Quantum Physics
Fast Nondestructive Readout for High-Clock-Rate Atom Array Quantum Processor
Xu-Zhao-Qiu Zeng, Chang You, Qing-Wei Wang et al. (+18 more)
Neutral-atom arrays have rapidly advanced to support thousands of
qubits and execute high-fidelity logical operations. However, these processors remain severely throttled by their slowest fundamental operation: nondestructive
qubit measurement, which requires milliseconds and fundamentally limits the system's clock rate. This bottleneck arises from both an inherent
photon-budget dilemma—sufficient fluorescence for reliable state discrimination must be collected without excessive heating or loss—and frame-based imaging, which imposes one common exposure and decision latency on intrinsically independent, site-local measurements. Here, we overcome these limitations with a fast, nondestructive readout architecture based on real-time, site-resolved adaptive protection. By integrating continuous
photon counting with a dynamic feedforward framework, we decode
qubit states with sub-microsecond latency and instantly shield atoms from redundant scattering. Demonstrated in parallel across a 100-
qubit reconfigurable atom array, with adaptive protection on a 25-site subarray, this dynamic decision protocol reduces the average probe time to just $15\ \mu\text{s}$. Model-free benchmarking yields a discrimination infidelity of $4.1 \times 10^{-5}$ and an atom loss of $2.1 \times 10^{-4}$, simultaneously setting new performance records for atom arrays. Exploiting this capability, we operate repeated
quantum circuits at an unprecedented 1.7 kHz clock rate with atoms reused over 120 consecutive rounds—nearly sevenfold higher than the previous record—and enter the sub-millisecond cycle regime for the first time. By removing nondestructive readout as the dominant cycle-time bottleneck, this work unlocks high-clock-rate mid-
circuit syndrome extraction, paving the way for high-throughput, fault-tolerant
quantum computation.
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All authors Xu-Zhao-Qiu Zeng, Chang You, Qing-Wei Wang, Zi-Feng Li, Yi Ji, Dong An, Chao Yu, Jia-Rui Liu, Zi-Mo He, Jia-Rui Gu, Yuhao Mei, Hao-Wen Cheng, Yu-Chen Zhang, Rui Lin, Zhan Wu, Jun Rui, Jun Zhang, Ming-Cheng Chen, Yu-Hao Deng, Chao-Yang Lu, Jian-Wei Pan
Quantum Physics
Gate-level Implementation and Resource Analysis of Lackadaisical Quantum Walk Search
Amit Saha, Debanjan Kola, Nishanka Das et al. (+1 more)
Lackadaisical
quantum walks (LQW) extend discrete-time
quantum walks (DTQW) by introducing weighted self-loops, enabling improved spatial-search performance through controlled localization of the walker. Despite substantial theoretical progress, practical gate-level implementations suitable for
quantum hardware remain largely unexplored, limiting evaluation under realistic architectural constraints, noise, and resource requirements. In this work, we present a gate-level implementation framework for lackadaisical
quantum walk search. The proposed construction encodes the position and coin spaces into
qubit registers, and realizes the walk dynamics through oracle, coin, and flip-flop shift operations. We validate the
circuit by reproducing the expected search behavior for single and multiple marked vertices and by analyzing the effect of the self-loop weight on the success probability. We further evaluate the implementation under realistic noisy settings using superconducting hardware's noise models. Logical resource analysis shows that, for grids ranging from $8\times8$ to $64\times64$, the transpiled gate count increases from $3.63\times10^{5}$ to $4.38\times10^{6}$ and the
circuit depth from $2.13\times10^{5}$ to $2.56\times10^{6}$. Finally, fault-tolerant resource estimates based on a surface-code model using the Microsoft
Quantum Resource
Estimator demonstrate the substantial space-time trade-off associated with magic-state production. The results establish a practical
circuit-level pathway for implementing the LQW search and provide a basis for evaluating its performance.
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All authors Amit Saha, Debanjan Kola, Nishanka Das, Amlan Chakrabarti
Quantum Physics · Cross-listed from cs.LG
Iterative tensor network transformations for element-wise evaluation of elementary and filtering functions
Xiao Wang, Tomohiro Hashizume, Pia Siegl et al. (+1 more)
Tensor networks are powerful formats for compressing large-scale data. However, their application to general data processing has been limited by the difficulty of performing nonlinear operations. Here, we introduce iterative tensor network transformations (ITNTs), a general algorithmic framework for the element-wise evaluation of elementary and nonlinear filtering functions on data encoded as tensor trains (TTs), a class of tensor networks. Our approach operates entirely in the compressed domain, enabling efficient computation on exponentially large
datasets while maintaining a controlled computational cost. We demonstrate its power in two key areas: (I) evaluating highly nonlinear elementary and filtering functions on a 3D reactive flow field, enabling high-fidelity reaction rate computation and region filtering, and (II) finding extrema in complex optimization problems, such as solving Max-SAT instances on spaces up to $2^{70}$ configurations. These results establish ITNT as a foundational tool that provides tensor network methods with the capability for general-purpose data science and large-scale optimization.
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All authors Xiao Wang, Tomohiro Hashizume, Pia Siegl, Dieter Jaksch
Quantum Physics
Entanglement assisted quantum $(r,\delta)$-locally recoverable codes
Carlos Galindo, Fernando Hernando, Helena Martín-Cruz et al. (+1 more)
Quantum $(r,\delta)$-locally recoverable codes are
quantum error-correcting codes capable of correcting $\delta-1$ qudit erasures within one subset of qudits of cardinality at most $r+\delta-1$. In this paper, we introduce the more general framework of
entanglement-assisted
quantum $(r,\delta)$-locally recoverable codes, assuming that the local recovery operation is assisted by receiver-held qudits that remain unaffected by erasures. We establish necessary and sufficient conditions for these codes to satisfy this property. For codes derived from Hermitian or Euclidean constructions, we establish connections between
entanglement-assisted
quantum and classical notions of $(r,\delta)$-local recoverability, and derive a Singleton-like bound. Furthermore, we construct optimal pure entan\-gle\-ment-assisted
quantum $(r,\delta)$-locally recoverable codes from several families of classical codes, including bivariate $J$-affine variety codes, BCH codes, and homothetic-BCH codes.
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All authors Carlos Galindo, Fernando Hernando, Helena Martín-Cruz, Ryutaroh Matsumoto
Quantum Physics
Block Encoding Non-Abelian Lattice Gauge Theory
Patrick Draper
Gauge theories like
lattice QCD present a complex problem for
quantum simulation. In a basis where the electric part of the
Hamiltonian is simple, the
magnetic part, generally expressed as a sum over the plaquette operators of the
lattice, is quite complicated, producing correlated transitions between several link and site degrees of freedom. We provide an efficient block encoding of the plaquette operator in the irrep basis, a refinement of the electric basis where the internal gauge-variant degrees of freedom are integrated out. The construction removes the plaquette
matrix element scaling wall which has been a significant barrier for other approaches in this basis. The
algorithm leverages a convenient factorization property of the
matrix elements, cheap classical precomputation, and
quantum oracles built from lookup tables and programmed rotations.
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Quantum Physics
Hardness of approximation for minimum-weight decoding of two-dimensional topological quantum codes
Louay Bazzi and Georges Khater
Efficient decoding is essential for the practical realization of fault-tolerant
quantum computers. We study the computational complexity of minimum-weight decoding for topological
quantum codes. For surface codes under the depolarizing channel, we consider Minimum-Weight decoding, which seeks a minimum-weight Pauli error consistent with both the $X$- and $Z$-syndromes. For color codes under independent $X$- and $Z$-error models, we consider Separate Minimum-Weight decoding. Assuming $P\neq NP$, we establish
polynomial additive inapproximability gaps for these problems. Specifically, for the toric code and the $4.8.8$ color code on the
torus, there exists a constant $c>0$ such that no
polynomial-time
algorithm can always produce a solution whose weight is within $cN^{1/14}$ of the optimum, where $N$ is the number of
qubits, unless $P=NP$. For the planar surface code, we obtain an $\Omega(N^{1/18})$ gap. Our inapproximability results use Håstad's hardness of approximation for MAX-3SAT. Our reduction develops a general, modular framework for
embedding logical constraints into coupled primal–dual join problems on a
lattice. A key ingredient is a localization argument that controls unintended interactions between different parts of the construction.
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Quantum Physics
Lie-Algebraic Classical Simulation of Bosonic Systems Beyond Gaussian Dynamics
Adelina Bärligea, Timothy Heightman, Jakob S. Kottmann et al. (+1 more)
Classical simulability is ultimately determined by both the dynamics of a
quantum system and the observables being evaluated. Lie-algebraic simulation exploits the latter to make exact
polynomial-time classical simulations by propagating observables through low-dimensional invariant operator spaces. However, its conventional formulation in terms of
polynomial-dimensional dynamical Lie
algebras does not directly accommodate bosonic systems as their
algebras are neither compact nor semisimple. In this contribution, we overcome this limitation, making bosonic systems accessible to the Lie-algebraic programme of exact
polynomial-time classical simulation. We prove that expectation values, fixed-order correlation functions, including multi-time correlators and out-of-time-ordered correlators, and gradients are efficiently computable whenever their operator modules have
polynomial dimension. This recovers Gaussian
quantum optics and extends it to non-Gaussian input states, while identifying exact
polynomial regimes of interacting non-Gaussian dynamics including bounded-
photon Kerr and pair-hopping
Hamiltonians and nilpotent
polynomial phase dynamics. We show that unlike in the finite-dimensional
spin and fermionic setting treated previously, a finite-dimensional bosonic generator
algebra alone does not guarantee finite observable dynamics. We further derive a controlled perturbative hierarchy for squeezing beyond exact sector confinement and confirm the predicted error orders numerically. We also evaluate operator spreading on interacting chains of up to $400$ modes and connect a topological doublon band with flux-reversed edge motion. These results provide a unified formalism for classifying, discovering, and systematically approximating tractable bosonic
quantum dynamics with classical
polynomial-time simulation.
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All authors Adelina Bärligea, Timothy Heightman, Jakob S. Kottmann, Antonio Acín
Quantum Physics
Readout Orientation Controls Measurement-Accessible Quantum Tangent Geometry
Marwan Ait Haddou
A fixed
quantum measurement can expose substantially more tangent information than a restricted observable readout retains. We study this second restriction. For a normalized covariance $C \succeq 0$, $\mathrm{Tr} C = 1$, of measurement-induced tangent scores in an $N$-dimensional centered score space, and a rank-$r$ readout projector $P$, we quantify retained tangent mass by $R=\mathrm{Tr}(PC)$. The ratio $\rho=R/(r/N)$ separates the actual retained mass from a rank-only random-orientation reference. Standard Grassmann averaging gives $\mathbb{E}\rho=1$ and $\mathrm{Var}(\rho) \le 2/(r d_{\mathrm{eff}})$, where $d_{\mathrm{eff}}=1/\mathrm{Tr}(C^2)$. We use this identity as a null model rather than as a new random-projection
theorem. Numerically, family-balanced one- and two-body readouts remain close to the rank reference through $n=16$ even as the tangent covariance becomes strongly anisotropic. The decisive equal-rank comparison holds the
circuit, measurement record, readout rank, and evaluation shot budget fixed. For Haar-$U(4)$ at $n=12$, cross-fitted
alignment increases the mean directional gradient-energy proxy by a factor 9.584 and the finite-shot signal-to-noise ratio by a factor 3.111 relative to the physical one-body readout, while a random rank-matched subspace remains near the rank baseline. A half-filled $U(1)$-conserving family provides a structured counterexample to generic orientation: physical low-weight $Z$ readouts are already strongly aligned with leading tangent directions over the tested finite-size range. We treat this
symmetry result as a case study, not as a claim that $U(1)$
symmetry generically prevents barren plateaus or that hydrodynamics is the established mechanism. The results isolate readout orientation as a degree of freedom invisible to rank alone that directly controls how much measured tangent information remains usable after readout restriction.
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Quantum Physics
Aditya Kumar and Sumit Chongder
Federated deployments of variational
quantum classifiers are attractive for cross-organisation risk prediction in supply chains, because raw data never leaves the client, yet data-protection regulations such as the GDPR grant clients a right to request that their contribution be removed from a trained model after the fact. Retraining a
federated model from scratch to honour such a request is correct but wasteful, and it is not obvious which
quantum circuit parameters actually carry a given client's influence. We introduce
Entanglement-Weighted
Pruning (EWP), an unlearning procedure for
quantum federated learning that scores every trainable
circuit parameter with the product of two signals: the diagonal entry of the
quantum Fisher information
matrix estimated on the target client's data via the parameter-shift rule, and a structural
entanglement weight associated with the parameter's gate. Parameters with the lowest scores are pruned, optionally followed by a short fine-tuning pass on the retained clients. We implement the full pipeline in Qiskit for a four-
qubit data-re-uploading ansatz trained with FedAvg across five simulated supply-chain-risk clients, and
benchmark EWP against full retraining, fine-tuning alone, random
pruning, Fisher-only
pruning, and
entanglement-only
pruning, over three random seeds. EWP attains a mean post-unlearning accuracy statistically indistinguishable from the full-retraining oracle, while producing a lower forgetting score and requiring roughly 16 times less wall-clock time. Ablations over
pruning threshold, client count, and non-IID strength show that combining the two signals is necessary, as
entanglement-only and Fisher-only
pruning each substantially degrade accuracy relative to EWP.
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Quantum Physics
Exact Moments of Gaussian Gram Hafnians Reveal an $n^2/\log n$ Threshold for Weak Anticoncentration
Hongru Zhao
Anticoncentration is central to hardness arguments for approximate sampling. In the independent Gaussian surrogate for collision free Gaussian
boson sampling, the moment ratio studied here also determines the averaged ideal linear cross
entropy reference value. Let $H_{k,n}=\mathrm{haf}(X^{\mathsf T}X)$, where $X\in\mathbb{C}^{k\times 2n}$ has independent standard circular complex Gaussian entries. We evaluate $\mathbb{E}|H_{k,n}|^2$ and $\mathbb{E}|H_{k,n}|^4$ exactly by reducing four hafnian copies to a rank two Gaussian integral. For $R_{k,n}=(\mathbb{E}|H_{k,n}|^2)^2/\mathbb{E}|H_{k,n}|^4$, we obtain $R_{k,n}=4^{-n}\binom{2n}{n}/F_{k,n}$, where $F_{k,n}={}3F_2(-n,-n,1/2;1,k/2;1)$ is a terminating generalized hypergeometric
polynomial. If $k/n^2\to c>0$, then $F{k,n}\to e^{1/c}I_0(1/c)$, where $I_0$ is the modified Bessel function of the first kind of order zero, and consequently $R_{k,n}\sqrt{\pi n}\to[e^{1/c}I_0(1/c)]^{-1}$. Thus $k\asymp n^2$ is a smooth Bessel crossover, whereas the scaling order boundary for inverse
polynomial weak anticoncentration is $k\asymp n^2/\log n$. These conclusions concern the Gaussian surrogate moment criterion; finite dimensional Haar moment transfer and high probability small ball anticoncentration remain separate problems.
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Quantum Physics · Cross-listed from cond-mat.mes-hall
Local magnetic resonance of scalar spin chirality
Mar Ferri-Cortés and Joaquin Fernández-Rossier
Quantum states with finite scalar
spin chirality carry an orbital
magnetic moment that has eluded direct measurement. We show that a local drive breaks the cyclic
symmetry and activates chirality-changing transitions. We propose two complementary probes: direct chirality resonance and chirality-resolved
spin resonance. Lindblad simulations demonstrate their feasibility in locally addressable
spin platforms, including scanning tunneling microscopy, silicon donors, and
quantum dots.
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Quantum Physics
Eigenframe Synchronization in Disordered Driven Quantum Ensembles
Saipriya Satyajit, Zechuan Yin, Jner Tzern Oon et al. (+5 more)
Periodic driving underlies many forms of
quantum control, including
spin-based
quantum sensing. However, in an ensemble sensor, one waveform must act on
spins with different detunings, drive amplitudes, hyperfine environments, and local fields. Existing robust-control approaches to such disorder are usually framed in terms of coherence, effective
Hamiltonians, filter functions, or refocusing. Here we identify a complementary
geometric requirement for collective ensemble Floquet control: disorder realizations must share a common Floquet eigenframe. When this condition is met, initialization, protection, signal coupling, and readout are defined in one dressed basis, so the ensemble responds as a collective Floquet sensor rather than as an average over inequivalent driven members. We make this condition measurable with an eigenvector-based synchronization order parameter and a complementary fragmentation metric that quantify the
alignment and spread of Floquet quantization axes across the ensemble. As one realization of this framework, we use a continuous counterdiabatic Floquet drive to derive synchronization criteria and predict resonance-governed breakdown at the first two low-order commensurabilities between the engineered Floquet gap and the drive modulation, with detuning and amplitude disorder producing distinct breakdown channels. Experiments on a nitrogen-vacancy (NV) ensemble in diamond verify the synchronized regime through long-lived collective oscillations, a two-dimensional disorder-robustness map, and breakdown resonances that shift with the modulation rate. Finally, we demonstrate a harmonic-free continuous-drive AC magnetometry protocol whose collective single-tone response is enabled by the synchronized Floquet eigenframe. These results establish Floquet eigenframe synchronization as a measurable condition for disorder-resilient collective control and
quantum sensing.
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All authors Saipriya Satyajit, Zechuan Yin, Jner Tzern Oon, Katrijn Everaert, Smriti Bhalerao, John W. Blanchard, Christopher Jarzynski, Ronald L. Walsworth
Quantum Physics
Hardware-Aware Compilation and Execution of Bivariate Bicycle Codes on Neutral-Atom Systems
Jason Ludmir, Aditya Ranjan, Nicholas S. DiBrita et al. (+2 more)
Quantum computers are noisy; without
quantum error correction (QEC), deep programs fail as
qubits lose information due to decoherence. Among QEC approaches, bivariate bicycle (BB) codes offer low overhead and constant-depth syndrome extraction, while neutral-atom arrays provide scalable, reconfigurable
qubit layouts. However, executing BB-code primitives on neutral-atom systems requires a hardware-aware mapping that respects movement, zoning, and interaction constraints. We present Park-n-Ride, a system for compiling and executing the BB code on neutral-atom processors. Park-n-Ride introduces a module layout and movement model aligned with neutral-atom constraints, exposes a compact BB-native logical interface for compilation, and integrates scheduling mechanisms that enable efficient execution on zoned architectures. By co-designing BB-code abstractions with hardware execution, Park-n-Ride provides a practical path from qLDPC primitives to resource-efficient, high-throughput execution on reconfigurable neutral-atom arrays.
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All authors Jason Ludmir, Aditya Ranjan, Nicholas S. DiBrita, Jason Han, Tirthak Patel
Quantum Physics
Multi-purpose quantum laboratories from superconducting circuits
Arpit Arora, Emily M. Been, William Munizzi et al. (+4 more)
Superconducting
circuits (SCs) are the cornerstone of modern
quantum technology, enabling scalable computing through coherent control of macroscopic
quantum states. Through a legacy that predates modern
quantum computing, SCs have emerged as high-precision instruments for discovery. In this review, we highlight the role of SCs as general-purpose
quantum laboratories, outlining the emerging landscape of correlated matter-
circuit science. We review and unify the capabilities of superconducting
quantum hardware across condensed matter, high energy and
quantum information sciences. We trace the technical
evolution of these architectures, illustrating how their foundational development has culminated in a toolkit for resolving the complexities of macroscopic
quantum states.
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All authors Arpit Arora, Emily M. Been, William Munizzi, Joel Wang, Taylor L. Patti, Aaron Chou, Prineha Narang
Quantum Physics · Cross-listed from gr-qc
Astrophysical Graviton Squeezing Can Be Hidden in the Far-Field
Cheng-Jun Fang, Zong-Kuan Guo, Zhen-Hong Lyu et al. (+3 more)
While localized astrophysical sources can generate macroscopic graviton squeezing, their observable
quantum signatures at far-field detectors remain unresolved. In this work, we investigate the propagation dynamics of the squeezed states using spatial
quantum optics methods to evaluate correlation functions accessible to a local observer. Crucially, we reveal a severe kinematic conflict in same-cone measurements, which highly suppresses local
quantum coherence. Consequently, these macroscopically squeezed states appear classically thermal to a single detector. Our results demonstrate that global squeezing does not guarantee local observability, and the measurable
quantum signatures may be significantly weaker than what would be expected from the overall squeezing parameter of the state.
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All authors Cheng-Jun Fang, Zong-Kuan Guo, Zhen-Hong Lyu, Jing Shu, Yu-Heng Sun, Zi-Zheng Zhou
Quantum Physics
Sound and Efficient Certification of High-Quality Qubit Operations: Theory and Experiment
Nikolai Miklin, Jan Nöller, José Martínez et al. (+4 more)
Can a high-quality
quantum gate be certified when uncharacterized state-preparation and measurement errors are dominant? Can this be achieved with low experimental overhead? Here, we introduce a sound black-box certification protocol for a single-
qubit gate based on a small set of fixed, deterministic sequences. From the data, the protocol derives finite-sample bounds on the gate's rotation
eigenvalue, a gauge-invariant property. Its phase reveals the accuracy of the rotation angle, while its modulus quantifies the loss of coherence under repeated gate applications. We implement the protocol on a $^{40}\mathrm{Ca}^{+}$ trapped-ion processor and certify the $\sqrt{\mathrm{X}}$-gate rotation
eigenvalue using $22\,000$
circuit executions, and demonstrate the robustness of certification to state-preparation and measurement errors by deliberately degrading the readout. Finally, we prove that these spectral constraints imply, up to a physically meaningful
unitary change of basis, a rigorous average gate-fidelity lower bound for every time-independent
qubit model compatible with the data. In both readout settings, the spectral bounds yield the same fidelity certificate of $99.94(3)\%$ with $99\%$ confidence. Our results establish a new standard for
quantum-gate certification by combining soundness and experimental efficiency without requiring trusted reference operations, randomized
circuits, or model fitting.
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All authors Nikolai Miklin, Jan Nöller, José Martínez, Lucas B. Vieira, Ulrich Poschinger, Ferdinand Schmidt-Kaler, Mariami Gachechiladze
Quantum Physics
Andrew C. Yuan and Nouédyn Baspin
We generalize the unified framework in [Phys. Rev. A 113, 022438 (2026)] to accommodate arbitrary stabilizer codes (referred as non-CSS for emphasis). The generalization has immediate consequences in areas including logical measurement,
quantum weight reduction and Euclidean
embedding. For example, currently CSS (pure $X,Z$-type) logical measurements are well-understood based on the (height-1) cone, while non-CSS (e.g., $Y$-type) logical measurements are ad hoc (e.g., rely on local Clifford transform). Similarly,
quantum weight reduction and optimal Euclidean
embeddings only exist for CSS input codes. Here, we show that our generalized framework addresses this issue, and thus many constructions, including qLDPC surgery, Layer Codes and
quantum weight reduction generalize to non-CSS codes in a relatively straightforward fashion. The previously mentioned examples are derived in detail for clarity.
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Quantum Physics
Basis-update and Galerkin time integration in canonical matrix-product-state form
Maximilian Fröhlich, Richard M. Milbradt, Martin Eigel et al. (+3 more)
Matrix product state
algorithms must enlarge their bond spaces as
entanglement grows and compress them to control cost. We formulate basis-update and Galerkin (BUG) time integration as a sequence of canonical MPS sweeps for
Hamiltonians represented as
matrix product operators. We show when two natural basis updates produce the same trial space and when transporting coefficients between successive bases preserves the represented state. Under these conditions, the existing first-order error bound for uncompressed tree-tensor-network BUG also applies to the alternating-endpoint MPS schedule. We verify the uncompressed implementation against an independent six-site calculation. We then compare BUG with two-site TDVP for 16-site transverse-field Ising and Haldane-Shastry dynamics. At matched timestep and truncation settings, BUG performs fewer local exponential actions and has lower runtime. These settings do not produce equal accuracy. The runtime versus accuracy curves cross for the Ising model and are close for the Haldane-Shastry model. The comparison therefore identifies model-dependent trade-offs rather than a general advantage for either method.
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All authors Maximilian Fröhlich, Richard M. Milbradt, Martin Eigel, Aaron Sander, Robert Wille, Christian B. Mendl
Quantum Physics · Cross-listed from cond-mat.quant-gas
Hydrodynamization in 1D Bose gases at nonzero temperature
Jeff Leiberton and Marcos Rigol
Hydrodynamization refers to the remarkably rapid process in relativistic heavy-ion collisions by which hydrodynamic descriptions become applicable. Following the observation of analogous behavior in ultracold one-dimensional (1D) Bose gases, hydrodynamization has been conjectured to be a universal dynamical phenomenon in
quantum systems following high-energy quenches. Theoretical studies in this cold-atom setting have so far been restricted to quenches from ground states. Here we study how nonzero temperatures affect hydrodynamization. Specifically, using a homogeneous 1D gas of hard-core
bosons, we explore how the initial temperature affects the timescales associated with hydrodynamization and prethermalization following a Bragg-pulse quench. We find that while the hydrodynamization coherence time remains unchanged, increasing temperature shortens both the damping time of the hydrodynamization oscillations and the prethermalization time. We argue that this is mainly the result of the broadening of the initial rapidity distribution, and introduce a nonzero-temperature dephasing time defined in terms of the extent of the rapidity distribution.
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Quantum Physics · Cross-listed from cs.CC
Classical Adversarial Fault-Tolerance and PCPs
Anurag Anshu, Nikolas P. Breuckmann, Louis Golowich et al. (+2 more)
We show how to compile an arbitrary classical
circuit into a fault-tolerant
circuit, which performs the desired computation even when an almost-linear number of bits are adversarially chosen and corrupted in each timestep. Using a variant of this fault-tolerance scheme that only detects (rather than corrects) corruptions, we give a new construction of probabilistically checkable proofs (PCPs) for NP with polylogarithmic query complexity. This PCP construction from fault-tolerance presents a promising candidate for quantization by the work of Anshu, Breuckmann, and Nguyen (STOC'24), who provided a roadmap for constructing
quantum PCPs via fault-tolerance.
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All authors Anurag Anshu, Nikolas P. Breuckmann, Louis Golowich, Quynh T. Nguyen, Umesh Vazirani
Quantum Physics
Fault-Tolerant Quantum Computation with Adversarial Errors
Nikolas P. Breuckmann, Louis Golowich and Umesh Vazirani
We prove a fault-tolerance
theorem for
quantum computation against
adversarial noise. For every
quantum circuit on $\bar{N}$ logical qudits of depth $\bar{T}$, we construct a fault-tolerant
circuit on $N=\text{poly}(\bar{N})$ physical qudits of depth $\bar{T}\cdot\bar{N}^{o(1)}$, which is robust against an adversary who may arbitrarily choose and corrupt an almost-linear number $N^{1-o(1)}$ of physical qudits at each time step. This robustness significantly improves upon prior fault-tolerance
theorems, which assumed corruptions were either local and
stochastic, or else only act on a polynomially vanishing fraction of qudits. Our fault-tolerance scheme addresses a key bottleneck towards constructing
quantum PCPs via the
circuit-to-
Hamiltonian mapping of Anshu, Breuckmann, and Nguyen (STOC'24). More fundamentally, our result demonstrates that fault-tolerant
quantum computation remains possible under noise models that are global, worst-case, and non-Markovian over the full duration of the computation, directly countering concerns that correlated noise could fundamentally undermine
quantum fault tolerance. Our construction is based on a new family of subsystem product codes we develop, which have large dimension and distance along with low-weight parity-checks, and which support transversal non-Clifford gates. We show how to perform single-shot fault-tolerant error correction on these codes using a Floquet-like procedure based on the local testability of classical tensor codes. We then obtain a universal fault-tolerance scheme using repeated code switching in a hypercubic qudit architecture. Finally, we recursively compose our scheme with itself to reduce an initially exponential qudit dimension down to a constant.
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Quantum Physics · Cross-listed from cond-mat.dis-nn
Spectral Edge Rigidity of Quantum Chaotic States
Joaquim Telles de Miranda and Tobias Micklitz
We determine the distribution of fidelity susceptibility for chaotic eigenstates at the spectral edge of Gaussian random-
matrix ensembles. Previous work showed that, in the
unitary class, the characteristic susceptibility scale of edge states grows as $D^{1/3}$, rather than proportionally to $D$ as in the spectral bulk, reflecting Airy-edge level
rigidity. Extending a determinant-based framework introduced for bulk states, we derive the universal edge distributions for both the orthogonal and
unitary ensembles. The two
symmetry classes share the scaling variable $g/D^{1/3}$ and exhibit a
symmetry-dependent cubic suppression of small susceptibilities, while their algebraic large-$g$ tails reflect the corresponding
symmetry-dependent level repulsion. Although eigenvector statistics retain their random-
matrix form throughout the spectrum, edge
rigidity makes low-lying chaotic states parametrically less sensitive to generic perturbations than bulk states. Our results establish universal,
symmetry-dependent spectral-edge fidelity-susceptibility statistics in systems whose chaotic dynamics extends down to the ground state.
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Quantum Physics
Global Minimax Readout of a Qubit Direction
Abbas Taherpour, Amirhossein Taherpour and Tamer Khattab
We determine the exact worst-direction Fisher-information cost of using a parameter-independent readout to estimate an unknown
qubit direction at known Bloch-vector length $\eta$. Every fixed-local architecture, including recorded classical randomization, heterogeneous single-copy measurements, and arbitrary outcome spaces, reduces exactly to a zero-barycenter probability measure on the Bloch ball. For every full-rank
qubit and every trace-balanced spectral Fisher loss, the resulting minimax problem is rigid: the unique optimal aggregate design is the
spin-coherent Haar positive-operator-valued measure (POVM). For $N$ copies, inverse-Fisher $A$ loss has the exact value $2/[Nf(\eta)]$, where $ f(\eta)= \frac{2\eta-(1-\eta^2)\log[(1+\eta)/(1-\eta)]}{4\eta}$. This uniqueness has an immediate finite-readout consequence. No finite-support measurement attains the unrestricted mixed-state optimum, while at the smallest globally regular support the tetrahedral symmetric informationally complete (SIC) measurement is uniquely $A$- and $D$-minimax, with exact worst-direction values. Relaxing the fixed-readout constraint separates the asymptotic resources: one-way local operations and classical communication (LOCC), unrestricted LOCC, and separable measurements have $A$-loss coefficient $4/\eta^2$, whereas collective measurements attain $2(1+\eta)/\eta^2$. We further classify the
rigidity conditions for unequal contrasts and show that Haar uniqueness survives at the nonregular pure-state endpoint.
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Quantum Physics
Classical-limit formula for matrix elements between bound states of distinct one-dimensional potentials
K. Beloy
A classical-limit formula is derived for
matrix elements between bound states of distinct one-dimensional potentials. We leave open the physical interpretation of the potentials, but generally envision them to be Born-Oppenheimer-type potentials with the position variable $x$ identifying with a slowly evolving degree of freedom of the system. For instance, $x$ could represent the internuclear separation in a diatomic molecule, with the potentials being potential energy curves for different electronic states. In this scenario, the
matrix elements could be, e.g., conventional Franck-Condon factors. To test the derived formula, we assume functional forms for the potentials and operator that afford analytical solutions for the
matrix elements. As the classical limit is approached, the computed
matrix elements exhibit a clear tendency towards the classical-limit formula, providing strong validation for the formula. In future work, we anticipate using the formula to model inhomogeneous excitation spectra of atoms in one-dimensional optical
lattices, with an eye towards improved optical
lattice clock performance.
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Quantum Physics
Hundred-hertz quantum circuit iteration rate in a reusable neutral-atom array
Liang Chen, Wen-Yi Zhu, Dong-Qi Ma et al. (+16 more)
Neutral-atom
quantum processors have rapidly advanced in scale and coherence, yet their practical performance remains constrained by limited
quantum circuit iteration rates (qCIRs) and information throughput. Here we experimentally demonstrate a high-throughput neutral-atom system based on non-destructive readout and atom reuse. By integrating a chip-based photonic interface with a 10-
qubit array, we implement non-destructive readout with a retention probability of 99.7%, and further achieve a raw qCIR of 101Hz and a post-selected qCIR of 74.8Hz. More importantly, we verify a general throughput optimization methodology and obtain a normalized Fisher information rate of 57.7Hz, improving the achievable throughput by more than one order of magnitude compared with conventional methods. Our results establish a practical route toward high-throughput neutral-atom
quantum processors.
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All authors Liang Chen, Wen-Yi Zhu, Dong-Qi Ma, Tian-Yang Zhang, Zi-Jie Chen, Yi-Chen Zhang, Hong-Jie Fan, Guang-Jie Chen, Qing-Xuan Jie, Wei-Zhou Cai, Tian-Cai Zhang, Luyan Sun, Yan-Lei Zhang, Xi-Feng Ren, Guang-Can Guo, Zhu-Bo Wang, Ya-Dong Hu, Gang Li, Chang-Ling Zou
Quantum Physics · Cross-listed from hep-lat
Quantum Simulation of QCD in Axial Gauge
Xiaojun Yao
We study
quantum simulation of SU(3) non-Abelian gauge theory dynamically coupled with fundamental
fermions in $3+1$ dimensions by employing the
lattice Hamiltonian in axial gauge that avoids Gauss's law constraints. The temporal component of the gauge field is analytically solved in terms of independent field degrees of freedom and a
lattice regulated Green's function. The axial gauge condition is trivially maintained in time
evolution, even under Trotterization. The gauge field degrees of freedom are expressed in the local field basis and can be efficiently transformed into the canonical conjugate momentum basis by local
quantum Fourier transforms. We prove the number of
qubits needed for describing all states up to an energy $E$ with an accuracy $\epsilon$ on a
lattice of volume $V$ at bare coupling $g$ is bounded as $16n_A V + 12n_f V$, where $n_A \approx \log_2 (\frac{64 E' V^{4/3}}{\pi^2\epsilon} + \frac{32\sqrt{2}g n_f E'^{1/2} V^{7/6}}{\sqrt{3}\pi^3\epsilon^{1/2}} ) $ is the number of
qubits needed for each independent gauge field per site with a shifted energy $E'$, and $n_f$ denotes the number of
fermion flavors. We then analyze a
quantum algorithm for time
evolution that is based on Trotterization,
quantum Fourier transform, and Jordan-Wigner transformation, for which
quantum circuits can be explicitly constructed under arbitrary gauge field truncation and digitization. We find the numbers of CNOT and single-
qubit rotation gates both scale as $O(n_A^4 V^{4/3}) + O(V^{5/3})$ per Trotter step for fixed $n_f\leq 6$. We conclude that
quantum resources needed for simulating real-time dynamics of
lattice QCD scale polynomially with volume, energy, time, accuracy, and bare
Hamiltonian parameters.
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Quantum Physics · Cross-listed from gr-qc
On the (Non)Unitarity with respect to the Clock of a Dynamical Local Observer and the Einstein Equivalence Principle
Kengo Shimada
We investigate the unitarity of
quantum evolution relative to an internal time defined by a local observer's clock. The observer is modeled as a relativistic particle carrying both a clock and a matter-field detector, analyzed first on a fixed curved background and subsequently within a fully diffeomorphism-invariant theory of dynamical
gravity. In the former case, we find that
evolution with respect to the internal clock time is generally nonunitary, implying a violation of the Einstein equivalence principle at the
quantum level. In contrast, in the latter case, diffeomorphism invariance allows us to adopt observer-centric coordinates without loss of generality. On the resulting partially-reduced phase space, one of the diffeomorphism generators becomes linear in the clock
Hamiltonian, generating a relational
evolution that is consistent with the remaining diffeomorphism constraints. Assuming that an effective
quantum field theory exists to be consistent with the diffeomorphism invariance, these features ensure
unitary evolution relative to the internal clock, thereby preserving the equivalence principle even in the
quantum regime. Our results highlight the fundamental role of diffeomorphism invariance in shaping relational
unitary evolution from the perspective of a local observer.
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Quantum Physics
The preferred-time problem in the conditional interpretation of time
Ovidiu Cristinel Stoica
In timeless formulations of
quantum theory, the Page-Wootters proposal (PW) recovers time and dynamics as relative clock-and-world states. By interpreting the total timeless system as a clock entangled with the world, the states having a definite clock reading appear to recover the temporal states of the world as relative states, and dynamics emerges. But an entangled state admits infinitely many decompositions as a superposition of product states, each decomposition corresponding to a different but equally valid time operator of the same clock system. Different valid choices of the time operator for the same clock system lead to different physical histories, where the world states in a history are superpositions of the world states from another history. Fixing one operator as "the" clock time would import the temporal meaning that the Page-Wootters proposal is meant to explain in the first place. Therefore, the interpretation of PW that the world state is passively conditioned on the clock state cannot hold. The timeless state is resolved into time-dependent states by the intrinsic pointer observables of the world, without having to outsource the role of the time operator to a separate clock. Fortunately, the formalism of PW remains valid, provided that it is interpreted in terms of intrinsic pointer observables of the world itself.
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Quantum Physics · Cross-listed from cond-mat.dis-nn
Exact mobility rings in non-Hermitian quasiperiodically decorated Lieb lattices
Ming-Jie Tao, Yi-Ting Wang, Jing Li et al. (+3 more)
The mobility ring (MR), a critical boundary in the complex energy plane separating extended and localized states, is fundamental to understanding the Anderson transition in non-Hermitian (NH) disordered systems. While MRs have been extensively studied in one-dimensional (1D) NH quasiperiodic models, rigorous analytical frameworks beyond 1D remain critically scarce. Here, we investigate a class of two-dimensional (2D) quasiperiodically decorated Lieb
lattices (QDLLs) featuring complex incommensurate potentials selectively applied to the
lattice vertices. By exactly mapping these 2D structures onto NH generalized Aubry-André-Harper (AAH) models and leveraging extended-localized transition point, we analytically derive the Lyapunov exponents and obtain exact expressions for the MRs. These exact theoretical boundaries are strongly corroborated by numerical computations of wavefunction fractal dimensions and real-space probability distributions. Furthermore, we reveal distinct evolutionary behaviors of the MRs driven by the quasiperiodic potential strength: systems characterized by $\kappa=2$ possess a single MR, whereas systems with $\kappa=3$ undergo a dynamic sequential
evolution from a single integrated ring into two independent rings. We hope that our exact results of MRs in 2D will benefit the study of Anderson localizations and MRs in high-dimensional NH systems.
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All authors Ming-Jie Tao, Yi-Ting Wang, Jing Li, Hongsheng Hou, Xiang-Ping Jiang, Lei Pan
Quantum Physics · Cross-listed from cond-mat.mes-hall
Engineering two-qubit gates via anisotropic exchange in germanium spin qubits
Leonardo Massai, Bence Hetényi, Eoin G. Kelly et al. (+14 more)
Germanium hole
spin qubits are a promising and versatile platform for
quantum computation and simulation. In this system, strong
spin-orbit interaction (SOI) renders the single-
qubit $g$-tensor anisotropic and electrically tunable, enabling operational sweet spots with reduced noise sensitivity. SOI also transforms the isotropic two-
qubit exchange coupling into an anisotropic tensor whose geometry is inherited from the single-
qubit $g$-tensors and
spin-flip tunnelling. Here, using two hole
spin qubits in a strained-germanium
quantum well and full vector control of the
magnetic field, we map this exchange tensor, separate it into longitudinal and transverse components, and show that they govern controlled-phase and SWAP-like dynamics, respectively. We find that the longitudinal exchange can be tuned via the
magnetic field orientation from a conventional positive value, through zero, to an effectively negative one, as measured by inverted exchange-split
spin transitions. The
magnetic field direction thus provides continuous control over the interaction
Hamiltonian: at a point of purely transverse exchange, we engineer a single-pulse baseband iSWAP, unattainable under isotropic exchange. Linking $g$-tensor geometry to exchange anisotropy establishes native
Hamiltonian engineering, enabling
spin-based
quantum simulation and gate sets selected by the global field orientation alone.
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All authors Leonardo Massai, Bence Hetényi, Eoin G. Kelly, Inga Seidler, Konstantinos Tsoukalas, Michele Aldeghi, Alexei Orekhov, Lisa Sommer, Marta Pita-Vidal, Uwe von Lüpke, Stephan Paredes, Stephen W. Bedell, Felix J. Schupp, Matthias Mergenthaler, Gian Salis, Andreas Fuhrer, Patrick Harvey-Collard