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Physics Quantum Physics

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Sunday 14 December

Quantum Physics · Cross-listed from cond-mat.mes-hall

Electrically Tuneable Variability in Germanium Hole Spin Qubits

Edmondo Valvo, Michele Jakob, Patrick Del Vecchio et al. (+2 more)

Hole spin qubits in planar germanium heterostructures are frontrunners for scalable semiconductor quantum computing. However, their current performance is mostly limited by large dot-to-dot variability that leads to uncontrolled qubit energies and random tilts in the spin quantization axis. Here, we propose a systematic and local method to engineer the spin qubit response by imprinting a controlled anisotropy in the quantum dot confinement, enabling on-demand electric g-tensor control. In particular, we find that both the quantum-dot size and asymmetry allow electrical tuning of the g-tensor and significantly suppress magnitude and angular variability of the spin response for selected magnetic field directions. We confirm this behavior by analyzing single-disorder realizations and statistical ensembles in state-of-the-art strained and unstrained germanium channels, showing that the latter provides an optimal path for $g$-tensor engineering. Our results provide practical design principles for on-demand control of the spin response and mitigating variability, paving the way towards large-scale germanium-based quantum computers.
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All authors Edmondo Valvo, Michele Jakob, Patrick Del Vecchio, Maximilian Rimbach-Russ, Stefano Bosco

Quantum Physics · Cross-listed from cond-mat.quant-gas

Probing the Crossover between Dynamical Phases with Local Correlations in a Rydberg Atom Array

Xiaofeng Wu, Xin Wang, Sixun Jia et al. (+1 more)

The experimental detection of non-equilibrium quantum criticality remains a challenge, as traditional signatures like dynamical quantum phase transitions rely on hard-to-measure global properties. Here, we demonstrate that local connected correlation functions provide a superior, practical means to directly probe the dynamics of magnetic order in a quenched Rydberg atom array. Using a Magnus expansion formalism, we derive analytic expressions for these correlations that capture a smooth crossover from antiferromagnetic to ferromagnetic dominance. Our analytic results, which reveal the critical parameter relationship $U_{c}(\delta)$, are validated against exact numerical simulations and exhibit robustness to finite-size effects. By shifting the focus from global singularities to local correlations, our protocol establishes a direct and feasible path to observe the rich critical dynamics in scalable quantum simulators.
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All authors Xiaofeng Wu, Xin Wang, Sixun Jia, Bo Xiong

Quantum Physics

FiD-QAE: A Fidelity-Driven Quantum Autoencoder for Credit Card Fraud Detection

Mansour El Alami, Adam Innan, Nouhaila Innan et al. (+2 more)

Credit card fraud detection is a critical task in financial security, as fraudulent transactions are rare, highly imbalanced, and often resemble legitimate ones. A wide range of classical machine learning methods, as well as more recent quantum machine learning approaches, have been investigated to address this challenge, each providing valuable progress but also leaving open questions regarding scalability, robustness, and adaptability to evolving fraud patterns. In this work, we introduce the Fidelity-based Quantum Autoencoder (FiD-QAE), a quantum architecture that employs fidelity estimation as the decision criterion for anomaly detection. Transactions are encoded into quantum states, compressed through a variational quantum circuit, and evaluated using the SWAP test to distinguish legitimate from fraudulent transactions. We conduct a comprehensive evaluation of FiD-QAE, including statistical analyses, multiple performance metrics, and robustness tests under quantum noise models. The results show that FiD-QAE maintains consistent performance across different imbalance levels and preserves robustness in noisy conditions. Moreover, validation on IBM Quantum hardware backends confirms the feasibility of our approach on real devices, with outcomes consistent with simulation. These findings position quantum fidelity as a powerful criterion for anomaly detection and highlight FiD-QAE as a promising direction that complements existing classical and quantum approaches, offering robustness and generalizability for financial fraud detection in realistic environments.
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All authors Mansour El Alami, Adam Innan, Nouhaila Innan, Muhammad Shafique, Mohamed Bennai

Quantum Physics

Quantum Implicit Neural Representations for 3D Scene Reconstruction and Novel View Synthesis

Yeray Cordero, Paula García-Molina and Fernando Vilariño

Implicit neural representations (INRs) have become a powerful paradigm for continuous signal modeling and 3D scene reconstruction, yet classical networks suffer from a well-known spectral bias that limits their ability to capture high-frequency details. Quantum Implicit Representation Networks (QIREN) mitigate this limitation by employing parameterized quantum circuits with inherent Fourier structures, enabling compact and expressive frequency modeling beyond classical MLPs. In this paper, we present Quantum Neural Radiance Fields (Q-NeRF), the first hybrid quantum-classical framework for neural radiance field rendering. Q-NeRF integrates QIREN modules into the Nerfacto backbone, preserving its efficient sampling, pose refinement, and volumetric rendering strategies while replacing selected density and radiance prediction components with quantum-enhanced counterparts. We systematically evaluate three hybrid configurations on standard multi-view indoor datasets, comparing them to classical baselines using PSNR, SSIM, and LPIPS metrics. Results show that hybrid quantum-classical models achieve competitive reconstruction quality under limited computational resources, with quantum modules particularly effective in representing fine-scale, view-dependent appearance. Although current implementations rely on quantum circuit simulators constrained to few-qubit regimes, the results highlight the potential of quantum encodings to alleviate spectral bias in implicit representations. Q-NeRF provides a foundational step toward scalable quantum-enabled 3D scene reconstruction and a baseline for future quantum neural rendering research.
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Quantum Physics · Cross-listed from physics.bio-ph

Quantum Correlation and Synchronisation-Enhanced Energy Transfer in Driven-Dissipative Light-Harvesting Dimers

Wenhao Xu

Quantum synchronisation has recently been proposed as a mechanism for electronic excitation energy transfer in light-harvesting complexes, yet its robustness in driven-dissipative settings remains under active investigation. Here, we revisit this mechanism in cryptophyte photosynthetic antennae using an exciton–vibrational dimer model. By comparing the full open quantum dynamics with semi-classical rate equations for electronic density-matrix elements and vibrational observables, we demonstrate that quantum correlations between electronic and vibrational degrees of freedom, beyond the semi-classical factorised limit, underpin the emergence of quantum synchronisation. Furthermore, we introduce an environment-assisted transfer mechanism arising as a nonlinear, non-Condon correction to the dipole–dipole interaction. This mechanism enables long-lived quantum coherence and continuous, synchronisation-enhanced energy transfer in a driven-dissipative regime, thereby suggesting new avenues for investigating photosynthetic energy-transfer dynamics.
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Quantum Physics

Mid-circuit logic executed in the qubit layer of a quantum processor

Cameron Jones, Piper Wysocki, MengKe Feng et al. (+16 more)

Practical quantum computers need to continuously exchange data between classical and quantum subsystems during a computation. Mid-circuit measurements of a qubits state are transferred to the classical electronics layer, and their outcome can inform feedforward operations that close the loop back to the quantum layer. These operations are crucial for fault-tolerant quantum computers, but the quantum-classical loop must be completed before the qubits decohere, presenting a substantial engineering challenge for full-scale systems comprising millions of qubits. Here we perform the first mid-circuit measurements in a system of silicon spin qubits, and show that feedforward operations can be performed without needing to route information to the classical layer. This in-layer approach leverages a backaction-driven control technique that has previously been considered a source of error. We benchmark our in-layer strategy, together with the standard FPGA-enabled approach, and analyse the performance of both methods using gate set tomography. Our results provide the first step towards moving resource-intensive classical processing into the quantum layer, an advance that could solve key engineering challenges, and drastically reduce the power budget of future quantum computers.
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All authors Cameron Jones, Piper Wysocki, MengKe Feng, Gerardo A. Paz-Silva, Corey I. Ostrove, Tuomo Tanttu, Kenneth M. Rudinger, Samuel K. Bartee, Kevin Young, Fay E. Hudson, Wee Han Lim, Nikolay V. Abrosimov, Hans-Joachim Pohl, Michael L. W. Thewalt, Robin Blume-Kohout, Andrew S. Dzurak, Andre Saraiva, Arne Laucht, Chih Hwan Yang

Quantum Physics

Expected values for SUSY hierarchies of Jaynes-Cummings Hamiltonian

İsmail Burak Ateş, Şengül Kuru, Javier Negro et al. (+1 more)

The aim of this letter is to compute the evolution of some expected values, such as the field operators $a^\pm$, quadratures and atomic inversion, under supersymmetric (SUSY) partner Hamiltonians associated to the Jaynes-Cummings Hamiltonian of quantum optics. This kind of SUSY partners are characterized by having spectra which differ in a finite number of energy levels. We wish to elucidate if the partner connection has any influence on these expected values. In particular, we want also to know in which way the classical and revival times are affected by such SUSY partners.
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All authors İsmail Burak Ateş, Şengül Kuru, Javier Negro, Ege Özkan

Quantum Physics

Quantum Reference Frames in Quantum Circuits: Perspective Dependent Entangling Cost and Coherence Entanglement Trade Offs

Salman Sajad Wani and Saif Al-Kuwari

The perspective-neutral formulation of quantum reference frames (QRFs) treats observers as quantum systems and describes physics relationally from within the composite system. While frame-change maps and frame-invariant resource sums are theoretically understood, their impact on circuit-based quantum information processing has largely remained unexplored. We formulate QRF transformations as circuit compilation rules and, for systems with finite Abelian symmetry described by the regular representation, derive a gate-level dictionary that maps local operations in one frame to their images in another. This yields a group-theoretic classification of gates where symmetry-commuting operators remain local, up to frame-dependent phases, while generic gates are promoted to controlled entangling operations in which the original frame acts as a control register. The resulting frame-dependence entangling-gate count defines a relational circuit complexity where the cost of a computation depends on the internal reference frame of the observer. We instantiate the framework in a three-qubit model and show that the QRF unitary acts as a lossless converter between a purity-based local coherence and concurrence, preserving their invariant sum and giving a concrete realization of the relativity of entanglement. We implement the corresponding circuits on an IBM Quantum superconducting platform, using full state tomography to reconstruct the redistribution of resources between internal frames. The hardware data reproduce the predicted conversion of local coherence into entanglement, and the observed deviations from exact conservation quantify the effect of realistic device noise on relational quantum protocols.
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Quantum Physics

Causal Consistency Selects the Born Rule: A Derivation from Steering in Generalized Probabilistic Theories

Enso O. Torres Alegre

Within finite-dimensional generalized probabilistic theories (GPTs), we distinguish between the geometric transition probability tau(psi,phi), defined as the maximum probability of accepting phi when the state is psi, and the predictive probability P(phi|psi) assigned to measurement outcomes. We ask what functional relationship P = Phi(tau) is compatible with relativistic causality. We prove that in any GPT satisfying purification, and therefore admitting steering, the only such relationship consistent with no-signaling is the identity Phi(p) = p. Any strictly convex or concave deviation from linearity enables superluminal signaling through steering scenarios. We provide an explicit qubit example showing how nonlinear probability rules generate detectable signaling channels. Combined with standard reconstruction results, this yields the Born rule |<phi|psi>|^2 as the unique causally consistent probability assignment. Our analysis clarifies the distinction between geometric structure and probabilistic prediction in quantum theory, and identifies steering as the mechanism enforcing the Born rule.
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Quantum Physics

A $k$-entanglement measure complying with the many-body resource theory and its evaluation

Jie Guo, Shuyuan Yang, Jinchuan Hou et al. (+2 more)

$k$-entanglement provides a hierarchical characterization of multipartite correlations according to their entanglement structure, ranging from multipartite entanglement ($k=n$) to genuine multipartite entanglement ($k=2$). Its quantitative treatment for mixed states faces three related obstacles: the standard axioms for such quantifications does not incorporate the requirements from many-body resource theory, as it does not regulate how to quantify the entanglement assigned to part systems of the same multipartite state and how to describe the rule that the entanglement possessed by a part system never exceeds the entanglement possed by whole system; no explicit measures are known that satisfy the above requirements from many-body resource theory; and the extreme difficulty in numerical evaluation at mixed states of known quantifications. In this work, we first formulate an axiomatic framework for true $k$-entanglement measures that obeys the many-body resource theory, by supplementing usual faithfulness and LOCC monotonicity with two new ones: unification condition and hierarchy condition. Then, for every $2\leq k\leq n$, we construct a witness-based true $k$-entanglement measure $E_w^{(k,n)}$ without the convex-roof extension, which is valid for both finite- and infinite-dimensional $n$-partite systems. Finally, we derive a method of constructing finite-dimensional $k$-entanglement witnesses from positive operator and $k$-separable-state optimizations, design an evaluation scheme of $E_w^{(k,n)}$ based on pre-established database of $k$-entanglement witnesses sampled by positive operators. To check the feasibility of this computing scheme, we develop a software tool, which implements the computation of the approximation of $E_w^{(k,n)}$ for systems up to four qubits. Numerical tests show that the software is sufficiently accurate and reliable.
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All authors Jie Guo, Shuyuan Yang, Jinchuan Hou, Xiaofei Qi, Kan He

Quantum Physics · Cross-listed from physics.chem-ph

Extended dissipaton theory for higher-order bath couplings and application to non-Condon spectroscopy with anharmonicity

Zi-Fan Zhu, Yu Su, Yao Wang et al. (+2 more)

In this work, we develop an extended dissipaton theory that generalizes the environmental couplings beyond the conventional linear and quadratic forms, enabling the treatment of arbitrary order of bath couplings. Applying this theoretical framework to the condensed-phase non-Condon spectroscopy, we demonstrate the interplay of anharmonicity, non-Condon and solvent effects on optical spectra. Precise simulations are carried out with high efficiency on linear absorption spectra involving the above mentioned correlated effects. We exhibit how an anharmonic potential modulates the vibronic feature, offering insights into the role of nonlinear environmental couplings in spectroscopic signatures and exemplifying the success of the extended dissipaton formalism as an exact and efficient method for higher-order bath couplings.
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All authors Zi-Fan Zhu, Yu Su, Yao Wang, Rui-Xue Xu, YiJing Yan

Quantum Physics

Scalable Quantum Error Mitigation with Neighbor-Informed Learning

Zhenyu Chen, Bin Cheng, Minbo Gao et al. (+4 more)

Noise in quantum hardware is the primary obstacle to realizing the transformative potential of quantum computing. Quantum error mitigation (QEM) offers a promising pathway to enhance computational accuracy on near-term devices, yet existing methods face a difficult trade-off between performance, resource overhead, and theoretical guarantees. In this work, we introduce neighbor-informed learning (NIL), a versatile and scalable QEM framework that unifies and strengthens existing methods such as zero-noise extrapolation (ZNE) and probabilistic error cancellation (PEC), while offering improved flexibility, accuracy, efficiency, and robustness. NIL learns to predict the ideal output of a target quantum circuit from the noisy outputs of its structurally related “neighbor” circuits. A key innovation is our 2-design training method, which generates training data for our machine learning model. In contrast to conventional learning-based QEM protocols that create training circuits by replacing non-Clifford gates with uniformly random Clifford gates, our approach achieves higher accuracy and efficiency, as demonstrated by both theoretical analysis and numerical simulation. Furthermore, we prove that the required size of the training set scales only logarithmically with the total number of neighbor circuits, enabling NIL to be applied to problems involving large-scale quantum circuits. Our work establishes a theoretically grounded and practically efficient framework for QEM, paving a viable path toward achieving quantum advantage on noisy hardware.
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All authors Zhenyu Chen, Bin Cheng, Minbo Gao, Xiaodie Lin, Ruiqi Zhang, Zhaohui Wei, Zhengfeng Ji

Quantum Physics

Quantum Encoding of Three-Dimensional Ligand Poses for Exhaustive Configuration Enumeration

Pei-Kun Yang

Classical molecular docking is fundamentally constrained by the combinatorial growth of ligand translational and rotational degrees of freedom, rendering exhaustive pose enumeration infeasible on classical hardware. This work introduces a quantum-native formulation that encodes ligand occupancy on discretized three-dimensional grids and coherently generates the full ensemble of spatial configurations within a single quantum state. Multi-step translations and rotational transformations are controlled by ancillary qubits, enabling all symmetry-related configurations to be activated simultaneously. This framework provides a scalable foundation for quantum-accelerated virtual screening and is amenable to integration with quantum scoring approaches as quantum hardware continues to advance.
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Quantum Physics · Cross-listed from physics.optics

Calibrated Plane–Convex Microcavity for Room-Temperature Polaritons with Geometric \(g\)-Scaling

Ling-Qi Huang, Shih-Chung Chen, Chia-Hao Lin et al. (+7 more)

We present a plane–convex open microcavity that supports room-temperature polariton spectroscopy and offers a simple geometric handle on the coupling rate. The effective length ($L_{\mathrm{eff}}$) is absolutely calibrated from the free-spectral range, and piezo tuning is performed at near-normal incidence ($k_{\parallel}!\approx!0$) to avoid angle-induced degradation. Using spin-coated PEA$2$PbI$4$ quasi-2D perovskites, we observe clear anti-crossings in reflection, with vacuum Rabi splittings up to $71~\mathrm{meV}$ (reflection) and $87~\mathrm{meV}$ (PL) near $L{\mathrm{eff}}!\approx!3~\mu\mathrm{m}$. A linewidth-corrected analysis converts the apparent splitting into the coherent exciton–photon coupling rate $g$, revealing a robust geometric scaling $g \propto L{\mathrm{eff}}^{-1/2}$ across multiple longitudinal orders and spatial sites, consistent with the filled-mode thin-film limit where the transverse area cancels in the mode volume. The platform establishes a compact, broadly compatible testbed for room-temperature polaritons and provides a practical design rule: shortening $L_{\mathrm{eff}}$ is a reliable geometric lever to strengthen collective coupling in plane–convex microcavities.
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All authors Ling-Qi Huang, Shih-Chung Chen, Chia-Hao Lin, Li-Tzu Wang, Khemendra Shukla, Kai-Peng Hsieh, Leng-Hsien Huang, Tsung-Sheng Kao, Hyeyoung Ahn, Tzu-Ling Chen

Quantum Physics

Robustness analysis in static and dynamic quantum state tomography

Alan Chen, Shuixin Xiao, Hailan Ma et al. (+1 more)

Quantum state tomography is a core task in quantum system identification. Real experimental conditions often deviate from nominal designs, introducing errors in both the measurement devices and the Hamiltonian governing the system's dynamics. In this paper, we investigate the robustness of quantum state tomography against such perturbations in both static and dynamic settings using linear regression estimation. We derive explicit bounds that quantify how bounded errors in the measurement devices and the Hamiltonian affect the mean squared error (MSE) upper bound in each scenario. Numerical simulations for qubit systems illustrate how these bounds scale with resources.
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All authors Alan Chen, Shuixin Xiao, Hailan Ma, Daoyi Dong

Quantum Physics

Opportunistic Scheduling for Single-downlink Satellite-based Quantum Key Distribution

Md Zakir Hossain, Nitish K. Panigrahy, Walter O. Krawec et al. (+2 more)

Satellite-based quantum key distribution (QKD), leveraging low photon loss in free-space quantum communication, is widely regarded as one of the most promising directions to achieve global-scale QKD. With a constellation of satellites and a set of ground stations in a satellite-based QKD system, how to schedule satellites to achieve efficient QKD is an important problem. This problem has been studied in the dual-downlink architecture, where each satellite distributes pairs of entanglements to two ground stations simultaneously. However, it has not been studied in the single downlink architecture, where satellites create keys with each individual ground station, and then serve as trusted nodes to create keys between pairs of ground stations. While the single downlink architecture provides weaker security in that the satellites need to be trusted, it has many advantages, including the potential of achieving significantly higher key rates, and generating keys between pairs of ground stations that are far away from each other and cannot be served using the dual-downlink architecture. In this paper, we propose a novel opportunistic approach for satellite scheduling that accounts for fairness among the ground station pairs, while taking advantage of the dynamic satellite channels to maximize the system performance. We evaluate this approach in a wide range of settings and demonstrate that it provides the best tradeoffs in terms of total and minimum key rates across the ground station pairs. Our evaluation also highlights the importance of considering seasonal effects and cloud coverage in evaluating satellite-based QKD systems. In addition, we show different tradeoffs in global and regional QKD systems.
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All authors Md Zakir Hossain, Nitish K. Panigrahy, Walter O. Krawec, Don Towsley, Bing Wang

Quantum Physics

A Comparative Study of Encoding Strategies for Quantum Convolutional Neural Networks

Xingyun Feng

Quantum convolutional neural networks (QCNNs) offer a promising architecture for near-term quantum machine learning by combining hierarchical feature extraction with modest parameter growth. However, any QCNN operating on classical data must rely on an encoding scheme to embed inputs into quantum states, and this choice can dominate both performance and resource requirements. This work presents an implementation-level comparison of three representative encodings – Angle, Amplitude, and a Hybrid phase/angle scheme – for QCNNs under depolarizing noise. We develop a fully differentiable PyTorch–Qiskit pipeline with a custom autograd bridge, batched parameter-shift gradients, and shot scheduling, and use it to train QCNNs on downsampled binary variants of MNIST and Fashion-MNIST at $4\times 4$ and $8\times 8$ resolutions. Our experiments reveal regime-dependent trade-offs. On aggressively downsampled $4\times 4$ inputs, Angle encoding attains higher accuracy and remains comparatively robust as noise increases, while the Hybrid encoder trails and exhibits non-monotonic trends. At $8\times 8$, the Hybrid scheme can overtake Angle under moderate noise, suggesting that mixed phase/angle encoders benefit from additional feature bandwidth. Amplitude-encoded QCNNs are sparsely represented in the downsampled grids but achieve strong performance in lightweight and full-resolution configurations, where training dynamics closely resemble classical convergence. Taken together, these results provide practical guidance for choosing QCNN encoders under joint constraints of resolution, noise strength, and simulation budget.
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Quantum Physics

Classical Second-Order Moments and Tensor Squeezing in Spin-1 Systems

K. S. Mallesh

We give a compact, frame-independent characterization of the set of classical second-order moments for a single spin-1 particle. Defining the moment matrix M = 2Q + (1/3) I, we show that a moment pair (s, Q) arises from a positive mixture of spin-coherent states if and only if M is positive semidefinite, M minus ss^T is positive semidefinite, and the trace of M equals one. These necessary and sufficient matrix conditions delimit the classical moment region and yield simple, basis-free witnesses of higher-order tensor nonclassicality, such as bounds on Tr(Q^2). A constructive proof of sufficiency is given in the appendix.
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Saturday 13 December

Quantum Physics · Cross-listed from hep-th

Complete Topological Quantization of Higher Gauge Fields

Hisham Sati and Urs Schreiber

After global completion of higher gauge fields (as appearing in higher-dimensional supergravity) by proper flux quantization in extraordinary nonabelian cohomology, the (non-perturbative, renormalized) topological quantum observables and quantum states of solitonic field histories are completely determined through a topological form of light-front quantization. We survey the logic of this construction and expand on aspects of the quantization argument. In the instructive example of 5D Maxwell-Chern-Simons theory (the gauge sector of 5D SuGra) dimensionally reduced to 3D, a suitable choice of flux quantization in Cohomotopy ("Hypothesis h") recovers this way the fine detail of the traditionally renormalized (Wilson loop) quantum observables of abelian Chern-Simons theory and makes novel predictions about anyons in fractional quantum (anomalous) Hall systems. An analogous choice ("Hypothesis H") of global completion of 11D higher Maxwell-Chern-Simons theory (the higher gauge sector of 11D SuGra) realizes various aspects of the topological sector of the conjectural "M-theory" and its M5-branes.
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Quantum Physics

Imaging Walk-Off Driven Distortions in EPR Photon Pair Correlations

Christian Howard, Roohollah Ghobadi, Nazanin Dehghan et al. (+2 more)

Spontaneous parametric down-conversion is the primary source of position-correlated and momentum-anticorrelated photon pairs that form the canonical Einstein-Podolsky-Rosen (EPR) state. Their transverse spatial correlations are usually analyzed within the thin-crystal approximation, where the two-photon wavefunction is assumed to factorize into independent functions of the sum and difference coordinates. In practice, however, birefringence-induced transverse walk-off breaks this factorization and couples these degrees of freedom. Here, we show that this coupling persists even for nominally thin crystals once the free-space propagation of the joint spatial intensity is taken into account. This sum-difference coordinate coupling leads to a distinctive tapering of the transverse correlations near the crystal image plane-an effect that standard factorized models cannot capture. Numerical simulations and experimental data clearly confirm this novel behavior. Our findings provide a more complete description of photon-pair generation in birefringent nonlinear media and clarify fundamental limits on spatially resolved quantum imaging and spatial-mode quantum information processing with EPR states.
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All authors Christian Howard, Roohollah Ghobadi, Nazanin Dehghan, Alessio D'Errico, Ebrahim Karimi

Quantum Physics · Cross-listed from hep-ph

The Entropic Skin: Spatial Entanglement from the QCD Confinement Boundary

Thomas B. Bahder

Recent investigations into High-Energy QCD have identified entanglement entropy as a crucial observable, linking parton distributions to the structure of the quantum vacuum. While momentum-space entanglement has been extensively studied in Deep Inelastic Scattering (DIS), the spatial realization of this entanglement in confined systems remains an open question. In this Letter, we demonstrate that the confining boundary of the MIT Bag Model acts as an “Entropic Skin,” generating maximal Spin-Position entanglement. We calculate the local reduced density matrix for the confined quark and show that the linear boundary condition, $i \gamma^\mu n_\mu \psi = \psi$, acts as an entangling gate. The surface entropy density reaches a geometric invariant of $\approx 0.918$ bits ($92\%$ of the qubit limit), independent of the bag radius. We discuss the implications of this result for Chiral Symmetry breaking and propose that this boundary entropy is the precursor to the pion cloud in effective field theories.
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Quantum Physics · Cross-listed from cond-mat.quant-gas

Interaction-assisted topological pumping in few- and many-atom Rydberg arrays

Chenxi Huang, Tao Chen, Qian Liang et al. (+7 more)

Topology can imbue lattice systems with special properties, notably the presence of robust eigenstates living at their boundary. Through dimensional reduction, the robust bulk band topology of, e.g., the integer quantum Hall system can be mapped onto similarly robust charge-pumping dynamics of a topological pump living in one lower dimension. Recent studies have uncovered a rich influence of interactions on the dynamics of topological pumps in nonlinear systems, including the robust pumping of self-bound solitons. These striking observations in classical nonlinear photonics have raised a number of questions, chiefly if and how this phenomenology persists in strongly correlated quantum systems and in the few-body limit. Here, using few- and many-atom arrays, we explore how dipolar interactions impact the dynamics of topological population pumping along a Rydberg synthetic dimension. In the few-body limit, we find that dipolar interactions lead to self-bound states that are efficiently pumped along the synthetic dimension, described by an emergent pair-state topological pump. We find that this interaction-assisted pumping persists in many-atom arrays, with a sharpened dependence on the dipolar interaction strength that stems from the enhanced spatial connectivity. These Rydberg-based studies on interaction-assisted topological pumping help connect observations from classical nonlinear photonics to the few-body quantum limit and pave the way for studies of new strongly correlated quantum pumping phenomena.
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All authors Chenxi Huang, Tao Chen, Qian Liang, Matthew A. Krebs, Ethan Springhorn, Ruiyu Li, Mingsheng Tian, Kaden R. A. Hazzard, Jacob P. Covey, Bryce Gadway

Quantum Physics

Quantum Coherence Dispersion

Fernando Parisio

We investigate how quantum coherence can be distributed among the several off-diagonal elements of an arbitrary density matrix. An easily computable quantity that captures this variability notion is proposed and it is argued that it presents marked features of complexity quantifiers. It turns out that this coherence dispersion ($\Delta_{\rm c}$) is maximized for intermediate values of an appropriate entropy (the relative entropy of coherence), a prevalent signature of complexity quantifiers across different fields, from evolutionary biology to linguistics and information science. The final part of the manuscript is dedicated to the connection between the proposed framework and non-equilibrium systems in the quantum regime.
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Quantum Physics · Cross-listed from physics.atom-ph

Coulomb crystallization of xenon highly charged ions in a laser-cooled Ca+ matrix

Leonid Prokhorov, Aaron A. Smith, Mingyao Xu et al. (+17 more)

We report on the sympathetic cooling and Coulomb crystallization of xenon highly charged ions (HCIs) with laser-cooled Ca$^+$ ions. The HCIs are produced in a compact electron beam ion trap, then charge selected, decelerated, and finally injected into a cryogenic linear Paul trap. There, they are captured into $^{40}$Ca$^+$ Coulomb crystals, and co-crystallized within them, causing dark voids in their fluorescence images. Fine control over the number of trapped ions and HCIs allows us to realize mixed-species crystals with arbitrary ordering patterns. By investigating Xe$^{q+}$–Ca$^+$ strings, we confirm the HCI charge states, measure their lifetime and characterize the mixed-species motional modes. Our system effectively combines the established quantum control toolbox for Ca$^+$ with the rich set of atomic properties of Xe highly charged ions, providing a resourceful platform for optical frequency metrology, searches for signatures of new physics, and quantum information science.
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All authors Leonid Prokhorov, Aaron A. Smith, Mingyao Xu, Kostas Georgiou, Vera Guarrera, Lakshmi P. Kozhiparambil Sajith, Elwin A. Dijck, Christian Warnecke, Malte Wehrheim, Alexander Wilzewski, Laura Blackburn, Matthias Keller, Vincent Boyer, Thomas Pfeifer, Ullrich Schwanke, Cigdem Issever, Steven Worm, Piet O. Schmidt, José R. Crespo Lopez-Urrutia, Giovanni Barontini

Quantum Physics

Measurement as Sheafification: Context, Logic, and Truth after Quantum Mechanics

Partha Ghose

Quantum measurement is commonly posed as a dynamical tension between linear Schrödinger evolution and an ad hoc collapse rule. I argue that the deeper conflict is logical: quantum theory is inherently contextual, whereas the classical tradition presupposes a single global, Boolean valuation. Building on Bohr's complementarity, the Einstein–Podolsky–Rosen argument and Bell's theorem, I recast locality and completeness as the existence of a global section of a presheaf of value assignments over the category of measurement contexts. The absence of global sections expresses the impossibility of context-independent description, and Čech cohomology measures the resulting obstruction. The internal logic of the presheaf topos is intuitionistic, and the seven-valued contextual logic proposed by Ghose and Patra is exhibited as a finite Heyting algebra capturing patterns of truth, falsity and indeterminacy across incompatible contexts. Classical physics corresponds to the sheaf case, where compatible local data glue and Boolean logic is effectively restored. Measurement is therefore reinterpreted as sheafification of presheaf-valued truth rather than as a physical breakdown of unitarity. Finally, a $\sigma$–$\lambda$ dynamics motivated by stochastic mechanics provides a continuous interpolation between strongly contextual and approximately classical regimes, dissolving the usual measurement paradoxes and apparent nonlocality as artefacts of an illegitimate demand for global truth.
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Quantum Physics · Cross-listed from physics.optics

Cavity Ring-down Spectroscopy with behavior of Hybrid Cavity Structures

Muhammad Junaid Khan and Rida Batool Sheraliyat

Cavity ring-down (CRD) spectroscopy represents a direct absorption technique of sample absorption measurement. Instead of measuring the amount of the absorbed light, this technique determines the rate at which light intensity decays inside an optical cavity. When using a pulsed or continuous-wave light source, CRD spectroscopy offers considerably higher sensitivity as compared with conventional spectroscopy of absorption, making even very weak absorptions easy to detect.
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Quantum Physics · Cross-listed from cond-mat.str-el

Experimental benchmark of the quantum-classical crossover in a spin ladder

Hironori Yamaguchi, Itsuki Shimamura, Akira Matsuo et al. (+4 more)

We report a spin-(1/2, 5/2) three-leg ladder realized in a radical-Mn polymer, exhibiting an antiferromagnetic transition and magnetization curves accurately described by classical mean-field theory. Although the underlying spin model intrinsically supports strong quantum fluctuations, as confirmed by quantum Monte Carlo simulations, the real system shows an anomalously complete suppression of quantum behavior. These findings provide a key experimental benchmark for the quantum-classical crossover and suggest that lattice topology can play a crucial role in tuning the balance between quantum and classical physics in strongly correlated systems.
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All authors Hironori Yamaguchi, Itsuki Shimamura, Akira Matsuo, Koichi Kindo, Koji Araki, Yoshiki Iwasaki, Masayuki Hagiwara

Quantum Physics · Cross-listed from hep-ph

Searching for axion dark matter with magnetic resonance force microscopy

Elham Kashi, Muhammad Hani Zaheer, Ryan Petery et al. (+1 more)

We propose a magnetic resonance force microscopy (MRFM) search for axion dark matter around 1 GHz. The experiment leverages the axion's derivative coupling to electrons, which induces an effective A.C. magnetic field on a sample of electron spins polarized by a D.C. magnetic field and a micromagnet. A second pump field at a nearby frequency enhances the signal, with the detuning matched to the resonant frequency of a magnet-loaded mechanical oscillator. The resulting spin-dependent force is detected with hih sensitivity via optical interferometry. Accounting for the relevant noise sources, we show that current technology can be used to put constraints competitive with those from laboratory experiments with just a minute of integration time. Furthermore, varying the pump field frequency and D.C. magnetic field allows one to scan the axion mass. Finally, we explore this setup's capability to put constraints on other dark matter - Standard Model couplings.
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All authors Elham Kashi, Muhammad Hani Zaheer, Ryan Petery, Swati Singh

Quantum Physics · Cross-listed from cond-mat.mes-hall

Perturbative Input-Output Theory of Floquet Cavity Magnonics and Magnon Energy Shifts

T. Aguiar and M. C. de Oliveira

We develop a perturbative input-output formalism to compute the reflectance and transmittance spectra of cavity magnonics systems subject to a Floquet modulation. The method exploits the strong hierarchy between the magnetic-dipole couplings transverse (drive field) and parallel (modulation field) to the static bias field, which naturally introduces the small parameter $\epsilon = (2Ns)^{-1/2}$ associated with the total spin $Ns$ of the ferromagnet. By organizing the cavity and magnon fields in a systematic expansion in $\epsilon$, we obtain compact analytic expressions for the spectra up to second order. Using these results, we reproduce the characteristic sideband structure observed in recent Floquet cavity electromagnonics experiments. Furthermore, accounting for the Zeeman interaction between the modulation field and the fully polarized ground state - a contribution typically neglected in previous treatments - we predict an additional magnon detuning of approximately $0.8\,\mathrm{GHz}$, independent of both modulation frequency and sample size and determined solely by the spatial volume occupied by the modulation field. This identifies a measurable and previously overlooked shift relevant for the interpretation and design of cavity magnonics experiments.
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Quantum Physics · Cross-listed from cond-mat.other

On the Bogoliubov-Valatin transformation for fermionic Hamiltonians without a linear part

Davide Bonaretti

A self-contained treatment of the Bogoliubov-Valatin transformation for homogeneous fermionic Hamiltonians is presented. The aim is to provide a quick reference that may also serve as supplementary material for a graduate-level course, and that can be understood with quantum mechanics knowledge up to the level of the second quantization's rules. The objective of the transformation is to cast a quadratic Hamiltonian into a diagonal form that resembles the Hamiltonian of a system of non-interacting particles. To obtain this, the first step consists in putting its coefficient matrix into its canonical form; the transformation can always be performed on fermionic Hamiltonians, only some care must be taken when this form is singular. Having explained how to cast a general matrix into its standard form, a complete description of the transformation is provided; a novel procedure is proposed here for the singular matrix case.
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