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Quantum Physics

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Showing new listings for Thursday, 18 September 2025

Total of 84 entries
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New submissions (showing 33 of 33 entries )

[1] arXiv:2509.13367 [cn-pdf, pdf, html, other]
Title: Numerical Optimization Methods in the environment with Quantum Noise
Tomáš Bezděk
Comments: Revised version of a Master's thesis originally submitted to VSB - Technical University of Ostrava in 2025. This updated version contains minor cosmetic changes, including typos, grammatical errors, and clarifying sentences. New citations were also added. No results or conclusions were changed from the original. The original source is at https://dspace.vsb.cz/handle/10084/156936
Subjects: Quantum Physics (quant-ph) ; Numerical Analysis (math.NA)

The accurate calculation of electronic potential energy surfaces for ground and excited states is crucial for understanding photochemical processes, particularly near conical intersections. While classical methods are limited by scaling and quantum algorithms by hardware, this thesis focuses on the State-Averaged Orbital-Optimized Variational Quantum Eigensolver (SA-OO-VQE). This hybrid quantum-classical algorithm provides a balanced description of multiple electronic states by combining quantum state preparation with classical state-averaged orbital optimization. A key contribution is the implementation and evaluation of the Differential Evolution algorithm within the SA-OO-VQE framework, with a comparative study against classical optimizers like the Broyden-Fletcher-Goldfarb-Shanno (BFGS) and Sequential Least Squares Programming (SLSQP) algorithms. The performance of these optimizers is assessed by calculating ground and first excited state energies for H$_2$, H$_4$, and LiH. The thesis also demonstrates SA-OO-VQE's capability to accurately model potential energy surfaces near conical intersections, using formaldimine as a case study. The results show that orbital optimization is essential for correctly capturing the potential energy surface topology, a task where standard methods with fixed orbitals fail. Our findings indicate that while Differential Evolution presents efficiency challenges, gradient-based methods like BFGS and SLSQP offer superior performance, confirming that the SA-OO-VQE approach is crucial for treating complex electronic structures.

[2] arXiv:2509.13377 [cn-pdf, pdf, html, other]
Title: Purification of quantum trajectories in infinite dimensions
Federico Girotti, Alessandro Vitale
Comments: 16 pages, no figures, comments are welcome
Subjects: Quantum Physics (quant-ph) ; Probability (math.PR)

In this work we exhibit a class of examples that show that the characterization of purification of quantum trajectories in terms of 'dark' subspaces that was proved for finite dimensional systems fails to hold in infinite dimensional ones. Moreover, we prove that the new phenomenon emerging in our class of models and preventing purification to happen is the only new possibility that emerges in infinite dimensional systems. Our proof strategy points out that the emergence of new phenomena in infinite dimensional systems is due to the fact that the set of orthogonal projections is not sequentially compact. Having in mind this insight, we are able to prove that the finite dimensional extends to a class of infinite dimensional models.

[3] arXiv:2509.13398 [cn-pdf, pdf, html, other]
Title: Quantum ground-state cooling of two librational modes of a nanorotor
Stephan Troyer, Florian Fechtel, Lorenz Hummer, Henning Rudolph, Benjamin A. Stickler, Uroš Delić, Markus Arndt
Subjects: Quantum Physics (quant-ph) ; Optics (physics.optics)

Controlling the motion of nanoscale objects at the quantum limit promises new tests of quantum mechanics and advanced sensors. Rotational motion is of particular interest, as it follows nonlinear dynamics in a compact, closed configuration space, which opens up a plethora of phenomena and applications beyond the possibilities of free or trapped linear motion. A prerequisite for such experiments is the capability to trap nanorotors and initialize them in a quantum ground state of libration. Here, we demonstrate the reliable, repetitive laser-induced loading of silica nanodimers and trimers into an optical tweezer. Coherent scattering in a high-finesse cavity allows us to cool two different librational modes to the quantum ground state with occupation numbers as low as $n_{\beta}=0.54\pm0.32$ and $n_{\alpha}=0.21\pm0.03$. By simultaneously cooling both degrees of freedom ($n_\beta=0.73\pm0.22$, $n_\alpha=1.02\pm0.08$) we align nanorotors to a space-fixed axis with precision better than 20$\,\mu$rad, close to the zero-point amplitude of librations.

[4] arXiv:2509.13405 [cn-pdf, pdf, html, other]
Title: Defining Security in Quantum Key Distribution
Carla Ferradini, Martin Sandfuchs, Ramona Wolf, Renato Renner
Comments: 21+3 pages. Comments are welcome
Subjects: Quantum Physics (quant-ph) ; Cryptography and Security (cs.CR)

The security of quantum key distribution (QKD) is quantified by a parameter $\varepsilon>0$, which -- under well-defined physical assumptions -- can be bounded explicitly. This contrasts with computationally secure schemes, where security claims are only asymptotic (i.e., under standard complexity assumptions, one only knows that $\varepsilon \to 0$ as the key size grows, but has no explicit bound). Here we explain the definition and interpretation of $\varepsilon$-security. Adopting an axiomatic approach, we show that $\varepsilon$ can be understood as the maximum probability of a security failure. Finally, we review and address several criticisms of this definition that have appeared in the literature.

[5] arXiv:2509.13406 [cn-pdf, pdf, html, other]
Title: Free mutual information and higher-point OTOCs
Shreya Vardhan, Jinzhao Wang
Comments: 45+38 pages, 24 figures. Comments are welcome!
Subjects: Quantum Physics (quant-ph) ; Statistical Mechanics (cond-mat.stat-mech) ; Strongly Correlated Electrons (cond-mat.str-el) ; High Energy Physics - Theory (hep-th) ; Mathematical Physics (math-ph)

We introduce a quantity called the free mutual information (FMI), adapted from concepts in free probability theory, as a new physical measure of quantum chaos. This quantity captures the spreading of a time-evolved operator in the space of all possible operators on the Hilbert space, which is doubly exponential in the number of degrees of freedom. It thus provides a finer notion of operator spreading than the well-understood phenomenon of operator growth in physical space. We derive two central results which apply in any physical system: first, an explicit ``Coulomb gas'' formula for the FMI of two observables $A(t)$ and $B$ in terms of the eigenvalues of the product operator $A(t)B$; and second, a general relation expressing the FMI as a weighted sum of all higher-point out-of-time-ordered correlators (OTOCs). This second result provides a precise information-theoretic interpretation for the higher-point OTOCs as collectively quantifying operator ergodicity and the approach to freeness. This physical interpretation is particularly useful in light of recent progress in experimentally measuring higher-point OTOCs. We identify universal behaviours of the FMI and higher-point OTOCs across a variety of chaotic systems, including random unitary circuits and chaotic spin chains, which indicate that spreading in the doubly exponential operator space is a generic feature of quantum many-body chaos. At the same time, the non-generic behavior of the FMI in various non-chaotic systems, including certain unitary designs, shows that there are cases where an operator spreads in physical space but remains localized in operator space. The FMI is thus a sharper diagnostic of chaos than the standard 4-point OTOC.

[6] arXiv:2509.13410 [cn-pdf, pdf, html, other]
Title: Symmetry Resolved Multipartite Entanglement Entropy
Ashwat Jain
Comments: 17 pages, 2 figures
Subjects: Quantum Physics (quant-ph) ; Mesoscale and Nanoscale Physics (cond-mat.mes-hall)

We perform the symmetry resolution of a multipartite entanglement measure, namely the global entanglement $Q$ introduced by Meyer and Wallach [2002, J. of Math. Phys., 43, pp. 4273] for all systems of distinguishable particles hosting a locally acting symmetry. For an ensemble of Haar random states we find agreement with equipartition, with leading order behaviour and finite size corrections which follow a power law scaling with the number of local degrees of freedom. Implications of this result for the general symmetry-resolved multipartite entanglement paradigm are discussed and some possible experimental verification methods are presented.

[7] arXiv:2509.13423 [cn-pdf, pdf, html, other]
Title: Computational complexity of Berry phase estimation in topological phases of matter
Ryu Hayakawa, Kazuki Sakamoto, Chusei Kiumi
Comments: 30 pages
Subjects: Quantum Physics (quant-ph) ; Strongly Correlated Electrons (cond-mat.str-el) ; Computational Complexity (cs.CC)

The Berry phase is a fundamental quantity in the classification of topological phases of matter. In this paper, we present a new quantum algorithm and several complexity-theoretical results for the Berry phase estimation (BPE) problems. Our new quantum algorithm achieves BPE in a more general setting than previously known quantum algorithms, with a theoretical guarantee. For the complexity-theoretic results, we consider three cases. First, we prove $\mathsf{BQP}$-completeness when we are given a guiding state that has a large overlap with the ground state. This result establishes an exponential quantum speedup for estimating the Berry phase. Second, we prove $\mathsf{dUQMA}$-completeness when we have \textit{a priori} bound for ground state energy. Here, $\mathsf{dUQMA}$ is a variant of the unique witness version of $\mathsf{QMA}$ (i.e., $\mathsf{UQMA}$), which we introduce in this paper, and this class precisely captures the complexity of BPE without the known guiding state. Remarkably, this problem turned out to be the first natural problem contained in both $\mathsf{UQMA}$ and $\mathsf{co}$-$\mathsf{UQMA}$. Third, we show $\mathsf{P}^{\mathsf{dUQMA[log]}}$-hardness and containment in $\mathsf{P}^{\mathsf{PGQMA[log]}}$ when we have no additional assumption. These results advance the role of quantum computing in the study of topological phases of matter and provide a pathway for clarifying the connection between topological phases of matter and computational complexity.

[8] arXiv:2509.13440 [cn-pdf, pdf, html, other]
Title: Simulation of bilayer Hamiltonians based on monitored quantum trajectories
Yuan Xue, Zihan Cheng, Matteo Ippoliti
Comments: 13 pages, 4 figures
Subjects: Quantum Physics (quant-ph) ; Statistical Mechanics (cond-mat.stat-mech) ; Strongly Correlated Electrons (cond-mat.str-el)

In the study of open quantum systems it is often useful to treat mixed states as pure states of a fictitious doubled system. In this work we explore the opposite approach: mapping isolated bilayer systems to open monolayer systems. Specifically, we show that arbitrary bilayer Hamiltonians possessing an antiunitary layer exchange symmetry, and subject to a constraint on the sign of interlayer couplings, can be mapped to Lindbladians on a monolayer system with some of the jump operators postselected on a fixed outcome ("monitored"). Low-energy states of the bilayer Hamiltonian then correspond to late-time states of the monolayer dynamics. Simulating the latter by quantum trajectory methods has the potential of substantially reducing the computational cost of estimating low-energy observables in the bilayer Hamiltonian by effectively halving the system size. The overhead due to sampling quantum trajectories can be controlled by a suitable importance sampling scheme. We show that, when the quantum trajectories exhibit free fermion dynamics, our approach reduces to the auxiliary field quantum Monte Carlo (AFQMC) method. This provides a physically transparent interpretation of the AFQMC sign-free criteria in terms of properties of quantum dynamics. Finally, we benchmark our approach on the 1D quantum Ashkin-Teller model.

[9] arXiv:2509.13451 [cn-pdf, pdf, other]
Title: Direct Experimental Observation of Quantum Mpemba Effect without Bath Engineering
Arijit Chatterjee, Sakil Khan, Sachin Jain, T S Mahesh
Subjects: Quantum Physics (quant-ph)

The quantum Mpemba effect refers to the phenomenon of a quantum system in an initial state, far away from equilibrium, relaxing much faster than a state comparatively nearer to equilibrium. We experimentally demonstrate that this highly counterintuitive effect can occur naturally during the thermalization of quantum systems. Considering dipolar relaxation as the dominant decoherence process, we theoretically derive the conditions that can lead to the Mpemba effect in nuclear spins. After experimentally preparing nuclear spin states dictated by those conditions, we observe the occurrence of the Mpemba effect when they are left to thermalize without any external control. We also experimentally observe the genuine quantum Mpemba effect during thermalization of nuclear spins. Our results establish that both these effects are natural in thermalization of quantum systems, and may show up without the need for any bath engineering.

[10] arXiv:2509.13453 [cn-pdf, pdf, other]
Title: From virtual Z gates to virtual Z pulses
Christopher K. Long, Crispin H. W. Barnes
Comments: 13 + (10) pages, 4 figs, comments are welcome
Subjects: Quantum Physics (quant-ph)

Virtual $Z$ gates have become integral for implementing fast, high-fidelity single-qubit operations. However, virtual $Z$ gates require that the system's two-qubit gates are microwave-activated or normalise the single-qubit $Z$ rotations$\unicode{x2014}$the group generated by $X$, $\operatorname{SWAP}$, and arbitrary phase gates. Herein, we extend the theory of virtual $Z$ gates to the pulse-level, which underlies both gate design and the recent advancements of pulse-level quantum algorithms. These algorithms attempt to utilise the full potential of present-day noisy intermediate-scale quantum (NISQ) devices by removing overheads associated with the compilation and transpilation of gates. To extend the theory of virtual $Z$ gates, we derive a platform-agnostic theoretical framework for virtual $Z$ pulses by employing time dilations of the pulse sequences that control the quantum processor. Additionally, we provide worked examples of the implementation of virtual $Z$ pulses on both semiconductor spin qubit and superconducting quantum processor architectures. Moreover, we present a general overview of the hardware support for virtual $Z$ pulses. We find virtual $Z$ pulses (and thus, virtual $Z$ gates) can be used on hardware that, with previous methods, did not support the virtual $Z$ gate. Finally, we present two additional applications of virtual $Z$ pulses to pulse-level algorithms. First, broadening the class of Hamiltonians that can be natively simulated in an analogue manner. Second, increasing the expressibility of pulse-based variational quantum algorithms.

[11] arXiv:2509.13470 [cn-pdf, pdf, html, other]
Title: The original Wigner's-Friend scenarios
Jay Lawrence
Comments: 6 pages, no figures
Subjects: Quantum Physics (quant-ph)

We describe the Wigner's-Friend scenario according to Wigner, then a similar but earlier version according to Everett. Wigner and Everett provide different resolutions of essentially the same paradox. Decoherence theory provides a third resolution. Despite different interpretations (or their absence), these three stories fit together to form a consistent picture without a paradox.

[12] arXiv:2509.13519 [cn-pdf, pdf, html, other]
Title: Quantum speed limit for the OTOC from an open systems perspective
Devjyoti Tripathy, Juzar Thingna, Sebastian Deffner
Comments: 10 pages, 7 figures
Subjects: Quantum Physics (quant-ph) ; Statistical Mechanics (cond-mat.stat-mech)

Scrambling, the delocalization of initially localized quantum information, is commonly characterized by the out-of-time ordered correlator (OTOC). Employing the OTOC-Renyi-2 entropy theorem we derive a quantum speed limit for the OTOC, which sets an lower bound for the rate with which information can be scrambled. This bound becomes particularly tractable by describing the scrambling of information in a closed quantum system as an effective decoherence process of an open system interacting with an environment. We prove that decay of the OTOC can be bounded by the strength of the system-environment coupling and two-point environmental correlation functions. We validate our analytic bound numerically using the non-integrable transverse field Ising model. Our results provide a universal and model-agnostic quantitative framework for understanding the dynamical limits of information spreading across quantum many-body physics, condensed matter, and engineered quantum platforms.

[13] arXiv:2509.13528 [cn-pdf, pdf, html, other]
Title: Evaluating the Limits of QAOA Parameter Transfer at High-Rounds on Sparse Ising Models With Geometrically Local Cubic Terms
Elijah Pelofske, Marek Rams, Andreas Bärtschi, Piotr Czarnik, Paolo Braccia, Lukasz Cincio, Stephan Eidenbenz
Subjects: Quantum Physics (quant-ph) ; Disordered Systems and Neural Networks (cond-mat.dis-nn)

The emergent practical applicability of the Quantum Approximate Optimization Algorithm (QAOA) for approximate combinatorial optimization is a subject of considerable interest. One of the primary limitations of QAOA is the task of finding a set of good parameters. Parameter transfer is a phenomenon where QAOA angles trained on problem instances that are self-similar tend to perform well for other problem instances from that similar class. This suggests a potentially highly efficient and scalable non-variational learning method for QAOA angle finding. We systematically study QAOA parameter transferability from small problems (16, 27 qubits) onto large problem instances (up to 156 qubits) for heavy-hex graph Ising models with geometrically local higher order terms using the Julia based QAOA simulation tool JuliQAOA to perform classical angle finding for up to 49 QAOA layers. Parameter transfer of the fixed angles is validated using a combination of full statevector, Projected Entangled Pair States, Matrix Product State, and LOWESA numerical simulations. We find that the QAOA parameter transfer from single instances applied to unseen problem instances does not in general provide monotonically improving performance as a function of p - there are many cases where the performance temporarily decreases as a function of p - but despite this the transferred angles have a general trend of improved expectation value as the QAOA depth increases, in many cases converging close to the true ground-state energy of the 100+ qubit instances. We also sample the hardware-compatible Ising models using the ensemble of fixed QAOA angles on several superconducting qubit IBM Quantum processors with 127, 133, and 156 qubits. We find continuous solution quality improvement of the hardware-compatible QAOA circuits run on the IBM NISQ processors up to p=5 on ibm_fez, p=9 on ibm_torino, and p=10 on ibm_pittsburgh.

[14] arXiv:2509.13546 [cn-pdf, pdf, other]
Title: End-to-End Complexity Analysis for Quantum Simulation of the Extended Jaynes-Cummings Models
Nam Nguyen, Michael Yu, Alan Robertson, Hiromichi Nishimura, Samuel J. Elman, Benjamin Koltenbah
Comments: 51 pages, 17 figures
Subjects: Quantum Physics (quant-ph)

The extended Jaynes-Cummings model (eJCM) is a foundational framework for describing multi-mode light-matter interactions, with direct applications in quantum technologies such as photon addition and quasi-noiseless amplification. However, the model's complexity makes classical simulation intractable for large systems that could be of practical interest. In this work, we present a comprehensive, end-to-end framework for the quantum simulation of the eJCM. We develop explicit quantum algorithms and circuits for simulating the system's time evolution using first and second-order product formulas, analyzing the dynamics in both the Schrodinger and interaction pictures. Our analysis includes rigorous, closed-form error bounds that guide the choice of simulation parameters, and we extend the methodology to efficiently handle both pure and mixed quantum states. Furthermore, we validate our theoretical cost models with numerical simulations and provide a detailed fault-tolerant resource analysis, compiling the simulation circuits for a surface-code architecture to yield concrete estimates for physical qubit counts and execution times. This work establishes a complete roadmap for simulating the eJCM on future quantum computers.

[15] arXiv:2509.13659 [cn-pdf, pdf, html, other]
Title: Quantum keystroke logging
En-Jui Chang
Comments: 6 pages
Subjects: Quantum Physics (quant-ph)

We propose a \textit{quantum keystroke logging} scheme in the context of GKP-based quantum communication. The central idea is that, if a communication provider controls the preparation of encoded states, it may be able to infer logical operations applied by users prior to transmission. We show that phase estimation can be adapted to this setting despite two obstacles: GKP codewords are not eigenstates of the logical operators, and realistic communication involves one-shot operations rather than repeated applications. Our approach relies on three observations: the geometric phase associated with closed trajectories in phase space manifests as an effective Pauli-$Z$ rotation on an ancilla; the quantum Fourier transform (QFT) need only reproduce the correct probability distribution and can thus be simplified using auxiliary ancilla; and, in oscillator systems, cross-Kerr nonlinearities provide a natural mechanism to reduce the circuit depth of the QFT. Together, these tools enable a malicious provider to extract user inputs without disturbing the transmitted codewords, thereby demonstrating a sufficient condition for quantum keystroke logging.

[16] arXiv:2509.13678 [cn-pdf, pdf, other]
Title: Rare Event Simulation of Quantum Error-Correcting Circuits
Carolyn Mayer, Anand Ganti, Uzoma Onunkwo, Tzvetan Metodi, Benjamin Anker, Jacek Skryzalin
Comments: 10 pages, 15 figures
Subjects: Quantum Physics (quant-ph) ; Numerical Analysis (math.NA) ; Probability (math.PR)

We describe a practical approach for accessing the logical failure rates of quantum error-correcting (QEC) circuits under low physical (component) failure rate regimes. Standard Monte Carlo is often the de facto approach for studying the failure rates of quantum circuits. However, in the study of fault-tolerant error-correcting circuits, the ability to extend this approach to low physical failure rates is limited. In particular, the use of Monte Carlo to access circuits that are relatively large or have high correcting power becomes more difficult as we lower the input failure rates of the individual components (gates) in the circuit. For these reasons, many simulations studying the circuit model go no lower than end-to-end logical failure rates in the 10^{-6} regime. In this report, we outline an approach that borrows from earlier work by Bravyi and Vargo to the more complex circuit noise model. Earlier works studied both the capacity and phenomenological noise models, but the work is insufficient for generating similar simulations in the circuit-noise model. To the best of our knowledge, our team is the first to develop a full prescription of the rare event simulation by splitting technique for the circuit-based noise model. We have also generated promising results that are confirmed by standard Monte Carlo simulation under an accessible regime. This work shows that we can access noise in the circuit-model prescription of quantum error-correcting code to failure rates below 10^{-20} regime.

[17] arXiv:2509.13705 [cn-pdf, pdf, html, other]
Title: Learning quantum many-body data locally: A provably scalable framework
Koki Chinzei, Quoc Hoan Tran, Norifumi Matsumoto, Yasuhiro Endo, Hirotaka Oshima
Comments: 38 pages, 5 figures
Subjects: Quantum Physics (quant-ph) ; Statistical Mechanics (cond-mat.stat-mech) ; Machine Learning (cs.LG)

Machine learning (ML) holds great promise for extracting insights from complex quantum many-body data obtained in quantum experiments. This approach can efficiently solve certain quantum problems that are classically intractable, suggesting potential advantages of harnessing quantum data. However, addressing large-scale problems still requires significant amounts of data beyond the limited computational resources of near-term quantum devices. We propose a scalable ML framework called Geometrically Local Quantum Kernel (GLQK), designed to efficiently learn quantum many-body experimental data by leveraging the exponential decay of correlations, a phenomenon prevalent in noncritical systems. In the task of learning an unknown polynomial of quantum expectation values, we rigorously prove that GLQK substantially improves polynomial sample complexity in the number of qubits $n$, compared to the existing shadow kernel, by constructing a feature space from local quantum information at the correlation length scale. This improvement is particularly notable when each term of the target polynomial involves few local subsystems. Remarkably, for translationally symmetric data, GLQK achieves constant sample complexity, independent of $n$. We numerically demonstrate its high scalability in two learning tasks on quantum many-body phenomena. These results establish new avenues for utilizing experimental data to advance the understanding of quantum many-body physics.

[18] arXiv:2509.13708 [cn-pdf, pdf, html, other]
Title: Observation of topological Phenomena in a Weyl Exceptional Ring with Single Photons
Zhong-Sheng Chen, Wei-Xin Chen, Fan Wu, Zhong-Wei Xu, Jing Ma, Yun-Kun Jiang, Huai-Zhi Wu, Shi-Biao Zheng
Comments: 11 pages, 6 figures
Subjects: Quantum Physics (quant-ph) ; Optics (physics.optics)

Compared with Hermitian theory, non-Hermitian physics offers a fundamentally different mathematical framework, enabling the observation of topological phenomena that have no analogue in Hermitian systems. Among these, the exceptional point (EP) ring stands out as a quintessential topological feature unique to non-Hermitian systems. In this study, we employ single-photon interferometry to overcome the experimental challenge of precise phase control in quantum systems, thereby enabling a complete simulation of the non-Hermitian EP ring in three-dimensional parameter space without invoking any additional symmetry assumptions. By measuring the non-Hermitian dynamics in three-dimensional parameter space, we determine the system's eigenstates, which allows us to characterize the topological band structure of the system under different conditions. We describe the topological properties of the EP ring by extracting the Chern number and Berry phase for different parameter manifolds and observe the topological critical phenomena of the system. Our work paves the way for further exploration of topological non-Hermitian systems.

[19] arXiv:2509.13810 [cn-pdf, pdf, html, other]
Title: Loss-tolerant detection of squeezed states in the 2 um region
K. M. Kwan, T. G. McRae, J. Qin, D. W. Gould, S. S. Y. Chua, J. Junker, R. Iden, V. B. Adya, M. J. Yap, B. J. J. Slagmolen, D. E. McClelland, R. L. Ward
Comments: 5 pages, 5 figures, presented at the Sept 2025 LVK conference
Subjects: Quantum Physics (quant-ph)

Squeezed states of light enable quantum-enhanced measurements but are limited by optical loss, particularly at 2 um where photodiode efficiency is low. We report the first loss-tolerant, audio-band squeezed light detection at 1984 nm by using a phase-sensitive amplifier to amplify the squeezed vacuum prior to detection. This technique increases the effective detection efficiency from 74% to 95% and increases the observed squeezing from 4 dB to 8 dB, the highest level of squeezing observed at this wavelength. Additionally, the shot-to-dark-noise clearance increases, extending the effective measurement bandwidth toward lower frequencies. This approach is largely wavelength-independent, extending high-fidelity quantum measurements to future gravitational-wave detectors and related quantum technologies.

[20] arXiv:2509.13821 [cn-pdf, pdf, html, other]
Title: Learning Minimal Representations of Many-Body Physics from Snapshots of a Quantum Simulator
Frederik Møller, Gabriel Fernández-Fernández, Thomas Schweigler, Paulin de Schoulepnikoff, Jörg Schmiedmayer, Gorka Muñoz-Gil
Comments: 13 pages, 7 figures
Subjects: Quantum Physics (quant-ph) ; Machine Learning (cs.LG)

Analog quantum simulators provide access to many-body dynamics beyond the reach of classical computation. However, extracting physical insights from experimental data is often hindered by measurement noise, limited observables, and incomplete knowledge of the underlying microscopic model. Here, we develop a machine learning approach based on a variational autoencoder (VAE) to analyze interference measurements of tunnel-coupled one-dimensional Bose gases, which realize the sine-Gordon quantum field theory. Trained in an unsupervised manner, the VAE learns a minimal latent representation that strongly correlates with the equilibrium control parameter of the system. Applied to non-equilibrium protocols, the latent space uncovers signatures of frozen-in solitons following rapid cooling, and reveals anomalous post-quench dynamics not captured by conventional correlation-based methods. These results demonstrate that generative models can extract physically interpretable variables directly from noisy and sparse experimental data, providing complementary probes of equilibrium and non-equilibrium physics in quantum simulators. More broadly, our work highlights how machine learning can supplement established field-theoretical techniques, paving the way for scalable, data-driven discovery in quantum many-body systems.

[21] arXiv:2509.13856 [cn-pdf, pdf, html, other]
Title: Trajectory-based Measure of Nonlocality in the Double Caldeira-Leggett Formalism
S. V. Mousavi
Comments: Accepted for Publication in Physica Scripta
Subjects: Quantum Physics (quant-ph)

We investigate the dynamics of quantum correlations in bipartite systems initially prepared in a squeezed state, comparing closed-system unitary evolution under the Schr\"odinger equation with open-system dynamics governed by the Caldeira-Leggett master equation in the high-temperature, weak-coupling regime, all within the Bohmian mechanics framework. Quantum nonlocality is quantified via the sensitivity of the Bohmian velocity of one particle to the position of the other. Our results show that in both distinct (local) and common bath scenarios, nonlocal correlations initially grow from zero, reach a peak, and then decay. In the case of local baths, the decay is smooth and monotonic; although the peak value increases with temperature, its temporal width (measured via the full width at half maximum) decreases, indicating a shorter duration of nonlocal correlations. For a common bath, the initial growth and decay are followed by revivals and oscillations, whose amplitude and timing vary with temperature. These non-monotonic behaviors arise despite the Markovian nature of the underlying dynamics and reflect the nontrivial role of system-bath correlations. We also analyze how both temperature and the squeezing decay parameter affect the structure of Bohmian trajectories and the evolution of nonlocal correlations. This trajectory-based, velocity-sensitivity measure offers an intuitive and quantitative understanding of entanglement degradation, decoherence, and their characteristic time scales. Our findings emphasize how the structure of the environment critically shapes the observable dynamics of quantum correlations, even in Markovian regimes.

[22] arXiv:2509.13862 [cn-pdf, pdf, html, other]
Title: Quantum Algorithm of the GLMY Homology on Digraphs
Yunpeng Zi, Muchun Yang, D. L. Zhou
Comments: 11 pages, 2 figures
Subjects: Quantum Physics (quant-ph)

Quantum algorithms for topological data analysis provide significant advantage over the best classical algorithm. Different from the previous simplical complex on points cloud, the GLMY homology introduced by Alexander Grigor'yan, Yong Lin, Yuri Muranov and Shing-Tung Yau, is defined on digraph and is a arising realm in Topological Data Analysis (TDA), which attracts more and more attention recently. We propose a quantum algorithm for the GLMY homology with significant advantage over the best classical algorithm. We design a universal encoding protocol for the quantum states and boundary operators of GLMY homology on digraphs. And a property of the GLMY homology is proved for the theoretical guarantee of the quantum algorithm. The quantum algorithm for GLMY homology gives a quadratic speedup in general cases, and it gives an exponential quantum advantage in the case of the input data is given as a specification of paths.

[23] arXiv:2509.13904 [cn-pdf, pdf, other]
Title: Coherent Driving of a Quantum System with Modulated Free-Space Electrons
Matthias Kolb, Thomas Spielauer, Thomas Weigner, Giovanni Boero, Dennis Rätzel, Philipp Haslinger
Comments: 18 pages, 13 figures
Subjects: Quantum Physics (quant-ph) ; Materials Science (cond-mat.mtrl-sci)

Control of quantum systems typically relies on the interaction with electromagnetic radiation. In this study, we experimentally show that the electromagnetic near-field of a spatially modulated freespace electron beam can be used to drive spin systems, demonstrating free-electron-bound-electron resonant interaction. By periodically deflecting the electron beam of a scanning electron microscope in close proximity to a spin-active solid-state sample, and sweeping the deflection frequency across the spin resonance, we directly observe phase coherent coupling between the electron beam's nearfield and the two spin states. This method relies only on classically shaping the electron beams transversal correlations and has the potential to enable coherent control of quantum systems with unprecedented, electron microscopic resolution, opening novel possibilities for advanced spectroscopic tools in nanotechnology.

[24] arXiv:2509.13909 [cn-pdf, pdf, html, other]
Title: A Tight Quantum Algorithm for Multiple Collision Search
Xavier Bonnetain, Johanna Loyer, André Schrottenloher, Yixin Shen
Subjects: Quantum Physics (quant-ph) ; Information Theory (cs.IT)

Searching for collisions in random functions is a fundamental computational problem, with many applications in symmetric and asymmetric cryptanalysis. When one searches for a single collision, the known quantum algorithms match the query lower bound. This is not the case for the problem of finding multiple collisions, despite its regular appearance as a sub-component in sieving-type algorithms. At EUROCRYPT 2019, Liu and Zhandry gave a query lower bound $\Omega(2^{m/3 + 2k/3})$ for finding $2^k$ collisions in a random function with m-bit output. At EUROCRYPT 2023, Bonnetain et al. gave a quantum algorithm matching this bound for a large range of $m$ and $k$, but not all admissible values. Like many previous collision-finding algorithms, theirs is based on the MNRS quantum walk framework, but it chains the walks by reusing the state after outputting a collision. In this paper, we give a new algorithm that tackles the remaining non-optimal range, closing the problem. Our algorithm is tight (up to a polynomial factor) in queries, and also in time under a quantum RAM assumption. The idea is to extend the chained walk to a regime in which several collisions are returned at each step, and the ``walks'' themselves only perform a single diffusion layer.

[25] arXiv:2509.13917 [cn-pdf, pdf, html, other]
Title: Global Mean-Amplitude Enhanced Spiking Neural Network Coherent Ising Machine
Yan Chen Jiang, Lu Ma, Chuan Wang, Tie Jun Wang
Subjects: Quantum Physics (quant-ph)

The coherent Ising machine (CIM) is a quantum-inspired computing platform that leverages optical parametric oscillation dynamics to solve combinatorial optimization problems by searching for the ground state of an Ising Hamiltonian. Conventional CIM implementations face challenges in handling non-uniform coupling strengths and maintaining amplitude stability during computation. In this paper, a new global mean-amplitude feedback-enhanced spiking neural network CIM (GFSNN-CIM) is introduced with a physics-driven amplitude stabilization mechanism to dynamically balance nonlinear gain saturation and coupling effects. This modification enhances synchronization in the optical pulse network, leading to more robust convergence under varying interaction strengths. Experimental validation on Max-Cut problems demonstrates that the GFSNN-CIM achieves up to a 27% improvement in solution success rates compared to conventional spiking neural network CIM, with scalability improving as problem complexity increases. Further application to the traffic assignment problem (TAP) confirms the method's generality; the GFSNN-CIM achieves near-continuous accuracy (deviations < 0.035%) even at coarse discretization, while large-scale tests on Beijing's road network (481 spins) validate its real-world applicability. These advances establish a physics-consistent optimization framework, where optical pulse dynamics directly encode combinatorial problems, paving the way for scalable, high-performance CIM implementations in complex optimization tasks.

[26] arXiv:2509.13946 [cn-pdf, pdf, html, other]
Title: Design and Dynamics of High-Fidelity Two-Qubit Gates with Electrons on Helium
Oskar Leinonen, Jonas B. Flaten, Stian D. Bilek, Øyvind S. Schøyen, Morten Hjorth-Jensen, Niyaz R. Beysengulov, Zachary J. Stewart, Jared D. Weidman, Angela K. Wilson
Comments: 17 pages, 12 figures
Subjects: Quantum Physics (quant-ph) ; Mesoscale and Nanoscale Physics (cond-mat.mes-hall)

Systems of individual electrons electrostatically trapped on condensed noble gas surfaces have recently attracted considerable interest as potential platforms for quantum computing. The electrons form the qubits of the system, and the purity of the noble gas surface protects the relevant quantum properties of each electron. Previous work has indicated that manipulation of a confining double-well potential for electrons on superfluid helium can generate entanglement suitable for two-qubit gate operations. In this work, we incorporate a time-dependent tuning of the potential shape to further explore operation of two-qubit gates with the superfluid helium system. Through numerical time evolution, we show that fast, high-fidelity two-qubit gates can be achieved. In particular, we simulate operation of the \sqiswap and CZ gates and obtain fidelities of 0.999 and 0.996 with execution times of 2.9~ns and 9.4~ns, respectively. Furthermore, we examine the stability of these gate fidelities under non-ideal execution conditions, which reveals new properties to consider in the device design. With the insights gained from this work, we believe that an experimental realization of two-qubit gates using electrons on helium is feasible.

[27] arXiv:2509.14026 [cn-pdf, pdf, html, other]
Title: Quantum Variational Activation Functions Empower Kolmogorov-Arnold Networks
Jiun-Cheng Jiang, Morris Yu-Chao Huang, Tianlong Chen, Hsi-Sheng Goan
Comments: 45 pages
Subjects: Quantum Physics (quant-ph) ; Machine Learning (cs.LG)

Variational quantum circuits (VQCs) are central to quantum machine learning, while recent progress in Kolmogorov-Arnold networks (KANs) highlights the power of learnable activation functions. We unify these directions by introducing quantum variational activation functions (QVAFs), realized through single-qubit data re-uploading circuits called DatA Re-Uploading ActivatioNs (DARUANs). We show that DARUAN with trainable weights in data pre-processing possesses an exponentially growing frequency spectrum with data repetitions, enabling an exponential reduction in parameter size compared with Fourier-based activations without loss of expressivity. Embedding DARUAN into KANs yields quantum-inspired KANs (QKANs), which retain the interpretability of KANs while improving their parameter efficiency, expressivity, and generalization. We further introduce two novel techniques to enhance scalability, feasibility and computational efficiency, such as layer extension and hybrid QKANs (HQKANs) as drop-in replacements of multi-layer perceptrons (MLPs) for feed-forward networks in large-scale models. We provide theoretical analysis and extensive experiments on function regression, image classification, and autoregressive generative language modeling, demonstrating the efficiency and scalability of QKANs. DARUANs and QKANs offer a promising direction for advancing quantum machine learning on both noisy intermediate-scale quantum (NISQ) hardware and classical quantum simulators.

[28] arXiv:2509.14098 [cn-pdf, pdf, html, other]
Title: A Closeness Centrality-based Circuit Partitioner for Quantum Simulations
Doru Thom Popovici, Harlin Lee, Mauro Del Ben, Naoki Yoshioka, Nobuyasu Ito, Katherine Klymko, Daan Camps, Anastasiia Butko
Comments: 14 pages, 10 figures
Subjects: Quantum Physics (quant-ph) ; Distributed, Parallel, and Cluster Computing (cs.DC)

Simulating quantum circuits (QC) on high-performance computing (HPC) systems has become an essential method to benchmark algorithms and probe the potential of large-scale quantum computation despite the limitations of current quantum hardware. However, these simulations often require large amounts of resources, necessitating the use of large clusters with thousands of compute nodes and large memory footprints. In this work, we introduce an end-to-end framework that provides an efficient partitioning scheme for large-scale QCs alongside a flexible code generator to offer a portable solution that minimizes data movement between compute nodes. By formulating the distribution of quantum states and circuits as a graph problem, we apply closeness centrality to assess gate importance and design a fast, scalable partitioning method. The resulting partitions are compiled into highly optimized codes that run seamlessly on a wide range of supercomputers, providing critical insights into the performance and scalability of quantum algorithm simulations.

[29] arXiv:2509.14125 [cn-pdf, pdf, html, other]
Title: Formalizing contextuality in sequential scenarios
Kim Vallée, Damian Markham
Comments: 25 pages, 1 figure
Subjects: Quantum Physics (quant-ph)

This paper provides a framework for characterizing sequential scenarios, allowing for the identification of contextuality given empirical data, and then provides precise operational interpretations in terms of the possible hidden variable model explanations of that data. Sequential scenarios are different in essence from non-local scenarios as each measurement instrument is allowed to change the state as it enters subsequent measurement instruments. Thus, it is necessary to formulate the possible state update in any hidden variable model description. Here we develop such hidden variable models for sequential scenarios, and we propose the notion of no-disturbance: an instrument $A$ does not disturb another instrument $B$ if the statistics of $B$ are independent of whether $A$ was measured or not. We define non-contextuality inequalities for the sequential scenario, and show that violation implies that the data cannot be explained by a hidden variable model that is both deterministic and not disturbing in this sense. We further provide a translation from standard contextuality frameworks to ours, providing sequential versions which carry over the same inequalities and measures of contextuality, but now with the sequential interpretations stated.

[30] arXiv:2509.14163 [cn-pdf, pdf, html, other]
Title: Quantum Reinforcement Learning-Guided Diffusion Model for Image Synthesis via Hybrid Quantum-Classical Generative Model Architectures
Chi-Sheng Chen, En-Jui Kuo
Subjects: Quantum Physics (quant-ph) ; Machine Learning (cs.LG)

Diffusion models typically employ static or heuristic classifier-free guidance (CFG) schedules, which often fail to adapt across timesteps and noise conditions. In this work, we introduce a quantum reinforcement learning (QRL) controller that dynamically adjusts CFG at each denoising step. The controller adopts a hybrid quantum--classical actor--critic architecture: a shallow variational quantum circuit (VQC) with ring entanglement generates policy features, which are mapped by a compact multilayer perceptron (MLP) into Gaussian actions over $\Delta$CFG, while a classical critic estimates value functions. The policy is optimized using Proximal Policy Optimization (PPO) with Generalized Advantage Estimation (GAE), guided by a reward that balances classification confidence, perceptual improvement, and action regularization. Experiments on CIFAR-10 demonstrate that our QRL policy improves perceptual quality (LPIPS, PSNR, SSIM) while reducing parameter count compared to classical RL actors and fixed schedules. Ablation studies on qubit number and circuit depth reveal trade-offs between accuracy and efficiency, and extended evaluations confirm robust generation under long diffusion schedules.

[31] arXiv:2509.14164 [cn-pdf, pdf, html, other]
Title: High-dimensional topological photonic entanglement
M. Javad Zakeri, Armando Perez-Leija, Andrea Blanco-Redondo
Subjects: Quantum Physics (quant-ph)

The robust generation and manipulation of high-dimensional quantum states lies at the heart of modern quantum computation. The use of topology to resiliently encode and transport quantum information has been widely investigated in condensed matter and has recently penetrated quantum photonics. However, a route to scale up to a large number of entangled topological photonic modes had been missing. Here, we propose and experimentally demonstrate a method to generate high-dimensional topological photonic entanglement. Our platform relies on carefully designed silicon photonic waveguide topological superlattices, which support nonlinear generation of energy-time entangled photon pairs on a superposition of multiple topological modes. Our measurements and theoretical analysis reveal entanglement of up to five topological modes with resilience to nanofabrication imperfections. This study, at the intersection of nonlinear integrated photonics, quantum information, and topology, opens a research avenue toward scalable, fault-tolerant quantum photonic states.

[32] arXiv:2509.14196 [cn-pdf, pdf, other]
Title: Quantum Utility in Simulating the Real-time Dynamics of the Fermi-Hubbard Model using Superconducting Quantum Computers
Talal Ahmed Chowdhury, Vladimir Korepin, Vincent R. Pascuzzi, Kwangmin Yu
Comments: 18 pages, 10 figures
Subjects: Quantum Physics (quant-ph) ; Strongly Correlated Electrons (cond-mat.str-el)

The Fermi-Hubbard model is a fundamental model in condensed matter physics that describes strongly correlated electrons. On the other hand, quantum computers are emerging as powerful tools for exploring the complex dynamics of these quantum many-body systems. In this work, we demonstrate the quantum simulation of the one-dimensional Fermi-Hubbard model using IBM's superconducting quantum computers, employing over 100 qubits. We introduce a first-order Trotterization scheme and extend it to an optimized second-order Trotterization for the time evolution in the Fermi-Hubbard model, specifically tailored for the limited qubit connectivity of quantum architectures, such as IBM's platforms. Notably, both Trotterization approaches are scalable and maintain a constant circuit depth at each Trotter step, regardless of the qubit count, enabling us to precisely investigate the relaxation dynamics in the Fermi-Hubbard model by measuring the expectation value of the N\'eel observable (staggered magnetization) for time-evolved quantum states. Finally, our successful measurement of expectation values in such large-scale quantum many-body systems, especially at longer time scales with larger entanglement, highlights the quantum utility of superconducting quantum platforms over conventional classical approximation methods.

[33] arXiv:2509.14212 [cn-pdf, pdf, other]
Title: Localized degenerate solutions to the massless Dirac and Weyl equations
Georgios N. Tsigaridas, Aristides I. Kechriniotis, Christos A. Tsonos, Konstantinos K. Delibasis
Subjects: Quantum Physics (quant-ph)

In this article we present a general class of degenerate solutions to the massless Dirac and Weyl equations, which can describe localized particles and/or particles with variable energy, that could be interpreted as virtual particles appearing either in the vacuum or in materials supporting massless Dirac or Weyl particles. These solutions exist in a wide range of electromagnetic 4-potentials and fields, which are explicitly calculated. In addition, we describe a method for controlling the transverse spatial distribution of Weyl particles and separating them according to their helicity and direction of motion using suitable magnetic fields.

Cross submissions (showing 12 of 12 entries )

[34] arXiv:2509.13362 (cross-list from cond-mat.str-el) [cn-pdf, pdf, html, other]
Title: From Quantum Tsallis Entropy to Strange Metals
Xian-Hui Ge
Comments: 18 pages
Subjects: Strongly Correlated Electrons (cond-mat.str-el) ; Statistical Mechanics (cond-mat.stat-mech) ; High Energy Physics - Theory (hep-th) ; Quantum Physics (quant-ph)

We develop a unified framework connecting quantum Tsallis statistics to electronic transport in strongly interacting systems. Starting from R\'enyi and Tsallis entropies, we construct a quantum Tsallis distribution that reduces to the conventional Fermi--Dirac distribution when $q=1$. For $q$ slightly deviating from unity, the correction term in the occupation function can be mapped to a $q$-deformed Schwarzian action, corresponding to soft reparametrization modes. Coupling these soft modes to electrons via the Fermi Golden Rule yields a modified scattering rate, which reproduces conventional Fermi-liquid behavior at low temperatures and linear-in-temperature resistivity at high temperatures. Using the memory matrix formalism, we analyze magnetotransport, finding a linear-in-field magnetoresistance and a Hall angle consistent with Anderson's two-lifetime scenario. At sufficiently low temperatures, both magnetoresistance and Hall response smoothly recover Fermi-liquid quadratic behaviors. This approach provides a controlled interpolation between Fermi-liquid and non-Fermi-liquid regimes, quantitatively linking $q$-deformation, soft-mode dynamics, and experimentally measurable transport coefficients in strange metals.

[35] arXiv:2509.13401 (cross-list from hep-th) [cn-pdf, pdf, html, other]
Title: An effective density matrix for vacua in asymptotically flat gravity
Temple He, Prahar Mitra, Kathryn M. Zurek
Comments: 11 pages, 1 figure
Subjects: High Energy Physics - Theory (hep-th) ; General Relativity and Quantum Cosmology (gr-qc) ; Quantum Physics (quant-ph)

We explicitly construct the density matrix associated to the vacuum state of a large spherically symmetric causal diamond of area $A$ in four-dimensional asymptotically flat gravity. We achieve this using the soft effective action, which characterizes the low-energy gravitational degrees of freedom that arise in the long-distance limit of the Einstein-Hilbert action and consists of both the soft graviton mode and the Goldstone mode arising from the spontaneous breaking of supertranslation symmetry. Integrating out the soft graviton mode, we obtain an effective action for purely the Goldstone mode, from which we extract the density matrix and therefore the modular Hamiltonian $K_{s}$ associated to the vacuum state. We explicitly compute the mean and variance of $K_{s}$, finding $\langle \Delta K_{s}^{2} \rangle = A/\epsilon_{\text{UV}}^{2}$, with $\epsilon_{\text{UV}}$ being a length-scale UV cutoff on the celestial sphere.

[36] arXiv:2509.13417 (cross-list from hep-ph) [cn-pdf, pdf, html, other]
Title: Coherently enhanced decoherence and cloud substructure of atom interferometers
Clara Murgui, Ryan Plestid
Subjects: High Energy Physics - Phenomenology (hep-ph) ; Atomic Physics (physics.atom-ph) ; Quantum Physics (quant-ph)

We study how coherent scattering of a background gas off an atom (or other matter) interferometer can lead to enhanced signals from phase shifts and contrast loss. We focus on the inclusion of realistic features of atom interferometers such as finite temperature, cloud substructure, and time-dependent cloud radii. The inclusion of these effects, extending beyond the previously considered point-like cloud approximation, naturally allow us to study the smooth transition between the coherent and incoherent scattering regimes. We discuss how the formalism presented herein can be tested in the lab (with near-infrared photons or an eV-scale electron gun), and discuss an application for the detection of dark matter interacting via long-range forces.

[37] arXiv:2509.13457 (cross-list from hep-th) [cn-pdf, pdf, html, other]
Title: Detector-based measurement-induced state updates in AdS/CFT
Vijay Balasubramanian, Esko Keski-Vakkuri, Nicola Pranzini
Comments: 26 pages, 3 figures
Subjects: High Energy Physics - Theory (hep-th) ; General Relativity and Quantum Cosmology (gr-qc) ; Quantum Physics (quant-ph)

Conventional understandings of quantum theory hold that measurements change the state of an observed system following the L\"{u}ders update rule. Textbooks describe the application of this idea to non-relativistic systems, but extensions to relativistic and gravitating systems encounter subtleties. One consistent approach is via detector-based measurements. We study the effects of such measurements in a CFT with a holographic dual. We work out the boundary space-time regions associated to a L\"{u}ders update and how the outcome extends to modifications of the bulk gravity state. We explore information-theoretic consequences of this picture, and relate the information extracted by a measurement to updates of the semiclassical parameters of the bulk state.

[38] arXiv:2509.13502 (cross-list from cond-mat.dis-nn) [cn-pdf, pdf, html, other]
Title: Effective delocalization in the one-dimensional Anderson model with stealthy disorder
Carlo Vanoni, Boris L. Altshuler, Paul J. Steinhardt, Salvatore Torquato
Comments: 6 pages, 5 figures
Subjects: Disordered Systems and Neural Networks (cond-mat.dis-nn) ; Statistical Mechanics (cond-mat.stat-mech) ; Quantum Physics (quant-ph)

We study analytically and numerically the Anderson model in one dimension with "stealthy" disorder, defined as having a power spectrum that vanishes in a continuous band of wave numbers. Motivated by recent studies on the optical transparency properties of stealthy hyperuniform layered media, we compute the localization length via the perturbation theory expansion of the self-energy. We find that, for fixed energy and small but finite disorder strength, there exists for any finite length system a range of stealthiness $\chi$ for which the localization length exceeds the system size. This kind of "effective delocalization" is the result of the novel kind of correlated disorder that spans a continuous range of length scales, a defining characteristic of stealthy systems. Moreover, we support our analytical results with numerical simulations. Our results may serve as a first step in investigating the role of stealthy disorder in quantum systems, which is of both theoretical and experimental relevance.

[39] arXiv:2509.13518 (cross-list from physics.optics) [cn-pdf, pdf, html, other]
Title: Quantum Dial for High-Harmonic Generation
Lu Wang, Andrew M. Parks, Adam Thorpe, Graeme Bart, Thomas Brabec
Subjects: Optics (physics.optics) ; Quantum Physics (quant-ph)

High-harmonic generation (HHG) is a highly nonlinear optical process that typically requires an intense laser to trigger emissions at integer multiples of the driving field frequency. Since HHG is commonly used as a spectroscopic tool to probe material properties, it becomes impossible to extract information about a material without introducing distortions caused by the strong driving field. Recent advances in bright squeezed vacuum sources have allowed HHG to be driven by purely quantum fields alone. Our work focuses on controlling and tuning HHG emission using a weak classical driving field with energy 1000 times less than that used in conventional HHG experiments, perturbed by an even weaker quantum field, such as bright squeezed vacuum (BSV). Our technique opens new avenues for nonlinear spectroscopy of materials by minimizing issues such as laser-induced damage, distortions, and heating. Our results show that a BSV pulse, containing less than 0.5% of the driving laser energy, can serve as an optical dial for tuning nonlinear emission, electron dynamics, and ionization.

[40] arXiv:2509.13619 (cross-list from physics.atom-ph) [cn-pdf, pdf, html, other]
Title: Broadband femtosecond lasers enable efficient two-photon excitation of the ultranarrow linewidth singlet 1s2s state in helium
Shashank Kumar, Justin D. Piel, Chris H. Greene, Niranjan Shivaram
Comments: 10 pages, 5 figures
Subjects: Atomic Physics (physics.atom-ph) ; Optics (physics.optics) ; Quantum Physics (quant-ph)

We propose a broadband, femtosecond two-photon excitation scheme for efficient population transfer to the ultra-narrow linewidth $1s2s\ ^1S_0$ metastable state in helium. Using $120$ nm vacuum ultraviolet (VUV) femtosecond laser pulses, we theoretically demonstrate that a direct two-photon excitation process can achieve a population transfer efficiency of $25-30\%$, even when photoionization losses are included. The use of broadband pulses enables multiple excitation pathways to populate the excited state, in addition to compensating for significant AC Stark shifts occurring within the pulse duration. Furthermore, we introduce a two-color two-photon extreme ultraviolet-near infrared (XUV-IR) excitation scheme that will further reduce ionization losses and can achieve significantly higher transfer efficiencies of $\sim 70\%$. These results demonstrate that high excitation probability of ultra-narrow linewidth ($\sim 50$ Hz) excited states can be achieved with experimentally accessible femtosecond laser sources with a few THz bandwidth.

[41] arXiv:2509.13800 (cross-list from cond-mat.quant-gas) [cn-pdf, pdf, html, other]
Title: Anomalous Trajectory Drift and Geometric Phases of Cyclic Spinor Solitons Induced by Virtual Magnetic Monopoles
Ruo-Yun Wu, Ning Mao, Xiao-Lin Li, Jie Liu, Li-Chen Zhao
Comments: Ruo-Yun Wu, Ning Mao, Xiao-Lin Li, Jie Liu, Li-Chen Zhao
Subjects: Quantum Gases (cond-mat.quant-gas) ; Pattern Formation and Solitons (nlin.PS) ; Quantum Physics (quant-ph)

We investigate the dynamics of a two-component Bose-Einstein condensate with spin-orbit coupling numerically and analytically. Under the drive of a weak segmented rotational external field, we observe that the system exhibits cyclic soliton motion; however, in contrast to the predictions of quasi-particle theory, the trajectory of the soliton center shows a distinct drift. The underlying mechanism of this anomalous drift is revealed: the moving soliton experiences a Lorentz force induced by a virtual magnetic monopole field in momentum space. We further calculate the phase evolution of the soliton during this cyclic motion and find that its geometric component comprises both an adiabatic Berry phase and a nonadiabatic Aharonov-Anandan phase. Notably, the Berry phase can be expressed in terms of the magnetic flux of the aforementioned virtual monopole field. Our findings hold implications for geometric phase theory and experiments on two-component Bose-Einstein condensates, and may establish a novel link between quantum geometry and soliton dynamics.

[42] arXiv:2509.13818 (cross-list from cs.LG) [cn-pdf, pdf, html, other]
Title: Hybrid Quantum-Classical Neural Networks for Few-Shot Credit Risk Assessment
Zheng-an Wang, Yanbo J. Wang, Jiachi Zhang, Qi Xu, Yilun Zhao, Jintao Li, Yipeng Zhang, Bo Yang, Xinkai Gao, Xiaofeng Cao, Kai Xu, Pengpeng Hao, Xuan Yang, Heng Fan
Subjects: Machine Learning (cs.LG) ; Quantum Physics (quant-ph)

Quantum Machine Learning (QML) offers a new paradigm for addressing complex financial problems intractable for classical methods. This work specifically tackles the challenge of few-shot credit risk assessment, a critical issue in inclusive finance where data scarcity and imbalance limit the effectiveness of conventional models. To address this, we design and implement a novel hybrid quantum-classical workflow. The methodology first employs an ensemble of classical machine learning models (Logistic Regression, Random Forest, XGBoost) for intelligent feature engineering and dimensionality reduction. Subsequently, a Quantum Neural Network (QNN), trained via the parameter-shift rule, serves as the core classifier. This framework was evaluated through numerical simulations and deployed on the Quafu Quantum Cloud Platform's ScQ-P21 superconducting processor. On a real-world credit dataset of 279 samples, our QNN achieved a robust average AUC of 0.852 +/- 0.027 in simulations and yielded an impressive AUC of 0.88 in the hardware experiment. This performance surpasses a suite of classical benchmarks, with a particularly strong result on the recall metric. This study provides a pragmatic blueprint for applying quantum computing to data-constrained financial scenarios in the NISQ era and offers valuable empirical evidence supporting its potential in high-stakes applications like inclusive finance.

[43] arXiv:2509.13826 (cross-list from cond-mat.mtrl-sci) [cn-pdf, pdf, html, other]
Title: Quantum Simulations of Battery Electrolytes with VQE-qEOM and SQD: Active-Space Design, Dissociation, and Excited States of LiPF$_6$, NaPF$_6$, and FSI Salts
Sk Mujaffar Hossain, Seung-Cheol Lee, Satadeep Bhattacharjee
Subjects: Materials Science (cond-mat.mtrl-sci) ; Quantum Physics (quant-ph)

Accurate prediction of excited states in battery electrolytes is central to understanding photostability, oxidative stability, and degradation. We employ hybrid quantum--classical algorithms -- the Variational Quantum Eigensolver (VQE) for ground states combined with the quantum equation of motion (qEOM) for vertical singlet excitations -- to study LiPF$_6$, NaPF$_6$, LiFSI, and NaFSI. Compact active spaces were constructed from frontier orbitals, mapped to qubits, and reduced via symmetry tapering and commuting-group measurements to lower sampling cost. Within $\sim$10-qubit models, VQE--qEOM agrees closely with exact diagonalization of the same Hamiltonians, while sample-based quantum diagonalization (SQD) in larger active spaces recovers near-exact (subspace-FCI) energies. The spectra display clear anion and cation trends: PF$_6$ salts exhibit higher first-excitation energies (e.g., LiPF$_6$ $\approx$13.2 eV) and a compact three-state cluster at 12--13 eV, whereas FSI salts show substantially lower onsets ($\approx$8--9 eV) with a near-degenerate (S$_1$,S$_2$) followed by S$_3$ $\sim$1.3 eV higher. Substituting Li$^+$ with Na$^+$ narrows the gap by $\sim$0.4--0.8 eV within each anion family. Converting S$_1$ to wavelengths places the onsets in the deep-UV (LiPF$_6$ $\sim$94 nm; NaPF$_6$ $\sim$100 nm; LiFSI $\sim$141 nm; NaFSI $\sim$148 nm). All results pertain to isolated species or embedded clusters appropriate to the NISQ regime; solvent shifts can be incorporated a posteriori via classical $\Delta$-solvation or static embedding. These results demonstrate that current quantum algorithms can deliver chemically meaningful excitation and binding trends for realistic electrolyte motifs and provide quantitative baselines to guide electrolyte screening and design.

[44] arXiv:2509.13925 (cross-list from math-ph) [cn-pdf, pdf, html, other]
Title: Three-dimensional ghost-free representations of the Pais-Uhlenbeck model from Tri-Hamiltonians
Alexander Felski, Andreas Fring, Bethan Turner
Comments: 14 pages, 1 figure
Subjects: Mathematical Physics (math-ph) ; Quantum Physics (quant-ph)

We present a detailed analysis of the sixth-order Pais-Uhlenbeck oscillator and construct three-dimensional ghost-free representations through a Tri-Hamiltonian framework. We identify a six-dimensional Abelian Lie algebra of the PU model's dynamical flow and derive a hierarchy of conserved Hamiltonians governed by multiple compatible Poisson structures. These structures enable the realisation of a complete Tri-Hamiltonian formulation that generates identical dynamical flows. Positive-definite Hamiltonians are constructed, and their relation to the full Tri-Hamiltonian hierarchy is analysed. Furthermore, we develop a mapping between the PU model and a class of three-dimensional coupled second-order systems, revealing explicit conditions for ghost-free equivalence. We also explore the consequences of introducing interaction terms, showing that the multi-Hamiltonian structure is generally lost in such cases.

[45] arXiv:2509.14027 (cross-list from cond-mat.stat-mech) [cn-pdf, pdf, html, other]
Title: Quantum vs Classical Thermal Transport at Low Temperatures
Zhixing Zou, Jiangbin Gong, Jiao Wang, Giulio Casati, Giuliano Benenti
Comments: 6+4 pages; comments are welcome
Subjects: Statistical Mechanics (cond-mat.stat-mech) ; Quantum Physics (quant-ph)

This work aims to understand how quantum mechanics affects heat transport at low temperatures. In the classical setting, by considering a simple paradigmatic model, our simulations reveal the emergence of Negative Differential Thermal Resistance (NDTR): paradoxically, increasing the temperature bias by lowering the cold bath temperature reduces the steady-state heat current. In sharp contrast, the quantum version of the model, treated via a Lindblad master equation, exhibits no NDTR: the heat current increases monotonically with thermal bias. This marked divergence highlights the fundamental role of quantum effects in low-temperature thermal transport and underscores the need to reconsider classical predictions when designing and optimizing nanoscale thermal devices.

Replacement submissions (showing 39 of 39 entries )

[46] arXiv:2310.16982 (replaced) [cn-pdf, pdf, html, other]
Title: Non-Clifford and parallelizable fault-tolerant logical gates on constant and almost-constant rate homological quantum LDPC codes via higher symmetries
Guanyu Zhu, Shehryar Sikander, Elia Portnoy, Andrew W. Cross, Benjamin J. Brown
Comments: 40 pages, 32 figures. In the updated version v2, we have simplified the TQFT derivation of the logical gates via an operator-valued cochain formalism in Sec. III, which also gives rise to the explicit construction of constant-depth circuits corresponding to logical CCZ and CZ gates in three copies of identical toric codes defined on arbitrary 3-manifolds
Subjects: Quantum Physics (quant-ph) ; Strongly Correlated Electrons (cond-mat.str-el) ; Information Theory (cs.IT) ; High Energy Physics - Theory (hep-th) ; Geometric Topology (math.GT)

We study parallel fault-tolerant quantum computing for families of homological quantum low-density parity-check (LDPC) codes defined on 3-manifolds with constant or almost-constant encoding rate. We derive generic formula for a transversal $T$ gate of color codes on general 3-manifolds, which acts as collective non-Clifford logical CCZ gates on any triplet of logical qubits with their logical-$X$ membranes having a $\mathbb{Z}_2$ triple intersection at a single point. The triple intersection number is a topological invariant, which also arises in the path integral of the emergent higher symmetry operator in a topological quantum field theory: the $\mathbb{Z}_2^3$ gauge theory. Moreover, the transversal $S$ gate of the color code corresponds to a higher-form symmetry supported on a codimension-1 submanifold, giving rise to exponentially many addressable and parallelizable logical CZ gates. A construction of constant-depth circuits of the above logical gates via cup product cohomology operation is also presented for three copies of identical toric codes on arbitrary 3-manifolds. We have developed a generic formalism to compute the triple intersection invariants for 3-manifolds. We further develop three types of LDPC codes supporting such logical gates: (1) A quasi-hyperbolic code from the product of 2D hyperbolic surface and a circle, with almost-constant rate $k/n=O(1/\log(n))$ and $O(\log(n))$ distance; (2) A homological fibre bundle code with $O(1/\log^{\frac{1}{2}}(n))$ rate and $O(\log^{\frac{1}{2}}(n))$ distance; (3) A specific family of 3D hyperbolic codes: the Torelli mapping torus code, constructed from mapping tori of a pseudo-Anosov element in the Torelli subgroup, which has constant rate while the distance scaling is currently unknown. We then show a generic constant-overhead scheme for applying a parallelizable universal gate set with the aid of logical-$X$ measurements.

[47] arXiv:2405.01722 (replaced) [cn-pdf, pdf, other]
Title: Quantifying spectral signatures of non-Markovianity beyond the Born-Redfield master equation
A. Keefe, N. Agarwal, A. Kamal
Comments: 19 pages, 8 figures including 3 appendices
Subjects: Quantum Physics (quant-ph) ; Mesoscale and Nanoscale Physics (cond-mat.mes-hall)

Memory or time-non-local effects in open quantum dynamics pose theoretical as well as practical challenges in the understanding and control of noisy quantum systems. While there has been a comprehensive and concerted effort towards developing diagnostics for non-Markovian dynamics, all existing measures rely on time-domain measurements which are typically slow and expensive as they require averaging several runs to resolve small transient features on a broad background, and scale unfavorably with system size and complexity. In this work, we propose a spectroscopic measure of non-Markovianity which can detect persistent non-Markovianity in the system steady state. In addition to being experimentally viable, the proposed measure has a direct information theoretic interpretation: a large value indicates the information loss per unit bandwidth of making the Markov approximation. In the same vein, we derive a frequency-domain quantum master equation (FD-QME) that goes beyond the standard Born-Redfield description and retains the full memory of the state of the reduced system. Using the FD-QME and the proposed measure, we are able to reliably diagnose and quantify non-Markovianity in several system-environment settings including those with environmental correlations and retardation effects.

[48] arXiv:2408.16378 (replaced) [cn-pdf, pdf, other]
Title: Unconditionally separating noisy $\mathsf{QNC}^0$ from bounded polynomial threshold circuits of constant depth
Min-Hsiu Hsieh, Leandro Mendes, Michael de Oliveira, Sathyawageeswar Subramanian
Comments: Close to published version
Journal-ref: Nat Commun 16, 3559 (2025)
Subjects: Quantum Physics (quant-ph) ; Computational Complexity (cs.CC)

The rapid evolution of quantum devices fuels concerted efforts to experimentally establish quantum advantage over classical computing. Many demonstrations of quantum advantage, however, rely on computational assumptions and face verification challenges. Furthermore, steady advances in classical algorithms and machine learning make the issue of provable, practically demonstrable quantum advantage a moving target. In this work, we unconditionally demonstrate that parallel quantum computation can exhibit greater computational power than previously recognized. We prove that polynomial-size biased threshold circuits of constant depth -- which model neural networks with tunable expressivity -- fail to solve certain problems solvable by small constant-depth quantum circuits with local gates, for values of the bias that allow quantifiably large computational power. Additionally, we identify a family of problems that are solvable in constant depth by a universal quantum computer over prime-dimensional qudits with bounded connectivity, but remain hard for polynomial-size biased threshold circuits. We thereby bridge the foundational theory of non-local games in higher dimensions with computational advantage on emerging devices operating on a wide range of physical platforms. Finally, we show that these quantum advantages are robust to noise across all prime qudit dimensions with all-to-all connectivity, enhancing their practical appeal.

[49] arXiv:2410.13559 (replaced) [cn-pdf, pdf, html, other]
Title: On estimating the trace of quantum state powers
Yupan Liu, Qisheng Wang
Comments: 57 pages, 3 tables, 3 algorithms. v3: Added a paragraph on recent developments, fixed the proof of Lemma 2.17 (Lemma 2.9 in the SODA proceedings), and made other minor changes. v2: Minor changes (particularly quantum query complexity lower bound for the hard regime, Theorem 5.8 in the SODA proceedings) and added references
Journal-ref: Proceedings of the 2025 Annual ACM-SIAM Symposium on Discrete Algorithms (SODA), pp. 947-993, 2025
Subjects: Quantum Physics (quant-ph) ; Computational Complexity (cs.CC) ; Data Structures and Algorithms (cs.DS)

We investigate the computational complexity of estimating the trace of quantum state powers $\text{tr}(\rho^q)$ for an $n$-qubit mixed quantum state $\rho$, given its state-preparation circuit of size $\text{poly}(n)$. This quantity is closely related to and often interchangeable with the Tsallis entropy $\text{S}_q(\rho) = \frac{1-\text{tr}(\rho^q)}{q-1}$, where $q = 1$ corresponds to the von Neumann entropy. For any non-integer $q \geq 1 + \Omega(1)$, we provide a quantum estimator for $\text{S}_q(\rho)$ with time complexity $\text{poly}(n)$, exponentially improving the prior best results of $\exp(n)$ due to Acharya, Issa, Shende, and Wagner (ISIT 2019), Wang, Guan, Liu, Zhang, and Ying (TIT 2024), and Wang, Zhang, and Li (TIT 2024), and Wang and Zhang (ESA 2024). Our speedup is achieved by introducing efficiently computable uniform approximations of positive power functions into quantum singular value transformation. Our quantum algorithm reveals a sharp phase transition between the case of $q=1$ and constant $q>1$ in the computational complexity of the Quantum $q$-Tsallis Entropy Difference Problem (TsallisQED$_q$), particularly deciding whether the difference $\text{S}_q(\rho_0) - \text{S}_q(\rho_1)$ is at least $0.001$ or at most $-0.001$: - For any $1+\Omega(1) \leq q \leq 2$, TsallisQED$_q$ is $\mathsf{BQP}$-complete, which implies that Purity Estimation is also $\mathsf{BQP}$-complete. - For any $1 \leq q \leq 1 + \frac{1}{n-1}$, TsallisQED$_q$ is $\mathsf{QSZK}$-hard, leading to hardness of approximating the von Neumann entropy because $\text{S}_q(\rho) \leq \text{S}(\rho)$, as long as $\mathsf{BQP} \subsetneq \mathsf{QSZK}$. The hardness results are derived from reductions based on new inequalities for the quantum $q$-Jensen-(Shannon-)Tsallis divergence with $1\leq q \leq 2$, which are of independent interest.

[50] arXiv:2411.00364 (replaced) [cn-pdf, pdf, html, other]
Title: Application of the Quantum Approximate Optimization Algorithm in Solving the Total Domination Problem
Haoqian Pan, Hang Yuan, Yang Liu, Changhong Lu, Wanfang Chen, Shiyue Wang
Comments: 25 pages, 13 figures
Subjects: Quantum Physics (quant-ph) ; Discrete Mathematics (cs.DM)

Recent advancements in quantum computing have spurred substantial research into the application of quantum algorithms to combinatorial optimization problems. Among these challenges, the Total Domination Problem (TDP) emerges as a classic and critical paradigm in the field. For a graph G(V, E), TDP entails finding a minimal subset D subset of V that contains no isolated vertices, where every vertex not in D has at least one neighbor in D. TDP finds extensive applications across domains such as computer networks, social networks, and communications. Since the latter half of the last century, research efforts have focused on establishing its NP-completeness and developing solution algorithms, which have become foundational to combinatorial mathematics. Despite this rich history, the application of quantum algorithms to TDP remains largely underexplored. In this study, we present a pioneering application of the Quantum Approximate Optimization Algorithm (QAOA) to tackle TDP, evaluating its efficacy across a diverse set of parameters. This paper proves that the upper bound on the number of qubits required to solve TDP is 2|V| + |V| log_2( (2|E|)/|V| - 1 ). Our experimental findings demonstrate that QAOA is effective in addressing TDP: under most parameter combinations, it successfully computes a valid total dominating set (TDS). However, the algorithm's performance in identifying the optimal TDS is contingent upon specific parameter choices, revealing a significant bias in the distribution of effective parameter points. This research contributes valuable insights into the potential of quantum algorithms for solving TDP and lays a solid groundwork for future investigations in this area.

[51] arXiv:2411.12608 (replaced) [cn-pdf, pdf, html, other]
Title: Exploring the Potential of Quantum Approximate Optimization Algorithm in Tackling the Perfect Domination Problem
Haoqian Pan, Changhong Lu, Yuqing Zheng, Chunxing Yan
Comments: 30 pages, 19 figures
Subjects: Quantum Physics (quant-ph)

Perfect Domination Problem (PDP), a canonical challenge in combinatorial optimization, finds critical applications in real-world systems such as error-correcting codes, wireless communication networks, and social networks. Decades of research have firmly established its NP-completeness across numerous graph classes. Motivated by rapid advances in quantum computing, significant effort has recently been directed toward quantum algorithms for NP-complete problems, most notably the Quantum Approximate Optimization Algorithm (QAOA). Nonetheless, the applicability and efficacy of quantum approaches to the PDP remain entirely unexplored. This paper initiates the first systematic investigation of the PDP via QAOA. We evaluate solution quality on three benchmark instances of 6, 7, and 8 vertices using 15-18 qubits on a quantum simulator, examining more than 400 distinct parameter configurations. Experimental results confirm the algorithm's effectiveness and expose discernible trends in parameter selection. These outcomes substantiate QAOA's viability for the PDP and mark a seminal step toward situating this classical problem within the quantum-computing paradigm.

[52] arXiv:2412.06631 (replaced) [cn-pdf, pdf, html, other]
Title: Recurrent convolutional neural networks for modeling non-adiabatic dynamics of quantum-classical systems
Alex P. Ning, Lingyu Yang, Gia-Wei Chern
Comments: 16 pages, 9 figures
Subjects: Quantum Physics (quant-ph) ; Computational Physics (physics.comp-ph)

Recurrent neural networks (RNNs) have recently been extensively applied to model the time-evolution in fluid dynamics, weather predictions, and even chaotic systems thanks to their ability to capture temporal dependencies and sequential patterns in data. Here we present a RNN model based on convolution neural networks for modeling the nonlinear non-adiabatic dynamics of hybrid quantum-classical systems. The dynamical evolution of the hybrid systems is governed by equations of motion for classical degrees of freedom and von Neumann equation for electrons. The physics-aware recurrent convolution (PARC) neural network structure incorporates a differentiator-integrator architecture that inductively models the spatiotemporal dynamics of generic physical systems. We apply our RNN approach to learn the space-time evolution of a one-dimensional semi-classical Holstein model after an interaction quench. For shallow quenches (small changes in electron-lattice coupling), the deterministic dynamics can be accurately captured using a single-CNN-based recurrent network. In contrast, deep quenches induce chaotic evolution, making long-term trajectory prediction significantly more challenging. Nonetheless, we demonstrate that the PARC-CNN architecture can effectively learn the statistical climate of the Holstein model under deep-quench conditions.

[53] arXiv:2501.02005 (replaced) [cn-pdf, pdf, html, other]
Title: Machine Learns Quantum Complexity
Dongsu Bak, Su-Hyeong Kim, Sangnam Park, Jeong-Pil Song
Comments: 18 pages, 8 figures, references added
Subjects: Quantum Physics (quant-ph) ; High Energy Physics - Theory (hep-th)

We study how a machine based on deep learning algorithms learns Krylov spread complexity in quantum systems with N x N random Hamiltonians drawn from the Gaussian unitary ensemble. Using thermofield double states as initial conditions, we demonstrate that a convolutional neural network-based algorithm successfully learns the Krylov spread complexity across all timescales, including the late-time plateaus where states appear nearly featureless and random. Performance strongly depends on the basis choice, performing well with the energy eigenbasis or the Krylov basis but failing in the original basis of the random Hamiltonian. The algorithm also effectively distinguishes temperature-dependent features of thermofield double states. Furthermore, we show that the system time variable of state predicted by deep learning is an irrelevant quantity, reinforcing that the Krylov spread complexity well captures the essential features of the quantum state, even at late times.

[54] arXiv:2501.03201 (replaced) [cn-pdf, pdf, html, other]
Title: Resonator-assisted quantum transduction between superconducting qubits and trapped atomic systems via Rydberg levels
Fernando L. Semião, Matthias Keller
Comments: 13 pages, 10 figures
Journal-ref: Phys. Rev. Research 7, 033210 (2025)
Subjects: Quantum Physics (quant-ph)

Using a shared microwave resonator, we propose a transduction scheme between superconducting qubits and qubit states encoded in the low-lying internal levels of trapped atomic systems. The approach employs atomic Rydberg levels together with laser pulses that connect them to the low-lying qubit states. We explore two coupling protocols: one based on resonant interactions between the subsystems, and another operating in the dispersive regime, where the resonator is far detuned from the transition frequencies of the matter qubits. These protocols enable the transfer of a general qubit state from the superconducting qubit to the atomic qubit. Transfer fidelity is evaluated across different coupling regimes and under various sources of dissipation and decoherence, including resonator decay, Rydberg state decay, and both relaxation and pure dephasing of the superconducting qubit, providing a detailed assessment of the performance of the proposed scheme.

[55] arXiv:2502.12905 (replaced) [cn-pdf, pdf, html, other]
Title: On the consistency of measurement protocols for quantum processes fluctuations
Thales Augusto Barbosa Pinto Silva, David Gelbwaser-Klimovsky
Subjects: Quantum Physics (quant-ph)

Quantum fluctuations are fundamental in quantum technologies, affecting computing, sensing, cryptography, and thermodynamics. These include fluctuations in the variation of energy, charge, and other observables driven by interactions with lasers and baths. Despite the precise rules quantum mechanics provides for measuring observables at instants of time, no standard framework exists for characterizing the fluctuations of their variations over time. This gap leads to inconsistencies in fluctuation predictions, impacting quantum technologies. In this work, we propose four basic criteria that any measurement of these variations must satisfy, grounded in conservation laws, the no-signaling principle, and expected constraints on physical realism. We demonstrate that only one protocol fulfills all these criteria: the two-times quantum observables. This result has the potential to establish the foundations for measurements of quantum processes, possibly resolving ambiguities in quantum fluctuation measurements. Moreover, it enables the extension of quantum information concepts, such as entanglement and Bell's inequalities, to processes rather than instantaneous observables.

[56] arXiv:2503.21596 (replaced) [cn-pdf, pdf, html, other]
Title: Classical bounds on two-outcome bipartite Bell expressions and linear prepare-and-measure witnesses: Efficient computation in parallel environments such as graphics processing units
István Márton, Erika Bene, Péter Diviánszky, Gábor Drótos
Comments: 34 pages, 3 figures, 3 tables
Journal-ref: Computer Physics Communications 316 (2025) 109809
Subjects: Quantum Physics (quant-ph)

The presented program aims at speeding up the brute force computation of the so-called $L_d$ norm of a matrix $M$ using graphics processing units (GPUs). Alternatives for CPUs have also been implemented, and the algorithm is applicable to any parallel environment. The $n\times m$ matrix $M$ has real elements which may represent coefficients of a bipartite Bell expression or those of a linear prepare-and-measure (PM) witness. In this interpretation, the $L_1$ norm is the local bound of the given correlation-type Bell expression, and the $L_d$ norm for $d\ge 2$ is the classical $d$-dimensional bound of the given PM witness, which is associated with the communication of $d$-level classical messages in the PM scenario. The program is also capable of calculating the local bound of Bell expressions including marginals. In all scenarios, the output is assumed to be binary. The code for GPUs is written in CUDA C and can utilize one NVIDIA GPU in a computer. To illustrate the performance of our implementation, we refer to Brierley et al. [arXiv:1609.05011] who needed approximately three weeks to compute the local bound on a Bell expression defined by a $42\times 42$ matrix on a standard desktop using a single CPU core. In contrast, our efficient implementation of the brute force algorithm allows us to reduce this to three minutes using a single NVIDIA RTX 6000 Ada graphics card on a workstation. For CPUs, the algorithm was implemented with OpenMP and MPI according to the shared and distributed memory models, respectively, and achieves a comparable speedup at a number of CPU cores around 100.

[57] arXiv:2504.06146 (replaced) [cn-pdf, pdf, html, other]
Title: Symmetry breaking in chaotic many-body quantum systems at finite temperature
Angelo Russotto, Filiberto Ares, Pasquale Calabrese
Comments: 7+7 pages, 3+2 figures, references added, final version published in Phys. Rev. E
Journal-ref: Phys. Rev. E 112, L032101 (2025)
Subjects: Quantum Physics (quant-ph) ; Statistical Mechanics (cond-mat.stat-mech)

Recent work has shown that the entanglement of finite-temperature eigenstates in chaotic quantum many-body local Hamiltonians can be accurately described by an ensemble of random states with an internal $U(1)$ symmetry. We build upon this result to investigate the universal symmetry-breaking properties of such eigenstates. As a probe of symmetry breaking, we employ the entanglement asymmetry, a quantum information observable that quantifies the extent to which symmetry is broken in a subsystem. This measure enables us to explore the finer structure of finite-temperature eigenstates in terms of the $U(1)$-symmetric random state ensemble; in particular, the relation between the Hamiltonian and the effective conserved charge in the ensemble. Our analysis is supported by analytical calculations for the symmetric random states, as well as exact numerical results for the Mixed-Field Ising spin-$1/2$ chain, a paradigmatic model of quantum chaoticity.

[58] arXiv:2505.02445 (replaced) [cn-pdf, pdf, html, other]
Title: Efficient Classical Sampling from Gaussian Boson Sampling Distributions on Unweighted Graphs
Yexin Zhang, Shuo Zhou, Xinzhao Wang, Ziruo Wang, Ziyi Yang, Rui Yang, Yecheng Xue, Tongyang Li
Comments: 34 pages, 7 figures
Subjects: Quantum Physics (quant-ph) ; Data Structures and Algorithms (cs.DS)

Gaussian Boson Sampling (GBS) is a promising candidate for demonstrating quantum computational advantage and can be applied to solving graph-related problems. In this work, we propose Markov chain Monte Carlo-based algorithms to sample from GBS distributions on undirected, unweighted graphs. Our main contribution is a double-loop variant of Glauber dynamics, whose stationary distribution matches the GBS distribution. We further prove that it mixes in polynomial time for dense graphs using a refined canonical path argument. Numerically, we conduct experiments on unweighted graphs with 256 vertices, larger than the scales in former GBS experiments as well as classical simulations. In particular, we show that both the single-loop and double-loop Glauber dynamics improve the performance of original random search and simulated annealing algorithms for the max-Hafnian and densest $k$-subgraph problems up to 10$\times$. Overall, our approach offers both theoretical guarantees and practical advantages for efficient classical sampling from GBS distributions on unweighted graphs.

[59] arXiv:2505.03686 (replaced) [cn-pdf, pdf, html, other]
Title: The response of a quantum system to a collision: an autonomous derivation of Kubo's formula
Samuel L. Jacob, John Goold
Comments: Final version, published in Journal of Physics A: Mathematical and Theoretical. Added a discussion connecting our results with the literature on quantum master equations, as well a numerical example of our results. 15 pages, 1 figure
Journal-ref: Samuel L. Jacob and John Goold, 2025 J. Phys. A: Math. Theor. 58 385001
Subjects: Quantum Physics (quant-ph) ; Statistical Mechanics (cond-mat.stat-mech)

We study the response of a quantum system induced by a collision with a quantum particle, using the time-independent framework of scattering theory. After deriving the dynamical map for the quantum system, we show that it encodes a non-perturbative response function obeying a general fluctuation-dissipation relation. We show that Kubo's formula emerges autonomously in the Born approximation, where the time-dependent perturbation is determined by particle's evolution through the potential region.

[60] arXiv:2505.11487 (replaced) [cn-pdf, pdf, other]
Title: Area and volume as emergent phenomena from entangled qubits
Juan M. Romero, Emiliano Montoya-González
Comments: 13 pages, 3 figures. Revised version. Title changed. Typos corrected. References added. Accepted for publicaction in Modern Physics Letters A
Subjects: Quantum Physics (quant-ph) ; General Relativity and Quantum Cosmology (gr-qc) ; High Energy Physics - Theory (hep-th)

Recently, a connection has been shown between certain geometric quantities and quantum information theory. In this paper, we demonstrate that geometric quantities such as area and volume can emerge directly from entangled multi-qubit states. In particular, the area of a two-dimensional parallelogram is derived from a 4-qubit entangled state, the vector area of a three-dimensional parallelogram from three 6-qubit entangled states, and the volume of a three-dimensional parallelepiped from a 9-qubit entangled state. Corresponding quantum circuits are constructed and implemented using Qiskit to generate the required entangled states. Given that parallelograms and parallelepipeds serve as elementary building blocks for more complex geometric structures, these results may offer a pathway toward exploring emergent geometry in quantum information frameworks

[61] arXiv:2505.14622 (replaced) [cn-pdf, pdf, html, other]
Title: Pontus-Mpemba effects
Andrea Nava, Reinhold Egger
Comments: 8 pages, 4 figures
Subjects: Quantum Physics (quant-ph) ; Statistical Mechanics (cond-mat.stat-mech)

Mpemba effects occur after a sudden quench of control parameters if for ''far'' (or ''hot'') initial states with respect to a final target state, the relaxation time toward the target state is shorter than for ''close'' (or ''cold'') initial states. Following a strategy of fishermen in Pontus described by Aristotle, we introduce the Pontus-Mpemba effect as a two-step protocol which includes the time needed for preparing the system in the ''far'' initial state that can now be an arbitrary nonequilibrium state. Our protocol needs no parameter distance concept and applies to general (classical or quantum) systems. We find that all possible Pontus-Mpemba effects fall into three classes and illustrate the theory for open Markovian two-state quantum systems.

[62] arXiv:2506.02226 (replaced) [cn-pdf, pdf, html, other]
Title: Prepare-and-Magic: Semi-Device Independent Magic Certification in the Prepare-and-Measure Scenario
Santiago Zamora, Rafael A. Macedo, Tailan S. Sarubi, Moisés Alves, Davide Poderini, Rafael Chaves
Comments: 12 + 4 pages, 5 figures
Subjects: Quantum Physics (quant-ph)

Non-stabilizerness is an essential resource for quantum computational advantage, as stabilizer states admit efficient classical simulation. We develop a semi-device-independent framework for certifying non-stabilizer states in prepare-and-measure (PAM) scenarios, relying only on assumptions about the system's dimension. Within this framework, we introduce prepare-and-measure witnesses that can distinguish stabilizer from non-stabilizer states, and we provide analytical proofs that threshold violations of these witnesses certify non-stabilizerness. In the simplest setting: three preparations, two measurements, and qubit systems, surpassing a specific threshold guarantees that at least one prepared state lies outside the stabilizer polytope, while a stronger violation can certify at least two. We extend this approach by linking it to quantum random access codes, also generalizing our results to qutrit systems and introducing a necessary condition for certifying non-stabilizerness based on state overlaps (Gram matrices). These results offer a set of semi-device-independent tools for practically and systematically verifying non-stabilizer states using prepare-and-measure inequalities.

[63] arXiv:2507.00908 (replaced) [cn-pdf, pdf, html, other]
Title: Quantum Imaginary-Time Evolution with Polynomial Resources in Time
Lei Zhang, Jizhe Lai, Xian Wu, Xin Wang
Comments: 28 pages including appendix
Subjects: Quantum Physics (quant-ph)

Imaginary-time evolution is fundamental to analyzing quantum many-body systems, yet classical simulation requires exponentially growing resources in both system size and evolution time. While quantum approaches reduce the system-size scaling, existing methods rely on heuristic techniques with measurement precision or success probability that deteriorates as evolution time increases. We present a quantum algorithm that prepares normalized imaginary-time evolved states using an adaptive normalization factor to maintain stable success probability over large imaginary times. Our algorithm approximates the target state to polynomially small errors in inverse imaginary time using polynomially many elementary quantum gates and a single ancilla qubit, achieving success probability close to one. When the initial state has reasonable overlap with the ground state, this algorithm also achieves polynomial resource complexity in the system size. We extend this approach to ground-state preparation and ground-state energy estimation, achieving reduced circuit depth compared to existing methods. Numerical experiments validate our theoretical results for evolution time up to 50, demonstrating the algorithm's effectiveness for long-time evolution and its potential applications for early fault-tolerant quantum computing.

[64] arXiv:2508.11308 (replaced) [cn-pdf, pdf, html, other]
Title: Spectral characterizations of entanglement witnesses
Zhiwei Song, Lin Chen
Comments: 17 pages, no figure
Subjects: Quantum Physics (quant-ph)

We present a systematic investigation of the spectral properties of entanglement witnesses (EWs). Specifically, we analyze the infimum and supremum of the largest eigenvalue, the smallest eigenvalue, the negativity (defined as the absolute value of the sum of negative eigenvalues), and the squared Frobenius norm of a unit-trace (normalized) entanglement witness, along with the conditions under which these values are attained. Our study provides distinct characterizations for decomposable (DEWs) and nondecomposable entanglement witnesses (NDEWs). While these two classes share many spectral similarities, we reveal a fundamental divergence by proving that the infimum of the smallest eigenvalue can be attained by DEWs, yet remains strictly unattainable for all NDEWs. We apply the results to provide necessary conditions for an EW to possess a mirrored EW. Furthermore, we demonstrate the superior detection capability of NDEWs by proving that any non-positive-transpose (NPT) state beyond the two-qubit and qubit-qutrit systems can be detected by an NDEW.

[65] arXiv:2508.14233 (replaced) [cn-pdf, pdf, html, other]
Title: Excitonic Coupling and Photon Antibunching in Venus Yellow Fluorescent Protein Dimers: A Lindblad Master Equation Approach
Ian T. Abrahams
Comments: 16 pages (excluding references), 4 figures, includes discussions of cryogenic exciton dynamics, quantum biophotonics, quantum technology, evolutionary adaptations in fluorescent proteins, and the potential application of Venus dimers as quantum bits (qubits) for quantum information processing
Subjects: Quantum Physics (quant-ph) ; Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ; Biological Physics (physics.bio-ph) ; Optics (physics.optics) ; Biomolecules (q-bio.BM)

Strong excitonic coupling and photon antibunching (AB) have been observed together in Venus yellow fluorescent protein dimers and currently lack a cohesive theoretical explanation. In 2019, Kim et al. demonstrated Davydov splitting in circular dichroism spectra, revealing strong J-like coupling, while antibunched fluorescence emission was confirmed by combined antibunching--fluorescence correlation spectroscopy (AB/FCS fingerprinting). To investigate the implications of this coexistence, Venus dimer population dynamics are modeled within a Lindblad master equation framework, justified by the separation of characteristic coupling, dephasing, and thermal relaxation rates. Simulations predict rapid decoherence, yielding bright/dark state mixtures consistent with antibunched fluorescence emission at room temperature. Thus, excitonic coupling and photon AB are reconciled without invoking long-lived quantum coherence. More broadly, fluorescent proteins emerge as tractable model systems for probing evolutionary pressures on chromoprotein photophysics and quantum dynamics. Cryogenic cooling may extend coherence time into the regime required for ultrafast gate operations, suggesting fluorescent protein dimers as a viable platform for bio-inspired qubits.

[66] arXiv:2508.15186 (replaced) [cn-pdf, pdf, html, other]
Title: Dirac monopole magnets in non-Hermitian systems
Haiyang Yu, Tao Jiang, Li-Chen Zhao
Comments: 15 pages, 6 figures
Subjects: Quantum Physics (quant-ph) ; Quantum Gases (cond-mat.quant-gas) ; Mathematical Physics (math-ph) ; Pattern Formation and Solitons (nlin.PS)

We theoretically establish that non-Hermitian perturbations induce a topological transformation of point-like Dirac monopoles into extended monopole distributions, characterized by distinct charge configurations emergent from three distinct Berry connection forms. Using piecewise adiabatic evolution, we confirm the validity of these configurations through observations of complex geometric phases. Most critically, we find a quantitative relation $\Delta \phi_d = \Delta \phi_g$, which quantifies how cumulative minute energy differences (\(\Delta \phi_d\)) manifest as geometric phase shifts (\(\Delta \phi_g\)) uniquely in non-Hermitian systems. We further propose a scheme leveraging soliton dynamics in dissipative two-component Bose-Einstein condensates, enabling direct measurement of these topological signatures. These results establish a milestone for understanding Dirac monopole charge distributions and measuring complex geometric phases in non-Hermitian systems, with far-reaching implications for topological quantum computing and non-Hermitian photonics.

[67] arXiv:2509.03495 (replaced) [cn-pdf, pdf, html, other]
Title: Learning AC Power Flow Solutions using a Data-Dependent Variational Quantum Circuit
Thinh Viet Le, Md Obaidur Rahman, Vassilis Kekatos
Comments: 7 pages, 6 figures, accepted for the IEEE International Conference on Communications, Control, and Computing Technologies for Smart Grids 2025
Subjects: Quantum Physics (quant-ph) ; Machine Learning (cs.LG) ; Systems and Control (eess.SY) ; Optimization and Control (math.OC)

Interconnection studies require solving numerous instances of the AC load or power flow (AC PF) problem to simulate diverse scenarios as power systems navigate the ongoing energy transition. To expedite such studies, this work leverages recent advances in quantum computing to find or predict AC PF solutions using a variational quantum circuit (VQC). VQCs are trainable models that run on modern-day noisy intermediate-scale quantum (NISQ) hardware to accomplish elaborate optimization and machine learning (ML) tasks. Our first contribution is to pose a single instance of the AC PF as a nonlinear least-squares fit over the VQC trainable parameters (weights) and solve it using a hybrid classical/quantum computing approach. The second contribution is to feed PF specifications as features into a data-embedded VQC and train the resultant quantum ML (QML) model to predict general PF solutions. The third contribution is to develop a novel protocol to efficiently measure AC-PF quantum observables by exploiting the graph structure of a power network. Preliminary numerical tests indicate that the proposed VQC models attain enhanced prediction performance over a deep neural network despite using much fewer weights. The proposed quantum AC-PF framework sets the foundations for addressing more elaborate grid tasks via quantum computing.

[68] arXiv:2509.09993 (replaced) [cn-pdf, pdf, html, other]
Title: No oscillating subradiant correlations in a strongly driven quantum emitter array
Jiaming Shi, Nikita Leppenen, Ran Tessler, Alexander N. Poddubny
Comments: 6 pages, 3 figures + End Matter -- one missing word corrected in abstract in v2
Subjects: Quantum Physics (quant-ph) ; Optics (physics.optics)

We theoretically study time-dependent correlations in a strongly driven array of $N$ two-level atoms, coupled to photons in a waveguide. We focus on the spectrum $\{\lambda\}$ of the Liouvillian superoperator, which determines the correlation decay rates $-\Re \lambda$ and the frequencies $\Im\lambda$. Our main finding is the suppression of subradiant oscillating correlations between atomic states by a strong coherent drive of amplitude $\Omega$: $|\Re \lambda|\ge m\gamma/2$, where $\gamma$ is the single-atom spontaneous decay rate and $m=|\Im \lambda/(2\Omega)|$ is a nonzero integer for correlations oscillating in time $\propto \exp(\pm 2i m|\Omega| t)$. This limit is independent of the number of atoms $N$; it holds both for small arrays and in the macroscopic limit. We demonstrate the suppression of subradiance numerically and provide a rigorous proof based on the analytical decomposition of the Liouvillian using spectral theory of simplicial complexes and posets.

[69] arXiv:2509.13017 (replaced) [cn-pdf, pdf, html, other]
Title: Mitigating the sign problem by quantum computing
Kwai-Kong Ng, Min-Fong Yang
Comments: 9 pages, 4 figures
Subjects: Quantum Physics (quant-ph) ; Other Condensed Matter (cond-mat.other) ; Computational Physics (physics.comp-ph)

The notorious sign problem severely limits the applicability of quantum Monte Carlo (QMC) simulations, as statistical errors grow exponentially with system size and inverse temperature. A recent proposal of a quantum-computing stochastic series expansion (qc-SSE) method suggested that the problem could be avoided by introducing constant energy shifts into the Hamiltonian. Here we critically examine this framework and show that it does not strictly resolve the sign problem for Hamiltonians with non-commuting terms. Instead, it provides a practical mitigation strategy that suppresses the occurrence of negative weights. Using the antiferromagnetic anisotropic XY chain as a test case, we analyze the dependence of the average sign on system size, temperature, anisotropy, and shift parameters. An operator contraction method is introduced to improve efficiency. Our results demonstrate that moderate shifts optimally balance sign mitigation and statistical accuracy, while large shifts amplify errors, leaving the sign problem unresolved but alleviated.

[70] arXiv:1005.0130 (replaced) [cn-pdf, pdf, html, other]
Title: The Existence and Role of Quantum-State Noise
Aleksandar Perisic
Journal-ref: Perisic, A. (2010). The Existence and Role of Quantum-state Noise. NeuroQuantology, 8(4)
Subjects: General Physics (physics.gen-ph) ; Quantum Physics (quant-ph)

The key observation about quantum reality is that it often appears as if, at some moment, the probability of a quantum event becomes a definite outcome for us. A careful analysis suggests, however, that what we perceive as a definite state -- the observed outcome of a quantum experiment -- is not strictly definite. From this, we conclude that the quantum world is active: its influence extends beyond a merely statistical and permanently fixed determination of reality as we experience it.

[71] arXiv:2502.02660 (replaced) [cn-pdf, pdf, html, other]
Title: Enhancing the Hyperpolarizability of Crystals with Quantum Geometry
Wojciech J. Jankowski, Robert-Jan Slager, Michele Pizzochero
Comments: 6+13 pages, 3+1 figures
Journal-ref: Phys. Rev. Lett. 135, 126606 (2025)
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ; Materials Science (cond-mat.mtrl-sci) ; Optics (physics.optics) ; Quantum Physics (quant-ph)

We demonstrate that higher-order electric susceptibilities in crystals can be enhanced and understood through nontrivial topological invariants and quantum geometry, using one-dimensional $\pi$-conjugated chains as representative model systems. First, we show that the crystalline-symmetry-protected topology of these chains imposes a lower bound on their quantum metric and hyperpolarizabilities. Second, we employ numerical simulations to reveal the tunability of nonlinear, quantum geometry-driven optical responses in various one-dimensional crystals in which band topology can be externally controlled. Third, we develop a semiclassical picture to deliver an intuitive understanding of these effects. Our findings offer a firm interpretation of otherwise elusive experimental observations of colossal hyperpolarizabilities and establish guidelines for designing topological materials of any dimensionality with enhanced nonlinear optical properties.

[72] arXiv:2503.06160 (replaced) [cn-pdf, pdf, html, other]
Title: Quantum response theory and momentum-space gravity
M. Mehraeen
Comments: 7+7 pages, 1+1 figures. To be published in Physical Review Letters
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ; General Relativity and Quantum Cosmology (gr-qc) ; High Energy Physics - Theory (hep-th) ; Quantum Physics (quant-ph)

We present a quantum response approach to momentum-space gravity in dissipative multiband systems, which dresses both the quantum geometry--through an interband Weyl transformation--and the equations of motion. In addition to clarifying the roles of the contorsion and symplectic terms, we introduce the three-state quantum geometric tensor as a necessary element in the geometric classification of nonlinear responses and discuss the significance of the emergent terms from a gravitational point of view. We also identify a dual quantum geometric drag force in momentum space that provides an entropic source term for the multiband matrix of Einstein field equations.

[73] arXiv:2504.21494 (replaced) [cn-pdf, pdf, html, other]
Title: Towards a $\cos(2\varphi)$ Josephson element using aluminum junctions with well-transmitted channels
J. Griesmar, H. Riechert, M. Hantute, A. Peugeot, S. Annabi, Ç. Ö. Girit, G. O. Steffensen, A. L. Yeyati, E. Arrighi, L. Bretheau, J.-D. Pillet
Comments: 10 pages, 12 figures
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ; Quantum Physics (quant-ph)

We introduce a novel method for fabricating all-aluminum Josephson junctions with highly transmitted conduction channels. Such properties are typically associated with structures requiring intricate fabrication processes, such as atomic contacts or hybrid junctions based on semiconducting nanowires and 2D materials. In contrast, our approach relies solely on standard nanofabrication techniques. The resulting devices exhibit a key signature of high-transmission junctions - Multiple Andreev Reflections (MAR) - in their current-voltage characteristics. Furthermore, we propose a straightforward superconducting circuit design based on these junctions, enabling the implementation of a parity-protected qubit.

[74] arXiv:2504.21828 (replaced) [cn-pdf, pdf, html, other]
Title: A Path to Quantum Simulations of Topological Phases: (2+1)D Wilson Fermions Coupled To U(1) Background Gauge Fields
Sriram Bharadwaj, Emil Rosanowski, Simran Singh, Alice di Tucci, Changnan Peng, Karl Jansen, Lena Funcke, Di Luo
Comments: 22 pages, 11 figures
Subjects: High Energy Physics - Lattice (hep-lat) ; High Energy Physics - Theory (hep-th) ; Quantum Physics (quant-ph)

Quantum simulation offers a powerful approach to studying quantum field theories, particularly (2+1)D quantum electrodynamics (QED$_3$), which hosts a rich landscape of physical phenomena. A key challenge in lattice formulations is the proper realization of topological phases and the Chern-Simons terms, where fermion discretization plays a crucial role. In this work, we analyze staggered and Wilson fermions coupled to $\text{U}(1)$ background gauge fields in the Hamiltonian formulation and demonstrate that staggered fermions fail to induce (2+1)D topological phases, while Wilson fermions admit a variety of topological phases including Chern insulator and quantum spin Hall phases. We additionally uncover a rich phase diagram for the two-flavor Wilson fermion model in the presence of a chemical potential. Our findings resolve existing ambiguities in Hamiltonian formulations and provide a theoretical foundation for future quantum simulations of gauge theories with topological phases. We further outline connections to experimental platforms, offering guidance for implementations on near-term quantum computing architectures.

[75] arXiv:2505.21788 (replaced) [cn-pdf, pdf, html, other]
Title: Optical Interference Effect in Strong-field Electronic Coherence Spectroscopy
Eleanor Weckwerth, Andrew J. Howard, Chuan Cheng, Ian Gabalski, Aaron M. Ghrist, Salma A. Mohideen, Chii-Dong Lin, Chi-Hong Yuen, Philip H. Bucksbaum
Subjects: Atomic Physics (physics.atom-ph) ; Chemical Physics (physics.chem-ph) ; Optics (physics.optics) ; Quantum Physics (quant-ph)

We have investigated strong-field-induced electronic coherences in argon and molecular nitrogen ions created by high-intensity, few-cycle infrared laser pulses. This is a step toward the long-sought goal of strong-field coherent control in molecular chemistry. We employed high-intensity, few-cycle infrared laser pulses in a pump-probe setup to investigate a recent prediction that electronic coherences in nitrogen molecules change the ion yields vs. pump-probe delay. [Yuen and Lin, Phys. Rev. A 109, L011101 (2024)]. The predicted coherence signals in molecular nitrogen could not be resolved above the optical interference of the pump and probe pulses; a simultaneous measurement clearly resolved the induced cation fine-structure coherence in strong-field-ionized argon. The results of our comparison with simulations suggest that optical interference effects manifest differently in each ionic species and must be carefully accounted for when interpreting experimental data. We found that nonsequential double ionization in the low-intensity region of the focal volume can reduce the visibility of coherence generated by two-pulse sequential ionization, and we quantify the importance of pulse shape and spectral characteristics for isolating the desired coherence signals.

[76] arXiv:2506.21529 (replaced) [cn-pdf, pdf, html, other]
Title: Landau levels of a Dirac electron in graphene from non-uniform magnetic fields
Aritra Ghosh
Comments: v2: Published in PLA
Journal-ref: Phys. Lett. A 561, 130956 (2025)
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ; Mathematical Physics (math-ph) ; Exactly Solvable and Integrable Systems (nlin.SI) ; Quantum Physics (quant-ph)

The occurrence of Landau levels in quantum mechanics when a charged particle is subjected to a uniform magnetic field is well known. Considering the recent interest in the electronic properties of graphene, which admits a dispersion relation which is linear in the momentum near the Dirac points, we revisit the problem of Landau levels in the spirit of the Dirac Hamiltonian and ask if there are certain non-uniform magnetic fields which also lead to a spectrum consisting of the Landau levels. The answer, as we show, is in the affirmative. In particular, by considering isospectral deformations of the uniform magnetic field, we present explicit analytical expressions for non-uniform magnetic fields that are strictly isospectral to their uniform counterpart, thus supporting the Landau levels.

[77] arXiv:2507.01689 (replaced) [cn-pdf, pdf, html, other]
Title: Superradiant Axionic Black-Hole Clouds as Seeds for Graviton Squeezing
Panagiotis Dorlis, Nick E. Mavromatos, Sarben Sarkar, Sotirios-Neilos Vlachos
Comments: 7 pages revtex, four pdf figures incorporated. Discussion and references added on observational prospects. No effects on conclusions. Version accepted for publication in Physical Review Letters
Subjects: General Relativity and Quantum Cosmology (gr-qc) ; High Energy Physics - Phenomenology (hep-ph) ; High Energy Physics - Theory (hep-th) ; Quantum Physics (quant-ph)

It is shown that both, standard general relativity (GR) and Chern-Simons (CS) gravity, the latter containing chiral gravitational anomaly terms, seed the production of pairs of entangled gravitons in a multi-mode squeezed state. This involves the interaction of gravitons with the axionic cloud surrounding a superradiant Kerr (rotating) black hole background. The order of magnitude of the squeezing effect, specifically the number of graviton excitations in the squeezed vacuum, is estimated in the non-relativistic limit, relevant for the superradiance process. It is found analytically that the squeezing from the GR process of annihilation of two axions into two gravitons, dominates, by many orders of magnitude, that coming from the axion decay into two gravitons, induced by the higher-derivative CS term. It is also shown that significant squeezing effects are produced in the case of long-lived axionic clouds, whose lifetimes are much longer than the timescale for which superradiance is effective.

[78] arXiv:2507.02033 (replaced) [cn-pdf, pdf, html, other]
Title: Growth of block diagonal operators and symmetry-resolved Krylov complexity
Pawel Caputa, Giuseppe Di Giulio, Tran Quang Loc
Comments: 21 pages, 3 figures; v2: typos corrected, references added, Fig. 3 added, and Conclusions section improved
Subjects: High Energy Physics - Theory (hep-th) ; Statistical Mechanics (cond-mat.stat-mech) ; Quantum Physics (quant-ph)

This work addresses how the growth of invariant operators is influenced by their underlying symmetry structure. For this purpose, we introduce the symmetry-resolved Krylov complexity, which captures the time evolution of each block into which an operator, invariant under a given symmetry, can be decomposed. We find that, at early times, the complexity of the full operator is equal to the average of the symmetry-resolved contributions. At later times, however, the interplay among different charge sectors becomes more intricate. In general, the symmetry-resolved Krylov complexity depends on the charge sector, although in some cases this dependence disappears, leading to a form of Krylov complexity equipartition. Our analysis lays the groundwork for a broader application of symmetry structures in the study of Krylov space complexities with implications for thermalization and universality in many-body quantum systems.

[79] arXiv:2507.03780 (replaced) [cn-pdf, pdf, html, other]
Title: Domain-wall melting and entanglement in free-fermion chains with a band structure
Viktor Eisler
Comments: 23 pages, 9 figures, minor revision
Subjects: Statistical Mechanics (cond-mat.stat-mech) ; Quantum Gases (cond-mat.quant-gas) ; Quantum Physics (quant-ph)

We study the melting of a domain wall in free-fermion chains, where the periodic variation of the hopping amplitudes gives rise to a band structure. It is shown that the entanglement grows logarithmically in time, and the prefactor is proportional to the number of filled bands in the initial state. For a dimerized chain the particle density and current are found to have the same expressions as in the homogeneous case, up to a rescaling of the velocity. The universal contribution to the entropy profile is then doubled, while the non-universal part can be extracted numerically from block-Toeplitz matrices.

[80] arXiv:2508.08548 (replaced) [cn-pdf, pdf, other]
Title: Emergence: from physics to biology, sociology, and computer science
Ross H. McKenzie
Comments: 160 pages, 414 references. Revised version has minor corrections and additions
Subjects: History and Philosophy of Physics (physics.hist-ph) ; Statistical Mechanics (cond-mat.stat-mech) ; Neurons and Cognition (q-bio.NC) ; Quantum Physics (quant-ph)

Many systems involve numerous interacting parts and the whole system can have properties that the individual parts do not. I take this novelty as the defining characteristic of an emergent property. Other characteristics associated with emergence discussed include universality, order, complexity, unpredictability, irreducibility, diversity, self-organisation, discontinuities, and singularities. Emergent phenomena are widespread across physics, biology, social sciences, and computing, and are central to major scientific and societal challenges. Understanding emergence involves considering the stratification of reality across different scales (energy, time, length, complexity), each with its distinct ontology and epistemology, leading to semi-autonomous scientific disciplines. A central challenge is bridging the gap between macroscopic emergent properties and microscopic component interactions. Identifying an intermediate mesoscopic scale where new, weakly interacting entities or modular structures emerge is key. Theoretical approaches, such as effective theories (describing phenomena at a specific scale) and toy models (simplified systems for analysis), are vital. The Ising model exemplifies how toy models can elucidate emergence characteristics. Emergence is central to condensed matter physics, chaotic systems, fluid dynamics, nuclear physics, quantum gravity, neural networks, protein folding, and social segregation. An emergent perspective should influence scientific strategy by shaping research questions, methodologies, priorities, and resource allocation. An elusive goal is the design and control of emergent properties.

[81] arXiv:2509.00104 (replaced) [cn-pdf, pdf, html, other]
Title: Enhanced Rényi Entropy-Based Post-Quantum Key Agreement with Provable Security and Information-Theoretic Guarantees
Ruopengyu Xu, Chenglian Liu
Comments: 31 pages, 4 tables
Subjects: Cryptography and Security (cs.CR) ; Information Theory (cs.IT) ; Quantum Physics (quant-ph)

This paper presents an enhanced post-quantum key agreement protocol based on R\'enyi entropy, addressing vulnerabilities in the original construction while preserving information-theoretic security properties. We develop a theoretical framework leveraging entropy-preserving operations and secret-shared verification to achieve provable security against quantum adversaries. Through entropy amplification techniques and quantum-resistant commitments, the protocol establishes $2^{128}$ quantum security guarantees under the quantum random oracle model. Key innovations include a confidentiality-preserving verification mechanism using distributed polynomial commitments, tightened min-entropy bounds with guaranteed non-negativity, and composable security proofs in the quantum universal composability framework. Unlike computational approaches, our method provides information-theoretic security without hardness assumptions while maintaining polynomial complexity. Theoretical analysis demonstrates resilience against known quantum attack vectors, including Grover-accelerated brute force and quantum memory attacks. The protocol achieves parameterization for 128-bit quantum security with efficient $\mathcal{O}(n^{2})$ communication complexity. Extensions to secure multiparty computation and quantum network applications are established, providing a foundation for long-term cryptographic security.

[82] arXiv:2509.01423 (replaced) [cn-pdf, pdf, other]
Title: Quantum Petri Nets with Event Structure semantics
Julien Saan Joachim (ENS Paris Saclay, LMF, Inria), Marc de Visme (LMF, Inria, CNRS, ENS Paris Saclay), Stefan Haar (Inria), Glynn Winskel (Queen Mary University of London)
Subjects: Logic in Computer Science (cs.LO) ; Quantum Physics (quant-ph)

Classical Petri nets provide a canonical model of concurrency, with unfolding semantics linking nets, occurrence nets, and event structures. No comparable framework exists for quantum concurrency: existing ''quantum Petri nets'' lack rigorous concurrent and sound quantum semantics, analysis tools, and unfolding theory. We introduce Quantum Petri Nets (QPNs), Petri nets equipped with a quantum valuation compatible with the quantum event structure semantics of Clairambault, De Visme, and Winskel (2019). Our contributions are: (i) a local definition of Quantum Occurrence Nets (LQONs) compatible with quantum event structures, (ii) a construction of QPNs with a well-defined unfolding semantics, (iii) a compositional framework for QPNs. This establishes a semantically well grounded model of quantum concurrency, bridging Petri net theory and quantum programming.

[83] arXiv:2509.10808 (replaced) [cn-pdf, pdf, html, other]
Title: Gaussian fixed lines of $S=1/2$ XXZ chain with next-nearest neighbor interaction and $sl_2$ loop algebra
Daiki Yomatsu, Kiyohide Nomura
Comments: 9 pages, 9 figures
Subjects: Statistical Mechanics (cond-mat.stat-mech) ; Quantum Physics (quant-ph)

Spin systems are important to understand various physical properties in quantum many-body systems. We numerically study the Gaussian fixed lines (GFLs) of the $S=1/2$ XXZ chain with next-nearest neighbor (NNN) interaction in the XY phase. The GFLs are the set of points where the coefficient of the umklapp scattering vanishes. We show that the GFLs pass through the ``special points'', which are defined as the points where the $sl_2$ loop algebra symmetry governs in low-energy physics. In addition, we have discussed the Tomonaga-Luttinger parameter K, and the metamagnetism influences the shape of the GFLs.

[84] arXiv:2509.13184 (replaced) [cn-pdf, pdf, html, other]
Title: Topological Photon Transport in Programmable Photonic Processors via Discretized Evolution of Synthetic Magnetic Fields
Andrea Cataldo, Rohan Yadgirkar, Ze-Sheng Xu, Govind Krishna, Ivan Khaymovich, Val Zwiller, Jun Gao, Ali W. Elshaari
Subjects: Optics (physics.optics) ; Quantum Physics (quant-ph)

Photons, unlike electrons, do not couple directly to magnetic fields, yet synthetic gauge fields can impart magnetic-like responses and enable topological transport. Discretized Floquet evolution provides a controlled route, where the time-ordered sequencing of non-commuting Hamiltonians imprints complex hopping phases and breaks time-reversal symmetry. However, stabilizing such driven dynamics and observing unambiguous topological signatures on a reconfigurable platform has remained challenging. Here we demonstrate synthetic gauge fields for light on a programmable photonic processor by implementing discretized Floquet drives that combine static and dynamic phases. This approach reveals hallmark features of topological transport: chiral circulation that reverses under drive inversion, flux-controlled interference with high visibility, and robust directional flow stabilized by maximizing the minimal Floquet quasi-energy gap. The dynamics are further characterized by a first-harmonic phase order parameter, whose per-period winding number quantifies angular drift and reverses sign with the drive order. These results establish discretized, gap-optimized Floquet evolution as a versatile and fully programmable framework for topological photonics, providing a compact route to engineer gauge fields, stabilize driven phases, and probe winding-number signatures of chiral transport.

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