stochastic work extraction. Additionally, we face the technical problem of computing parallel ergotropy. We derive analytical upper bounds for specific classes of states and Hamiltonians and provide receipts to obtain numerical upper bounds via semi-definite programming in the generic case. Finally, extending the concept of parallel ergotropy, we demonstrate that system's free-time evolution and application of local unitaries allow one to saturate the gap with the ergotropy of the whole system.
- [82] arXiv:2408.06587 (replaced) [pdf, html, other]
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Title: Establishing Quantum-Secured Channels in Large-Scale Optical NetworksComments: 5 pages. Information regarding the SPIE Conference Proceedings, where this preprint article was published later on was added to the second versionJournal-ref: Long-distance quantum-secured optical channels in operational environments, Proceedings of SPIE, Volume 13148, Quantum Communications and Quantum Imaging XXII; 1314803 (2024)Subjects: Quantum Physics (quant-ph)
Quantum-secured optical channels based on Quantum Key Distribution technology have generated a significant global interest. Although the maturity level of the short distance (less than 100 km) quantum-secured channels is at a deployment level, instituting such channels over long distance faces technological challenges, which is the subject of a world-wide research. In this article an industry perspective on establishing quantum-secured channels in large-scale optical networks in operational environments will be discussed, including the vision, requirements, and technical analysis of different approaches for establishing such channels.
- [83] arXiv:2408.10001 (replaced) [pdf, html, other]
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Title: Coprime Bivariate Bicycle CodesSubjects: Quantum Physics (quant-ph); Information Theory (cs.IT)
This work (1) proposes a novel numerical algorithm to accelerate the search process for good Bivariate Bicycle (BB) codes and (2) defines a new subclass of BB codes suitable for quantum error correction. The proposed acceleration search algorithm reduces the search space by excluding some equivalent codes from the search space, as well as setting thresholds to drop bad codes at an early stage. A number of new BB codes found by this algorithm are reported. The proposed subclass of BB codes employs coprimes to construct groups via polynomials as the basis for the BB code, rather than using the standard BB codes with unconstrained constructors. In contrast to vanilla BB codes, where parameters remain unknown prior to code discovery, the rate of the proposed code can be determined beforehand by specifying a factor polynomial as an input to the numerical search algorithm. Using this coprime BB construction, we found a number of surprisingly short to medium-length codes that were previously unknown.
- [84] arXiv:2408.12752 (replaced) [pdf, html, other]
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Title: High-distance codes with transversal Clifford and T-gatesComments: 2 tables, 3 figures. Updated version: Includes a family of triorthogonal codes with improved parameters. Includes a more in-depth discussion of T-gate code familiesSubjects: Quantum Physics (quant-ph); Information Theory (cs.IT); Number Theory (math.NT)
The non-local interactions in several quantum devices allow for the realization of more compact quantum encodings while retaining the same degree of protection against noise. Anticipating that short to medium-length codes will soon be realizable, it is important to construct stabilizer codes that, for a given code distance, admit fault-tolerant implementations of logical gates with the fewest number of physical qubits. We extract high-distance doubly even codes from the quantum quadratic-residue code family that admit a transversal implementation of the single-qubit Clifford group and block transversal implementation of the full Clifford group. Applying a doubling procedure [arXiv:1509.03239] to such codes yields a family of high-distance weak triply even codes which admit a transversal implementation of the logical $\texttt{T}$-gate. Relaxing the triply even property, we also obtain a family of triorthogonal codes which requires an even lower overhead at the cost of additional Clifford gates to achieve the same logical operation. To our knowledge, our doubly even and triorthogonal families are the shortest qubit stabilizer codes of the same distance that can realize their respective gates.
- [85] arXiv:2409.06083 (replaced) [pdf, html, other]
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Title: Information geometry approach to quantum stochastic thermodynamicsComments: 13 pages, 4 figures. Comments welcome!Subjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech)
Recent advancements have revealed new links between information geometry and classical stochastic thermodynamics, particularly through the Fisher information (FI) with respect to time. Recognizing the non-uniqueness of the quantum Fisher metric in Hilbert space, we exploit the fact that any quantum Fisher information (QFI) can be decomposed into a metric-independent incoherent part and a metric-dependent coherent contribution. We demonstrate that the incoherent component of any QFI can be directly linked to entropic acceleration, and for GKSL dynamics with local detailed balance, to the rate of change of generalised thermodynamic forces and entropic flow, paralleling the classical results. Furthermore, we tighten a classical uncertainty relation between the geometric uncertainty of a path in state space and the time-averaged rate of information change and demonstrate that it also holds for quantum systems. We generalise a classical geometric bound on the entropy rate for far-from-equilibrium processes by incorporating a non-negative quantum contribution that arises from the geometric action due to coherent dynamics. Finally, we apply an information-geometric analysis to the recently proposed quantum-thermodynamic Mpemba effect, demonstrating this framework's ability to capture thermodynamic phenomena.
- [86] arXiv:2409.06482 (replaced) [pdf, html, other]
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Title: Quantum-state texture and gate identificationComments: To appear on Phys. Rev. LettSubjects: Quantum Physics (quant-ph)
We introduce and explore the notion of texture of an arbitrary quantum state, in a selected basis. In the first part of this letter we develop a resource theory and show that state texture is adequately described by an easily computable monotone, which is also directly measurable. It is shown that textures are useful in the characterization of unknown quantum gates in universal circuit layers. By using randomized input states and recording the textures of the output qubits we are able to fully characterize the circuit layer, whenever it contains at least one CNOT gate. This can be done without the need of tomographic protocols and the use of ancillary systems.
- [87] arXiv:2409.17290 (replaced) [pdf, html, other]
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Title: Temporal Bell inequalities in non-relativistic many-body physicsComments: 7 pages, 1 figureSubjects: Quantum Physics (quant-ph); Quantum Gases (cond-mat.quant-gas)
Analyzing the spreading of information in many-body systems is crucial to understanding their quantum dynamics. At the most fundamental level, this task is accomplished by Bell inequalities, whose violation by quantum mechanics implies that information cannot always be stored locally. While Bell-like inequalities, such as the one of Clauser and Horne, envisage a situation in which two parties perform measurements on systems at different positions, one could formulate temporal inequalities, in which the two parties measure at different times. However, for causally-connected parties, these extensions are compatible with local hidden-variable theories, so that no intrinsically-quantum information spreading occurs in such temporal correlations. Here we show that a temporal Clauser-Horne inequality for two spins is violated for a nonzero time interval between the measurements if the two measured parties are connected by a spin chain. The chain constitutes a medium for the spreading of quantum information, which prevents the immediate signaling and thus the deterministic time evolution after the first measurement. Our result suggests that, as expected in a many-body setup, the Lieb-Robinson bound substitutes the speed of light as the fundamental limit for the spreading of information.
- [88] arXiv:2410.12733 (replaced) [pdf, html, other]
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Title: Quantum Embedding of Non-local Quantum Many-body Interactions in Prototypal Anti-tumor Vaccine Metalloprotein on Near Term Quantum Computing HardwareComments: 14 pages, 16 figuresSubjects: Quantum Physics (quant-ph); Strongly Correlated Electrons (cond-mat.str-el)
The real world obeys quantum physics and quantum computing presents an alternative way to map physical problems to systems that follow the same laws. Such computation fundamentally constitutes a better way to understand the most challenging quantum problems. One such problem is the accurate simulation of highly correlated quantum systems. Due to the high dimensionality of the problem classical computers require considerable computer power to accurately predict material properties, especially when strong electron interactions are present. Still, modern day quantum hardware has many limitations and only allows for modeling of very simple systems. Here we present for the first time a quantum computer model simulation of a complex hemocyanin molecule, which is an important respiratory protein involved in various physiological processes such as oxygen transport and immune defence, and is also used as a key component in therapeutic vaccines for cancer. To better characterise the mechanism by which hemocyanin transports oxygen, variational quantum eigensolver (VQE) based on fermionic excitations and quantum embedding methods is used in the context of dynamic mean field theory to solve Anderson impurity model (AIM). Finally, it is concluded that the magnetic structure of hemocyanin is largely influenced by the many-body correction and that the computational effort for solving correlated electron systems could be substantially reduced with the introduction of quantum computing algorithms. We encourage the use of the Hamiltonian systems presented in this paper as a benchmark for testing quantum computing algorithms efficiency for chemistry applications.
- [89] arXiv:2410.13934 (replaced) [pdf, html, other]
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Title: Extractable energy from quantum superposition of current statesComments: 15 pages, 9 figuresSubjects: Quantum Physics (quant-ph); Quantum Gases (cond-mat.quant-gas)
We explore the energy content of superpositions of current states. Specifically, we focus on the maximum energy that can be extracted from them through local unitary transformations. The figure of merit we employ is the local ergotropy. We perform a complete analysis in the whole range of the system's parameters. This way, we prove that superpositions of two current states in spatially closed spin networks are characterized by specific peaks in extractable energy, generally overcoming the ergotropy of each of the two separate current states characterized by a single winding number. The many-body state dynamics entails to ergotropy evolving in a controlled fashion. The implementation we suggest is based on a Rydberg-atom platform. Optimal transformations able to extract locally the maximum possible amount of energy are sorted out.
- [90] arXiv:2410.18044 (replaced) [pdf, html, other]
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Title: Time Evolution in Quantum Mechanics with a Minimal Time ScaleComments: 24 pages, 5 figuresJournal-ref: Symmetry 16, 1520 (2024)Subjects: Quantum Physics (quant-ph); Mathematical Physics (math-ph)
The existence of a minimum measurable length scale was suggested by various theories of quantum gravity, string theory and black hole physics. Motivated by this, we examine a quantum theory exhibiting a minimum measurable time scale. We use the Page-Wootters formalism to describe time evolution of a quantum system with the modified commutation relations between the time and frequency operator. Such modification leads to a minimal uncertainty in the measurement of time. This causes breaking of the time-translation symmetry and results in a modified version of the Schrödinger equation. A minimal time scale also allows us to introduce a discrete Schrödinger equation describing time evolution on a lattice. We show that both descriptions of time evolution are equivalent. We demonstrate the developed theory on a couple simple quantum systems.
- [91] arXiv:2410.18254 (replaced) [pdf, html, other]
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Title: Refining Ky Fan's majorization relation with linear programmingComments: 36 pages, 2 figures, error in version 1 correctedSubjects: Quantum Physics (quant-ph); Information Theory (cs.IT); Rings and Algebras (math.RA)
A separable version of Ky Fan's majorization relation is proven for a sum of two operators that are each a tensor product of two positive semi-definite operators. In order to prove it, upper bounds are established for the relevant largest eigenvalue sums in terms of the optimal values of certain linear programs. The objective function of these linear programs is the dual of the direct sum of the spectra of the summands. The feasible sets are bounded polyhedra determined by positive numbers, called alignment terms, that quantify the overlaps between pairs of largest eigenvalue spaces of the summands. By appealing to geometric considerations, tight upper bounds are established on the alignment terms of tensor products of positive semi-definite operators. As an application, the spin alignment conjecture in quantum information theory is affirmatively resolved to the 2-letter level. Consequently, the coherent information of platypus channels is additive to the 2-letter level.
- [92] arXiv:2411.04650 (replaced) [pdf, html, other]
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Title: Many-body nonequilibrium dynamics in a self-induced Floquet systemYuechun Jiao, Yu Zhang, Jingxu Bai, Suotang Jia, C. Stuart Adams, Zhengyang Bai, Heng Shen, Jianming ZhaoComments: 6 pages, 4 figuresSubjects: Quantum Physics (quant-ph); Quantum Gases (cond-mat.quant-gas); Atomic Physics (physics.atom-ph)
Floquet systems are periodically driven systems. In this framework, the system Hamiltonian and associated spectra of interest are modified, giving rise to new quantum phases of matter and nonequilibrium dynamics without static counterparts. Here we experimentally demonstrate a self-induced Floquet system in the interacting Rydberg gas. This originates from the photoionization of thermal Rydberg gases in a static magnetic field. Importantly, by leveraging the Rydberg electromagnetically induced transparency spectrum, we probe the nonequilibrium dynamics in the bistable regime and identify the emergence of a discrete time crystalline phase. Our work fills the experimental gap in the understanding the relation of multistability and dissipative discrete time crystalline phase. In this regard, it constitutes a highly controlled platform for exploring exotic nonequilibrium physics in dissipative interacting systems.
- [93] arXiv:2411.06650 (replaced) [pdf, other]
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Title: Quantum Policy Gradient in Reproducing Kernel Hilbert SpaceSubjects: Quantum Physics (quant-ph); Machine Learning (cs.LG)
Parametrised quantum circuits offer expressive and data-efficient representations for machine learning. Due to quantum states residing in a high-dimensional Hilbert space, parametrised quantum circuits have a natural interpretation in terms of kernel methods. The representation of quantum circuits in terms of quantum kernels has been studied widely in quantum supervised learning, but has been overlooked in the context of quantum reinforcement learning. This paper proposes parametric and non-parametric policy gradient and actor-critic algorithms with quantum kernel policies in quantum environments. This approach, implemented with both numerical and analytical quantum policy gradient techniques, allows exploiting the many advantages of kernel methods, including available analytic forms for the gradient of the policy and tunable expressiveness. The proposed approach is suitable for vector-valued action spaces and each of the formulations demonstrates a quadratic reduction in query complexity compared to their classical counterparts. Two actor-critic algorithms, one based on stochastic policy gradient and one based on deterministic policy gradient (comparable to the popular DDPG algorithm), demonstrate additional query complexity reductions compared to quantum policy gradient algorithms under favourable conditions.
- [94] arXiv:2411.13190 (replaced) [pdf, html, other]
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Title: Ab-Initio Approach to Many-Body Quantum Spin DynamicsComments: 12 pages, 9 figuresSubjects: Quantum Physics (quant-ph); Quantum Gases (cond-mat.quant-gas); Atomic Physics (physics.atom-ph); Computational Physics (physics.comp-ph)
A fundamental longstanding problem in studying spin models is the efficient and accurate numerical simulation of the long-time behavior of larger systems. The exponential growth of the Hilbert space and the entanglement accumulation at long times pose major challenges for current methods. To address these issues, we employ the multilayer multiconfiguration time-dependent Hartree (ML-MCTDH) framework to simulate the many-body spin dynamics of the Heisenberg model in various settings, including the Ising and XYZ limits with different interaction ranges and random couplings. Benchmarks with analytical and exact numerical approaches show that ML-MCTDH accurately captures the time evolution of one- and two-body observables in both one- and two-dimensional lattices. A comparison of ML-MCTDH with the discrete truncated Wigner approximation (DTWA) demonstrates that our approach excels in handling anisotropic models and consistently provides better results for two-point observables in all simulation instances. Our results indicate that the multilayer structure of ML-MCTDH is a promising numerical framework for handling the dynamics of generic many-body spin systems.
- [95] arXiv:2212.03780 (replaced) [pdf, other]
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Title: Multiple Landau level filling for a mean field limit of 2D fermionsJournal-ref: Journal of Mathematical Physics volume: 65 number: 2 pages: 021902 year: 2024Subjects: Mathematical Physics (math-ph); Quantum Gases (cond-mat.quant-gas); Functional Analysis (math.FA); Quantum Physics (quant-ph)
Motivated by the quantum hall effect, we study N two dimensional interacting fermions in a large magnetic field limit. We work in a bounded domain, ensuring finite degeneracy of the Landau levels. In our regime, several levels are fully filled and inert: the density in these levels is constant. We derive a limiting mean-field and semi classical description of the physics in the last, partially filled Landau level.
- [96] arXiv:2309.05594 (replaced) [pdf, html, other]
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Title: Insulator phases of Bose-Fermi mixtures induced by intraspecies next-neighbor interactionsComments: Substantially updated version that include order parameters for the three new CDW phases found and new figures. 30 pages, 12 figures. Comments are welcomeSubjects: Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)
We study a one-dimensional mixture of two-color fermions and scalar bosons at the hardcore limit, focusing on the effect that the intraspecies next-neighbor interactions have on the zero-temperature ground state of the system for different fillings of each carrier. Exploring the problem's parameters, we observed that the non-local interaction could favor or harm the well-known mixed Mott and spin-selective Mott insulators. We also found the emergence of three unusual insulating states with charge density wave (CDW) structures in which the orders of the carriers are out of phase with each other. For instance, the immiscible CDW appears only at half-filling bosonic density, whereas the mixed CDW state is characterized by equal densities of bosons and fermions. Finally, the spin-selective CDW couples the bosons and only one kind of fermions. Appropriate order parameters were proposed for each phase to obtain the critical parameters for the corresponding superfluid-insulator transition. Our results can inspire or contribute to understanding experiments in cold-atom setups with long-range interactions or recent reports involving quasiparticles in semiconductor heterostructures.
- [97] arXiv:2402.16807 (replaced) [pdf, html, other]
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Title: An $^{115}$In$^+$-$^{172}$Yb$^+$ Coulomb crystal clock with $2.5\times10^{-18}$ systematic uncertaintyH. N. Hausser, J. Keller, T. Nordmann, N. M. Bhatt, J. Kiethe, H. Liu, I. M. Richter, M. von Boehn, J. Rahm, S. Weyers, E. Benkler, B. Lipphardt, S. Doerscher, K. Stahl, J. Klose, C. Lisdat, M. Filzinger, N. Huntemann, E. Peik, T. E. MehlstäublerComments: 13 pages, 10 figuresSubjects: Atomic Physics (physics.atom-ph); Quantum Physics (quant-ph)
We present a scalable mixed-species Coulomb crystal clock based on the $^1S_0$ $\leftrightarrow$ $^3P_0$ transition in $^{115}$In$^+$. $^{172}$Yb$^+$ ions are co-trapped and used for sympathetic cooling. Reproducible interrogation conditions for mixed-species Coulomb crystals are ensured by a conditional preparation sequence with permutation control. We demonstrate clock operation with a 1In$^+$-3Yb$^+$ crystal, achieving a relative systematic uncertainty of $2.5\times10^{-18}$ and a relative frequency instability of $1.6\times10^{-15}/\sqrt{\tau/1\;\mathrm{s}}$. We report on absolute frequency measurements with an uncertainty of $1.3\times10^{-16}$ and optical frequency comparisons with clocks based on $^{171}$Yb$^+$ (E3) and $^{87}$Sr. With a fractional uncertainty of $4.4\times10^{-18}$, the former is - to our knowledge - the most accurate frequency ratio value reported to date. For the $^{115}$In$^+$/$^{87}$Sr ratio, we improve upon the best previous measurement by more than an order of magnitude. We also demonstrate operation with four $^{115}$In$^+$ clock ions, which reduces the instability to $9.2\times10^{-16}/\sqrt{\tau/1\;\mathrm{s}}$.
- [98] arXiv:2402.19244 (replaced) [pdf, html, other]
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Title: Electron conductance and many-body marker of a cavity-embedded topological 1D chainJournal-ref: Phys. Rev. B 110, 195416 (2024) (Editors' Suggestion)Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Other Condensed Matter (cond-mat.other); Quantum Physics (quant-ph)
We investigate many-body topological and transport properties of a one-dimensional Su-Schrieffer-Heeger (SSH) topological chain coupled to the quantum field of a cavity mode. The quantum conductance is determined via Green's function formalism in terms of the light-matter eigenstates calculated via exact diagonalization for a finite number of electrons. We show that the topology of the cavity-embedded many-electron system is described by a generalized electron-photon Zak marker. We reveal how the quantization of transport is modified by the cavity vacuum fields for a finite-size chain and how it is impacted by electronic disorder. Moreover, we show that electron-photon entanglement produces dramatic differences with respect to the predictions of mean-field theory, which strongly underestimates cavity-modified transport.
- [99] arXiv:2404.01756 (replaced) [pdf, html, other]
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Title: Antiparticles in non-relativistic quantum mechanicsComments: 18 pages; v3: some clarificationsSubjects: Mathematical Physics (math-ph); High Energy Physics - Theory (hep-th); Quantum Physics (quant-ph)
Non-relativistic quantum mechanics was originally formulated to describe particles. Using ideas from the geometric quantization approach, we show how the concept of antiparticles can and should be introduced in the non-relativistic case without appealing to quantum field theory. We discuss this in detail using the example of the one-dimensional harmonic oscillator.
- [100] arXiv:2404.17445 (replaced) [pdf, html, other]
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Title: Metrology of microwave fields based on trap-loss spectroscopy with cold Rydberg atomsRomain Duverger, Alexis Bonnin, Romain Granier, Quentin Marolleau, Cédric Blanchard, Nassim Zahzam, Yannick Bidel, Malo Cadoret, Alexandre Bresson, Sylvain SchwartzComments: 12 pages, 9 figuresSubjects: Atomic Physics (physics.atom-ph); Quantum Physics (quant-ph)
We demonstrate a new approach for the metrology of microwave fields based on the trap-loss-spectroscopy of cold Rydberg atoms in a magneto-optical trap. Compared to state-of-the-art sensors using room-temperature vapors, cold atoms allow longer interaction times, better isolation from the environment and a reduced Doppler effect. Our approach is particularly simple as the detection relies on fluorescence measurements only. Moreover, our signal is well described by a two-level model across a broad measurement range, allowing in principle to reconstruct the amplitude and the frequency of the microwave field simultaneously without the need for an external reference field. We report on a scale factor linearity at the percent level and no noticeable drifts over two hours, paving the way for new applications of cold Rydberg atoms in metrology such as calibrating blackbody shifts in state-of-the-art optical clocks, monitoring the Earth cryosphere from space, measuring the cosmic microwave background or searching for dark matter.
- [101] arXiv:2405.09217 (replaced) [pdf, html, other]
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Title: Augmenting Density Matrix Renormalization Group with Clifford CircuitsSubjects: Strongly Correlated Electrons (cond-mat.str-el); Quantum Physics (quant-ph)
Density Matrix Renormalization Group (DMRG) or Matrix Product States (MPS) are widely acknowledged as highly effective and accurate methods for solving one-dimensional quantum many-body systems. However, the direct application of DMRG to the study two-dimensional systems encounters challenges due to the limited entanglement encoded in the wave-function ansatz. Conversely, Clifford circuits offer a promising avenue for simulating states with substantial entanglement, albeit confined to stabilizer states. In this work, we present the seamless integration of Clifford circuits within the DMRG algorithm, leveraging the advantages of both Clifford circuits and DMRG. This integration leads to a significant enhancement in simulation accuracy with small additional computational cost. Moreover, this framework is useful not only for its current application but also for its potential to be easily adapted to various other numerical approaches
- [102] arXiv:2406.16898 (replaced) [pdf, html, other]
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Title: Detecting kHz gravitons from a neutron star merger with a multi-mode resonant mass detectorComments: 8 + 3 pages, 2 FiguresSubjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Astrophysical Phenomena (astro-ph.HE); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th); Instrumentation and Detectors (physics.ins-det); Quantum Physics (quant-ph)
We propose a multi-mode bar consisting of mass elements of decreasing size for the implementation of a gravitational version of the photo-electric effect through the stimulated absorption of up to kHz gravitons from a binary neutron star merger and post-merger. We find that the multi-mode detector has normal modes that retain the coupling strength to the gravitational wave of the largest mass-element, while only having an effective mass comparable to the mass of the smallest element. This allows the normal modes to have graviton absorption rates due to the tonne-scale largest mass, while the single graviton absorption process in the normal mode could be resolved through energy measurements of a mass-element in-principle smaller than pico-gram scale. We argue the feasibility of directly counting gravito-phonons in the bar through energy measurements of the end mass. This improves the transduction of the single-graviton signal, enhancing the feasibility of detecting single gravitons.
- [103] arXiv:2406.17417 (replaced) [pdf, html, other]
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Title: Plaquette-type valence bond solid state in the $J_1$-$J_2$ square-lattice Heisenberg modeComments: close to the published versionJournal-ref: Phys.Rev.B 110,195111 (2024)Subjects: Strongly Correlated Electrons (cond-mat.str-el); Quantum Physics (quant-ph)
We utilize Density Matrix Renormalization Group (DMRG) and Fully Augmented Matrix Product States (FAMPS) methods to investigate the Valence Bond Solid (VBS) phase in the $J_1$-$J_2$ square lattice Heisenberg model. To differentiate between the Columnar Valence Bond Solid (CVBS) and Plaquette Valence Bond Solid (PVBS) phases, we introduce an anisotropy $\Delta_y$ in the nearest neighboring coupling in the $y$-direction, aiming at detecting the possible spontaneous rotational symmetry breaking in the VBS phase. In the calculations, we push the bond dimension to as large as $D = 25000$ in FAMPS, simulating systems at a maximum size of $14 \times 14$. With a careful extrapolation of the truncation errors and appropriate finite-size scaling, followed by finite $\Delta_y$ scaling analysis of the VBS dimer order parameters, we identify the VBS phase as a PVBS type, meaning there is no spontaneous rotational symmetry breaking in the VBS phase. This study not only resolves the long-standing issue of the characterization of the VBS order in the $J_1$-$J_2$ square lattice Heisenberg model but also highlights the capabilities of FAMPS in the study of two-dimensional quantum many-body systems.
- [104] arXiv:2408.16466 (replaced) [pdf, html, other]
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Title: Topological zero modes and bounded modes at smooth domain walls: Exact solutions and dualitiesComments: 16 pages, 4 figures, typos fixed, some equations addedSubjects: High Energy Physics - Theory (hep-th); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Superconductivity (cond-mat.supr-con); Quantum Physics (quant-ph)
Topology describes global quantities invariant under continuous deformations, such as the number of elementary excitations at a phase boundary, without detailing specifics. Conversely, differential laws are needed to understand the physical properties of these excitations, such as their localization and spatial behavior. For instance, topology mandates the existence of solitonic zero-energy modes at the domain walls between topologically inequivalent phases in topological insulators and superconductors. However, the spatial dependence of these modes is only known in the idealized (and unrealistic) case of a sharp domain wall. Here, we find the analytical solutions of these zero-modes by assuming a smooth and exponentially-confined domain wall. This allows us to characterize the zero-modes using a few length scales: the domain wall width, the exponential decay length, and oscillation wavelength. These quantities define distinct regimes: featureless modes with "no hair" at sharp domain walls, and nonfeatureless modes at smooth domain walls, respectively, with "short hair", i.e., featureless at long distances, and "long hair", i.e., nonfeatureless at all length scales. We thus establish a universal relation between the bulk excitation gap, decay rate, and oscillation momentum of the zero modes, which quantifies the bulk-boundary correspondence in terms of experimentally measurable physical quantities. Additionally, we reveal an unexpected duality between topological zero modes and Shockley modes, unifying the understanding of topologically-protected and nontopological boundary modes. These findings shed some new light on the localization properties of edge modes in topological insulators and Majorana zero modes in topological superconductors and on the differences and similarities between topological and nontopological zero modes in these systems.
- [105] arXiv:2409.19249 (replaced) [pdf, html, other]
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Title: Enhancing the ODMR Signal of Organic Molecular QubitsComments: 11 pages, 5 figures. Some rephrasing was done for better readability and the figure texts have been enlargedSubjects: Chemical Physics (physics.chem-ph); Materials Science (cond-mat.mtrl-sci); Quantum Physics (quant-ph)
In quantum information science and sensing, electron spins are often purified into a specific polarisation through an optical-spin interface, a process known as optically-detected magnetic resonance (ODMR). Diamond-NV centres and transition metals are both excellent platforms for these so-called colour centres, while metal-free molecular analogues are also gaining popularity for their extended polarisation lifetimes, milder environmental impacts, and reduced costs. In our earlier attempt at designing such organic high-spin $\pi$-diradicals, we proposed to spin-polarise by shelving triplet $M_{S}=\pm1$ populations as singlets. This was recently verified by experiments albeit with low ODMR contrasts of $<1\%$ at temperatures above 5 K. In this work, we propose to improve the ODMR signal by moving singlet populations back into the triplet $M_{S}=0$ sublevel, designing a true carbon-based molecular analogue to the NV centre. Our proposal is based upon transition-orbital and group-theoretical analyses of beyond-nearest-neighbour spin-orbit couplings, which are further confirmed by ab initio calculations of a realistic trityl-based radical dimer. Microkinetic analyses point towards high ODMR contrasts of around $30\%$ under experimentally-feasible conditions, a stark improvement from previous works. Finally, in our quest towards ground-state optically-addressable molecular spin qubits, we exemplify how our symmetry-based design avoids Zeeman-induced singlet-triplet mixings, setting the scene for realising electron spin qubit gates.
- [106] arXiv:2410.16402 (replaced) [pdf, html, other]
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Title: Universal time evolution of string order parameter in quantum critical systems with boundary invertible or non-invertible symmetry breakingComments: are welcome. 32 pages, many figures; v2: Refs addedSubjects: Strongly Correlated Electrons (cond-mat.str-el); Statistical Mechanics (cond-mat.stat-mech); High Energy Physics - Theory (hep-th); Mathematical Physics (math-ph); Quantum Physics (quant-ph)
The global symmetry, either invertible or non-invertible, has been extensively studied in two dimensional conformal field theories in recent years. When the theory is defined on a manifold with open boundaries, however, many interesting conformal boundary conditions will fully or partially break such global symmetry. In this work, we study the effect of symmetry-breaking boundaries or interfaces when the system is out of equilibrium. We show that the boundary or interface symmetry-breaking can be detected by the time evolution of string order parameters, which are constructed from the symmetry operators that implement the symmetry transformations. While the string order parameters are independent of time if the symmetry is preserved over the whole system, they evolve in time in a universal way if the boundary or interface breaks the symmetry. More explicitly, in the presence of boundary or interface symmetry-breaking, the string order parameters decay exponentially in time after a global quantum quench, and decay as a power-law in time after a local quantum quench. We also generalize our study to the case when the string order parameters are defined in a subsystem, which are related to the full counting statistics. It is found there are also universal features in the time evolution of string order parameters in this case. We verify our field theory results by studying the time evolution of these two different types of string order parameters in lattice models.
- [107] arXiv:2411.09067 (replaced) [pdf, html, other]
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Title: Critical states exhibit invariance in both position and momentum spacesComments: Comments are welcomeSubjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Gases (cond-mat.quant-gas); Statistical Mechanics (cond-mat.stat-mech); Quantum Physics (quant-ph)
The critical states of disordered systems are intriguing subjects within the realm of condensed matter physics and complex systems. These states manifest in materials where disorder plays a significant role, and are distinguished by their multifractal structure and self-similarity. However, accurately characterizing critical states continues to pose a significant challenge. In this study, we argue that critical states exhibit a certain invariance in both position and momentum spaces, leading to their delocalization in both domains. More specifically, it is expected that typical physical quantities characterizing critical states, such as the inverse participation ratio and information entropy, should exhibit invariance in both position space and momentum space. Subsequent numerical simulations validate the correctness of this invariance, thereby establishing a robust foundation for future experimental validation of critical states.