In briefSemigroup Quantum Dynamics Beyond the Standard GKSL Master Equation
SummaryThis paper studies semigroup dynamics for open quantum systems that do not take the standard GKSL master equation form. Such dynamics can arise in physical systems describing long-time asymptotic behavior and apply only to a restricted set of initial states. The authors review the single-mode Gaussian quantum Brownian motion channel and then analyze a family of qubit semigroup generators, identifying parameter regions that are completely positive, merely positive, or non-positive. They call the non-positive case restricted-positive, since the generator may remain physically meaningful for admissible initial states.
Nadine Diesel, Charlotte B\"acker, Walter T. Strunz
In briefA single quantum interferometer that switches between HOM and N00N-state interference
SummaryThis paper presents a hybrid quantum interferometer that can switch dynamically between Hong-Ou-Mandel and N00N-state interference by adjusting two time delays, τ1 and τ2. HOM interference is phase-insensitive and robust to noise, while N00N-state interference offers higher phase sensitivity. The authors report that theory and experiment confirm operation in phase-insensitive, phase-sensitive, or hybrid modes.
In briefBounds on success probability for an extended WZP linear-system algorithm
SummaryThe paper extends the WZP algorithm from real symmetric to complex Hermitian linear systems and studies its postselection success probability through a resource-theoretic lens. It derives upper and lower bounds on the maximal success probability over separable, incoherent, and real pure states, linking these to geometric entanglement, coherence, and imaginarity. It also analyzes permutation-averaged success probability and preprocessing under subgroup constraints.
In briefQuantized six-vertex models realizing frustration graphs
SummaryA recent graph-theoretic criterion holds that a Hamiltonian whose frustration graph is an indifference graph has a free-parafermion spectrum. This paper shows that any finite indifference graph can be realized as the frustration graph of the quantized six-vertex model at odd roots of unity, using a suitable wiring diagram and parameters. The result gives a concrete realization of the criterion via the quantum Frobenius property of the quantized six-vertex model.
In briefExact analytical solutions for a field-modified radial Schrödinger equation via the Nikiforov–Uvarov method
SummaryThis paper revisits an effective radial Schrödinger equation for a charged spinless particle in collinear static electric and magnetic fields, previously formulated with the tridiagonal representation approach. Using the Nikiforov–Uvarov method instead, the authors solve it exactly once the potential component is specified, giving closed-form examples of Kratzer-type, pseudoharmonic-type, and Hulthén-type (Manning–Rosen form) central potentials. The spectra are independent of the orientation angle and the electric field, which enters through the potential shape, radial moments, and expectation values. All analytical results are confirmed by finite-difference diagonalization.
In briefSingle-Impurity Pinning of a High-Energy Wavepacket: How One Local Defect Steers Quantum Propagation
SummaryThe paper studies how a single repulsive impurity strengthens the directional confinement of a high-energy wavepacket in a finite two-dimensional lattice of quantum wells. At energies far above the interwell barriers, the impurity suppresses transverse dynamical tunneling while preserving propagation along a principal lattice axis. Confinement is strongest when impurity strength is comparable to the barrier height and weakens for stronger perturbations.
Fartash Chalangari, Anant Vijay Varma, Joonas Keski-Rahkonen et al.
In briefDirectional effects of the Unruh effect on steering harvesting: a study of how acceleration changes the direction of quantum correlations drawn from vacuum.
SummaryThe paper studies directional quantum steering harvested by two uniformly accelerated Unruh-DeWitt detectors with different energy gaps, coupled to a massless scalar field in Minkowski vacuum. It finds that the Unruh effect does not simply degrade steering but reshapes its directionality depending on parameters, and within a finite acceleration window can enhance steering in one direction while suppressing it in the other. Energy-gap mismatch also serves as a control mechanism, and the maximal steering asymmetry approximately marks the transition from two-way to one-way steering.
In briefLoss-tolerant quantum key distribution over untrusted repeaters using high-dimensional time-bin multiplexing
SummaryThe paper proposes a measurement-device-independent QKD protocol in which time-bin-multiplexed single photons are entangled with qubits stored in nitrogen-vacancy centers. An untrusted intermediary performs entanglement swapping to establish EPR pairs between the users. Using d time bins per photon can generate log2 d + 1 EPR pairs per transmitted photon, and a memory-insensitive architecture reduces memory lifetime requirements. The authors prove security without trusting intermediate nodes using the Lo-Chau EPR-QKD framework and Shor-Preskill reduction.
In briefA low-cost compact muon detector for operation at millikelvin temperatures.
SummaryThe paper presents a low-cost, compact cosmic muon detector made of two plastic scintillator modules read out by silicon photomultipliers (SiPMs) in coincidence. The SiPMs were characterized from room temperature down to 10 mK, and the detector's coincidence rate was found to be temperature-independent and consistent with predictions. Below about 8 K, each muon produces two pulses, a phenomenon not previously reported, which appears to be linked to a superconducting layer in the SiPM; the underlying mechanism remains unexplained.
Tengiz Ibrayev, Danish Khan, Alex Herscovics et al.
In briefTopological entropy's strong subadditivity on the torus across Rényi orders
SummaryThe paper classifies when canonical Rényi strong subadditivity holds on an unpunctured torus for finite unitary modular categories. For 0<α<1 it holds for all pure logical states and admissible region pairs exactly when the category is Abelian, while at α=1 it holds universally. It also shows that each finite non-Abelian group has a D(G) ground state that violates the inequality at order two under ordinary edge partial traces.
In briefDicke model for open-shell atoms with tensor polarizability, explaining how atomic polarization couples to a shared cavity
SummaryThis paper studies an extended Dicke model derived from the scalar, vector, and tensor polarizabilities of open-shell atoms coupled to a shared cavity mode. Using 168Er with J=6 as an example, it examines the tensor-to-vector ratio fixed by rotational symmetry in a single electric-dipole channel. It analyzes phase transitions under circular and linear pumping, along with cavity-loss dynamics.
In briefReview of quantum optomechanical control using cavity cold-atom systems
SummaryThis review surveys recent progress in controlling optomechanical interactions with cavity cold-atom systems. It outlines the basic principles of standard cavity optomechanics, then describes experimental realizations of linear and nonlinear couplings in cold-atom platforms. The paper highlights applications in high-precision quantum sensing, quantum memory, and preparing macroscopic nonclassical states, and closes with an outlook and open challenges.
In briefMechanical trisqueezing in circuit quantum acoustodynamics using SNAIL devices
SummaryThe paper proposes a circuit quantum acoustodynamics architecture that couples a mechanical mode in a high-overtone bulk acoustic-wave resonator to a superconducting nonlinear asymmetric inductive element (SNAIL). Using the SNAIL's cubic nonlinearity with parametric flux driving, it engineers a three-wave mixing interaction that generates trisqueezed mechanical states. These states show a star-shaped Wigner function with negative regions, indicating non-Gaussianity.
In briefNormalized Loschmidt amplitude and complex-time zeros in metric-changing quasi-Hermitian quenches
SummaryThis paper studies quasi-Hermitian mixed-state quenches in which the initial and final Hamiltonians have different positive-definite metrics. Using metric-compatible purifications, it derives a normalized mixed-state Loschmidt amplitude whose normalization factor encodes the metric mismatch. The factor is shown to be strictly positive on the real-time axis, and its complex-time zeros produce branch singularities distinct from Fisher zeros. Analytic results are given for a general two-level system.
In briefMulti-instanton expansions and exact-WKB Stokes jumps in multi-well quantum mechanics
SummaryThe paper studies how exact-WKB Stokes jumps relate to the multi-instanton expansion of a one-dimensional potential with N equal-depth wells. It extends the single-barrier Bogomolny-Zinn-Justin cancellation to every consecutive barrier interval and to the integration contours. A numerical solution for a symmetric triple well confirms the resulting two-barrier level splitting. The results are stated to hold within the regular dilute, one-loop, local Weber approximation.
In briefHyperentanglement in intermediate phase-space planes for photon-pair key distribution
SummaryThe paper characterizes a photon-pair source whose photons are entangled in both polarization and transverse spatial degrees of freedom, with spatial measurements taken in intermediate fractional Fourier transform planes. Detection in the crystal plane reveals which crystal produced each photon and destroys polarization entanglement, while intermediate planes preserve it. The authors evaluate quantum bit error rates and asymptotic secret key rates for each degree of freedom and find two simultaneously usable channels per photon pair.
Murilo H. Magiotto, Millena B. Novaes, Wesley B. Cardoso et al.
In briefKeeping photon statistics intact when shifting light frequency in hollow-core fibers
SummaryThis paper tests whether Raman molecular modulation in a hydrogen-filled hollow-core fiber can change a light signal's frequency while preserving its photon-number statistics. Weak 585 nm signals were converted to 773 nm and 471 nm with near-unity efficiency, and the photon statistics were kept. The authors present this fiber-based approach as a platform for connecting spectrally distinct quantum systems.
Arturo Mena, Pau Arcos, Mar\'ia S\'anchez-Hern\'andez et al.
In briefTesting graph isomorphism with simple quantum circuits: using graph-dependent IQP and QAOA circuits to tell apart non-isomorphic graphs.
SummaryThe paper studies the graph isomorphism problem, which asks whether two graphs are equivalent under a permutation of vertices. It examines whether simple graph-dependent IQP and QAOA circuits can distinguish non-isomorphic graphs, and shows that the underlying graph can be reconstructed from a polynomial number of samples. Using Hamming weight distributions and graph invariants on ZZ correlator matrices, the authors report distinguishing all 10,486 cospectral regular graph pairs tested at QAOA depth p=2, as well as every tested non-isomorphic pair for IQP circuits. Whether this extracts structural information efficiently for general graph isomorphism remains an open question.
In briefObserved correlations beyond single-particle electron transport in counting statistics
SummaryThe paper examines charge fluctuations in mesoscopic devices to test whether a single-particle description of electron transport holds despite Coulomb interaction. The authors experimentally observe a violation of the sign rule for factorial cumulants of the full counting statistics in a single-level quantum dot. A theoretical model reproduces the experimental data quantitatively, revealing correlations introduced by electron-electron interaction.
Johann Z\"ollner, Hendrik Mannel, Daniel Oppers et al.
In briefJoint-measurement advantage and finite-time transitions in accelerated detector registers
SummaryThis paper studies how much entanglement distributed measurements can recover in a four-qubit cluster state when two assisting nodes independently undergo generalized amplitude damping. The authors derive exact joint-assisted concurrence and one-way values for local measurements, and give a necessary and sufficient condition for separable measurements to reach the joint optimum. For detectors at equal temperature with relaxation-rate ratio above one, joint advantage exists only when the thermal factor is below 1/r, and it ends at a unique finite time at positive temperature.
In briefImproved Quantum Algorithms for Rényi Entropy Estimation
SummaryThis paper studies estimating the Rényi entropy of a discrete probability distribution given purified quantum query access. For non-integer α>1, the algorithm improves the best known upper bound in its dependence on both n and 1/ε. For 0<α<1, it improves the dependence on 1/ε without increasing the dependence on n. The authors also strengthen the precision-dependent lower bound for 0<α<1, identifying the optimal precision dependence of their algorithm.
WhyImproves quantum query complexity for Rényi entropy estimation in both n and 1/ε, with a strengthened matching lower bound, though its scope is limited to the quantum query model.
In briefPhoton demultiplexing via spatial routing for multiparty quantum links
SummaryThis paper studies spatially sectioning the far-field noncollinear light from spontaneous parametric down-conversion to serve multiple quantum communication users. It offers a practical framework linking input parameters and a design theorem. In a representative setup, the authors realize 12 user-pair channels with routing consistency above 0.9999 at a 12% photon flux reduction.
In briefDeterministic, programmable fusion for building larger photonic graph states
SummaryThe paper introduces and experimentally demonstrates a deterministic fusion operation that connects small time-bin-encoded cluster states, generated on demand from a quantum emitter, into larger reconfigurable photonic graph states. The fusion is performed on flying microwave photonic qubits using superconducting circuits with in-situ programmability. The protocol uses active reset and reuse of matter qubits, producing genuine multipartite entanglement across 13 photonic qubits.
In briefEdge Majorana modes alter Kibble-Zurek scaling in Kitaev honeycomb ribbons
SummaryThis paper studies how the Kitaev honeycomb model behaves when its bond coupling J_z is ramped linearly through critical regions, comparing zigzag and armchair ribbons with periodic tubes. Excitation production follows a finite-size crossover set by the ribbon width relative to the Kibble-Zurek length. The authors find that boundary Majorana edge modes cause departures from ideal Kibble-Zurek scaling, with defect plateaus that depend on width parity.
In briefQuantum folding to seed Chebyshev-based quantum subspace diagonalization for ground-state finding
SummaryThis paper studies quantum subspace diagonalization (QSD) with a Chebyshev-polynomial Krylov space, a ground-state method for fault-tolerant quantum computers. The authors propose quantum folding, which seeds QSD with a product of subsystem ground states rather than a product state, and prove a nonasymptotic error bound linear in measurement noise. Exact simulations of antiferromagnetic Heisenberg chains show a reduced Krylov dimension and much lower noisy-regime error compared with the Néel state.
In briefStructure of low-rank PPT entangled states that violate the Peres conjecture
SummaryThis paper examines whether known counterexamples to the Peres conjecture, which are bound-entangled states with positive partial transpose (PPT), share a common structural origin. The authors ask whether these states can be obtained from the complement of an unextendible product basis (UPB) via invertible local filtering. They find that this holds in the 3⊗3 case but not for three qubits. The results suggest that nonlocal bound entanglement is not, in general, a UPB phenomenon.
WhyUnifies known PPT bound-entangled counterexamples via UPB complements under local filtering, with a rigorous negative result for three qubits; influence is confined to entanglement theory.
In briefQuantum van der Pol oscillators, alone and coupled: Wigner dynamics, exact qutrit solutions, and synchronization
SummaryThe paper studies quantum van der Pol oscillators, where single-photon pumping competes with a nonlinear two-photon dissipative channel to form a quantum limit cycle. The authors derive the Wigner-function evolution equation and an equivalent classical stochastic description that closely matches full Lindblad dynamics and is efficient in the semiclassical regime. For two coupled oscillators with different frequencies, they characterize phase locking via a stationary order parameter and find that stronger nonlinear dissipation shrinks the synchronized region. Restricting to the three-level subspace reduces the problem to an exact 41-dimensional linear system.
In briefTrading energy for coherence in optimal mode discrimination
SummaryThis paper studies how energy and quantum coherence, two resources, interact in optimal mode discrimination, the task of identifying which mode from a finite set a signal was encoded in. The task is relevant to cryptography and metrology. For two-mode discrimination under a hard energy constraint n ≤ N, the authors fully solve the problem. For some mode overlaps, the maximal-energy Fock state with N excitations is the best choice, while for other overlaps, access to coherence yields better discrimination.
In briefSound scattering explained through quantum dynamics of non-Hermitian operators
SummaryThe paper links the scattering of sound waves in a compressible fluid to the quantum dynamics generated by a class of non-Hermitian Hamiltonian operators. It expresses the scattering amplitude through the corresponding evolution operator. This yields a new proof of the acoustic scattering reciprocity theorem and supports analytic low-frequency calculations. The authors also study scattering from a finite planar array of delta-function point scatters in an infinite acoustic slab.
In briefScalable Coherent-Noise Tomography Using Stabilizer-Code Polarization
SummaryThe paper proposes a constant-cost method for characterizing coherent noise in quantum error correction, which is hard to detect with standard Pauli-twirl techniques. Measurement-free error correction projects few-qubit coherent noise onto a single-logical-qubit effective channel, and a concatenated fingerprint built from bit-flip and phase-flip codes is shown to uniquely recover the noise parameters. A synthetic numerical test over 500 sampled parameter points found full-rank Jacobians, supporting first-order identifiability. The authors expect the recovered model to lower logical error rates for surface-code decoders, but this is an anticipated benefit rather than a demonstrated result.
In briefQuantum-boosted fiber-optic strain sensor measurement
SummaryThis paper uses entangled two-photon interference to measure strain-induced optical phase shifts in an all-fiber Fabry-Perot resonator. A narrow-linewidth laser is locked to the cavity resonance, and an in-fiber Mach-Zehnder interferometer reads out the signal. The sensor works with both classical coherent light and entangled photon pairs. Using an N = 2 NOON state, the authors report measurement noise below the standard quantum limit.
Romain Dalidet, Marialuisa Capezzuto, Hugo Degert et al.
In briefQuantum-enhanced search for galactic dark photons using cat-state cavities
SummaryThis paper reanalyzes an existing quantum-enhanced dataset from a superconducting circuit experiment to search for a galactic dark-photon background. Such a background could arise from dark-matter decay or annihilation in the Milky Way halo. The authors use four-component cat states and repeated parity measurements to extract photon-transition probabilities and test for a daily modulation. Finding no such modulation, they set 90% confidence-level bounds on the kinetic-mixing parameter for two production mechanisms.
In briefVoid-free glass through-vias for multilayer ion traps on fused silica
SummaryThis paper reports a surface-electrode ion trap fabricated on fused silica with through-glass vias (TGVs). The vias are formed by selective laser-induced etching and filled with gold by constant-current electroplating without additives. Electrical tests across multiple wafers show a TGV yield above 98.8%. A glass interposer and thermocompression bonding are used to form a compact chip-to-chip assembly.
In briefCoherent-state integrals that extend beyond the domain of operator products
SummaryThe paper studies matrix elements of products of unbounded operators, which are converted into phase-space integrals by inserting a resolution of the identity. Using the chain of two-photon exponentials e^{μa²}e^{λa†²} as an example, it analyzes parameter regions where the product exists, where the integral converges, and where the Fock-space series converges. The integral is shown to provide an analytic continuation of the matrix element beyond the domain of the product and the convergence region of the series.
In briefDynamical decoupling of nonclassical states in a noise-biased spin qudit
SummaryThis paper studies how to extend the coherence of nonclassical states in high-dimensional qudits. By exploiting noise bias, the authors reduce the overhead of the decoupling sequence from quadratic to linear scaling. They demonstrate this on an antimony donor nuclear spin (d=8) in silicon, with coherence gains of 5 to 10 times for uniform superposition, cat, and Haar random states. For a spin-cat code, the logical superposition coherence time reaches 225 ms, versus 19 ms under free evolution and 85 ms with a Hahn echo.
In briefTransport Information Beyond Strong Eigenstate Thermalization
SummaryThis paper examines whether Floquet eigenstates in non-chaotic, operationally mean-ergodic systems retain information about classical transport beyond their leading thermodynamic behavior. Using the double kicked top model, the authors show that the finite-size correction coefficient m of normalized eigenstate entanglement entropy tracks shifts between transport regimes even when the thermodynamic-limit entropy is nearly insensitive to them.
Avadhut V. Purohit, Harshit Sharma, Udaysinh T. Bhosale
In briefA cryogenic chip that lets one microwave line control many superconducting qubits
SummaryThis paper proposes a cryogenic multiplexing control chip (MCC) that allows one microwave cable to control many superconducting qubits. Based on adjustable inductors, it generates 4 to 8 GHz microwave signals to form XY control circuits. Frequency-domain and time-domain simulations evaluate its performance, and the authors state it can be packaged with qubits at 20 mK and greatly reduce the number of control lines.
In briefRebuilding Michelson Interference Using Only On-Off Detection Data
SummaryThis paper reconstructs Michelson interference using only the binary on-off statistics of a single-photon counter and macroscopic path-difference data, without assuming complex wave superposition or prior spectral information. The authors show that discrete response data across path differences form a positive semi-definite matrix and apply Herglotz's theorem. They conclude that the harmonic interference fringe decomposes uniquely into a cosine average of wavenumbers, dictated by testable algebraic constraints on the statistics.
In briefShot- and noise-aware Pauli correlation encoding for Max-Cut experiments on IBM Heron
SummaryThe paper studies Pauli correlation encoding (PCE) for the Max-Cut problem and shows that the sharpness parameter in its training loss acts as a hidden shot budget. The authors propose a schedule that sets sharpness according to the number of measurement shots, which outperforms published schedules on five G-set graphs in simulation. On the IBM Heron processor ibm_fez, a 96-CZ hardware-native circuit retained up to 0.919 of the best-known cut.
WhyLinks PCE sharpness to a finite shot budget, proposes a shot-aware schedule, and validates it on IBM hardware, with strong novelty.
In briefA compact six-beam 3D magneto-optical trap using metasurface chips for cold-atom experiments
SummaryThis paper presents a compact six-beam 3D magneto-optical trap that replaces bulky free-space optics with two multifunctional metasurface chips to cool and trap atoms. The photonic-integrated cell module measures only 73×73×107 mm³. The system trapped about 1.3×10³ Rb atoms and cooled them to roughly 183 μK. Laser light is delivered to the metasurfaces through optical fiber, giving a fully fiber-coupled design intended for stable and portable operation.
In briefExtracting Metrology Signals from Noisy Squeezed Spins via Bayesian Optimization
SummaryThis paper studies interacting spin-1/2 ensembles with static local frequency disorder, which can hide the metrological advantage of squeezed spin states. The authors use Bayesian optimization over the full measurement-outcome distribution to find observables combining dipole and quadrupole operators. For ensembles of up to 17 spins, these readouts exceed the standard quantum limit at both disorder strengths studied.
In briefQuantum LDPC codes built from polynomial minors
SummaryThe paper builds quantum codes from codewords of a cyclic code and the minors of a polynomial matrix. A two-row, three-column matrix yields a second matrix satisfying the CSS orthogonality condition. The code dimension is derived from greatest common divisors of entries and minors, and polynomial selection controls the dimension. Explicit constructions give 13 quantum codes with verified minimum distances, including a [[255,80,12]] code of rate 80/255.
Vahid Nourozi, Roxana Smarandache, and David G. M. Mitchell
In briefA note on the absolutely continuous spectrum of limit-periodic Jacobi matrices
SummaryThe paper studies limit-periodic Jacobi matrices in the weak exponential class EC(η) and shows that, for sufficiently large η depending only on the R-boundedness constant, their spectrum is purely absolutely continuous. The argument first derives homogeneity of the spectrum from the weak exponential approximation rate. A closure theorem for reflectionless Jacobi matrices then carries reflectionlessness from periodic approximants to the limit, and a result of Poltoratski and Remling excludes singular spectrum on a homogeneous set.
In briefBenchmarking qubit leakage with decohering subgroups under preparation and measurement errors
SummaryQubits can leak outside the computational subspace, so it is useful to measure both leakage probability and gate fidelity inside that subspace. The authors model randomized benchmarking sequences with leakage-level decoherence as a Markov process with noisy classical preparations and measurements, and characterize the resulting parameter degeneracies. They develop an inference method that uses known conservative SPAM bounds to constrain fidelity, leakage, and other parameters. The method is tested experimentally on a qubit encoded in the one-excitation subspace of two transmons, and its confidence intervals are compared with conventional leakage benchmarking methods.
Shawn Geller, Tongyu Zhao, Alex Kwiatkowski et al.
In briefDynamic |T⟩ state selection and budget-aware factory setup for quantum computing
SummaryThis paper presents GP|T⟩-S, a lattice surgery scheduler and factory allocator for fault-tolerant quantum computing on surface codes. It jointly optimizes |T⟩-state cultivation and distillation under a total T-error budget, using each cultivated state's complementary gap as a fidelity estimate to adjust post-selection. Across sixteen benchmarks, it stays within the error budget and achieves geometric mean speedups of 5.5× in logical cycle count and 3.4× reduction in space-time volume over baselines.
Maxwell Poster, Sayam Sethi, Steven Hofmeyr et al.
In briefMeasurement mutual information in conformal field theories: how much measuring one region reduces uncertainty about outcomes in another.
SummaryThe paper studies the Rényi-Shannon mutual information of measurement in conformal field theories for scalar primaries and descendants in large N CFTs. Calculations are carried out for adjacent and widely separated intervals, and the results depend only on the cross ratio and the scaling dimension of the measured operator. A quadratic dependence (Δ−1/2)² appears for adjacent intervals, which seems to violate the information processing inequality; the authors discuss and resolve this. A holographic interpretation is also provided.
Israel Klich, Ravisankar Rajagopal, and Diana Vaman
In briefQuantum reservoir computing for cued selective reproduction of input streams
SummaryThe paper introduces a new task in which a binary cue tells a quantum reservoir computing (QRC) system which of two simultaneous input streams to reproduce. In simulated spin reservoirs with a trained linear readout, exact expectation values let the reservoir reproduce the cued stream accurately. With finite measurements, it beats a linear readout of raw inputs only at large measurement counts due to sampling noise. Performance rises with entanglement and computational-basis coherence, then saturates.
In briefSpectra of random Lindblad operators with a Hamiltonian component
SummaryThis paper studies random Lindblad operators, the generators of continuous-time Markovian evolution in open quantum systems, that include a Hamiltonian component. The authors analyze three ensembles of increasing complexity, with the first two solvable exactly using standard probabilistic and free-probability methods. For the general case of independently random Hamiltonian and dissipative parts, they introduce a framework combining operator-valued free probability with sequential noise averaging, deriving a general equation for the spectral boundary. They also describe how Hamiltonian-induced spectral squeezing and the spectral support depend on relative Hamiltonian strength and the rank of the dissipative component.
Mykhailo Hontarenko, Wojciech Tarnowski, Sergey Denisov et al.
In briefHybrid quantum-classical spatial search that trades circuit depth for query cost
SummaryThis paper proposes a parameterised family of hybrid quantum-classical algorithms for spatial search that smoothly interpolates between classical and fully coherent quantum approaches. A parameter γ controls the trade-off between circuit depth and total query complexity, aiming at near-term and early fault-tolerant devices. The authors also derive an optimal continuous depth-query trade-off for fixed-point amplitude amplification.
WhyIntroduces a continuous interpolation between classical and quantum spatial search with an optimal depth-query trade-off, a substantial theoretical advance with rigorous derivations but limited immedi
In briefUsing a quantum simulator to selectively excite and image Higgs and Goldstone modes
SummaryThe authors realize a mesoscopic Bose-Hubbard model at unit filling on a two-dimensional array of transmon qubits. They selectively excite collective modes tied to amplitude or phase fluctuations of the superfluid order parameter, identifying them as Higgs and Goldstone modes by measuring particle numbers on each site. Because the finite system has spectral gaps, the Higgs mode can be detected as a coherent, long-lived excitation.
Connie Miao, Pranjal Praneel, Thomas G. Kiely et al.
In briefCavity-assisted dynamic nuclear polarisation via Purcell-enhanced electron spin relaxation
SummaryThis paper proposes a dynamic nuclear polarisation method that uses the radiative relaxation of electron spins, enhanced by the Purcell effect in a cavity, to polarise nuclear spins. It was demonstrated on bismuth donor spins in isotopically purified silicon coupled to a superconducting resonator. A single cycle raised a target ground-state population by 1.79 times, and repeated cycles reached a cumulative enhancement of 4.6, below the theoretical ninefold limit. The authors attribute the gap to competition between Purcell and intrinsic relaxation and a collective slowing effect.
WhyProposes a new cavity-based polarisation mechanism via Purcell relaxation, experimentally demonstrating a 4.6-fold cumulative nuclear polarisation enhancement in bismuth donors.
Tristan Lorriaux, Yutian Wen, Patrice Bertet et al.
In briefPost-optimization corrections to adaptive quantum variational algorithms
SummaryThis paper addresses the high circuit depth and measurement counts that limit chemical applications of adaptive variational quantum algorithms such as ADAPT-VQE. The authors apply two post-optimization corrections, Hamiltonian-moment Krylov subspace diagonalization and identity-augmented q-sc-EOM, to optimized ADAPT-VQE states without further ansatz growth. On molecules with up to 20 qubits, first-order Krylov correction reduces the adaptive layers needed to reach 1.6 mEh accuracy by up to about sixfold, with measurement cost reductions of up to about fortyfold.
Prince Frederick Kwao, Bharath Sambasivam, Jason Saroni et al.
In briefGravity from generalized entropy: a theory of gravity built on generalized entropy families
SummaryThis paper links the gravitational Lagrangian to the geometric quantum relative entropy between the spacetime metric and a metric induced by matter and curvature, extending the construction to Tsallis, Rényi and Sharma-Mittal entropy families. It examines their common Einstein limit, weak-field spectra, auxiliary-field formulation and horizon entropy. The linearized spectrum is reported to contain a Planck-scale tachyonic spin-2 ghost, and conditions under which this ghost is removed are identified.
In briefViscous fluid behavior from two-body loss-induced collisions
SummaryThis paper shows that two-body loss can replace interactions in turning a nondegenerate gas into a fluid. Correlated loss induces elastic scattering as required by the optical theorem, which dominates at strong loss through the quantum Zeno effect. Such a gas exhibits viscosity and thermal conductivity close to those of the unitary Fermi gas, and both grow over time with a universal exponent of 3/8 as loss heats the gas.
Aleksandr N. Mikheev, Orjan Ameye, Oded Zilberberg et al.
In briefForgetting Quantum Training Data in Federated Learning Using Classical Shadows
SummaryThe paper proposes SHADE, in which each node stores a classical shadow of each quantum training state, made from a few random single-qubit measurements. Later, SHADE estimates the gradient and curvature of the forget data from these shadows and removes their effect with a federated Newton correction, so only classical estimates are sent. In simulations with 50 nodes and on edge boards, it matches retraining's forget accuracy within 0.5 points in under 0.2 s without replay. The authors also prove that the required shadow size grows exponentially with the backward light cone of the measured observable, not with the number of qubits.
In briefA modular quantum computer built on Cornucopia error-correction codes that performs universal logic at low qubit overhead
SummaryThe paper proposes the Cornucopia architecture, which implements universal logical operations on ultra-high-rate Cornucopia codes with low overhead. It uses the [[2844,1426,18]] code as an example, building a modular quantum computer from code blocks linked by bridges, where each block stores 1,426 logical qubits. By exploiting translation symmetry, the authors construct reusable gadgets that address 1,422 logical qubits per block and support three universal instruction sets.
In briefClassically simulating quantum communication requires maximal cost
SummaryThe paper studies the classical communication needed to reproduce correlations from measurements on finite-dimensional quantum systems in the prepare-and-measure setting. It constructs an exact classical simulation using a finite average number of bits of one-way communication for arbitrary d-dimensional states and measurements. It further shows that for d ≥ 4, no simulation with finite average message dimension exists, strengthening a recent result by de Gois, Santos and Vieira.
WhyConstructs an exact classical simulation with finite expected bits and proves impossibility for finite message dimension when d≥4, strengthening prior results.
Riccardo Castellano, Pavel Sekatski, and Nicolas Brunner
In briefGeneralized BEADS Representation: Visualizing Mixed Quantum States Completely
SummaryThis paper extends the BEADS representation, previously used for pure quantum states, to mixed quantum states. It introduces spherical functions, called beads, to visualize correlation structures, and uses a recursive optimization to find minimum-entanglement pure-state decompositions of subsystems. The correlation components are separated into total, genuine multipartite entanglement, quantum-discord-type, and classical correlations. The authors illustrate the representation on several classes of mixed states and show examples of entanglement distillation and noise channels.
Celina Br\"autigam, Steffen J. Glaser, Dennis Huber
In briefLogical gate set tomography: a full characterization of noise in error-corrected logical gates
SummaryThis paper introduces logical gate set tomography (logical GST), a method for detailing the noise in logical operations after quantum error correction, from which gate fidelity and diamond distance can be derived and non-Markovian and coherent logical errors can be tested. The authors apply it on Quantinuum's H1 trapped-ion processor to characterize a universal single-qubit logical gate set in the seven-qubit Steane code, the first full, self-consistent characterization of such a set. Experimental data showed mainly logical Pauli-stochastic errors, no evidence of logical non-Markovianity, and weak signs of coherent logical error. Higher-shot data from Quantinuum's system emulator revealed weak but statistically significant non-Markovian mechanisms and strong evidence of coherent logical error.
WhyIntroduces logical gate set tomography and gives the first full characterization of a universal logical gate set, validated on hardware and an emulator.
Piper C. Wysocki, Juan Gonzalez De Mendoza, Karl Mayer et al.
In briefInstability of Markov chains under infinitesimal coherent dissipation
SummaryThis paper studies how conditional mutual information and the associated Markov length grow under local Lindbladian evolution. The authors show that even an arbitrarily short, strictly local Lindbladian can generate infinite Markov length from a product state. They also construct strictly local Lindbladians that converge rapidly to steady states whose conditional mutual information decays algebraically, and these states are locally reversibly connected to a product state by sublinear-depth circuits.
In briefProgrammable polaron models and tomography in trapped-ion quantum simulators
SummaryThe paper proposes a trapped-ion scheme for realizing spin-phonon Hamiltonians with programmable spatial coupling between excitation density and phonon displacements, including local Holstein and long-range Fröhlich-type interactions. The authors introduce displaced Green's functions implemented via spin-dependent phonon displacements to access strongly dressed polarons. Spectral and spatially resolved measurements are proposed to probe polaron band structure and the phonon dressing cloud.
Filip Marijanovic, Utso Bhattacharya, Abhishek Menon et al.
In briefMeasurement-Induced Criticality in Non-Abelian Anyon Chains: The Monitored Golden Chain
SummaryThe paper studies a chain of non-Abelian anyons evolving only through measurements, which is described as a non-unitary conformal field theory. The authors map the monitored dynamics to a random tensor network and numerically find Lyapunov gaps scaling as 1/L, logarithmic entanglement growth with chord length, and an effective central charge in the measurement-record Shannon entropy. The conserved topological charge sharpens with dynamical exponent z=1 and can be learned by a decoder on an O(L) timescale.
In briefPhase-averaged stabilizer Rényi entropy: a magic measure that does not depend on phase conventions
SummaryThe paper defines a phase-averaged stabilizer Rényi entropy that averages Pauli moments before taking the logarithm, making it exactly invariant under independent local rephasings. For pure states it vanishes only when the state is a stabilizer state in every phase convention. The authors apply it to tree-level gluon scattering at four and five points, where helicity-basis phases are unspecified, and report results independent of the fixed external colors.
In briefBest disorder level for spin chains to approximate random quantum operations
SummaryThe paper studies how disordered spin-chain quantum simulators can approximate Haar-like unitary ensembles, a task where stronger disorder adds randomness but also suppresses dynamics. The authors derive perturbative scalings for the moment gap between the k-th moment operator and its Haar value, finding different behavior at weak and strong disorder and an optimal crossover strength. They also show a multi-quench protocol suppresses the gap exponentially in the number of quenches, supported by numerical simulations.
Tian-Gang Zhou, Yi-Neng Zhou, Thierry Giamarchi et al.
In briefInvertible subalgebras for chiral semion topological order: a framework for chiral topological states that avoids the usual obstruction for 2D local Hamiltonians.
SummaryChiral topological order cannot be realized by strictly two-dimensional local commuting-projector Hamiltonians on finite-dimensional tensor-product spaces, so the paper uses invertible subalgebras (ISAs) instead. It constructs a chiral semion ISA and its anti-semion commutant on a square lattice with one qubit per edge, and proves that together they generate all local operators. Pumping the semion ISA along the z direction yields an explicit three-dimensional non-Clifford quantum cellular automaton.
WhyConstructs an invertible subalgebra for chiral semion order, proves it generates all local operators, and extends to QCAs and higher dimensions; rigorous but impact mainly theoretical.
Yu-An Chen, Meng Sun, Nathanan Tantivasadakarn et al.
In briefGaussian entanglement and quantum communication: optimization bounds for light-based links
SummaryThis paper studies how loss and noise limit using light to distribute entanglement, transmit quantum information, and establish secret keys. It develops a framework for computing Gaussian-restricted relative entropy of entanglement and Rains entanglement, with a convex algorithm that has an explicit convergence rate and a polynomial bit-complexity bound. Using these calculations, the authors bound quantum and private communication under an input-energy constraint. Two- and three-mode examples compare these bounds with achievable rates, including pure-loss benchmarks.
WhyReduces Gaussian-restricted entanglement measures to convex geometric optimization with proven convergence and complexity bounds, advancing quantum communication limits though scope is mainly Gaussian
In briefShowing discrete and continuous definitions of entanglement of formation agree in infinite dimensions
SummaryThe paper proves that any Borel ensemble of pure states on a separable bipartite Hilbert space with finite average entanglement can be replaced by a countable ensemble with the same barycenter and arbitrarily small extra average entanglement. As a result, the discrete and continuous versions of entanglement of formation coincide across all states of infinite-dimensional bipartite systems, including infinite values. The proof lifts the ensemble to a measure on the unit sphere of Hilbert-Schmidt operators, partitions its support into cells, replaces each cell by its conditional barycenter, and builds the countable ensemble recursively.
In briefEntropy-based descent for nonconvex secure communication optimization with convergence guarantees
SummaryThis paper develops an entropic descent method for a nonconvex optimization problem over probability simplices that arises in classical and quantum secure communication. The variables describe a randomized encoder, optimizing its input distribution and stochastic preprocessing together, and an exact relative-entropy identity yields a fixed-step mirror-descent iteration. The authors prove descent and convergence of objective values and stationarity of accumulation points for arbitrary finite classical channels, with full-sequence convergence and an O(1/t) bound under additional conditions. The approach is extended to noncommuting quantum outputs, and numerical experiments show multiple attracting values and strict gains from stochastic preprocessing.
In briefDeterministic, programmable creation of entangled states across mechanical resonator modes
SummaryThe paper demonstrates deterministic, programmable preparation of multipartite entangled states among phonon modes of a high-overtone bulk acoustic wave resonator coupled to a superconducting transmon qubit. Using optimal-control-engineered isometries applied sequentially between the qubit and each mode, the authors generate bond-dimension-two matrix product states, including W, GHZ, and cluster states. Quantum state tomography characterizes these states and certifies genuine multipartite entanglement among up to four modes.
WhyDeterministically prepares and tomographically verifies multipartite mechanical entangled states beyond prior pairwise entanglement, with genuine four-mode certification.
Isabelle Franzen, Max-Emanuel Kern, Q. Rumman Rahman et al.
In briefQuantum-enhanced mechanical sensing using machine-learning estimation
SummaryThe paper uses a microgram-scale acoustic mode of a high-overtone bulk acoustic wave resonator as a phase-insensitive quantum-enhanced sensor. A transmon qubit prepares Fock states of up to seven phonons and reads out the phonon-number distribution after a weak resonant signal. The Fisher information is five times the vacuum value, a 7.0 dB gain over classical probes, limited by state preparation infidelity. A neural network trained on the sensor response achieves the same gain with half the systematic bias, without an analytical model.
WhyFirst demonstration of non-Gaussian phonon states in a microgram acoustic mode giving quantum-enhanced phase-insensitive sensing, with experimentally measured Fisher information gain and neural estima
Finn M\"u{\ss}igbrodt, Andra\v{z} Omahen, Q. Rumman Rahman et al.
In briefExact limits on two-way quantum communication over lossy, fading optical channels
SummaryThis paper studies quantum communication, entanglement distribution and secret-key generation over multimode bosonic loss and fading channels, aided by local operations and two-way classical communication. Under a mean photon-number constraint, it gives exact two-way quantum and secret-key capacities for multimode pure-loss channels, extended to frequency-dependent loss under a power constraint. It also derives capacity bounds and formulas for fading channels, depending on whether the channel realization is revealed, along with strong-converse thresholds.
WhyUses sector teleportation to derive exact two-way capacities for multimode loss channels, extending to fading and finite-energy settings with strong-converse thresholds.
In briefPULSUS: Direct Frequency-Domain Multidimensional Spectroscopy Beyond the Impulsive Rotating-Wave Approximation
SummaryThis paper introduces PULSUS, a direct frequency-domain method for computing multidimensional spectra of open quantum systems with finite Gaussian pulses, without relying on the impulsive rotating-wave approximation. It is validated against analytical and independent time-domain benchmarks, and a hierarchy of finite-pulse, rotating-wave, short-pulse and impulsive models separates the errors of each approximation. For a coupled electronic dimer, the total impulsive-RWA error is nonmonotonic in pulse duration, with intermediate durations giving the highest accuracy.
In briefFeedback-free hybrid algorithm for explicitly correlated ground states
SummaryThe paper proposes a hybrid quantum-classical algorithm in which a quantum processor prepares a low-entanglement momentum-space matrix product state, precomputed classically, rotates it to real space, and measures in Hamiltonian-fixed bases. The correlator is optimized variationally in classical post-processing, so no quantum-classical feedback loop is needed. The authors demonstrate it on 32 qubits of Quantinuum's H2-2 for the half-filled 4×4 lattice, reporting a relative ground-state energy error of 16 ± 4% after postselection, reduced to 3.5 ± 0.5% with calibration.
In briefPreparing dark states in a molecule's zero-field-split triplet
SummaryThis paper proposes a method to prepare and detect dark states in single-molecule electron spin resonance using atomic force microscopy (ESR-AFM), extending existing Rabi oscillation techniques. Borrowing from atomic physics, the authors coherently control a three-level V-configuration system with a multifrequency magnetic field and analyze the total triplet population within a pump-probe scheme. They use an open-system density-matrix approach to compute expected dark state signatures for ideal cases and for realistic ESR-AFM parameters on pentacene.
In briefFaster T-efficient quantum unitary synthesis using block-sparse Hamiltonian simulation
SummaryThis paper builds Clifford+T circuits for arbitrary n-qubit unitaries, with worst-case T-count Õ(N^{8/7}) at constant operator-norm error, where N=2^n. This improves the previous exponent of 5/4. The method splits a transformed Hermitian logarithm of the target into block-sparse pieces and combines their evolutions using qDRIFT. The authors also prove that the exponent 8/7 is optimal within a sequential block-SELECT model at constant precision.
WhyImproves the T-count exponent via random similarity transforms and block-sparse simulation, with a proven optimality result within a sequential block-SELECT model.
In briefCan system dynamics stay non-Markovian when measurable memory effects vanish?
SummaryThe study examines how unresolved quasistatic disorder in system-bath coupling affects non-Markovian dynamics in spin environments. For pure dephasing Ising interactions with fixed bath states, disorder can make dynamics CP-divisible, but physically fluctuating bath states keep the averaged dynamics CP-indivisible at any finite disorder. Anisotropic Heisenberg interactions with any nonzero transverse exchange prevent this disorder-driven transition. Increasing disorder suppresses experimentally visible memory revivals, which can become unresolvable at finite measurement resolution.
Sayan Sengupta, Anish Sharma, George Biswas et al.
In briefWhether Boltzmann entropy grows over time in closed macroscopic quantum systems
SummaryThis paper studies a closed macroscopic quantum system in a pure state that evolves unitarily under a Hamiltonian. The Hilbert space is split into orthogonal subspaces, each representing a macro state, and a quantum Boltzmann entropy is defined for each macro state. The authors discuss precise versions of the claim that this entropy mostly increases over time for realistic macroscopic systems, and they check these versions for several simple models.
In briefPhase behavior of a rotating Bose-Einstein condensate in a hard-wall trap
SummaryThis paper studies the rotational behavior of a zero-temperature Bose-Einstein condensed gas confined by a hard-wall potential. Depending on interaction strength and trap rotation frequency, the authors map phases including multiply-quantized vortices, vortex lattices, a lattice with a central hole, a giant vortex, and states that break axial symmetry. For strongly attractive interactions, the system is found to become unstable and collapse.
