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Physics Quantum Physics

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Monday 5 January

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

Two-Qubit Module Based on Phonon-Coupled Ge Hole-Spin Qubits: Design, Fabrication, and Readout at 1-4 K

D.-M. Mei, S. A. Panamaldeniya, K.-M. Dong et al. (+2 more)

We present a device-level design study for a two-qubit module based on phonon-coupled germanium (Ge) hole-spin qubits targeted for operation at $1$–$4~\mathrm{K}$. Building on prior theoretical modeling of phonon-engineered Ge qubits and phononic-crystal (PnC) cavities, we translate those modeling results into a fabrication-oriented two-qubit layout that integrates two gate-defined hole-spin qubits in a strained Ge quantum well with a GHz PnC defect mode intended to mediate a coherent phonon-based interaction. We specify the SiGe/Ge heterostructure, electrostatic gate layout, PnC cavity geometry, and a compatible nanofabrication pathway, including gate-stack formation, membrane patterning and release, RF/DC wiring, and process-risk mitigation. We further develop a readout architecture combining spin-to-charge conversion with RF reflectometry on a proximal charge sensor, and we provide a link-budget estimate that states the assumed system noise temperature, RF signal contrast, and integration-time requirements for single-shot readout at elevated cryogenic temperatures. Finally, we outline a stepwise benchmarking program for charge stability, single-qubit control, phonon-bandgap modification of relaxation, and resolvable phonon-mediated two-qubit coupling. The manuscript does not report experimental device data; rather, it provides an experimentally actionable bridge from prior modeling to future fabrication and measurement of phonon-coupled Ge hole-spin modules.
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All authors D.-M. Mei, S. A. Panamaldeniya, K.-M. Dong, S. Bhattarai, A. Prem

Sunday 4 January

Quantum Physics

A Geometric Approach to Strongly Correlated Bosons: From $N$-Representability to the Generalized BEC Force

Chih-Chun Wang and Christian Schilling

Building on recent advances in reduced density matrix theory, we develop a geometric framework for describing strongly correlated lattice bosons. We first establish that translational symmetry, together with a fixed pair interaction, enables an exact functional formulation expressed solely in terms of momentum occupation numbers. Employing the constrained-search formalism and exploiting a geometric correspondence between $N$-boson configuration states and their one-particle reduced density matrices, we derive the general form of the ground-state functional. Its structure highlights the omnipresent significance of one-body $N$-representability: (i) the domain is exactly determined by the $N$-representability conditions; (ii) at its boundary, the gradient of the functional diverges repulsively, thereby generalizing the recently discovered Bose-Einstein condensate (BEC) force; and (iii) an explicit expression for this boundary force follows directly from geometric arguments. These key results are demonstrated analytically for few-site lattice systems, and we illustrate the broader significance of our functional form in defining a systematic hierarchy of functional approximations.
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Quantum Physics

Design and Characterization of Compact Acousto-Optic-Deflector Individual Addressing System for Trapped-Ion Quantum Computing

Jiyong Yu, Kavyashree Ranawat, Andrew Van Horn et al. (+4 more)

We present a compact design for a beam-steering system based on acousto-optic-deflectors (AODs) used as an individual addressing system for trapped-ion quantum computing. The design targets to minimize the optomechanical degrees of freedom and the optical beam paths to improve optical stability, and we successfully implemented a solution with a compact footprint of less than 1 square foot. The system characterization results show that we achieve clean Gaussian beams at 355nm wavelength with a beam steering range of $\sim$50 times the beam diameter, and an intensity crosstalk of $< 9 \times 10^{-4}$ at all neighboring ions in a five-ion chain. Based on these capabilities, we experimentally demonstrate individual addressing of a 30-ion chain. We estimate the beam switching time of the AOD to be $\sim$240 ns. The compact system design is expected to provide high optical stability, providing the potential for high-fidelity trapped-ion quantum computing with long ion chains.
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All authors Jiyong Yu, Kavyashree Ranawat, Andrew Van Horn, Jacob Whitlow, Seunghyun Baek, Junki Kim, Jungsang Kim

Quantum Physics · Cross-listed from cond-mat.stat-mech

Variation on the theme of Jarzynski's inequality

Dani R. Castellanos and Petr Jizba

The Jarzynski equality, which relates equilibrium free-energy difference to an average of non-equilibrium work, plays a central role in modern non-equilibrium statistical thermodynamics. In this paper, we study a weaker consequence of this relation, known as Jarzynski's inequality, which can be formally obtained from the Jarzynski equality via Jensen's inequality. We identify and analyze several extensions of Jarzynski's inequality that go beyond its direct derivation from the Jarzynski equality. In particular, we consider chemical systems both in the linear-response regime and away from linear thermodynamics. Furthermore, by employing functional-integral techniques, we extend Jarzynski's inequality to many-body statistical systems described by quantum field theory. Salient issues, such as connections of the Jarzynski inequality with the maximum work theorem and the Landau–Lifshitz theory of fluctuations, are also discussed.
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Quantum Physics

Quantum simulation with Rydberg ions in a Penning trap

Wilson S. Martins, Markus Hennrich, Ferdinand Schmidt-Kaler et al. (+1 more)

Quantum simulation of interacting many-body spin systems is routinely performed with cold trapped ions, and systems with hundreds of spins have been studied in one and two dimensions. In the most common realizations of these platforms, spin degrees of freedom are encoded in low-lying electronic levels, and interactions among the spins are mediated through crystal vibrations. Here we propose a new approach which enables the quantum simulation of two-dimensional spin systems with interaction strengths that are increased by orders of magnitude. This, together with the unprecedented longevity of trapped ions, opens an avenue for the exploration of phenomena that take place on long timescales, e.g., slow and collective relaxation in frustrated and kinetically constrained systems. Our platform makes use of the strong dipolar interactions among electronic Rydberg states and planar confinement provided by a Penning trap. We investigate how the strong electric and magnetic fields that form this trap affect the properties of the Rydberg states and show that spin-spin interaction strengths on the order of MHz are achievable under experimentally realistic conditions. As a brief illustration of the capabilities of this quantum simulator, we study the entanglement in a frustrated spin system realized by three ions.
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All authors Wilson S. Martins, Markus Hennrich, Ferdinand Schmidt-Kaler, Igor Lesanovsky

Quantum Physics

Scattering Cross Section Formula Derived From Macroscopic Model of Detectors

Rashi Kaimal and Roderich Tumulka

We are concerned with the justification of the statement, commonly (explicitly or implicitly) used in quantum scattering theory, that for a free non-relativistic quantum particle with initial wave function $\Psi_0(\boldsymbol{x})$, surrounded by detectors along a sphere of large radius $R$, the probability distribution of the detection time and place has asymptotic density (i.e., scattering cross section) $\sigma(\boldsymbol{x},t)= m^3 \hbar^{-3} R t^{-4} |\widehat{\Psi}_0(m\boldsymbol{x}/\hbar t)|^2$ with $\widehat{\Psi}_0$ the Fourier transform of $\Psi_0$. We give two derivations of this formula, based on different macroscopic models of the detection process. The first one consists of a negative imaginary potential of strength $\lambda>0$ in the detector volume (i.e., outside the sphere of radius $R$) in the limit $R\to\infty,\lambda\to 0, R\lambda\to \infty$. The second one consists of repeated nearly-projective measurements of (approximately) the observable $1_{|\boldsymbol{x}|>R}$ at times $\mathscr{T},2\mathscr{T},3\mathscr{T},\ldots$ in the limit $R\to\infty,\mathscr{T}\to\infty,\mathscr{T}/R\to 0$; this setup is similar to that of the quantum Zeno effect, except that there one considers $\mathscr{T}\to 0$ instead of $\mathscr{T}\to\infty$. We also provide a comparison to Bohmian mechanics: while in the absence of detectors, the arrival times and places of the Bohmian trajectories on the sphere of radius $R$ have asymptotic distribution density given by the same formula as $\sigma$, their deviation from the detection times and places is not necessarily small, although it is small compared to $R$, so the effect of the presence of detectors on the particle can be neglected in the far-field regime. We also cover the generalization to surfaces with non-spherical shape, to the case of $N$ non-interacting particles, to time-dependent surfaces, and to the Dirac equation.
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Quantum Physics

Generation of circular polarized high-order harmonics from single color quantum light

Lidija Petrovic, Philipp Stammer, Maciej Lewenstein et al. (+1 more)

The atomic response to an ultra-intense driving field produces a characteristic high-harmonic spectrum featuring a rapid drop in intensity for the lower harmonics, followed by a plateau and a sharp cutoff. This response vanishes for circularly polarized classical drivers – a limitation that can be overcome by introducing quantum features into the driving field. In this work, we show that squeezed highly elliptically polarized drivers not only enable the high-harmonic generation (HHG) process in classically forbidden regimes of large ellipticity, but also yield highly elliptical harmonic radiation with pronounced super-Poissonian photon statistics. Moreover, we show that the HHG spectral features encode information about the quantum nature of the driving field, revealing the presence of its squeezed field fluctuations. By analyzing the HHG spectral intensity dependence as a function of the driver's ellipticity and squeezing orientation, we identify a means to probe the driving field's quantum properties that intrinsically lie in the high-photon number regime.
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All authors Lidija Petrovic, Philipp Stammer, Maciej Lewenstein, Javier Rivera-Dean

Quantum Physics

Learning Relationship between Quantum Walks and Underdamped Langevin Dynamics

Yazhen Wang

Fast computational algorithms are in constant demand, and their development has been driven by advances such as quantum speedup and classical acceleration. This paper intends to study search algorithms based on quantum walks in quantum computation and sampling algorithms based on Langevin dynamics in classical computation. On the quantum side, quantum walk-based search algorithms can achieve quadratic speedups over their classical counterparts. In classical computation, a substantial body of work has focused on gradient acceleration, with gradient-adjusted algorithms derived from underdamped Langevin dynamics providing quadratic acceleration over conventional Langevin algorithms. Since both search and sampling algorithms are designed to address learning tasks, we study learning relationship between coined quantum walks and underdamped Langevin dynamics. Specifically, we show that, in terms of the Le Cam deficiency distance, a quantum walk with randomization is asymptotically equivalent to underdamped Langevin dynamics, whereas the quantum walk without randomization is not asymptotically equivalent due to its high-frequency oscillatory behavior. We further discuss the implications of these equivalence and nonequivalence results for the computational and inferential properties of the associated algorithms in machine learning tasks. Our findings offer new insight into the relationship between quantum walks and underdamped Langevin dynamics, as well as the intrinsic mechanisms underlying quantum speedup and classical gradient acceleration.
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Quantum Physics

Utilizing intermediate states in quantum annealing for multi-objective optimization

Keita Takahashi and Shu Tanaka

We investigate obtaining intermediate quantum states during the quantum annealing process to address the limitation of the linear weighted sum method in multi-objective optimization, which inherently fails to reach non-convex regions of the Pareto front. We validate this approach through physical experiments utilizing quench-based readout and numerical simulations assuming ideal mid-anneal measurements. Both methods consistently demonstrate a clear trade-off where earlier timing enhances diversity of the solutions, whereas later timing ensures convergence to non-dominated solutions. Notably, a practical compromise timing balances both metrics. The qualitative agreement between practical quench and ideal simulation indicates the potential of accessing the intermediate states for comprehensive Pareto front exploration.
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Quantum Physics

Time-Dependent Low-Energy Simulation Accelerates Adiabatic State Preparation

Shuo Zhou, Zhaokai Pan, Weiyuan Gong et al. (+1 more)

Hamiltonian simulations are key subroutines in adiabatic quantum computation and quantum many-body physics, where quantum dynamics often happen in the low-energy sector. Previous studies have shown that the low-energy assumption can reduce the resource requirements of standard time-independent Hamiltonian simulation algorithms. However, whether such advantages extend to time-dependent Hamiltonian simulation remains open. In this paper, we consider the adiabatic regime where the relevant low-energy subspace is spanned by a fixed number of low-energy eigenstates and separated from the rest of the spectrum by a gap. We show that, for simulating spin Hamiltonians by product formulas, the explicit system size dependence in the leading commutator-scaling term can be replaced by a low-energy scale up to logarithmic factors. Technically, we derive the low-energy simulation error with commutator scaling for product formulas by leveraging adiabatic perturbation theory to analyze the time-variant energy spectrum of the underlying Hamiltonian. We further conduct numerical experiments on adiabatic state preparation of an illustrative example system to support our theoretical findings. Finally, we prove a lower bound of query complexity for generic time-dependent Hamiltonian simulations.
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All authors Shuo Zhou, Zhaokai Pan, Weiyuan Gong, Tongyang Li

Quantum Physics

Non-Hermitian second-order topological insulator with point gap

Xue-Min Yang, Hao Lin, Jian Li et al. (+3 more)

The zero-mode corner states in the gap of two-dimensional non-Hermitian Su-Schrieffer-Heeger model are robust to infinitesimal perturbations that preserve chiral symmetry. However, we demonstrate that this general belief is no longer valid in large-sized systems. To reveal the higher-order topology of non-Hermitian systems, we establish a correspondence between the stable zero-mode singular states and the topologically protected corner states of energy spectrum in the thermodynamic limit. Within this framework, the number of zero-mode singular values is directly linked to the number of mid-gap corner states. The winding numbers in real space can be defined to count the number of stable zero-mode singular states. Our results formulate a bulk-boundary correspondence for both static and Floquet non-Hermitian systems, where topology arises intrinsically from the non-Hermiticity, even without symmetries.
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All authors Xue-Min Yang, Hao Lin, Jian Li, Jia-Ji Zhu, Jun-Li Zhu, Hong Wu

Quantum Physics

Overcoming Stark-Shift Constraints in Phase-Controlled Rydberg Two-Qubit Gates

Ignacio R. Sola, Sebastian C. Carrasco, Vladimir S. Malinovsky et al. (+2 more)

Stark shifts introduce additional phases that constrain the set of entangling gates that can be prepared via two-photon transitions in the strong Rydberg blockade limit. For non-independently addressed qubits, by controlling the absolute phases and the local amplitudes of the pulses at each qubit, we show that any two-qubit phase gate can be prepared with high fidelity using a three-pulse sequence. Based on these insights, we introduce two robust control schemes tailored to different phase gates that yield better results with pulse sequences of either even or odd length.
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All authors Ignacio R. Sola, Sebastian C. Carrasco, Vladimir S. Malinovsky, Seokmin Shin, Bo Y. Chang

Quantum Physics

Entropy and Variance Squeezing of V-type Atom in Dissipative Cavity

Zijin Liang, Qiying Pan, Hong-Mei Zou et al. (+1 more)

Based on Ref.\cite{Riccardi A}, we investigate the entropy and variance squeezing of a V-type atom in a dissipative cavity, and discuss the influences of parameters including the spontaneously generated interference (SGI) ($\theta$), the cavity-environment coupling ($\gamma_0/\kappa$) and the atom-cavity detuning ($\Delta$) on the atomic squeezing by using different initial states. The results show that no squeezing of $S_y$ occurs under any condition and that variance squeezing of $S_x$ appears only when $\Delta>0$. Entropy squeezing quantifies quantum fluctuations more precisely than variance squeezing. Moreover, the atomic squeezing of $S_x$ clearly depends on $\theta$, $\gamma_0/\kappa$, $\Delta$ and the initial state. These findings are meaningful for quantum information processing as an ultra-low-noise resource.
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All authors Zijin Liang, Qiying Pan, Hong-Mei Zou, Chenrui Bi

Quantum Physics

Constraint-Aware Quantum Optimization via Hamming Weight Operators

Yajie Hao, Qiming Ding, Xiao Yuan et al. (+1 more)

Constrained combinatorial optimization with strict linear constraints underpins applications in drug discovery, power grids, logistics, and finance, yet remains computationally demanding for classical algorithms, especially at large scales. The Quantum Approximate Optimization Algorithm (QAOA) offers a promising quantum framework, but conventional penalty-based formulations distort optimization landscapes and demand deep circuits, undermining scalability on near-term hardware. In this work, we introduce Hamming Weight Operators, a new class of constraint-aware operators that confine quantum evolution strictly within the feasible subspace. Building on this idea, we develop Adaptive Hamming Weight Operator QAOA, which dynamically selects the most effective operators to construct shallow, problem-tailored circuits. We validate our approach on benchmark tasks from both finance and high-energy physics, specifically portfolio optimization and two-jet clustering with energy balance. Across these problems, our method inherently satisfies all constraints by construction, converges faster, and achieves higher Approximation Ratios than penalty-based QAOA, while requiring roughly half as many gates. By embedding constraint-aware operators into an adaptive variational framework, our approach establishes a scalable and hardware-efficient pathway for solving practical constrained optimization problems on near-term quantum devices.
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All authors Yajie Hao, Qiming Ding, Xiao Yuan, Xiaoting Wang

Quantum Physics

A Logical Formalism of Hardy-type Paradox

Songyi Liu, Yongjun Wang, Baoshan Wang et al. (+2 more)

Hardy-type paradoxes provide elegant, inequality-free proofs of quantum contextuality. We introduce a unified logical formalism for these paradoxes, termed logical Hardy-type paradoxes. For any finite quantum scenario of ideal measurements, we prove that the existence of a logical Hardy-type paradox is equivalent to logical contextuality. Specifically, strong contextuality is equivalent to logical Hardy-type paradoxes with success probability SP = 1. These results generalize prior work on (2,k,2), (2,2,d), and n-cycle scenarios. We analyze logical Hardy-type paradoxes in the Mansfield and Klyachko-Can-Binicioglu-Shumovsky (KCBS) scenarios. In the KCBS scenario, we show that there is exactly one type of logical Hardy-type paradox, achieving SP\approx 10.56% for a specific parameter setting.
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All authors Songyi Liu, Yongjun Wang, Baoshan Wang, Chang He, Yunyi Jia

Quantum Physics

Implicitly Restarted Lanczos Enables Chemically-Accurate Shallow Neural Quantum States

Wei Liu and Wenjie Dou

The variational optimization of high-dimensional neural network models, such as those used in neural quantum states (NQS), presents a significant challenge in machine intelligence. Conventional first-order stochastic methods (e.g., Adam) are plagued by slow convergence, sensitivity to hyperparameters, and numerical instability, preventing NQS from reaching the high accuracy required for fundamental science. We address this fundamental optimization bottleneck by introducing the implicitly restarted Lanczos (IRL) method as the core engine for NQS training. Our key innovation is an inherently stable second-order optimization framework that recasts the ill-conditioned parameter update problem into a small, well-posed Hermitian eigenvalue problem. By solving this problem efficiently and robustly with IRL, our approach automatically determines the optimal descent direction and step size, circumventing the need for demanding hyperparameter tuning and eliminating the numerical instabilities common in standard iterative solvers. We demonstrate that IRL enables shallow NQS architectures (with orders of magnitude fewer parameters) to consistently achieve extreme precision (1e-12 kcal/mol) in just 3 to 5 optimization steps. For the F2 molecule, this translates to an approximate 17,900-fold speed-up in total runtime compared to Adam. This work establishes IRL as a superior, robust, and efficient second-order optimization strategy for variational quantum models, paving the way for the practical, high-fidelity application of neural networks in quantum physics and chemistry.
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Quantum Physics

Noise-Resilient Heisenberg-limited Quantum Sensing via Indefinite-Causal-Order Error Correction

Hang Xu, Xiaoyang Deng, Ze Zheng et al. (+2 more)

Quantum resources can, in principle, enable Heisenberg-limited (HL) sensing, yet no-go theorems imply that HL scaling is generically unattainable in realistic noisy devices. While quantum error correction (QEC) can suppress noise, its use in quantum sensing is constrained by stringent requirements, including prior noise characterization, restrictive signal-noise compatibility conditions, and measurement-based syndrome extraction with global control. Here we introduce an ICO-based QEC protocol, providing the first application of indefinite causal order (ICO) to QEC. By coherently placing auxiliary controls and noisy evolution in an indefinite causal order, the resulting noncommutative interference enables an auxiliary system to herald and correct errors in real time, thereby circumventing the limitations of conventional QEC and restoring HL scaling. We rigorously establish the protocol for single- and multi-noise scenarios and demonstrate its performance in single-qubit, many-body, and continuous-variable platforms. We further identify regimes in which error correction can be implemented entirely by unitary control, without measurements. Our results reveal ICO as a powerful resource for metrological QEC and provide a broadly applicable framework for noise-resilient quantum information processing.
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All authors Hang Xu, Xiaoyang Deng, Ze Zheng, Tailong Xiao, Guihua Zeng

Quantum Physics

Distant Entanglement Generation between Magnon and Superconducting Qubits in Magnon-Mediated Hybrid Systems

Guosen Liu and Pei Pei

We propose an efficient two-stage protocol for generating distant entanglement in a magnon-mediated hybrid quantum system, where magnons serve dual roles as both interaction mediators and qubits. This integrated design reduces the physical component count while leveraging the inherent advantages of magnons, such as their strong coupling via magnetic dipole interactions, low dissipation, and high integrability. In our setup, a superconducting resonator interfaces between a local superconducting qubit (SQ) and a local magnonic system (QM1), which is waveguide-coupled to a remote magnonic system (QM2). The protocol comprises two stages: (i) deterministic Bell-state generation between the SQ and QM1 using shortcuts to adiabaticity, and (ii) coherent state transfer to QM2 via engineered Hamiltonian dynamics. This adiabatic characteristic enhances robustness against environmental dissipation. Numerical simulations under realistic noise conditions confirm strong resilience to decoherence, achieving fidelity $F > 0.90$ and negativity $\mathcal{N}_2 > 0.40$. These results establish the protocol as a scalable and practical building block for distributed quantum networks.
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Quantum Physics · Cross-listed from nlin.PS

Soliton Thouless pumping engineered by inter-site nonlinearities

Tao Jiang and Li-Chen Zhao

We study soliton Thouless pumping in an extended diagonal Aubry-André-Harper model with on-site nonlinearities and inter-site nonlinearities. We show that the inter-site nonlinearities can make solitons acquire anomalous transport distances far beyond the ones predicted by the linear bands, and the quantized displacements can be engineered well. We uncover that nonlinear instabilities require lower limits on sweeping rates for soliton pumping, challenging the common notion that slower modulation enables a more favorable realization of topological transport. The nonlinear interactions between solitons make multi-soliton pumping generally lack the robustness characteristic of Thouless pumping as linear systems. Our results provide many possibilities to engineer topological pumping by nonlinearities, and further make a step for applications of soliton pumping.
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Quantum Physics

Benchmarking Quantum Data Center Architectures: A Performance and Scalability Perspective

Shahrooz Pouryousef, Eneet Kaur, Hassan Shapourian et al. (+3 more)

Scalable distributed quantum computing (DQC) has motivated the design of multiple quantum data-center (QDC) architectures that overcome the limitations of single quantum processors through modular interconnection. While these architectures adopt fundamentally different design philosophies, their relative performance under realistic quantum hardware constraints remains poorly understood. In this paper, we present a systematic benchmarking study of four representative QDC architectures-QFly, BCube, Clos, and Fat-Tree-quantifying their impact on distributed quantum circuit execution latency, resource contention, and scalability. Focusing on quantum-specific effects absent from classical data-center evaluations, we analyze how optical-loss-induced Einstein-Podolsky-Rosen (EPR) pair generation delays, coherence-limited entanglement retry windows, and contention from teleportation-based non-local gates shape end-to-end execution performance. Across diverse circuit workloads, we evaluate how architectural properties such as path diversity and path length, and shared BSM (Bell State Measurement) resources interact with optical-switch insertion loss and reconfiguration delay. Our results show that distributed quantum performance is jointly shaped by topology, scheduling policies, and physical-layer parameters, and that these factors interact in nontrivial ways. Together, these insights provide quantitative guidance for the design of scalable and high-performance quantum data-center architectures for DQC.
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All authors Shahrooz Pouryousef, Eneet Kaur, Hassan Shapourian, Don Towsley, Ramana Kompella, Reza Nejabati

Quantum Physics

Quantum Kaczmarz Algorithm for Solving Linear Algebraic Equations

Nhat A. Nghiem, Tuan K. Do and Trung V. Phan

We introduce a quantum linear system solving algorithm based on the Kaczmarz method, a widely used workhorse for large linear systems and least-squares problems that updates the solution by enforcing one equation at a time. Its simplicity and low memory cost make it a practical choice across data regression, tomographic reconstruction, and optimization. In contrast to many existing quantum linear solvers, our method does not rely on oracle access to query entries, relaxing a key practicality bottleneck. In particular, when the rank of the system of interest is sufficiently small and the rows of the matrix of interest admit an appropriate structure, we achieve circuit complexity $\mathcal{O}\left(\frac{1}{\varepsilon}\log m\right)$, where $m$ is the number of variables and $\varepsilon$ is the target precision, without dependence on the sparsity $s$, and could possibly be without explicit dependence on condition number $\kappa$. This shows a significant improvement over previous quantum linear solvers where the dependence on $\kappa,s$ is at least linear. At the same time, when the rows have an arbitrary structure and have at most $s$ nonzero entries, we obtain the circuit depth $\mathcal{O}\left(\frac{1}{\varepsilon}\log s\right)$ using extra $\mathcal{O}(s)$ ancilla qubits, so the depth grows only logarithmically with sparsity $s$. When the sparsity $s$ grows as $\mathcal{O}(\log m)$, then our method can achieve an exponential improvement with respect to circuit depth compared to existing quantum algorithms, while using (asymptotically) the same amount of qubits.
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Quantum Physics

Bond Additivity and Persistent Geometric Imprints of Entanglement in Quantum Thermalization

Chun-Yue Zhang, Shi-Xin Zhang and Zi-Xiang Li

Characterizing the intricate structure of entanglement in quantum many-body systems remains a central challenge, as standard measures often obscure underlying geometric details. In this Letter, we introduce a powerful framework, termed multi-bipartition entanglement tomography, which probes the fine structure of entanglement across an exhaustive ensemble of distinct bipartitions. Our cornerstone is the discovery of a “bond-additive law”, which reveals that the entanglement entropy can be precisely decomposed into a bulk volume-law baseline plus a geometric correction formed by a sum of local contributions from crossed bonds of varying ranges. This law distills complex entanglement landscapes into a concise set of entanglement bond tensions $\{\omega_j\}$, serving as a quantitative fingerprint of interaction locality. By applying this tomography to Hamiltonian dynamics, random quantum circuits, and Floquet dynamics, we resolve a fundamental distinction between thermalization mechanisms: Hamiltonian thermalized states retain a persistent geometric imprint characterized by a significantly non-zero $\omega_1$, while this structure is completely erased in random quantum circuit and Floquet dynamics. Our work establishes multi-bipartition entanglement tomography as a versatile toolbox for the geometric structure of quantum information in many-body systems.
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Quantum Physics

Multifractal and Glassy Signatures of Non-Ergodic 2D Quantum Dynamics

Aleksey Lunkin, Nicole S. Ticea, Michael T. Solomon et al. (+296 more)

The fate of ergodicity and localization in disordered, interacting quantum systems in two spatial dimensions remains an outstanding open problem in non-equilibrium physics. Theoretical and numerical approaches are severely constrained by exponential Hilbert space growth. Here, we leverage the high data-acquisition rates of superconducting quantum processors to extensively sample Hilbert space configurations, effectively imaging the state as a wavefunction network (WFN). Tracking the bitstring return probability across varied disorder strengths, we find heavy-tailed distributions and power-law typical decay characteristic of glassy relaxation. Furthermore, the distribution of bitstring probabilities transitions from a Porter-Thomas form at low disorder to an eight-decade power law at stronger disorder. In the reconstructed configuration space, WFN connectivity is compatible with a random geometric network at low disorder and becomes scale-free at stronger disorder. Finally, a multifractal analysis based on the binary intrinsic dimension (BID) reveals a non-ergodic regime where the wavefunction support saturates to a finite fraction of the total Hilbert space. Together, these results rule out a direct ergodic-to-localized transition, pointing instead to an extended multifractal regime. By visualizing wavefunction dynamics directly in configuration space, this work complements traditional real-space studies, showing the potential of quantum processors to resolve long-standing questions in non-equilibrium physics.
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All authors Aleksey Lunkin, Nicole S. Ticea, Michael T. Solomon, Riccardo Andreoni, Shashwat Kumar, Connie Miao, Jaehong Choi, Mohammed Alghadeer, Ilya Drozdov, Dmitry Abanin, Amira Abbas, Rajeev Acharya, Laleh Beni, Georg Aigeldinger, Ross Alcaraz, Sayra Alcaraz, Markus Ansmann, Frank Arute, Kunal Arya, Walt Askew, Nikita Astrakhantsev, Juan Atalaya, Ryan Babbush, Brian Ballard, Joseph C. Bardin, Hector Bates, Andreas Bengtsson, Majid Karimi, Alexander Bilmes, Simon Bilodeau, Felix Borjans, Alexandre Bourassa, Jenna Bovaird, Dylan Bowers, Leon Brill, Peter Brooks, Michael Broughton, David A. Browne, Brett Buchea, Bob B. Buckley, Tim Burger, Brian Burkett, Nicholas Bushnell, Jamal Busnaina, Anthony Cabrera, Juan Campero, Hung-Shen Chang, Silas Chen, Zijun Chen, Ben Chiaro, Liang-Ying Chih, Agnetta Y. Cleland, Bryan Cochrane, Matt Cockrell, Josh Cogan, Paul Conner, Harold Cook, Rodrigo G. Cortiñas, William Courtney, Alexander L. Crook, Ben Curtin, Martin Damyanov, Sayan Das, Dripto M. Debroy, Sean Demura, Paul Donohoe, Andrew Dunsworth, Valerie Ehimhen, Alec Eickbusch, Aviv Moshe Elbag, Lior Ella, Mahmoud Elzouka, David Enriquez, Catherine Erickson, Lara Faoro, Vinicius S. Ferreira, Marcos Flores, Leslie Burgos, Sam Fontes, Ebrahim Forati, Jeremiah Ford, Brooks Foxen, Masaya Fukami, Alan Wing Fung, Lenny Fuste, Suhas Ganjam, Gonzalo Garcia, Christopher Garrick, Robert Gasca, Helge Gehring, Robert Geiger, William Giang, Dar Gilboa, James E. Goeders, Edward C. Gonzales, Raja Gosula, Stijn J. Graaf, Alejandro Dau, Dietrich Graumann, Joel Grebel, Alex Greene, Jonathan A. Gross, Jose Guerrero, Loïck Guevel, Tan Ha, Steve Habegger, Tanner Hadick, Ali Hadjikhani, Michael C. Hamilton, Monica Hansen, Matthew P. Harrigan, Sean D. Harrington, Jeanne Hartshorn, Stephen Heslin, Paula Heu, Oscar Higgott, Reno Hiltermann, Jeremy Hilton, Hsin-Yuan Huang, Mike Hucka, Christopher Hudspeth, Ashley Huff, William J. Huggins, Evan Jeffrey, Shaun Jevons, Zhang Jiang, Xiaoxuan Jin, Cody Jones, Chaitali Joshi, Pavol Juhas, Andreas Kabel, Dvir Kafri, Hui Kang, Kiseo Kang, Amir H. Karamlou, Ryan Kaufman, Kostyantyn Kechedzhi, Julian Kelly, Tanuj Khattar, Mostafa Khezri, Seon Kim, Paul V. Klimov, Can M. Knaut, Bryce Kobrin, Alexander N. Korotkov, Fedor Kostritsa, John Mark Kreikebaum, Ryuho Kudo, Ben Kueffler, Arun Kumar, Vladislav D. Kurilovich, Vitali Kutsko, Tiano Lange-Dei, Brandon W. Langley, Pavel Laptev, Kim-Ming Lau, Emma Leavell, Justin Ledford, Joonho Lee, Joy Lee, Kenny Lee, Brian J. Lester, Wendy Leung, Lily Li, Wing Yan Li, Ming Li, Alexander T. Lill, William P. Livingston, Matthew T. Lloyd, Laura Lorenzo, Erik Lucero, Daniel Lundahl, Aaron Lunt, Sid Madhuk, Aniket Maiti, Ashley Maloney, Salvatore Mandrà, Leigh S. Martin, Orion Martin, Eric Mascot, Paul Das, Dmitri Maslov, Melvin Mathews, Cameron Maxfield, Jarrod R. McClean, Matt McEwen, Seneca Meeks, Anthony Megrant, Kevin C. Miao, Zlatko K. Minev, Reza Molavi, Sebastian Molina, Shirin Montazeri, Charles Neill, Michael Newman, Anthony Nguyen, Murray Nguyen, Chia-Hung Ni, Murphy Yuezhen Niu, Logan Oas, William D. Oliver, Raymond Orosco, Kristoffer Ottosson, Alice Pagano, Agustin Paolo, Sherman Peek, David Peterson, Alex Pizzuto, Elias Portoles, Rebecca Potter, Orion Pritchard, Michael Qian, Chris Quintana, Ganesh Ramachandran, Arpit Ranadive, Matthew J. Reagor, Rachel Resnick, David M. Rhodes, Daniel Riley, Gabrielle Roberts, Roberto Rodriguez, Emma Ropes, Lucia B. Rose, Eliott Rosenberg, Emma Rosenfeld, Dario Rosenstock, Elizabeth Rossi, David A. Rower, Robert Salazar, Kannan Sankaragomathi, Murat Can Sarihan, Kevin J. Satzinger, Max Schaefer, Sebastian Schroeder, Henry F. Schurkus, Aria Shahingohar, Michael J. Shearn, Aaron Shorter, Vladimir Shvarts, Volodymyr Sivak, Spencer Small, W. Clarke Smith, David A. Sobel, Barrett Spells, Sofia Springer, George Sterling, Jordan Suchard, Aaron Szasz, Alexander Sztein, Madeline Taylor, Jothi Priyanka Thiruraman, Douglas Thor, Dogan Timucin, Eifu Tomita, Alfredo Torres, M. Mert Torunbalci, Hao Tran, Abeer Vaishnav, Justin Vargas, Sergey Vdovichev, Guifre Vidal, Benjamin Villalonga, Catherine Heidweiller, Meghan Voorhees, Steven Waltman, Jonathan Waltz, Shannon X. Wang, Brayden Ware, James D. Watson, Yonghua Wei, Travis Weidel, Theodore White, Kristi Wong, Bryan W. Woo, Christopher J. Wood, Maddy Woodson, Cheng Xing, Z. Jamie Yao, Ping Yeh, Bicheng Ying, Juhwan Yoo, Noureldin Yosri, Elliot Young, Grayson Young, Adam Zalcman, Ran Zhang, Yaxing Zhang, Ningfeng Zhu, Nicholas Zobrist, Zhenjie Zou, Sergio Boixo, Hartmut Neven, Vadim Smelyanskiy, Trond I. Andersen, Markus Heyl, Marcello Dalmonte, Pedram Roushan, Mikhail V. Feigelman, Lev B. Ioffe

Quantum Physics

Einstein-Podolsky-Rosen Steering in Three Coupled Harmonic Oscillators

Ayoub Ghaba, Radouan Hab Arrih, Elhoussine Atmani et al. (+1 more)

Quantum steering is one of the most intriguing phenomena in quantum mechanics and is essential for understanding correlations in multi-body systems. Despite its importance, analytical results for coupled three-body oscillators remain scarce. In this work, we investigate this phenomenon through a geometrical diagonalization approach, which reduces the degrees of freedom associated with the system's steering properties. Specifically, we derive analytical expressions for quantum steering in all possible directions using the Wigner function framework, as it provides a complete description of the system's quantum state. Our results indicate that excitations significantly enhance quantum steering across the system; this stands in contrast to the ground state $(0,0,0)$, which exhibits no steerable correlations. Furthermore, both the directionality and topology of these correlations are governed by the spatial distribution of the excitations rather than their magnitude. We also observe symmetric steering behavior between oscillators $x$, $y$, and $z$ under equivalent excitation conditions, which can be formalized as $S^{(n,m,l)}_{x\to z}(\theta)=S^{(n,m,l)}_{x\to y}(-\theta),\quad S^{(n,m,l)}_{z\to x}(\theta)=S^{(n,m,l)}_{y\to x}(-\theta)$, and $S^{(n,m,l)}_{y\to z}(\theta)=S^{(n,m,l)}_{z\to y}(-\theta)$. Therefore, we elucidate how excitation levels and mixing angles generate and enhance steering in three coupled harmonic oscillators.
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All authors Ayoub Ghaba, Radouan Hab Arrih, Elhoussine Atmani, Abdallah Slaoui

Saturday 3 January

Quantum Physics · Cross-listed from cs.AI

Comment on arXiv:2511.21731v1: Identifying Quantum Structure in AI Language: Evidence for Evolutionary Convergence of Human and Artificial Cognition

Krzysztof Sienicki

This note is a friendly technical check of arXiv:2511.21731v1. I highlight a few places where the manuscript's interpretation of (i) the reported CHSH/Bell-type calculations and (ii) Bose–Einstein (BE) fits to rank-frequency data seems to go beyond what the stated procedures can firmly support. I also point out one internal inconsistency in the "energy-level spacing" analogy. The aim is constructive: to keep the interesting empirical observations, while making clear what they do (and do not) imply about quantum entanglement in the usual Hilbert-space sense, especially when "energy" is defined by rank.
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Quantum Physics

How Alice, long before her time, derived the principles of quantum mechanics

Marcello Poletti

This philosophical dialogue explores the idea that the foundational principles of quantum mechanics need not be interpreted as describing a new physics, but may instead arise from the logical necessity of formalising the act of measurement within a coherent algebraic framework. By pushing this perspective to its extreme, the dialogue argues that the core structures of quantum mechanics can be derived independently of any specifically quantum properties of atomic particles, and can be formulated within an otherwise classical theory once limitations of observability and measurement context are taken seriously.
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Quantum Physics

Minimal length: A source of quantum non-locality

H. Moradpour and S. Jalalzadeh

The narrow and subtle difference between the Hilbert spaces of operators corresponding to the canonical momentum and the generalized momentum that includes minimal length effects is polished. Consequently, complex eigenvalues may be allowed for the canonical momentum operator due to the existence of minimal length. A novel quantum entanglement generation is also reported indicating the power of theories including a minimal length in enriching the current understanding of quantum non-locality.
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Quantum Physics

Assessing the entanglement of three coupled harmonic oscillators

Ayoub Ghaba, Radouan Hab Arrih, Elhoussine Atmani et al. (+2 more)

Quantum entanglement serves as a key phenomenon in understanding correlations in many-body systems, but analytical results remain scarce for coupled three-body oscillators. In this work, we address this gap by introducing a geometrical diagonalization approach that constrains Euler angles, thereby reducing the degrees of freedom in the entanglement analysis. It consists of deriving analytical expressions for linear entropy and purity under the bipartitions $(x|yz)$, $(y|xz)$, and $(xy|z)$ using the Wigner function framework. Our results indicate that excitations in any oscillator basically enhance the redistribution of correlations across the system. The mixing angle $\theta$ governs entanglement intensity, ranging from separability to maximal correlation. Moreover, we reveal the symmetry relations, notably $S_{Ly}[(n,m,l),\theta]=S_{Lz}[(n,m,l),-\theta]$ and an intrinsic symmetry within $(x|yz)$. Hence, we clarify how excitation levels and mixing angles create and enhance entanglement in the three coupled harmonic oscillators.
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All authors Ayoub Ghaba, Radouan Hab Arrih, Elhoussine Atmani, Abderrahim El Allati, Abdallah Slaoui

Quantum Physics

Thermodynamic analysis of autonomous quantum systems

Tiago F. F. Santos and Camille Latune

Traditional quantum thermodynamic frameworks associate work to energy exchanges induced by unitary transformations generated by external controls, and heat to energy exchanges induced by bath interaction. Recently, a framework was introduced aiming at extending the thermodynamic formalism to genuine quantum settings, also referred to as autonomous quantum systems: free from external controls, only quantum systems interacting with each other. In this paper, we apply such a thermodynamic framework to common experimental situations of interacting quantum systems. In situations where traditional frameworks detect only heat exchanges, the recent autonomous thermodynamic framework points at work exchanges based on two mechanisms: population inversion and coherence generation / consumption. Such mechanisms are well known in the literature for being related to work expenditure and extraction, in particular in relation with ergotropy, which emphasizes the relevance of the autonomous framework and the limitations of traditional ones. Furthermore, the autonomous framework also identifies a genuine non-unitary mechanism of work exchange related to athermality. %, also pointed out as a resource for work extraction. Finally, in the semi-classical limit, the autonomous framework identifies all energy exchanges as pure work, but distinguishes between local work and interaction energy. Our results show that the autonomous framework provides a refined analysis of work exchange mechanisms in the quantum realm and serves as a consistent approach to analyze thermodynamic processes in realistic quantum devices.
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Quantum Physics

Simulating Wigner Localisation with the IBM Heron 2 Quantum Processor: A Proof-of-Principle Benchmarking Study

Airat Kiiamov and Dmitrii Tayurskii

We report on a high-fidelity digital quantum simulation of Wigner localisation in a quasi-one-dimensional (quasi-1D) electron system using a 6-qubit segment of the state-of-the-art IBM\,Heron\,2 quantum processor. By mapping the Coulomb interaction Hamiltonian onto a 6-qubit ring lattice, we reconstruct the ground-state energy landscape for a 2-electron Wigner dimer across fifteen interaction regimes in the range $U \in [5, 75]$. This study serves as a rigorous benchmarking exercise, translating foundational experimental models originally developed for electrons on liquid helium into the domain of modern quantum computing. Leveraging the enhanced gate fidelity and tunable coupler architecture of the Heron 2, we demonstrate that the digital simulation accurately captures the energy minimisation trends associated with Wigner dimer formation, achieving a relative error below 7% in the strong-interaction limit. Our results provide a crucial proof-of-principle validation for using superconducting quantum hardware to probe strongly correlated phases of matter with high precision, establishing a baseline for future simulations beyond the classical limit.
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