In briefSeparating Types of Quantum Oracles: How Different Quantum Oracle Models Differ in Separating Complexity Classes
SummaryThe paper introduces the notion of meta-complexity of quantum relativization, studying which types of quantum oracles, such as unitary versus state oracles or those closed under inverse, can separate two quantum complexity classes. Using PostBQP and PreciseBQP as a test case, the authors give a complete classification, within their defined oracle families, of which models can separate these classes. The results show that some oracle types leave the classes equal while others, such as superpolynomial-dimensional forward-only diagonal unitaries, produce separations.
Scott Aaronson, Adam Bouland, Jordan Docter et al.
In briefPolarisation-based identification of photon-pair generation processes in a multimode fibre coupler
SummaryThis paper studies photon pairs generated by spontaneous four-wave mixing in a multimode fused tapered-fibre coupler made from two single-mode fibres. Pumping near 800 nm produced two photon-pair wavelength sets, which were attributed to specific processes using phase-matching calculations, selection rules, pump-polarisation dependence, and polarisation tomography. The authors also theoretically identify simultaneous processes driven by one pump that could yield polarisation or composite spatial-polarisation entanglement.
Jefferson Fl\'orez, Chams Baker, Benjamin J. Sussman et al.
In briefExponential gap in sensing time for changing signals using squeezing
SummaryThis paper studies quantum sensing of continuously evolving signals rather than fixed ones. The authors show that a sensor with squeezing at least ω(√log T) can sense such signals in poly(T) time. Sensors with squeezing at most o(√log T), by contrast, require sensing time exponential in T.
Francesco Anna Mele, Nadine Meister, Haimeng Zhao et al.
In briefA new quantum magnetometer design using direct ultraviolet detection of noble gas spins
SummaryThis paper analyzes a quantum magnetic sensor that optically detects nuclear spin precession in a noble gas using an ultraviolet frequency comb laser. Because no alkali vapor needs to be mixed in during sensing, spin relaxation can last hours at room temperature. The authors find that high laser power combined with low intensity noise is key to matching or exceeding state-of-the-art performance, including cryogenic magnetometers. They calculate a sensitivity of 24 aT/√Hz in 10 minutes using a 10 W ultraviolet laser with -100 dBc/Hz relative intensity noise.
In briefWhether open-system dynamics can hide quantum measurement disturbance and keep passive realism intact
SummaryThe paper introduces "passive realism," the assumption that a system's pre-existing properties can be observed without changing its later dynamics. It uses no-signalling in time (NSIT) as a necessary condition and studies whether open-system evolution can dissipate measurement back action into the environment. The authors find this masking is possible only in two special cases, and otherwise there exist binary projective measurements violating NSIT, with a constructive procedure demonstrated for depolarizing and dephasing channels.
In briefAlgebraic framework for biphoton spatial-mode entanglement in higher-order LG-pumped SPDC
SummaryThis paper presents an algebraic framework that splits Laguerre-Gaussian (LG) pumped spontaneous parametric down-conversion into a spatial-mode beam-splitter step and a spatial two-mode squeezing step. When the pump-beam radius matches the correlation width, squeezing vanishes and orbital angular momentum and total spatial mode number are conserved. The authors derive an analytical Schmidt number for arbitrary LG pump modes and squeezing strengths, showing how radial and azimuthal indices set the dimensionality of the spatial entanglement.](https://arxiv.org)
In briefNormal-ordered perturbative expansion for matter systems interacting with quantum light fields
SummaryThis paper presents a normal-ordered perturbative expansion method for computing the reduced dynamics of a matter system interacting with a general continuous-mode photon field. Field correlations are automatically normal-ordered, and free evolution includes spontaneous emission. At intermediate coupling strengths, the method converges much faster than the conventional expansion, extending perturbative applicability to larger matter-light couplings. The approach is demonstrated numerically for a two-level system with coherent, Fock, and cat state inputs.
In briefThermal gauge theories at finite θ and μ via real-time quantum simulation
SummaryThis paper shows how imaginary-time evolution can be reconstructed from real-time quantum simulations using exact integral transforms. It reinterprets an existing construction by Guo, Shibu, Lin, and Zhao as a continuous linear combination of Hamiltonian simulations, and attributes its slow convergence to a redundant kernel component. The method is extended to thermal traces and correlators, allowing inverse temperatures, Euclidean separations, and chemical potentials to be reconstructed from one real-time dataset through classical post-processing. It is benchmarked on one- and two-flavor lattice Schwinger models, including circuit-level simulations with depolarizing noise.
In briefProposed matter-wave interferometer using a rare-earth-doped microparticle
SummaryThis paper proposes demonstrating matter-wave interference with a microparticle containing an embedded rare-earth ion. Optical transitions of the ion impart momentum to the particle's center of mass, and a time-symmetric geometry with J = 1/2 is used to remove sensitivity to initial conditions. The authors argue that external decoherence rates either decrease or stay constant as particle mass increases, so larger particles can avoid decoherence.
In briefA framework for quantum light spectroscopy using input-output theory
SummaryThe paper combines input-output theory from quantum optics with perturbative expansion methods from chemical physics to formulate quantum light spectroscopy. It examines linear spectroscopy, fluorescence, intra-beam G(2), and Hong-Ou-Mandel correlation as examples. The authors show that for certain initial photon states, signal expectation values can be evaluated non-perturbatively, while for general states the signals are obtained by perturbatively expanding the input-output relation.
In briefSingle-particle imaging of the Néel transition in LaCrO3 microcrystals using widefield NV magnetometry
SummaryResearchers used widefield nitrogen-vacancy (NV) magnetometry to image the stray magnetic fields of individual LaCrO3 microcrystals made by molten salt synthesis, resolving the antiferromagnetic Néel transition in single particles. Of 18 particles measured between 278 and 298 K, five showed a clear magnetization onset near the ensemble Néel temperature, four showed no measurable signal, and nine showed temperature-independent signatures consistent with localized magnetic impurities. The authors conclude that single-particle NV magnetometry is a sensitive probe of magnetic ordering and domain structure in individual microcrystals.
Carson O. Patterson, Ethan Q. Williams, Eden Tzanetopoulos et al.
In briefLearning ground states when copies are scarce: optimal trade-offs between copies and Hamiltonian evolution time
SummaryThis paper studies how to estimate multiple observables or fully reconstruct a unique gapped ground state when only a limited number of initial copies is available. The authors derive a unifying inequality that gives worst-case lower bounds on the Hamiltonian evolution time any protocol must use. They construct parallel catalytic readout protocols that return nearly all initial copies unchanged while nearly reaching these bounds up to poly-logarithmic factors. Numerical benchmarks show large reductions in end-to-end evolution time compared with a copy-consuming protocol.
WhyDerives optimal copy-versus-Hamiltonian-time trade-off lower bounds and near-optimal catalytic readouts, a clear theoretical advance, supported by numerical benchmarks but mainly theoretical.
In briefQ-SPARSE: a quantum method for estimating angle and range in near-field signals
SummaryThis paper proposes Q-SPARSE, a quantum subspace-projection algorithm for super-resolution parameter estimation in the near field, with a spectral signature similar to MUSIC. Each spherical steering hypothesis is prepared as a quantum state, quantum phase estimation is applied to covariance-generated evolution, and the resolved spectral mass is converted into a localization spectrum. Numerical results on IBM's QISKIT platform are presented for near-field array processing.
Mostafizur Rahaman Laskar, Sajad Daei, Gabor Fodor et al.
In briefQuantum Secure Non-Interactive Reductions: a quantum extension of a framework that converts one correlation into another while preserving privacy
SummaryThis paper extends secure non-interactive reductions (SNIR) to the quantum setting (QSNIR), where both source and target resources are bipartite quantum states. When the target is classical, the framework analyzes distributing private correlations from entanglement as well as classical resources. The authors show that QSNIR privacy can be computed exactly via a pair of semidefinite programs, and that it is lower-bounded by a problem related to minimum-error state discrimination. They use these to compute exact one-shot privacy errors for universal two-party computation preprocessing correlations.
WhyExtends secure non-interactive reductions to quantum resources, with exact SDP-based privacy error computation and a rigorous theoretical analysis, though no experiments.
In briefPosition verification with a classical verifier, using non-local games
SummaryThe paper presents a general compiler that turns any complete-support non-local game with a quantum advantage into a multi-prover position verification protocol. Verifiers and provers communicate only classically, while quantum resources are limited to shared entanglement and local measurements. Using the CHSH game, the authors show the scheme can be implemented near-term on existing platforms and prove finite-size security in the quantum random oracle model.
WhyProposes a general compiler turning complete-support non-local games into classical-verifier position verification with finite-size security proofs; novel, but lacks experiments and impact is confined
Wen Yu Kon, Fatih Kaleoglu, and Kaushik Chakraborty
In briefShows that inverse access to state-preparation unitaries is needed for quantum PAC learning sample-complexity gains
SummaryThis paper asks whether quantum computation can reduce the data needed to learn a prediction rule from an unknown distribution. In the worst case, the authors prove that forward-only access to state-preparation unitaries achieves query complexities of Θ((d+log(1/δ))/ε) for realizable learning and Θ((d+log(1/δ))/ε²) for agnostic learning, matching classical and quantum-copy bounds. The results indicate that inverse access is essential for the known improvement in the realizable setting.
WhyProves matching tight bounds showing forward-only access gives no asymptotic query advantage in worst case, via a new reduction framework.
In briefPriority-Aware Routing for Quantum Networks: Adding Coherence-Time Limits to Scheduling
SummaryIn quantum networks, limited memory coherence time means queuing delay can directly cause decoherence and reduce information quality. The paper proposes a coherence-aware routing protocol that incorporates decoherence constraints into path selection using a priority-modulated aging model derived from Weighted Fair Queueing theory. Evaluated with a discrete-event simulator checked against NetSquid, it is compared with loss-only Dijkstra routing and FIFO scheduling, showing that high-priority traffic keeps fidelity under load and that the gains come mainly from routing rather than scheduling.
In briefTime-integrated leakage as a dynamic benchmark for superconducting qubit reset
SummaryThis paper argues that endpoint population alone does not capture the reset process in superconducting qubits, and proposes time-integrated leakage alongside endpoint population to evaluate a multi-mode dissipative reset model under flux-frequency control. The authors simulate finite thermal occupation, parameter sweeps, frequency disorder, auxiliary-chain ablation, and a literature-based rate benchmark. The two metrics can favor different reset configurations, and the authors suggest time-integrated leakage is a useful quantity to report alongside endpoint residuals.
In briefReading out momentum-space topology from a programmable dissipative photonic circuit
SummaryThis paper shows how topological information in non-Hermitian dynamics can be read out even when strong dissipation suppresses the relevant amplitudes. The authors implement the dynamics in synthetic momentum space on a programmable photonic integrated circuit using unitary dilation, recovering the phase with phase-shifted interferometry. For the non-Hermitian SSH model, the method distinguishes trivial from non-trivial Zak phases and finds a coherence winding of ±1 induced by an exceptional point. Extended to a synthetic torus with a Rice-Mele pump, it yields first Chern numbers of 0 and 1 for trivial and non-trivial cycles.
Andrea Cataldo, Emil J. Bergholtz, Daniel Leykam et al.
In briefCollective Dynamics in Constrained Spin Chains: Fragile to Classical, Robust to Quantum Fluctuations
SummaryThis paper studies a kinetically constrained spin chain, the dissipative far-East model, to compare classical and quantum fluctuations. Without fluctuations the system shows phase coexistence, which quantum fluctuations further stabilize while classical fluctuations suppress over long times. The authors map the steady-state phase diagram with a cluster mean-field approach and analyze dynamics with stochastic tensor-network methods.
Pietro Brighi, Gianluca Frazzei, Igor Lesanovsky et al.
In briefExponential strong converse for blind quantum data compression
SummaryThis paper proves exponential strong converse theorems for blind quantum data compression of finite-dimensional mixed-state sources, with and without entanglement assistance. Below the optimal compression rate, accuracy decays exponentially with block length. The proof introduces a new overlap quantity based on quantum state structure that links source information preservation to the dimension of the transmitted system.
WhyProves exponential strong converse for blind mixed-state quantum compression at optimal rate via a new overlap quantity; substantial theoretical advance, influence confined to quantum information theo
In briefWhy some symmetries limit quantum magic in many-body states
SummaryThis paper studies nonstabilizerness, or "magic," a resource for quantum advantage. The authors prove that the Robustness of Magic for N-qubit X-states is at most √3, showing a symmetry restricts magic. They use this constraint to build a scalable method that lower-bounds magic for arbitrary many-body states, tested on spin-1/2 Hamiltonian ground states beyond exact evaluation. For Hamiltonians whose equilibrium states are X-states, they analytically derive the critical temperature at which magic emerges.
A. de Oliveira Junior, Jake Xuereb, Rafael A. Mac\^edo et al.
In briefMaking the Most of Leftovers: Better Privacy Amplification for Quantum Key Distribution
SummaryThe secret key extractable from a quantum key distribution run depends on observed error rates and the mathematical bounds used to certify security. With finite datasets, conservative bounds force users to discard much of the available key. This paper refines and extends privacy amplification bounds using the recent leftover hash lemma of Regula and Tomamichel, and incorporates them into a security analysis based on entropic uncertainty relations. In finite-block settings it certifies more secret key from the same data than entropy accumulation-based techniques.
Matthew Simon Tan, Bartosz Regula, Marco Tomamichel
In briefExact operator complexity measures from random matchgate circuits
SummaryThis paper studies how typical Heisenberg-picture operator complexity measures behave in random matchgate circuits, which are classically simulable free-fermionic systems. The authors develop a free-fermionic unitary Weingarten calculus in the Majorana basis for computing operator moments. Using it, they derive closed-form expressions for local-operator entanglement, operator stabiliser entropy, and higher-order out-of-time-ordered correlators. For extensive initial Majorana strings, operator entanglement and stabiliser entropy follow volume laws even though the circuits remain classically simulable.
WhyIntroduces a Majorana-basis free-fermionic Weingarten calculus yielding closed-form operator entanglement and stabiliser entropy, showing volume laws in classically simulable matchgate circuits via an
In briefA study showing classical correlations can certify entanglement recovery, linking entanglement to state distinguishability in quantum information.
SummaryThe paper examines the link between entanglement and quantum state distinguishability, which previously was known mainly for measurements in complementary bases. The authors show that for POVMs satisfying an irreducibility condition, a quantitative relation holds between the infidelity of one-sided local transformation to a maximally entangled state and the failure probability in state discrimination. The results apply to entanglement distillation and quantum error correction, where errors can be certified using classical input-output correlations from local measurements.
WhyExtends entanglement-distinguishability links beyond complementary measurements via irreducibility, giving quantitative bounds unifying distillation, error correction, and measurement trade-offs.
Takeru Utsumi, Yota Tachibana, Yoshifumi Nakata et al.
In briefOptimal Tolerant Testing of Lindblad Dissipation
SummaryThe paper studies how to check whether the dissipation strength of an unknown, time-independent Lindblad generator stays within a tolerance threshold. The authors give an algorithm that distinguishes strength at most ε1 from strength at least ε2 using total evolution time O(ε2/(ε2−ε1)²). A matching lower bound shows this is optimal even for adaptive protocols. The method removes the bounded-degree requirement.
WhyExtends dissipation testing to tolerant setting, removes bounded-degree assumption, and gives matching lower bound establishing optimality for adaptive protocols.
In briefOptimal-query learning of unknown unitary channels in diamond distance using only parallel queries
SummaryThe paper studies how to learn an unknown d-dimensional unitary channel within diamond distance ε using parallel queries, where sequential strategies were previously thought to be more powerful. The authors give a protocol using O(d²/ε) parallel queries, which matches an existing lower bound. This closes the gap between parallel and sequential strategies for unitary channel tomography. The method also yields optimal query complexity for boundary-regime channel tomography and improves the best known protocol for fermionic linear optics tomography.
WhyGives a parallel protocol matching a known lower bound for unitary channel tomography, closing the gap with sequential strategies.
In briefExact strong converse exponent for secret communication over quantum channels
SummaryThis paper determines the exact strong converse exponent for secret-key transmission and generation over general finite-dimensional quantum wiretap channels, measuring reliability and secrecy jointly by squared fidelity to an ideal key. It introduces a novel Rényi private information whose regularization characterizes this exponent. An integral representation in terms of ordinary private information yields a uniform continuity bound, showing convergence to private capacity as the Rényi order approaches one. The result establishes exponential fidelity decay at every rate above private capacity for any wiretap channel.
WhyIntroduces a novel Rényi private information exactly characterizing the strong converse exponent, with integral representation and uniform continuity bound.
Hao-Chung Cheng, Christoph Hirche, Marco Tomamichel
In briefLocal self-running decoders for quantum LDPC codes using belief propagation and feedback
SummaryThis paper presents a local, distributed framework for decoding quantum LDPC codes, built on belief propagation (BP) with local syndrome processing, feedback, and autonomous parallel operation. It shows that codes already exhibiting a threshold under iterative BP can be converted into autonomous local measurement-and-feedback dynamics that keep this threshold. For codes where naive BP shows no threshold, syndrome defects use local BP beliefs to move, pair, and annihilate asynchronously, and numerical results show threshold behavior in point-like sectors of two- and three-dimensional toric codes where standard BP fails. The authors further study the inference dynamics on the membrane-like sector of the three-dimensional toric code and on a family of bivariate-bicycle quantum LDPC codes.
In briefWhether optimal quantum symmetry testing can avoid the quantum resource tied to the symmetry
SummaryThe paper asks whether a symmetry can be tested optimally without using the quantum resource naturally associated with it, such as coherence. For parallel subgroup-versus-Haar testing, it proves a representation-theoretic lower bound on excess type-II error for all zero-type-I-error protocols and shows that optimal system marginals must satisfy structural constraints. Specific results are given for the diagonal torus, the orthogonal subgroup, and the qutrit Clifford group, and some cases, such as beyond nine queries for the Clifford group, remain open.
WhyProves a quantitative representation-theoretic lower bound on type-II error and exact resource-compatibility conditions for optimal symmetry testing, a substantial theoretical advance.
In briefRadiation pressure driving of a mechanical resonator in multiple modes using a spatial mode sorter
SummaryThis paper demonstrates driving a nanomechanical membrane with radiation pressure using dynamically structured light from a spatial mode demultiplexer (SPADE). Using single- and two-mode illumination, the authors directly image position-dependent coupling between Hermite-Gauss modes caused by the membrane's motion. They also use multimode radiation pressure feedback to cool two nearly degenerate membrane modes simultaneously.
Morgan E. Choi, Daniel Allepuz-Requena, Diego Torres-Barajas et al.
In briefPrinciple of Minimum Justified Correlation: Unifying Entropy, Fisher Information, and Kinetic Energy as Correlation Measures
SummaryThe paper argues that Shannon entropy, Fisher information, and quantum kinetic energy can all be viewed as measures of correlation. It starts from a map that replaces a joint density with the product of its marginals and shows how the resulting correlation measures behave under this map. For a real normalized quantum wavefunction, the decrease in mean kinetic energy is shown to be proportional to the relative Fisher information. The authors state a principle of minimum justified correlation, and this is Part I of a two-part paper.
In briefOptimal ground-state preparation using a guiding state
SummaryThe paper studies how to prepare a Hamiltonian's ground state to high accuracy, given an energy estimate, a spectral gap, and a unitary that produces a guiding state with sufficient overlap with the ground state. It presents two algorithms, one interleaving amplitude amplification with error reduction and one composing transducers, and bounds the number of uses of the time evolution and of the guiding-state unitary. Combined with prior energy-estimation results, the authors state the bound is optimal up to a constant factor when the two error parameters are equal.
WhyImproves the Hamiltonian-query complexity of ground-state preparation to a near-optimal bound with rigorous analysis and reusable transducer constructions.
Stacey Jeffery, Rolando D. Somma, Freek Witteveen et al.
In briefLearning quantum symmetries: quantum algorithms for finding the symmetries of quantum objects
SummaryThis paper studies quantum algorithms that learn the symmetries of quantum objects, building on the State Hidden Subgroup Problem (StateHSP). The authors extend efficient algorithms to non-abelian groups with normal hidden subgroups and introduce anyonic state symmetry learning, based on invariance up to global phase. They also obtain an improved algorithm for learning stabiliser groups of mixed qudit states and extend symmetry learning to unitaries, Hamiltonians, and finite collections of states.
WhyExtends StateHSP to non-abelian normal hidden subgroups and introduces global-phase-invariant Anyonic symmetry learning via a new projective-representation/error-correcting-code correspondence, a subs
In briefCommuting operator self-test for exact entanglement embezzlement
SummaryThe paper shows that the optimal commuting operator correlation for a variant of Coladangelo's two-player generalized nonlocal game is a commuting operator self-test. It is the first correlation self-test for an exact entanglement embezzlement protocol in this framework. The unique optimal correlation requires exact embezzlement, so it cannot be realized with quantum tensor-product models, even with infinite-dimensional local spaces. The proof relies on Harris's unique abstract state characterization of exact embezzlement using Cuntz algebras.
In briefRamanujan quantum expanders built from the Weil representation
SummaryThe paper constructs an infinite family of Ramanujan quantum expanders of degree D = q+1 for every odd prime power q. It transfers Morgenstern's Ramanujan Cayley graphs on PSL_2(F_p), for p an even power of q, through an odd irreducible subrepresentation of the Weil representation of SL_2(F_p). For dimension N, the implementation uses O(log² N) elementary gates and O(log N) ancilla qudits. Assuming exact circuit implementation, it meets the 2√(D-1)/D singular value bound exactly, with no additive error, unlike the prior work of Iyer, Jain, Jordan, and Somma.
WhyTransfers Morgenstern's Ramanujan graphs via Weil representation to exact-bound quantum expanders with improved gate complexity and no additive error.
In briefOptimal quantum-classical query separations for exact learning
SummaryThis paper studies exact learning with membership queries and compares deterministic, randomized, and quantum query complexities. The authors construct concept classes that refute a longstanding conjecture relating randomized and quantum query complexity, with bounds matching known upper bounds up to constant factors. The results also show that quantum speedups for learning can go beyond the Grover search and Bernstein-Vazirani paradigms.
WhyConstructs concept classes giving tight bounds that refute a longstanding conjecture on classical versus quantum query complexity, matching known upper bounds.
Srinivasan Arunachalam, Amin Shiraz Gilani, Nikhil S. Mande
SummaryThe paper revisits von Mises' frequency interpretation of probability and argues it contains key elements of any coherent scientific interpretation, despite criticism. It proposes a modified definition that drops von Mises' infinite collectives while keeping the requirement that probabilities apply to events repeatable under similar conditions and showing frequency stabilisation. The author partitions probabilistic systems into object and environment, arguing this solves several classic problems and can unify frequentism with other consistent interpretations.
In briefA Tale of Two Walks: Linking Kac's Quantum Random Walk to the KMP Process
SummaryThe paper shows that the parallel Kac walk's twirling channel on the symmetric subspace is exactly encoded by a classical Markov chain on partitions, which lifts to a parallel KMP process on complete graphs. The authors prove that O(log d + log(1/ε)) repetitions approximate Haar twirling to error ε, uniformly in the number of copies t. They also give a mixing-time bound for standard KMP on general graphs and apply it to improve coordinate hit-and-run mixing on the simplex.
WhyReveals a new link between parallel Kac walk and KMP, with rigorous uniform mixing bounds improving coordinate hit-and-run mixing time.
In briefUniversal quantum coding using Schur-Weyl duality for error correction without prior channel knowledge
SummaryThis paper addresses entanglement distillation from unknown noisy bipartite states and reliable quantum communication over noisy channels without prior knowledge of the state or channel. Using Schur-Weyl duality, the authors treat the irreducible permutation spaces from multiple copies of an unknown mixed state as maximally entangled code spaces and correct their symmetry-resolved errors. The work unifies entanglement distillation, quantum error correction and quantum communication within one representation-theoretic framework, with finite-copy guarantees.
WhyUses Schur-Weyl duality for universal quantum codes, unifying entanglement distillation and communication with worst-case optimal finite-copy guarantees.
Jacopo Rizzo, Filippo Girardi, Ludovico Lami et al.
In briefDensity matrices describing pulsed quantum light
SummaryThis paper represents pulsed light with density matrices whose correlation functions differ in stationarity and coherence. The authors show that, once finite detection times are taken into account, these matrices yield equivalent measurement results. This gives a physical meaning to the length of a quantization cavity and explains where the physical spectrum of pulsed light comes from. By generalizing density matrices for pulsed Gaussian light states, the authors describe pulsed light with varying statistics in one basis and relate the photocount rate to the pulse spectrum.
In briefSharper bounds on local Markov properties of quantum Gibbs states
SummaryThis paper shows that quantum Gibbs states at any fixed positive temperature satisfy stronger local Markov properties. For finite-range interactions, the conditional mutual information decays exponentially with distance, with a prefactor depending only on the boundary of one region, improving earlier results by Chen and Rouzé. Decay estimates are also given for exponentially, stretched-exponentially, and power-law decaying interactions. The proof uses a static method rather than the dynamical approach of Chen and Rouzé.
In briefFast mixing of parallel Kac's walk from spheres to Stiefel manifolds
SummaryThe paper studies how the parallel Kac's walk mixes when it acts on k orthonormal quantum states at once. The authors show that after O((k+log d)log(d/ε)) steps, the joint distribution of the k outputs is ε-close to that from applying a shared Haar-random unitary. Equivalently, the walk mixes rapidly on the complex Stiefel manifold.
WhyExtends parallel Kac's walk fast mixing from one quantum state to k orthonormal states, with proven Stiefel manifold mixing bounds improving prior results.
In briefStrong-to-weak symmetry breaking in dephased fermion mixed states
SummaryThis paper studies fermions with U(1) symmetry under infinite density dephasing, a setting where mixed states lose global charge information, which is the hallmark of strong-to-weak spontaneous symmetry breaking (SWSSB). The authors show that at infinite dephasing each Rényi correlator equals a spin correlator of a compact XY model and develop a diagrammatic expansion and replica field theory. Fully dephased metals show long-range SWSSB in dimensions two and higher, and quasi-long-range SWSSB in one dimension, while insulators depend on microscopic details.
In briefOptimal Quantum Junta Testing Without Inverse Queries
SummaryThis paper studies how many queries are needed to test whether an unknown n-qubit unitary or quantum channel acts nontrivially on at most k qubits. The authors consider a forward-only query model without inverse or controlled access, and prove tight bounds of Θ(k/(ε²log k)) for a broad range of ε. For channels, this closes the gap between earlier upper and lower bounds at constant ε. The results rely on a connection between quantum junta testing and classical support-size testing.
WhyConnects quantum junta testing to classical support-size testing, giving matching tight bounds that close a known gap with complete proofs.
In briefNeutral-atom hybrid quantum-classical method for entanglement routing
SummaryThis paper studies entanglement routing in quantum networks, maximizing admitted requests under fidelity constraints. The authors use neutral-atom quantum optimization as a pricing oracle within a hybrid column-generation framework, formulating the constrained shortest-path pricing problem as a QUBO. On small benchmark instances evaluated with emulators, the method with warm-start and post-processing achieves an optimality gap below 1%, while the simulated-annealing baseline reaches up to 6%. The authors state this is a proof of concept that does not establish quantum utility or scalability.
M. Yassine Naghmouchi, Quentin Ma, Agathe Blaise et al.
In briefRandom-circuit observables that keep circuit differences despite concentration
SummaryThis paper asks whether out-of-time-order correlators (OTOCs) in random quantum circuits can support verifiable quantum advantage. The authors prove that for broad classes of local random circuits in any fixed spatial dimension, fixed-order OTOC fluctuations between circuit instances decay only inverse-polynomially at system-scale depths. For one-dimensional Haar-random brickwork circuits, they show the fluctuations involve many gates yet stay confined to sublinear-width regions. They also give a classical algorithm rigorously improving on brute-force simulation of 1D OTOCs, though classical hardness remains open.
WhyProves inverse-polynomial fluctuations of fixed-order OTOCs in local random circuits and gives the first rigorous 1D OTOC classical improvement over brute force, with solid theoretical evidence.
Antonio A. Mele, Francesco A. Mele, Jarrod R. McClean et al.
In briefAttosecond correlation interferometry: a new way to probe ultrafast optical correlations
SummaryThe study perturbs gas-phase high-harmonic generation with two-mode bright squeezed vacuum to produce and characterize correlated attosecond extreme-ultraviolet (XUV) emission. Correlated amplitude and phase fluctuations from the signal and idler fields are transferred onto two families of harmonics, with even harmonics acting as an attosecond phase-sensitive probe via interference between indistinguishable pathways. The authors report a transition from maximal fluctuations to near-silence within about 30 attoseconds.
In briefMeasuring a spin-1/2 spin and getting 7: an anomalous weak value experiment
SummaryThis study realizes the weak Stern-Gerlach experiment proposed by Albert, Aharonov, and Vaidman in 1988, which aims to measure anomalous weak values lying outside an operator's eigenvalue spectrum. The authors placed a 87Rb Bose-Einstein condensate in a magnetic gradient and used an unlikely postselection to amplify a weak magnetic momentum kick by a factor of 14. They also show that larger momentum kicks reduce the measurement's weakness and decrease the amplification.
Joseph McGowan IV, Nicholas Mantella, Noah Baker et al.
In briefQuery complexity of ancilla-free quantum circuits for simulating nonlinear dynamics
SummaryThis paper studies how nonlinear dynamics can be simulated with fully coherent, ancilla-free unitary quantum circuits. The authors generalize the ancilla-free double-bracket algorithm for imaginary-time evolution by using a state-dependent Hermitian operator. They relate query costs to how sensitive the dynamics are to initial conditions, giving bounds for contractive, nonexpansive, and expansive cases. For the discrete Gross–Pitaevskii equation, they report optimal worst-case query complexity over a specified family of single-qubit initial states.
In briefHow many copies are needed to estimate quantum state moments, and why third and fourth moments are equally hard
SummaryThe paper studies how many single-copy measurements are needed to estimate the moments Tr(ρ^t) of an unknown quantum state. For each fixed integer t≥2 it gives matching upper and lower bounds on the optimal sample complexity. The exponent follows a dyadic pattern, so the third and fourth moments both require Θ(d^{2/3}) copies.
WhyTightly characterizes optimal single-copy sample complexity for state moments with a dyadic hierarchy, using matching upper and lower bounds that advance quantum learning theory.
In briefMultistate Torsion in Zitterbewegung: how band twisting shapes electrons' jittery motion in crystals
SummaryThis paper derives the nonlinear Zitterbewegung velocity of electrons in crystals, including the effect of band torsion. Its equation of motion, built from multistate quantum geometric tensors and torsion, predicts transient nonlinear photocurrent responses that differ from the recently measured steady-state photovoltaic effect induced by circularly polarized light. The authors also propose tomography protocols for measuring the multistate quantum geometric torsion tensors.
In briefLong-duration spin-exchange between circular Rydberg atoms
SummaryThe authors observe spin-exchange interactions between two spin-1/2 states in laser-trapped circular Rydberg atoms for over 60 microseconds and about 40 spin-oscillation periods, an order-of-magnitude improvement. They record a collapse and revival of the oscillation contrast caused by spin-motion coupling. A novel dynamical decoupling method is demonstrated that prevents this collapse, aiming at long-duration quantum simulation.
Andr\'es Dur\'an-Hern\'andez, Gautier Creutzer, Aurore Alice Young et al.
