Quantum Physics · Cross-listed from cond-mat.quant-gas
An efficient preconditioned conjugate-gradient solver for a two-component dipolar Bose-Einstein condensate
Weijing Bao, Zhenhao Wang, Jia-Rui Luo et al. (+1 more)
We develop a preconditioned nonlinear conjugate-gradient solver for ground states of binary dipolar Bose-Einstein condensates within the extended Gross-Pitaevskii equation including Lee-Huang-Yang corrections. The optimization is carried out on the product-of-spheres normalization
manifold and combines a
manifold-preserving analytic line search, derived from a second-order energy expansion and validated along the exact normalized path, with complementary
Fourier-space kinetic and real-space diagonal (Hessian-inspired) preconditioners. The method enforces monotonic energy descent and exhibits robust convergence across droplet, stripe, and supersolid regimes while retaining spectrally accurate discretizations and FFT-based evaluation of the dipolar term. In head-to-head
benchmarks against imaginary-time
evolution on matched grids and tolerances, the solver reduces iteration counts by one to two orders of magnitude and overall time-to-solution, and it typically attains slightly lower energies, indicating improved resilience to metastability. We reproduce representative textures and droplet-stability windows reported for dipolar mixtures. These results establish a reliable and efficient tool for large-scale parameter scans and phase-boundary mapping, and for quantitatively linking numerically obtained metastable branches to experimentally accessible states.
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All authors Weijing Bao, Zhenhao Wang, Jia-Rui Luo, Kui-Tian Xi
Quantum Physics
Quantum-Resistant Networks Using Post-Quantum Cryptography
Xin Jin, Nitish Kumar Chandra, Mohadeseh Azari et al. (+2 more)
Quantum networks rely on both
quantum and classical channels for coordinated operation. Current architectures employ
entanglement distribution and key exchange over
quantum channels but often assume that classical communication is sufficiently secure. In practice, classical channels protected by traditional cryptography remain vulnerable to
quantum adversaries, since large-scale
quantum computers could break widely used public-key schemes and reduce the effective security of symmetric cryptography. This perspective presents a
quantum-resistant network architecture that secures classical communication with post-
quantum cryptographic techniques while supporting
entanglement-based communication over
quantum channels. Beyond cryptographic protection, the framework incorporates continuous monitoring of both
quantum and classical layers, together with orchestration across heterogeneous infrastructures, to ensure end-to-end security. Collectively, these mechanisms provide a pathway toward scalable, robust, and secure
quantum networks that remain dependable against both classical and
quantum-era threats.
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All authors Xin Jin, Nitish Kumar Chandra, Mohadeseh Azari, Kaushik P. Seshadreesan, Junyu Liu
Quantum Physics · Cross-listed from physics.space-ph
LEVITAS: Levitodynamics for Accurate Individual Particle Sensing in Space
Rafal Gajewski, Ravindra T Desai, James Bateman et al. (+3 more)
Accurately observing the rarefied media of the upper atmosphere, exosphere, and planetary and
solar system environments and beyond requires highly sensitive metrological techniques. We present the operating concept and architecture of an in-situ sensing solution based on the dynamics of a levitated nanoparticle (levitodynamics). It can detect and measure impacts of individual particles in rarefied media. Dubbed `LEVITAS', our sensor consists of a dispenser of dielectric nanoparticles and optical trapping of a single nanoparticle in the focus of a
laser beam. The trapped nanoparticle constitutes a harmonic oscillator at frequencies in the kilohertz range whose position can be tracked at the standard
quantum limit by interferometric detection of the
laser photons it scatters. Here, we simulate microcanonical impacts on the nanoparticle and show that the density, velocity, temperature, and composition of the surrounding medium can be estimated accurately. We illustrate the performance of LEVITAS in circumstances ranging from low Earth orbit out to exospheric distances, across which individual impacts can be detected at favourable rates. Furthermore, LEVITAS may be employed to accurately measure highly rarefied neutral distributions within vastly different areas of momentum space. This we demonstrate by simulating the measurement of high-velocity neutral gas particles from the interstellar medium penetrating the heliosphere and flowing through our
solar system.
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All authors Rafal Gajewski, Ravindra T Desai, James Bateman, Bengt Eliasson, Daniel K L Oi, Animesh Datta
Quantum Physics
Carlos Flores-Garrigos, Gaurav Dev, Michael Falkenthal et al. (+5 more)
We design and implement a
quantum combinatorial
reasoning framework for large
language models (QCR-LLM), integrating a real
quantum computer in the hybrid workflow. QCR-LLM reformulates
reasoning aggregation as a higher-order unconstrained binary optimization (HUBO) problem. In this sense,
reasoning fragments are represented as binary variables and their interactions encode statistical relevance, logical coherence, and semantic redundancy. We tackle the resulting high-order optimization problem both classically, via simulated annealing, and quantumly through the bias-field digitized counterdiabatic
quantum optimizer (BF-DCQO) executed on IBM's superconducting digital
quantum processors. Experiments on BIG-Bench Extra Hard (BBEH)
benchmarks demonstrate that our QCR-LLM consistently improves
reasoning accuracy across multiple LLM backbones, surpassing
reasoning-native systems such as o3-high and DeepSeek R1 by up to $+9\,$pp. Despite requiring multiple
reasoning samples per query, our QCR-LLM remains approximately five times more energy-efficient than o3-high, owing to the low per-
token energy footprint of its GPT-4o backbone. These results constitute the first experimental evidence of
quantum-assisted
reasoning, showing that hybrid
quantum-classical optimization can efficiently enhance
reasoning coherence, interpretability, and sustainability in large-scale
language models. We have opened the doors to the emergence of
quantum intelligence, where harder
prompts require
quantum optimizers at
quantum-advantage level.
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All authors Carlos Flores-Garrigos, Gaurav Dev, Michael Falkenthal, Alejandro Gomez Cadavid, Anton Simen, Shubham Kumar, Enrique Solano, Narendra N. Hegade
Quantum Physics · Cross-listed from hep-th
From Quantum Relative Entropy to the Semiclassical Einstein Equations
Philipp Dorau and Albert Much
We provide arguments indicating that the semiclassical Einstein equations follow from
quantum relative
entropy and its proportionality to an area variation. Using modular theory, we establish that the relative
entropy between the
vacuum state and coherent excitations of a scalar
quantum field on a bifurcate Killing horizon is given by the energy flux across the horizon. Under the assumption of the Bekenstein-Hawking
entropy-area formula, this energy flux is proportional to a variation in the surface area of the horizon cross section. The semiclassical Einstein equations follow automatically from this identification. Our approach provides a
quantum field theoretic generalization of Jacobson's thermodynamic derivation of the Einstein equations, replacing classical thermodynamic
entropy with the well-defined
quantum relative (Araki-Uhlmann)
entropy. This suggests that
quantum information plays a central role in what is often seen as a zeroth order approximation of a theory of
quantum gravity, namely
quantum field theory in curved spacetimes.
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Quantum Physics
Comparing physical quantities with finite-precision: beyond standard metrology and an illustration for cooling in quantum processes
Anindita Sarkar, Paranjoy Chaki, Priya Ghosh et al. (+1 more)
We propose a general framework to compare the values of a physical quantity pertaining to two - or more - physical setups, in the finite-precision scenario. Such a situation requires us to compare between two "patches" on the real line instead of two numbers. Identification of extent of the patches is typically done via standard deviation, as obtained within usual
quantum metrological considerations, but can not be always applied, especially for asymmetric error distributions. The extent can however be universally determined by utilizing the concept of percentiles of the probability distribution of the corresponding
estimator. As an application, we introduce the concept of finite-precision cooling in a generic
quantum system. We use this approach in the working of a three-
qubit quantum refrigerator governed by Markovian dynamics, and demonstrate the occurrence of cooling within finite precision for both transient and steady-state regimes, across strong- and weak-coupling limits of the inter-
qubit interaction.
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All authors Anindita Sarkar, Paranjoy Chaki, Priya Ghosh, Ujjwal Sen
Quantum Physics
Fundamental limit on the heralded single photons' spectral brightness
Tse-Yu Lin, Wei-Kai Huang, Pei-Yu Tu et al. (+2 more)
Heralded single
photons (HSPs) are the versatile flying
qubits in
quantum communication and networks due to their ability to remove the randomness of arrival time and enhance the transmission reliability. As the generation rate of HSPs increases or their linewidth narrows, both of which are desirable for
quantum information processing, the fundamental limit of spectral brightness (SB), defined as the generation rate per unit linewidth, remains unclear. To examine the existence and value of such a limit, we systematically studied the SB together with the cross-correlation function, or equivalently, the signal-to-background ratio (SBR). We ultimately derive an upper bound on SB that applies universally to all types of HSP sources. A newly defined quantity governs this limit, the quality factor, which is the product of SBR and effective SB. The quality factor indicates how closely an HSP source approaches an ideal noise-free source. Furthermore, by employing an HSP source based on hot atomic vapor, we achieved an SB of $(8.5\pm0.3)$$\times$$10^5$ pairs/s/MHz and a quality factor of $0.73\pm0.02$ under the single-
photon criterion. Both values represent the highest reported performance to date among all HSP platforms. These results provide a unified
benchmark for evaluating and optimizing HSP sources.
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All authors Tse-Yu Lin, Wei-Kai Huang, Pei-Yu Tu, Yong-Fan Chen, Ite A. Yu
Quantum Physics · Cross-listed from cond-mat.other
Strong quantum interaction between excitons bound by cavity photon exchange
Miguel S. Oliveira and Cristiano Ciuti
We theoretically predict the interaction between polaritonic excitations arising from the coupling of a cavity
photon mode with bound to continuum intersubband transitions in a doped
quantum well. The resulting
exciton bound by
photon exchange, recently demonstrated experimentally, exhibits a binding energy that can be continuously tuned by varying the cavity frequency. We show that polariton-polariton interactions, originating from both Coulomb interactions and Pauli blocking, can be dramatically enhanced by reducing the
exciton binding energy, thereby increasing the effective Bohr radius along the growth direction. This regime is reminiscent of Rydberg atoms, where weak binding leads to strong
quantum interactions. Our predictions indicate that this physics can give rise to
giant quantum optical nonlinearities in the mid and far infrared, a spectral region that remains largely unexplored in
quantum optics and offers exciting opportunities for both fundamental studies and applications.
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Quantum Physics · Cross-listed from cond-mat.quant-gas
Thermal effects on density-modulated phases in a dipolar Bose–Einstein condensate
Changjian Yu, Jinbin Li and Kui-Tian Xi
Density-modulated phases in dipolar Bose–Einstein condensates arise from the competition between contact repulsion, long-range dipole–dipole interactions, and beyond-mean-field fluctuations. We examine finite-temperature stationary states of a harmonically trapped dipolar Bose gas using a temperature-dependent extended Gross–Pitaevskii equation within the local-density approximation. In this framework, the thermal correction shifts some structural boundaries toward larger scattering lengths and changes the parameter region in which connected density-modulated states are obtained. The density contrast changes sharply at $T = 0$, whereas at finite temperature it varies more gradually, consistent with a smooth crossover-like
evolution in the finite trapped system. We also use Leggett's bound to estimate a
geometric upper limit on the possible superfluid response for representative density profiles. These results suggest that finite-temperature corrections can reshape pattern formation in dipolar
quantum gases.
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Quantum Physics · Cross-listed from math-ph
A Remarkable Application of Zassenhaus Formula to Strongly Correlated Electron Systems
Louis Jourdan and Patrick Cassam-Chenaï
We show that the Zassenhaus decomposition for the exponential of the sum of two non-commuting operators, simplifies drastically when these operators satisfy a simple condition, called the no-mixed adjoint property. An important application to a
Unitary Coupled Cluster method for strongly correlated electron systems is presented. This ansatz requires no Trotterization and is exact on a
quantum computer with a finite number of Givens gate equals to the number of free parameters. The formulas obtained in this work also shed light on why and when optimization after Trotterization gives exact solutions in disentangled forms of
unitary coupled cluster.
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Quantum Physics
Tight Generalization Bound for Supervised Quantum Machine Learning
Xin Wang and Rebing Wu
We derive a tight generalization bound for
quantum machine learning that is applicable to a wide range of supervised tasks, data, and models. Our bound is both efficiently computable and free of big-O notation. Furthermore, we point out that previous bounds relying on big-O notation may provide misleading suggestions regarding the generalization error. Our generalization bound demonstrates that for
quantum machine learning models of arbitrary size and depth, the sample size is the most dominant factor governing the generalization error. Additionally, the spectral norm of the measurement observable, the bound and Lipschitz constant of the selected risk function also influence the generalization upper bound. However, the number of
quantum gates, the number of
qubits, data encoding methods, and hyperparameters chosen during the learning process such as batch size, epochs, learning rate, and optimizer do not significantly impact the generalization capability of
quantum machine learning. We experimentally demonstrate the tightness of our generalization bound across classification and regression tasks. Furthermore, we show that our tight generalization upper bound holds even when labels are completely randomized. We thus bring clarity to the fundamental question of generalization in
quantum machine learning.
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Quantum Physics
Mind, Matter, and Freedom in Quantum Mechanics and the de Broglie-Bohm Theory
Valia Allori
There are several important philosophical problems to which
quantum mechanics is often said to have made significant contributions: - Determinism:
quantum theory has been taken to refute determinism; -Free Will: in turn, this is thought to open the door to free will; - The mind-body problem: relatedly, it is sometimes said to shed light on consciousness; - Idealism: more radically,
quantum theory is assumed to have refuted realism and to have placed the observer at the center of the world; - Reductionism: even granting realism, it has been claimed that
quantum theory undermines reductionism. Our main thesis in this paper is that none of this is either necessary or desirable. By adopting the de Broglie–Bohm theory (or Bohmian mechanics), one can straightforwardly account for
quantum phenomena without endorsing any of these claims.
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Quantum Physics · Cross-listed from nucl-th
Spin Teleportation via Bell-Triplet States Emergent from Proton-Proton Scattering
Z. X. Shen, H. Y. Shang, Y. G. Ma et al. (+5 more)
Entanglement is a key resource in
quantum information science, yet its properties and applications in
nuclear systems remain largely unexplored. Here, using
proton-
proton scattering as a
quantum laboratory, we report the emergence of a near-pure Bell-triplet state at a laboratory energy of 151 MeV and a center-of-mass scattering angle of 90 degrees. In this unique kinematic regime, the scattering amplitude functions as a transition operator connecting distinct Bell states. Building upon this emergent resource, we propose a
quantum teleportation protocol for
proton spins, exploiting the intrinsic
Hamiltonian of the strong interaction to perform the requisite Bell measurement effectively. These findings effectively bridge few-body
nuclear physics and
quantum technology, establishing
proton-
proton scattering as both a source of high-fidelity
entanglement and a natural processor for
quantum information.
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All authors Z. X. Shen, H. Y. Shang, Y. G. Ma, D. Bai, S. M. Wang, Z. C. Xu, Y. Ayyad, C. Filgueira
Quantum Physics
Optimizing Quantum Compilation via High-Level Quantum Instructions
Evandro C. R. Rosa, Jerusa Marchi, Eduardo I. Duzzioni et al. (+1 more)
Current
quantum programming is dominated by low-level,
circuit-centric approaches that limit the potential for compiler optimization. This work presents how a high-level programming construct provides compilers with the semantic information needed for advanced optimizations. We introduce a novel optimization that leverages a
quantum-specific instruction to automatically substitute
quantum gates with more efficient, approximate decompositions, a process that is transparent to the programmer and significantly reduces
quantum resource requirements. Furthermore, we show how this instruction guarantees the correct uncomputation of auxiliary
qubits, enabling safe, dynamic
quantum memory management. We illustrate these concepts by implementing a V-chain decomposition of the multi-controlled NOT gate, showing that our high-level approach not only simplifies the code but also enables the compiler to generate a
circuit with up to a 50% reduction in CNOT gates. Our results suggest that high-level abstractions are crucial for unlocking a new class of powerful compiler optimizations, paving the way for more efficient
quantum computation.
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All authors Evandro C. R. Rosa, Jerusa Marchi, Eduardo I. Duzzioni, Rafael de Santiago
Quantum Physics
Jacobi-Anger Density Estimation for Energy Distribution of Quantum States
Kyeongan Park, Gwonhak Lee, Minhyeok Kang et al. (+2 more)
The energy distribution of a
quantum state is essential for accurately estimating a molecule's ground state energy in
quantum computing. Directly obtaining this distribution requires full
Hamiltonian diagonalization, which is computationally prohibitive for large-scale systems. A more practical strategy is to approximate the distribution from a finite set of
Hamiltonian moments. However, reconstructing an accurate distribution from only a limited number of moments remains a significant challenge. In this work, we introduce Jacobi-Anger Density Estimation (JADE), a non-parametric,
quantum-inspired method designed to overcome this difficulty. JADE reconstructs the characteristic function from a finite set of moments using the Jacobi-Anger expansion and then estimates the underlying distribution via an inverse
Fourier transform. We demonstrate that JADE can accurately recover the energy distribution of a
quantum state for a molecular system. Beyond
quantum chemistry, we also show that JADE is broadly applicable to the estimation of complicated probability density functions in various other scientific and engineering fields. Our results highlight JADE as a powerful and versatile tool for practical
quantum systems, with the potential to significantly enhance ground state energy estimation and related applications.
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All authors Kyeongan Park, Gwonhak Lee, Minhyeok Kang, Youngjun Park, Joonsuk Huh
Quantum Physics · Cross-listed from cond-mat.mes-hall
Bounds on Lorentz-violating parameters in magnetically confined 2D systems: A phenomenological approach
Edilberto O. Silva
We present a unified, SI-consistent framework to constrain minimal SME coefficients $a_\mu$ and $b_\mu$ using magnetically confined two-dimensional electron systems under a uniform
magnetic field. Working in the nonrelativistic (Schrödinger–Pauli) limit with effective mass, we derive the radial problem for cylindrical geometries and identify how spatial components ($\mathbf a,\mathbf b$) reshape the effective potential, via $1/r$ and $r$ terms or
spin-selective offsets, while scalar components ($a_0,b_0$) act through a global energy shift and a
spin-momentum coupling. Phenomenological upper bounds follow from requiring LV-induced shifts to lie below typical spectroscopic resolutions: $|a_0|\lesssim\delta E$, $|b_z|\lesssim\delta E/\hbar$, and compact expressions for $|a_\varphi|$ and $|b_0|$ that expose their dependence on device scales ($r_0$, $B_0$, $\mu$, $m$). Dimensional analysis clarifies that, in this regime, spatial $a_i$ carry momentum dimension and $b_i$ carry inverse-time/length dimensions, ensuring gauge-independent, unit-consistent reporting. Finite-difference
eigenvalue calculations validate the scaling laws and illustrate spectral signatures across realistic parameter sets. The results show that scalar sectors (notably $a_0$) are tightly constrained by state-of-the-art $\mu$eV-resolution probes, while spatial and axial sectors benefit from
spin- and $m$-resolved spectroscopy and
geometric leverage, providing a reproducible pathway to test Lorentz
symmetry in condensed-matter platforms.
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Quantum Physics
Christof Wetterich
Wave guides for classical electromagnetic fields can realize the discrete
quantum evolution of the wave function for a system of
qubits. Phase shifts, switches and beam splits allow for the construction of arbitrary
quantum gates. They can act at once on a large number of
qubits. For this correlation based photonic
quantum computer the channels of the wave guides represent basis states of a multi-
qubit system rather than individual
qubits. With probabilistic initial conditions for a large number of channels the classical fields in wave guides realize the density
matrix for a probabilistic
quantum computer obeying the von Neumann equation.
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Quantum Physics
Equivalence of Discrete and Continuous Otto-Like Engines assisted by Catalysts: Mapping Catalytic Advantages from the Discrete to the Continuous Framework
Marcin Łobejko, Tanmoy Biswas and Michał Horodecki
The catalytic extension of a discrete two-stroke engine employs a cyclic auxiliary system - the catalyst - that remains decoupled from the baths and performs no work, yet enhances power and efficiency beyond the corresponding non-catalytic counterpart. Theoretical models of discrete engines are relatively easy to analyze but remain challenging for experimental implementation due to the required control over individual strokes. In contrast, externally driven engines that are simultaneously coupled to both heat baths - the so-called continuous engines - are more experimentally feasible. Here, we establish an equivalence between discrete and continuous machines, both with and without a catalyst, by mapping the discrete
unitary processes and thermalization steps onto an interaction
Hamiltonian and a Markovian model of dissipation. As a result, by replacing probability flows with probability currents, we construct an analogous continuous machine corresponding to previously demonstrated catalytic schemes that generalize Otto engines. We illustrate this mapping for the simplest catalytic extension of the Otto engine, demonstrating catalytic enhancement in the continuous regime.
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Quantum Physics
Pilot-Wave Simulator: Exact Classical Sampling from Ideal and Noisy Quantum Circuits up to Hundreds of Qubits
Gleb Kalachev, Pavel Mosharev, Zuoheng Zou et al. (+2 more)
Quantum circuit simulators running on classical computers offer a vital platform for designing, testing, and optimizing
quantum algorithms, driving innovation despite limited access to real
quantum hardware. However, their scalability is inherently constrained by exponential
memory and computational overhead, which restricts accurate simulation of large-scale
quantum circuits and often results in approximate output distributions. Here, we propose an exact sampling
algorithm that integrates tensor network contraction techniques with a Markov process, wherein a classical state evolves according to the local structure of the
quantum circuit. As a demonstration, we target the challenge of generating samples from ideal and noisy QAOA
circuits with up to 476
qubits, incorporating both depolarizing and amplitude damping noise models. These results enable further validation of several assumptions and
conjectures at a scale previously out of reach, significantly expanding the scope of classical simulation in
quantum algorithm research.
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All authors Gleb Kalachev, Pavel Mosharev, Zuoheng Zou, Pavel Panteleev, Man-Hong Yung
Quantum Physics
A Sub-kHz Mechanical Resonator Passively Cooled to 6 mK
Loek van Everdingen, Jaimy Plugge, Tim Fuchs et al. (+6 more)
Highly coherent mechanical resonators are invaluable to ultrasensitive detection techniques by enabling detection of small forces. Studying mechanical resonators in a thermal
equilibrium state at millikelvin temperatures provides a promising path to increase their coherence time. Here, we passively cool a 700 Hz massive (1.5 ng) mechanical cantilever down to 6.1(4) mK by means of
nuclear demagnetization, as confirmed by detecting its thermal motion via a lock-in based detection scheme. At the lowest temperatures the thermal motion of the resonator is still clearly distinguishable from the background noise. Our data analysis confirms that at these temperatures the motion is still thermally distributed. These results pave the way for passive cooling low-frequency resonators to the sub-millikelvin regime, which would enable new tests of
quantum mechanics and advances in ultrasensitive force detection.
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All authors Loek van Everdingen, Jaimy Plugge, Tim Fuchs, Guido van de Stolpe, Dalal Benali, Thijmen de Jong, Jasper Bijl, Wim Bosch, Tjerk Oosterkamp
Quantum Physics
An exact Error Threshold of Surface Code under Correlated Nearest-Neighbor Errors: A Statistical Mechanical Analysis
SiYing Wang, ZhiXin Xia, Yue Yan et al. (+1 more)
The surface code represents a promising candidate for fault-tolerant
quantum computation due to its high error threshold and experimental accessibility with nearest-neighbor interactions. However, current exact surface code threshold analyses are based on the assumption of independent and identically distributed (i.i.d.) errors. Though there are numerical studieds for threshold with correlated error, they are only the lower bond ranther than exact value, this offers potential for higher error thresholds.Here, we establish an error-edge map, which allows for the mapping of
quantum error correction to a square-octagonal random bond Ising model. We then present the exact threshold under a realistic noise model that combines independent single-
qubit errors with correlated errors between nearest-neighbor data
qubits. Our method is applicable for any ratio of nearest-neighbor correlated errors to i.i.d. errors. We investigate the error correction threshold of surface codes and we present analytical constraints giving exact value of error threshold. This means that our error threshold is both upper bound and achievable and hence on the one hand the existing numerical threshold values can all be improved to our threshold value, on the other hand, our threshold value is highest achievable value in principle.
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All authors SiYing Wang, ZhiXin Xia, Yue Yan, Xiang-Bin Wang
Quantum Physics
Experimental Demonstration of the Timelike Unruh Effect with a Trapped-Ion System
Zhenghao Luo, Yi Li, Xingyu Zhao et al. (+3 more)
The Unruh effect predicts that an accelerated observer perceives the Minkowski
vacuum as a thermal bath, but its direct observation requires extreme accelerations beyond current experimental reach. Foundational theory [Olson & Ralph, Phys. Rev. Lett. 106, 110404 (2011)] shows that an equivalent thermal response, known as the timelike Unruh effect, can occur for detectors following specific timelike trajectories without acceleration, enabling laboratory tests with stationary yet time-dependent detectors. Here, we report a proof-of-principle demonstration of the timelike Unruh effect in a
quantum system of trapped ion, where a two-level
spin serves as the detector and is temporally coupled to the ambient field encoded in the ion's vibrational motion. Specifically, we study both excitation and emission dynamics of the detector moving along a spacetime trajectory in the future/past light cone, and demonstrate the thermal response of the detector to the Minkowski
vacuum that resembles the Unruh effect. This work establishes a controllable tabletop platform for exploring relativistic
quantum physics under accessible laboratory conditions.
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All authors Zhenghao Luo, Yi Li, Xingyu Zhao, Zihan Xie, Zehua Tian, Yiheng Lin
Quantum Physics
Quantum advantage bounds for a multipartite Gaussian battery
F. Cavaliere, D. Ferraro, M. Carrega et al. (+2 more)
We demonstrate the possibility of a genuine
quantum advantage in the efficiency of
quantum batteries by analyzing a model that enables a consistent comparison between
quantum and classical regimes. Our system consists of $N$ harmonic oscillator
cells coupled to a common thermal reservoir, evolving through Gaussian states. We define the global efficiency as the ratio of extractable work (ergotropy) to stored energy, and derive analytical bounds that distinguish, in order of increasing efficiency, regimes characterized by classical squeezing,
quantum squeezing without
entanglement, and genuine
entanglement. Moreover, numerical simulations support the emergence of a similar hierarchy for the thermodynamic efficiency, defined as the ratio between ergotropy and the total thermodynamic cost of the charging process.
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All authors F. Cavaliere, D. Ferraro, M. Carrega, G. Benenti, M. Sassetti
Quantum Physics
Matrix product state approach to lossy boson sampling and noisy IQP sampling
Sojeong Park and Changhun Oh
Sampling problems have emerged as a central avenue for demonstrating
quantum advantage on noisy intermediate-scale
quantum devices. However, physical noise can fundamentally alter their computational complexity, often making them classically tractable. Motivated by the recent success of
matrix product state (MPS)-based classical simulation of Gaussian
boson sampling (Oh et al., 2024), we extend this framework to investigate the classical simulability of other noisy
quantum sampling models. We develop MPS-based classical
algorithms for lossy
boson sampling and noisy instantaneous
quantum polynomial-time (IQP) sampling, both of which retain the tunable accuracy characteristic of the MPS approach through the bond dimension. Our approach constructs pure-state decompositions of noisy or lossy input states whose components remain weakly entangled after
circuit evolution, thereby providing a means to systematically explore the boundary between
quantum-hard and classically-simulable regimes. For
boson sampling, we analyze single-
photon, Fock, and cat-state inputs, showing that classical simulability emerges at transmission rates scaling as $O(1/\sqrt{N})$, reaching the known boundary of
quantum advantage with a tunable and scalable method. Beyond reproducing previous thresholds, our
algorithm offers significantly improved control over the accuracy-efficiency trade-off. It further extends the applicability of MPS-based simulation to broader classes of noisy
quantum sampling models, including IQP
circuits.
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Quantum Physics
Quantum separability criteria from bipartite systems to multipartite systems based on generalized Bloch representation
Linwei Li, Chunlin Yang, Hongmei Yao et al. (+3 more)
Quantum entanglement serves as a fundamental resource in
quantum information theory. This paper presents a comprehensive framework of separability criteria for detecting bipartite and multipartite entanglements. We construct a novel parameterized extended correlation tensor via the generalized Bloch representation under an arbitrary orthogonal basis, which improves the performance of
entanglement detection. Moreover, we employ the generalized
matrix unfolding to generalize the extended correlation tensor construction to multipartite systems, obtaining separability criteria for multipartite
entanglement. Detailed examples demonstrate that our separability criteria exhibit enhanced capability in detecting
entanglement.
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All authors Linwei Li, Chunlin Yang, Hongmei Yao, Aimin Xu, Zhaobing Fan, Shao-Ming Fei
Quantum Physics
Dynamical system analysis of quantum tunneling in an asymmetric double-well potential
Swetamber Das and Arghya Dutta
We study
quantum tunneling in an asymmetric double-well potential using a dynamical systems–based approach rooted in the Ehrenfest formalism. In this framework, the time
evolution of a Gaussian wave packet is governed by a hierarchy of coupled equations linking lower- and higher-order position moments. An approximate closure scheme, required to render the system tractable, yields a reduced dynamical system for the mean and variance, with skewness explicitly entering due to the potential's asymmetry. Stability analysis of this system identifies energy thresholds for detectable tunneling across the barrier and reveals regimes where tunneling, though theoretically allowed, remains practically undetectable. Comparison with full numerical solutions of the time-dependent Schrödinger equation shows that, beyond reproducing key tunneling features, the dynamical systems approach provides an interpretable description of
quantum transport through tunneling in an effective asymmetric two-level system.
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Quantum Physics
Topological shaping of vortex neutron beams using forked phase gratings
S. McKay, S. R. Parnell, R. M. Dalgliesh et al. (+6 more)
Beams of light or matter that carry well-defined states of orbital angular momentum (OAM) are promising probes of topological and textured condensed matter systems such as
magnetic skyrmions. Using
spin-echo small-angle
neutron scattering (SESANS), we demonstrate the production of
vortex neutron beams from forked phase gratings of various topological charges. In contrast to some previous techniques used to verify OAM production, SESANS is a more precise measurement of the
neutron's OAM as it is a phase-sensitive, interferometric technique that directly measures the phase between the scattered
neutron spin states.
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All authors S. McKay, S. R. Parnell, R. M. Dalgliesh, N. V. Lavrik, I. I. Kravchenko, Q. Le Thien, D. V. Baxter, G. Ortiz, R. Pynn
Quantum Physics
Exploring the Fidelity of Flux Qubit Measurement in Different Bases via the Quantum Flux Parametron
Yanjun Ji, Susanna Kirchhoff and Frank K. Wilhelm
High-fidelity
qubit readout is a fundamental requirement for practical
quantum computing systems. In this work, we investigate methods to enhance the measurement fidelity of flux
qubits via a
quantum flux parametron-mediated readout scheme. Through theoretical modeling and numerical simulations, we analyze the impact of different measurement bases on fidelity in single-
qubit and coupled two-
qubit systems. For single-
qubit systems, we show that energy bases consistently outperform flux bases in achieving higher fidelity. In coupled two-
qubit systems, we explore two measurement models: sequential and simultaneous measurements, both aimed at reading out a single target
qubit. Our results indicate that the highest fidelity can be achieved either by performing sequential measurement in a dressed basis over a longer duration or by conducting simultaneous measurement in a bare basis over a shorter duration. Importantly, the sequential measurement model consistently yields more robust and higher fidelity readouts compared to the simultaneous approach. These findings quantify achievable fidelities and provide valuable guidance for optimizing measurement protocols in emerging
quantum computing architectures.
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Quantum Physics
Fock space prethermalization and time-crystalline order on a quantum processor
Zehang Bao, Zitian Zhu, Yang-Ren Liu et al. (+31 more)
Periodically driven
quantum many-body systems exhibit a wide variety of exotic nonequilibrium phenomena and provide a promising pathway for
quantum applications. A fundamental challenge for stabilizing and harnessing these highly entangled states of matter is system heating by energy absorption from the drive. Here, we propose and demonstrate a disorder-free mechanism, dubbed Fock space prethermalization (FSP), to suppress heating. This mechanism divides the Fock-space network into linearly many sparse sub-networks, thereby prolonging the thermalization timescale even for initial states at high energy densities. Using 72 superconducting
qubits, we observe an FSP-based time-crystalline order that persists over 120 cycles for generic initial Fock states. The underlying kinetic constraint of approximately conserved domain wall (DW) numbers is identified by measuring site-resolved correlators. Further, we perform finite-size scaling analysis for DW and Fock-space dynamics by varying system sizes, which reveals size-independent regimes for FSP-thermalization crossover and links the dynamical behaviors to the eigenstructure of the Floquet
unitary. Our work establishes FSP as a robust mechanism for breaking ergodicity, and paves the way for exploring novel nonequilibrium
quantum matter and its applications.
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All authors Zehang Bao, Zitian Zhu, Yang-Ren Liu, Zixuan Song, Feitong Jin, Xuhao Zhu, Yu Gao, Chuanyu Zhang, Ning Wang, Yiren Zou, Ziqi Tan, Aosai Zhang, Zhengyi Cui, Fanhao Shen, Jiarun Zhong, Yiyang He, Han Wang, Jia-Nan Yang, Yanzhe Wang, Jiayuan Shen, Gongyu Liu, Yihang Han, Yaozu Wu, Jinfeng Deng, Hang Dong, Pengfei Zhang, Hekang Li, Zhen Wang, Chao Song, Chen Cheng, Rubem Mondaini, Qiujiang Guo, Biao Huang, H. Wang
Quantum Physics · Cross-listed from physics.hist-ph
Algorithmic Randomness, Exchangeability, and the Principal Principle
Jeffrey A. Barrett and Eddy Keming Chen
We introduce a framework uniting algorithmic randomness with exchangeable credences to address foundational questions in philosophy of probability and philosophy of science. To demonstrate its power, we show how one might use the framework to derive the Principal Principle – the norm that rational credence should match known objective chance – without circularity. The derivation brings together de Finetti's exchangeability, Martin-Löf randomness, Lewis's and Skyrms's chance-credence norms, and statistical constraining laws (arXiv:2303.01411). Laws that constrain histories to algorithmically random sequences naturally pair with exchangeable credences encoding inductive
symmetries. Using the de Finetti representation
theorem, we show that this pairing directly entails the Principal Principle of this framework. We extend the proof to partial exchangeability and provide finite-history bounds that vanish in the infinite limit. The Principal Principle thus emerges as a mathematical consequence of the
alignment between nomological constraints and inductive learning. This reveals how algorithmic randomness and exchangeability can illuminate foundational questions about chance, frequency, and rational belief.
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