Peer Revenue Past citations are no guarantee of future returns

Papers

Fresh from arXiv, typeset properly. Highlighted words trade on the market.

Physics Quantum Physics

quant-ph Watch Quantum Physics

Sunday 7 December

Quantum Physics · Cross-listed from cs.LG

Mitigating Barren Plateaus in Quantum Denoising Diffusion Probabilistic Model

Haipeng Cao, Kaining Zhang, Dacheng Tao et al. (+1 more)

Quantum generative models exploit quantum superposition and entanglement to enhance learning efficiency for both classical and quantum data. Recently, inspired by classical diffusion frameworks, the quantum denoising diffusion probabilistic model has emerged as a powerful tool for learning correlated noise models, many-body phases, and topological data structures. However, we demonstrate that this framework is currently restricted to small-scale systems. As the system size increases, a severe barren plateau problem emerges, fundamentally limiting the model's scalability. We provide rigorous theoretical proofs and experimental validation to identify the origin of this barren plateau, distinct from previously known causes. To restore trainability, we introduce an enhanced architecture that effectively mitigates the barren plateau phenomenon and guarantees the model's trainability in the tested settings. Building on this architecture, we further propose a conditional quantum denoising diffusion probabilistic model, capable of generating ground states based on Hamiltonian parameters, expanding the utility of quantum generative models for complex quantum state preparation to a certain extent. Our approach not only holds the potential to address the scalability and trainability bottlenecks of quantum diffusion models, but also provides a robust tool for exploring complex quantum matter and state preparation in the NISQ era.
Read the full abstract

All authors Haipeng Cao, Kaining Zhang, Dacheng Tao, Zhaofeng Su

Quantum Physics · Cross-listed from cond-mat.str-el

Spurious Strange Correlators in Symmetry-Protected Topological Phases

Wei-Liang Gao, Jie-Yu Zhang, Zheng-Xin Liu et al. (+1 more)

Strange correlator is a powerful tool widely used in detecting symmetry-protected topological (SPT) phases. However, the result of strange correlator crucially relies on the adoption of the reference state. In this work, we report that an ill-chosen reference state can induce spurious long-range strange correlators in trivial SPT phases, leading to false positives in SPT diagnosis. Focusing on 1D gapped bosonic/spin systems described by matrix product states (MPS), we trace the origin of these spurious signals in trivial SPT phases to the magnitude-degeneracy of the transfer matrix. We systematically classify three distinct mechanisms responsible for such degeneracy, each substantiated by concrete examples: (1) the presence of high-dimensional irreducible representations (abbreviated as irrep) in the eigenspace corresponding to the entanglment spectrum (entanglement space); (2) a phase mismatch in symmetry representations between the target and reference states; and (3) long-range order arising from symmetry breaking. Our findings clarify the importance of the choice of proper reference states, providing a guideline to avoid pitfalls and correctly identify SPT order using strange correlators.
Read the full abstract

All authors Wei-Liang Gao, Jie-Yu Zhang, Zheng-Xin Liu, Peng Ye

Quantum Physics

Experimental demonstration of asynchronous measurement-device-independent quantum cryptographic conferencing

Haotao Zhu, Zhenhua Li, Shuai Zhao et al. (+6 more)

Quantum network enable a variety of quantum information processing tasks, where multi-user quantum communication is one of the important objectives. Quantum cryptographic conferencing (QCC) serves as an essential solution to establish secure keys to realize secure multi-user communications. However, existing QCC implementations have been fundamentally limited by the low probability of multi-user coincidence detection to measure or construct the Greenberger-Horne-Zeilinger (GHZ) entangled state. In this work, we report the experimental realization of QCC eliminating the need for coincidence detection, where the GHZ state is constructed by correlating detection events occurring within the coherence time, thereby greatly enhancing the success probability of GHZ-state measurement. Meanwhile, to establish and maintain high-visibility GHZ measurement among three independent users, we developed a three-party phase compensation scheme combined with precise temporal and polarization alignment within a time-bin-phase encoding framework. Furthermore, we designed an efficient pairing strategy to simplify subsequent data processing and enhance processing efficiency. Based on these techniques, we successfully performed QCC experiments over total loss of 66.3 dB, with the channel loss of 51.24 dB, achieving secure key rates of 5.4 bit/s, whereas previous QCC experiments have been limited to 100 km. The results establish a new regime of scalable, multi-user quantum communication and paving the way for metropolitan quantum networks.
Read the full abstract

All authors Haotao Zhu, Zhenhua Li, Shuai Zhao, Xiaodan Lyu, Shihao Ru, Yizhi Huang, Zitong Xu, Rui Qu, Weibo Gao

Quantum Physics

Efficient graph-diagonal characterization of noisy states distributed over quantum networks via Bell sampling

Zherui Jerry Wang, Joshua Carlo A. Casapao, Naphan Benchasattabuse et al. (+6 more)

Graph states are an important class of entangled states that serve as a key resource for distributed information processing and communication in quantum networks. In this work, we propose a protocol that utilizes a Bell sampling subroutine to characterize the diagonal elements in the graph basis of noisy graph states distributed across a network. Our approach offers significant advantages over direct diagonal estimation using unentangled single-qubit measurements in terms of scalability. Specifically, we prove that estimating the full vector of diagonal elements requires a sample complexity that scales linearly with the number of qubits ($\mathcal{O}(n)$), providing an exponential reduction in resource overhead compared to the best known $\mathcal{O}(2^n)$ scaling of direct estimation. Furthermore, we demonstrate that global properties, such as state fidelity, can be estimated with a sample complexity independent of the network size. Finally, we present numerical results indicating that the estimation in practice is more efficient than the derived theoretical bounds. Our work thus establishes a promising technique for efficiently estimating noisy graph states in large networks under realistic experimental conditions.
Read the full abstract

All authors Zherui Jerry Wang, Joshua Carlo A. Casapao, Naphan Benchasattabuse, Ananda G. Maity, Jordi Tura, Akihito Soeda, Michal Hajdušek, Rodney Van Meter, David Elkouss

Quantum Physics · Cross-listed from cs.LG

Quantum Temporal Convolutional Neural Networks for Cross-Sectional Equity Return Prediction: A Comparative Benchmark Study

Chi-Sheng Chen, Xinyu Zhang, En-Jui Kuo et al. (+3 more)

Quantum machine learning offers a promising pathway for enhancing stock market prediction, particularly under complex, noisy, and highly dynamic financial environments. However, many classical forecasting models struggle with noisy input, regime shifts, and limited generalization capacity. To address these challenges, we propose a Quantum Temporal Convolutional Neural Network (QTCNN) that combines a classical temporal encoder with parameter-efficient quantum convolution circuits for cross-sectional equity return prediction. The temporal encoder extracts multi-scale patterns from sequential technical indicators, while the quantum processing leverages superposition and entanglement to enhance feature representation and suppress overfitting. We conduct a comprehensive benchmarking study on the JPX Tokyo Stock Exchange dataset and evaluate predictions through long-short portfolio construction using out-of-sample Sharpe ratio as the primary performance metric. QTCNN achieves a Sharpe ratio of 0.538, outperforming the best classical baseline by approximately 72%. These results highlight the practical potential of quantum-enhanced forecasting model, QTCNN, for robust decision-making in quantitative finance.
Read the full abstract

All authors Chi-Sheng Chen, Xinyu Zhang, En-Jui Kuo, Rong Fu, Qiuzhe Xie, Fan Zhang

Quantum Physics

Fault-Tolerant Information Processing with Quantum Weak Measurement

Qi Song, Hongjing Li, Chengxi Yu et al. (+4 more)

Noise is an important factor that influences the reliability of information acquisition, transmission, processing, and storage. In order to suppress the inevitable noise effects, a fault-tolerant information processing approach via quantum weak measurement is proposed, where pairwise orthogonal postselected measurement bases with various tiny angles and optimal compositions of measured results are chosen as a decoding rule. The signal to be protected can be retrieved with a minimal distortion after having been transmitted through a noisy channel. Demonstrated by typical examples of encoding signal on two-level superposition state or Einstein-Podolsky-Rossen state transmitted through random telegraph noise and decoherence noises channel, the mean squared error distortion may be close to $0$ and the fault-tolerant capability could reach $1$ with finite quantum resources. To verify the availability of the proposed approach, classic coherent light and quantum coherent state are used for encoding information in the experiment. Potentially, the proposed approach may provide a solution for suppressing noise effects in long-distance quantum communication, high-sensitivity quantum sensing, and accurate quantum computation.
Read the full abstract

All authors Qi Song, Hongjing Li, Chengxi Yu, Jingzheng Huang, Ding Wang, Peng Huang, Guihua Zeng

Quantum Physics · Cross-listed from physics.optics

Geometry-Induced Vacuum Polarization and Mode Shifts in Maxwell-Klein-Gordon Theory

Li Wang, Jun Wang and Yong-Long Wang

Geometric confinement is known to modify single-particle dynamics through effective potentials, yet its imprint on the interacting quantum vacuum remains largely unexplored. In this work, we investigate the Maxwell–Klein–Gordon system constrained to curved surfaces and demonstrate that the geometric potential $\Sigma_{\mathrm{geom}}(\mathbf{r})$ acts as a local renormalization environment. We show that extrinsic curvature modifies the scalar loop spectrum, entering the vacuum polarization as a position-dependent mass correction $M^2(\mathbf{r}) \to m^2 + \Sigma_{\mathrm{geom}}(\mathbf{r})$. This induces a finite, gauge-invariant “geometry-induced running” of the electromagnetic response. In the long-wavelength regime ($|{\bf Q}|R \ll 1$), we derive a closed-form expression for the relative frequency shift $\Delta\omega/\omega$, governed by the overlap between the electric energy density and the geometric potential. Applying this formalism to Gaussian bumps, cylindrical shells, and tori, we identify distinct spectral signatures that distinguish these quantum loop corrections from classical geometric optics. Our results suggest that spatial curvature can serve as a tunable knob for “vacuum engineering,” offering measurable shifts in high-$Q$ cavities and plasmonic systems.
Read the full abstract

Quantum Physics

High-harmonic generation driven by temporal-mode quantum states of light

Juan M. González-Monge, Felipe Reibnitz Willemann and Johannes Feist

We develop a theoretical framework for high-harmonic generation (HHG) driven by quantum states of light based on a temporal-mode expansion of the electromagnetic field. This approach extends previous single plane-wave mode treatments to realistic pulse configurations and arbitrary multi-mode states of light, resolving conceptual inconsistencies arising from non-normalizable infinite plane waves and establishing consistency between analytical and numerical methods. We derive a correction factor that quantifies deviations from the diagonal approximation (in which the yield becomes a statistical average over classical-field simulations) both for the response of a single atom and in the many-atom regime. Our results confirms that the HHG spectrum for atoms driven by any quantum state of light in free space is accurately described by averaging semi-classical calculations over the Husimi distribution, with no observable genuine quantum effects in the spectrum. We also demonstrate that in the many-atom regime, the mean-field coherent-state approximation underlying this treatment does not preserve probabilities, although unitarity is restored by in the diagonal approximation. The absence of genuine quantum effects in the HHG yield is attributed to the large photon numbers ($\sim 10^{11}$) required to reach HHG intensities in free space, which render quantum fluctuations negligible. We discuss nanophotonic environments with ultrasmall mode volumes as potential platforms where few-photon strong-field processes could exhibit genuine quantum signatures.
Read the full abstract

Saturday 6 December

Quantum Physics · Cross-listed from cs.AI

Anubuddhi: A Multi-Agent AI System for Designing and Simulating Quantum Optics Experiments

S. K. Rithvik

We present Anubuddhi, a multi-agent AI system that designs and simulates quantum optics experiments from natural language prompts without requiring specialized programming knowledge. The system composes optical layouts by arranging components from a three-tier toolbox via semantic retrieval, then validates designs through physics simulation with convergent refinement. The architecture combines intent routing, knowledge-augmented generation, and dual-mode validation (QuTiP and FreeSim). We evaluated 13 experiments spanning fundamental optics (Hong-Ou-Mandel interference, Michelson/Mach-Zehnder interferometry, Bell states, delayed-choice quantum eraser), quantum information protocols (BB84 QKD, Franson interferometry, GHZ states, quantum teleportation, hyperentanglement), and advanced technologies (boson sampling, electromagnetically induced transparency, frequency conversion). The system achieves design-simulation alignment scores of 8–9/10, with simulations faithfully modeling intended physics. A critical finding distinguishes structural correctness from quantitative accuracy: high alignment confirms correct physics architecture, while numerical predictions require expert review. Free-form simulation outperformed constrained frameworks for 11/13 experiments, revealing that quantum optics diversity demands flexible mathematical representations. The system democratizes computational experiment design for research and pedagogy, producing strong initial designs users can iteratively refine through conversation.
Read the full abstract

Quantum Physics · Cross-listed from physics.optics

Laser-written reconfigurable photonic integrated circuit directly coupled to a single-photon avalanche diode array

Giulio Gualandi, Simone Atzeni, Marco Gardina et al. (+8 more)

To date, most integrated quantum photonics experiments rely on single-photon detectors operating at cryogenic temperatures coupled to photonic integrated circuits (PICs) through single-mode optical fibers. This approach presents significant challenges due to the detection complexity, as cryogenic conditions hinder the development of scalable systems. In addition, going towards fully-integrated devices or, at least, removing the optical fibers would be also advantageous to develop compact and cost-efficient solutions featuring a high number of optical modes. This work reports on the direct coupling of a PIC, fabricated by femtosecond laser writing (FLW), and a silicon single-photon avalanche diode (SPAD) array, fabricated in a custom planar technology and compatible with the operation at room temperature. The effectiveness of this solution is shown by achieving perfect coupling and a system detection efficiency as high as 41.0% at a wavelength of 561 nm, which is the highest value reported to date among both heterogeneous/hybrid integrated and directly coupled systems. We also show the robustness of the coupling to misalignments, demonstrating that costly alignment procedures are not needed. Finally, we exploit the SPAD array to characterize a reconfigurable Mach-Zehnder interferometer, i.e., the basic building block of multimode reconfigurable PICs. This solution provides a new avenue to the design and implementation of quantum photonics experiments, especially effective when compact and cost-efficient systems are needed.
Read the full abstract

All authors Giulio Gualandi, Simone Atzeni, Marco Gardina, Antonino Caime, Giacomo Corrielli, Ivan Labanca, Angelo Gulinatti, Ivan Rech, Roberto Osellame, Giulia Acconcia, Francesco Ceccarelli

Quantum Physics

Solving larger Travelling Salesman Problem networks with a penalty-free Variational Quantum Algorithm

Daniel Goldsmith, Xing Liang, Dimitrios Makris et al. (+1 more)

The Travelling Salesman Problem (TSP) is a well-known NP-hard combinatorial optimisation problem with important industrial applications. Although extensively studied, quantum solutions for instances beyond a dozen locations remain uncommon. We present a hybrid penalty-free Variational Quantum Algorithm (VQA) that significantly reduces both the qubit count and the runtime through a compact penalty-free formulation scaling as $\mathcal{O}(nlog_2 n)$ qubits compared to conventional formulations with $\mathcal{O}(n^2)$ scaling. The VQA achieves solution qualities exceeding 90% on Rigetti quantum hardware for instances of up to 17 locations. To the best of our knowledge, this represents the largest TSP instance solved on gate-based hardware. We systematically evaluate multiple encoding and optimisation strategies, and show that warm-start initialisation improves solution quality, while runtime is reduced by nearly two orders of magnitude through the use of gradient-free optimisation methods and cost-function caching. We additionally introduce a novel VQA inspired classical machine learning model (VQAi-CML) and benchmark the VQA against VQAi-CML, a greedy heuristic, a Monte Carlo baseline, and a strong classical optimisation baseline. Across the networks evaluated, the VQA consistently achieves superior solution quality relative to VQAi-CML, greedy heuristic, and Monte Carlo baselines, but not the classical solver
Read the full abstract

All authors Daniel Goldsmith, Xing Liang, Dimitrios Makris, Hongwei Wu

Quantum Physics

Efficient quantum algorithm for solving differential equations with Fourier nonlinearity via Koopman linearization

Judd Katz, Gopikrishnan Muraleedharan and Abhijeet Alase

Quantum algorithms offer an exponential advantage with respect to the number of dependent variables for solving certain nonlinear ordinary differential equations (ODEs). These algorithms typically begin by transforming the original nonlinear ODE into a higher-dimensional linear ODE using a linearization technique, most commonly Carleman linearization. Existing works restrict their analysis to ODEs where the nonlinearities are polynomial functions of the dependent variables, significantly limiting their applicability. In this work we construct an efficient quantum algorithm for solving ODEs with `Fourier' nonlinear terms expressible as $d{\bf u}/dt = G_0 + G_1 e^{i{\bf u}}$, where ${\bf u}$ denotes a vector of $n$ complex variables evolving with $t$, $G_0$ is an $n$-dimensional complex vector, $G_1$ is an $n \times n$ complex matrix and $e^{i{\bf u}}$ denotes the vector with entries $\{e^{iu_j}\}$. To tackle the Fourier nonlinear term, which is not expressible as a finite sum of polynomials of ${\bf u}$, our algorithm employs a generalization of the Carleman linearization technique known as Koopman linearization. We also make other methodological advances towards relaxing the stringent dissipativity condition required for efficient solution extraction and towards integrated readout of classical quantities from the solution state. Our results open avenues to the development of efficient quantum algorithms for a significantly wider class of high-dimensional nonlinear ODEs, thereby broadening the scope of their applications.
Read the full abstract

Quantum Physics

PureMagic: A Dynamic Scheduler for Lattice Surgery

Steven Hofmeyr, Mathias Weiden, Justin Kalloor et al. (+2 more)

Fault-tolerant quantum computation on surface codes requires magic states for universal computation. Traditional distillation factories deliver magic states deterministically but consume large areas of logical qubits, forcing static, peripheral placement. Magic state cultivation reduces magic state preparation to a single logical qubit, but is inherently stochastic, making static scheduling infeasible. We introduce PureMagic, a dynamic scheduler that eliminates dedicated bus patches by repurposing all ancilla patches for both routing and cultivation. When a patch is needed for routing, cultivation is interrupted and restarted afterward, naturally cutting off the long tail of cultivation times and ensuring no ancilla is ever idle. We also introduce a weight limit on Tableau transpilation that trades gate count for parallelism, which PureMagic is particularly well-suited to exploit. Across 29 benchmark circuits, PureMagic achieves 43% to 152% efficiency improvement over bus routing, uses 19% to 80% fewer logical qubits, and reduces average magic state preparation time by 4.5x. Compared to DASCOT, a state-of-the-art static scheduler, PureMagic is up to 21x more efficient when magic state preparation costs are included. PureMagic's scheduled volumes fall between the conservative and optimistic FLASQ theoretical lower bounds, demonstrating near-optimal use of ancilla resources.
Read the full abstract

All authors Steven Hofmeyr, Mathias Weiden, Justin Kalloor, John Kubiatowicz, Costin Iancu

Quantum Physics

Nonreciprocal photon blockade in a spinning microwave magnomechanical system through kerr-magnon and optical parametric amplifier

S. K. Singh, Mohamed Amazioug, Jia-Xin Peng et al. (+3 more)

Unconventional quantum antibunching, arising from quantum interference effects, represents a notable form of quantum correlation that has attracted significant attention for its ability to generate high-quality single-quantum sources. In this work, we propose a scheme to achieve and actively control strong photon blockade in a spinning microwave magnomechanical system by leveraging the combined nonlinear effects of Kerr-induced magnon interactions and an optical parametric amplifier. By exploiting the Sagnac-Fizeau shift, we establish nonreciprocal photon blockade and verify this effect through a combination of analytical modelling and numerical simulations. To gain intuitive insight into the underlying nonreciprocity, we approximate the equal-time second-order correlation function using the analytical solution of the Schrödinger equation. This analytical result is then compared with the full numerical solution derived from the Lindblad master equation. The influences of thermal noise, the probe field amplitude, and the magnetic-dipole coupling strength are investigated within the constraints of the weak-coupling regime. The system's nonclassicality is characterized using the Mandel parameter, complemented by an analysis of the time evolution of the second-order correlation function. Our work provides a pathway for realizing nonreciprocal photon blockade in a nonlinear spinning microwave magnomechanical system.
Read the full abstract

All authors S. K. Singh, Mohamed Amazioug, Jia-Xin Peng, Wedad Albalawi, Mohammad Khalid, Abdel-Haleem Abdel-Aty

Quantum Physics

Hybrid qubit-oscillator module from motional states of two interacting atoms

Jaeyong Hwang, Tianrui Xu, Sean R. Muleady et al. (+5 more)

We propose a qubit-oscillator platform based on the motional states of two interacting atoms in an optical tweezer. By stroboscopically modulating an engineered trap with tunable anharmonicity, we implement a complete set of bosonic operations and their qubit-controlled counterparts with high fidelity. This motional control enables accurate detection of magnetic dipolar interactions with $\sim10$ Hz sensitivity in one second, reaching sub-Hz resolution within a few minutes in a $20\times20$ tweezer array under realistic experimental imperfections. Our approach establishes a versatile platform for motional quantum control of two atoms, with applications to spin-boson physics and precision sensing of interaction potentials and trapping environments.
Read the full abstract

All authors Jaeyong Hwang, Tianrui Xu, Sean R. Muleady, Steven K. Pampel, Gur Lubin, Dawson P. Hewatt, Cindy A. Regal, Ana Maria Rey

Quantum Physics

Generalized product-form monogamy relations in multi-qubit systems

Wen Zhou, Zhong-Xi Shen, Hong-Xing Wu et al. (+2 more)

Monogamy of entanglement essentially characterizes the entanglement distributions among the subsystems. Generally it is given by summation-form monogamy inequalities. In this paper, we present the product-form monogamy inequalities satisfied by the $\nu$-th ($\nu\geq2$) power of the concurrence. We show that they are tighter than the existing ones by detailed example. We then establish tighter product-form monogamy inequalities based on the negativity. We show that they are valid even for high dimensional states to which the well-known CKW inequality is violated.
Read the full abstract

All authors Wen Zhou, Zhong-Xi Shen, Hong-Xing Wu, Zhi-Xi Wang, Shao-Ming Fei

Quantum Physics

Mitigating the Transition of SiV$^-$ in Diamond to an Optically Dark State

Manuel Rieger, Rubek Poudel, Tobias Waldmann et al. (+7 more)

Negatively charged silicon vacancy centers in diamond (SiV$^-$) are promising for quantum photonic technologies. However, when subject to resonant optical excitation, they can inadvertently transfer into a zero-spin optically dark state. We show that this unwanted change of charge state can be quickly reversed by the resonant laser itself in combination with static electric fields. By defining interdigitated metallic contacts on the diamond surface, we increase the steady-state SiV$^-$ photoluminescence under resonant excitation by a factor $\ge3$ for most emitters, making it practically constant for certain individual emitters. We electrically activate single \sivs near the positively biased electrode, which are entirely dark without applying local electric fields. Using time-resolved 3-color experiments, we show that the resonant laser not only excites the SiV$^-$, but also creates free holes that convert SiV$^{2-}$ to SiV$^-$ on a timescale of milliseconds. Through analysis of several individual emitters, our results show that the degree of electrical charge state controllability differs between individual emitters, indicating that their local environment plays a key role. Our proposed electric-field-based stabilization scheme enhances deterministic charge state control in group-IV color centers and improves its understanding, offering a scalable path toward quantum applications such as entanglement generation and quantum key distribution.
Read the full abstract

All authors Manuel Rieger, Rubek Poudel, Tobias Waldmann, Lina M. Todenhagen, Stefan Kresta, Nori N. Chavira Leal, Viviana Villafañe, Martin S. Brandt, Kai Müller, Jonathan J. Finley

Quantum Physics

Bound state in the continuum and multiple atom state transfer applications in a waveguide QED setup

Xiang Guo, Xiaojun Zhang, Mingzhu Weng et al. (+5 more)

Bound states in the continuum (BICs) have been extensively exploited to enhance light–matter interactions in metamaterials, yet their emergence and utility in multi-atom waveguide platforms remain far less explored. Here we study atom–waveguide-dressed BICs in a one-dimensional coupled-resonator waveguide, where two spatially separated atomic arrays couple to distinct resonators with time-dependent strengths. We show that these BICs support a standing-wave photonic mode and enable the transfer of an arbitrary unknown quantum state between the two arrays with fidelities exceeding $99\%$. The protocol remains robust against both disorder and intrinsic dissipation. Our results establish BICs as long-lived resources for high-fidelity quantum information processing in waveguide-QED architectures.
Read the full abstract

All authors Xiang Guo, Xiaojun Zhang, Mingzhu Weng, Qian Bin, Hao-di Liu, Hai-Jun Xing, Xin-You Lü, Zhihai Wang

Quantum Physics

Testing the weak equivalence principle for nonclassical matter with torsion balances

Roberto Onofrio, Alexander R. H. Smith and Lorenza Viola

We propose tests of the weak equivalence principle (WEP) using a torsion balance, in which superposition of energy eigenstates are created in a controllable way for the test masses. After general considerations on the significance of tests of the WEP using quantum states and the need for considering inertial and gravitational masses as operators, we develop a model to derive the matrix elements of the free-fall operator, showing that the variance of the acceleration operator, in addition to its mean, enables estimation of violations of the WEP due to quantum coherence in a way that is robust with respect to shot-to-shot fluctuations. Building on this analysis, we demonstrate how the validity of the WEP may be tested in a torsion balance setup, by accessing the mean and variance of a torque operator we introduce and quantize. Due to the long acquisition times of the signal as compared to the timescale on which coherent superposition states may survive, we further propose a dynamical setting, where the torsion balance is subject to a time-dependent gravitational field, and measurements of angular acceleration encode possible violations of the WEP.
Read the full abstract

Quantum Physics

Exploring the topology induced by non-Markovian Liouvillian exceptional points

Hao-Long Zhang, Yan Wang, Wen Ning et al. (+6 more)

Non-Hermitian (NH) systems can display exotic topological phenomena without Hermitian counterparts, enabled by exceptional points (EPs). So far, investigations of NH topology have been restricted to EPs of the NH Hamiltonian, which governs the system dynamics conditional upon no quantum jumps occurring. The Liouvillian superoperator, which combines the effects of quantum jumps with NH Hamiltonian dynamics, possesses EPs (LEPs) that are significantly different from those of the corresponding NH Hamiltonian. We here study the topological features of the LEPs in the system consisting of a qubit coupled to a non-Markovian reservoir. We find that two distinct winding numbers can be simultaneously produced by executing a single closed path encircling the twofold LEP2, formed by two coinciding LEP2s, each involving a pair of coalescing eigenvectors of the extended Liouvillian superoperator. We experimentally demonstrate this purely non-Markovian phenomenon with a circuit, where a superconducting qubit is coupled to a decaying resonator which acts as a reservoir with memory effects. The results push the exploration of exceptional topology from the Markovian to non-Markovian regime.
Read the full abstract

All authors Hao-Long Zhang, Yan Wang, Wen Ning, Shou-Bang Yang, Jia-Hao Lü, Fan Wu, Pei-Rong Han, Zhen-Biao Yang, Shi-Biao Zheng

Quantum Physics · Cross-listed from nlin.SI

Integrable construction of a two-dimensional lattice model with anisotropic Hubbard couplings

Ze Tao and Fujun Liu

By defining a graded global R-operator $\mathbb{R}_{ab}^{(2D,2S)}$ that couples free-fermion structures and incorporates anisotropic Hubbard interactions while satisfying the Yang–Baxter equation, we construct a strictly solvable two-dimensional lattice model. We then build the layer-to-layer transfer matrix through a bidirectional-monodromy construction and prove the model's integrability via the associated global RTT relations. Using the nested algebraic Bethe ansatz, we obtain the exact eigenvalues of the transfer matrix and derive the corresponding first- and second-level Bethe equations. Finally, by taking the logarithmic derivative of the transfer matrix at the regular point, we recover explicitly a local Hamiltonian that features anisotropic hopping, an on-site Hubbard interaction, and orbital-coupling contributions.
Read the full abstract

Quantum Physics

Entanglement Witness Derived By Using Kolmogorov-Arnold Networks

Fatemeh Lajevardi, Azam Mani and Ali Fahim

We utilize Kolmogorov-Arnold Networks to design an interpretable model capable of detecting quantum entanglement within a set of nine-parameter two-qubit states. This network serves as an entanglement witness, achieving an accuracy of $94\%$ in distinguishing entangled states. Additionally, by analyzing the output functions of the KAN models, we explore the significance of each parameter (feature) in identifying the presence of entanglement. This analysis enables us to rank the features and eliminate the less significant ones, leading to the development of new entanglement witness functions that rely on fewer number of features, and hence do not require complete state tomography for their evaluation.
Read the full abstract

Quantum Physics

Wigner-Husimi phase-space structure of quasi-exactly solvable sextic potential

Angelina N. Mendoza Tavera, Adrian M. Escobar Ruiz and Robin P. Sagar

In this study, we compare the Wigner function $W$, its modulus, and the Husimi distribution $H$ in a one-dimensional quantum system exhibiting a transition from a single-well to a double-well configuration, using the quasi-exactly solvable sextic oscillator as a representative example. High-accuracy variational wavefunctions for the lowest states are used to compute two-dimensional phase-space structures, one-dimensional marginals, and the corresponding Shannon entropies, mutual information, and Cumulative Residual Jeffreys divergences. The analysis shows that the Wigner representation is uniquely responsive to interference effects and displays clear, nonmonotonic entropic behavior as the wells separate, whereas the modulus-Wigner and Husimi distributions account only for geometric splitting or coarse-grained delocalization. These findings establish a quantitative hierarchy in the ability of $W$, $|W|$, and $H$ to resolve structural changes in a quantum state and provide a general framework for assessing the descriptive power of different phase-space representations in systems with emerging bimodality or tunneling.
Read the full abstract

Quantum Physics

Spin-photon Qubits for Scalable Quantum Network

Md Sakibul Islam, Kuldeep Singh, Yunhe Zhao et al. (+2 more)

Solid-state quantum light sources offer a scalable pathway for interfacing stationary spin qubits with flying photonic qubits, forming the backbone of future quantum networks. Telecom-band spin-photonic qubits, operating in the 1260-1675 nm wavelength range, are particularly well-suited for long-distance quantum communication due to minimal loss in standard optical fibers. Achieving scalability, however, hinges on fulfilling several stringent criteria: coherent spin-state control, deterministic and indistinguishable single-photon emission, and integration with nanophotonic structures that enhance radiative properties, such as lifetime, coherence, and photon indistinguishability. This study explores the state-of-the-art spin-photonic qubits across solid-state platforms, including diamond color centers, silicon carbide defect centers, quantum dots, and two-dimensional materials. Special attention is given to silicon-based emitters, particularly G, T, C- and Ci-centers, which promise monolithic integration with complementary metal-oxide-semiconductor (CMOS) technology and telecom-band operation. We classify these systems based on spin-photon interface availability, CMOS process compatibility, and emitter scalability. We also discuss recent advances in cavity quantum electrodynamics (cQED), including Purcell enhancement and quality factor engineering in integrated photonic (circuits) environments. The work highlights emerging demonstrations of quantum networking over metropolitan scales and outlines the trajectory toward chip-scale quantum photonic integrated circuits (QPICs). It combines deterministic emitter creation, coherent spin manipulation, and quantum information processing. These developments pave the way for global quantum networks, enabling secure communication, distributed quantum computing, and quantum-enhanced sensing.
Read the full abstract

All authors Md Sakibul Islam, Kuldeep Singh, Yunhe Zhao, Nitesh Singh, Wayesh Qarony

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

Robust AC vector sensing at zero magnetic field with pentacene

Boning Li, Garrett Heller, Jungbae Yoon et al. (+6 more)

Quantum sensors based on electronic spins have emerged as powerful probes of microwave-frequency fields. Among other solid-state platforms, spins in molecular crystals offer a range of advantages, from high spin density to functionalization via chemical tunability. Here, we demonstrate microwave vector magnetometry using the photoexcited spin triplet of deuterated pentacene molecules, operating at zero external magnetic field and room temperature. We achieve full three-dimensional microwave field reconstruction by detecting the Rabi frequencies of anisotropic spin-triplet transitions associated with two crystallographic orientations of pentacene in naphthalene crystals. We further introduce a phase alternated protocol that extends the rotating-frame coherence time by an order of magnitude and enables sensitivities of $1~\mu\mathrm{T}/\sqrt{\mathrm{Hz}}$ with sub-micrometer spatial resolution. These results establish pentacene-based molecular spins as a practical and high-performance platform for microwave quantum sensing, and the control techniques are broadly applicable to other molecular and solid-state spin systems.
Read the full abstract

All authors Boning Li, Garrett Heller, Jungbae Yoon, Alexander Ungar, Hao Tang, Guoqing Wang, Patrick Hautle, Yifan Quan, Paola Cappellaro

Quantum Physics

Adiabaticity Crossover: From Anderson Localization to Planckian Diffusion

Tiange Xiang, Yubo Zhang, Joonas Keski-Rahkonen et al. (+2 more)

We investigate electron transport in one dimension from the quantum-acoustic perspective, where the coherent-state representation of lattice vibrations results in a time-dependent deformation potential whose rate is set by the sound speed, fluctuation spectrum is set by the temperature, and overall amplitude is set by the electron-lattice coupling strength. We introduce an acceleration-based adiabatic criterion, consistent with the adiabatic theorem and Landau-Zener theory, that separates adiabatic and diabatic dynamics across the $(T,v)$ plane. The discrete classification agrees with a continuous mean-squared acceleration scale and correlates with a coherence measure given by the ratio of coherence length to the initial packet width $L_\phi(t)/\sigma_0$. We identify a broad Planckian domain in which the dimensionless diffusivity $\alpha\!=\!Dm/\hbar$ is of order unity and only weakly depends on the parameters. This domain is more prevalent in diabatic regions and in areas of reduced phase coherence, indicating a dephasing driven crossover from Anderson localization to Planckian diffusion. Using the Einstein relation together with nearly constant $\alpha$, we directly obtain a low temperature tendency $1/\tau_{\rm tr}\propto T$, offering a insight to $T$-linear resistivity in strange metals. These results provide a unified picture that links adiabaticity, dephasing, and Planckian diffusion in dynamically disordered quantum-acoustics.
Read the full abstract

All authors Tiange Xiang, Yubo Zhang, Joonas Keski-Rahkonen, Anton M. Graf, Eric J. Heller

Quantum Physics

Trade-offs between Quantum and Classical Resources in the Linear Combination of Unitaries

Kaito Wada, Hiroyuki Harada, Yasunari Suzuki et al. (+3 more)

The randomized linear combination of unitaries (LCU) method with many applications to early fault-tolerant quantum computing algorithms has been proposed. This quantum algorithm computes the same expectation values as the original, fully coherent LCU algorithm using a shallower quantum circuit with a single ancilla qubit, at the cost of a quadratically larger sampling overhead. In this work, we propose a quantum algorithm intermediate between the original and randomized LCU that manages the trade-off between the sampling overhead and circuit complexity. Our algorithm divides the set of unitary operators into several groups and then randomly samples LCU circuits from these groups to evaluate the target expectation value. Notably, we reveal that across all grouping strategies, the mechanism of the sampling overhead reduction can be solely characterized by a metric we call the reduction factor. Moreover, we analytically prove an underlying monotonicity of the reduction factor in the group size: larger group sizes entail smaller sampling overhead. Finally, our framework enables a more flexible algorithmic design by systematically yielding intermediate implementations of LCU-based algorithms; we provide intermediate implementations of non-Hermitian dynamics simulation, ground-state property estimation, and quantum error detection. Besides, we demonstrate this principle by deriving intermediate trade-off scaling in sample complexity and ancillary space for quantum linear system solver.
Read the full abstract

All authors Kaito Wada, Hiroyuki Harada, Yasunari Suzuki, Yuuki Tokunaga, Naoki Yamamoto, Suguru Endo

Quantum Physics

Quantum Interior Point Methods: A Review of Developments and An Optimally Scaling Framework

Mohammadhossein Mohammadisiahroudi, Zeguan Wu, Pouya Sampourmahani et al. (+2 more)

The growing demand for solving large-scale, data-intensive linear and conic optimization problems, particularly in applications such as artificial intelligence and machine learning, has highlighted the limitations of classical interior point methods (IPMs). Despite their favorable polynomial-time convergence, conventional IPMs often suffer from high per-iteration computational costs, especially for dense problem instances. Recent advances in quantum computing, particularly quantum linear system solvers, offer promising avenues to accelerate the most computationally intensive steps of IPMs. However, practical challenges such as quantum error, hardware noise, and sensitivity to poorly conditioned systems remain significant obstacles. In response, a series of Quantum IPMs (QIPMs) has been developed to address these challenges, incorporating techniques such as feasibility maintenance, iterative refinement, and preconditioning. In this work, we review this line of research with a focus on our recent contributions, including an almost-exact QIPM framework. This hybrid quantum-classical approach constructs and solves the Newton system entirely on a quantum computer, while performing solution updates classically. Crucially, all matrix-vector operations are executed on quantum hardware, enabling the method to achieve an optimal worst-case scalability w.r.t dimension, surpassing the scalability of existing classical and quantum IPMs.
Read the full abstract

All authors Mohammadhossein Mohammadisiahroudi, Zeguan Wu, Pouya Sampourmahani, Adrian Harkness, Tamás Terlaky

Friday 5 December

Quantum Physics

The State-Operator Clifford Compatibility: A Real Algebraic Framework for Quantum Information

Kagwe A. Muchane

We revisit the Pauli-Clifford connection to introduce a real, grade-preserving algebraic framework for $n$-qubit quantum computation based on the tensor product $C\ell_{2,0}(\mathbb{R})^{\otimes n}$. In this setting, the bivector $J = e_{12}$ satisfies $J^{2} = -1$ and supplies the complex structure on the $J$-closure of a minimal left ideal via right multiplication, while Pauli operations arise as left actions of Clifford elements. The Peirce decomposition organizes the algebra into sector blocks determined by primitive idempotents, with nilpotent elements generating transitions between sectors. Quantum states are represented as equivalence classes modulo the left annihilator, exhibiting the quotient description underlying the minimal left ideal. Adopting a canonical stabilizer mapping, the $n$-qubit computational basis state $|0\cdots 0\rangle$ is given natively by a tensor product of these idempotents. This structural choice leads to a compatibility law that is stable under the geometric product for $n$ qubits and aligns symbolic Clifford multiplication with unitary evolution on the Hilbert space.
Read the full abstract

Quantum Physics

Highly robust logical qubit encoding in an ensemble of V-symmetrical qutrits

Luis Octavio Castaños-Cervantes, Manuel Calixto and Julio Guerrero

We propose using even and odd Schödinger cat states formed from coherent states of U(3) of an ensemble of qutrits with a symmetrical V-configuration (a qubit-disguised qutrit) to encode a logical qubit. These carefully engineered logical qubit states are parameter independent stationary states of the effective master equation governing the evolution of the ensemble and, consequently, constitute dark states and are invulnerable to dissipation and correlated collective dephasing. In particular, the logical qubit states are immune to single qutrit decay (the analogous of single photon loss process for qutrits) and simultaneous decay and driving of two qutrits (the analogous two-photon loss and driving processes for qutrits). In addition, we show how to implement the single-qubit quantum NOT gate and the Hadamard gate followed by either the phase gate or the phase and $Z$ gates. We study analytically the case of two qutrits and conclude that the logical qubit states exhibit parity-sensitive inhomogeneous broadening and local correlated dephasing: the even logical state is completely immune to these processes, while odd one is vulnerable. Nevertheless, in the presence of these interactions one can also define another odd state with mixed permutation symmetry that is immune to both inhomogeneous broadening and local correlated dephasing. We suggest that these results can be extrapolated to an arbitrary number of qutrits. The effective master equation is deduced from a physical system composed of two parametrically coupled cavities with one of them interacting dispersively with an ensemble of three-level atoms (the qutrits). In principle this physical system can be implemented by means of two coplanar waveguide resonators, a SQUID parametrically coupling them, and a cloud of alkali atoms close to one of the resonators.
Read the full abstract