In briefOptical circuit design for computing any nonlinear function
SummaryThe paper presents an exact method for evaluating any finite Fourier series using a two-mode linear optical circuit, where only single-mode phase shifters encoding the input variable are tunable. The authors prove that such a circuit exists for every Fourier series and give an analytical construction based on spectral factorisation. For an N-harmonic expansion the optical system has depth O(N), and numerical tests show correct synthesis of continuous and discontinuous functions even with thousands of terms.
Martin F. X. Mauser, Joshua Morris, Sara Galatro et al.
In briefNeural network models of molecular energy landscapes that generalize to unseen geometries
SummaryThe paper introduces geometry-conditioned foundation neural-network quantum states for molecular electronic structure in second quantization. A single autoregressive model learns ground states from sparse anchor geometries and provides wavefunctions at untrained geometries without further optimization, using orbital alignment to share an aligned orbital basis. For N2, CO, and H4, frozen energies reach chemical accuracy at every untrained query geometry.
In briefQuantum codes with constant rate and low-weight stabilizers that realize all logical Clifford gates using transversal and fold-transversal operations
SummaryThe paper introduces a family of quantum error-correcting codes whose encoding rate stays constant asymptotically while stabilizer weight grows sublogarithmically. Using only transversal and fold-transversal gates, these codes support the entire logical Clifford group. The construction uses classical codes whose code spaces are absolutely irreducible Steinberg modules of Tanner-graph automorphism groups, and takes hypergraph products of them to obtain the quantum codes.
In briefCMOS-based balanced homodyne detector for quantum optical measurements
SummaryThe paper demonstrates a low-noise, high-speed balanced homodyne detector that pairs a 28 nm CMOS capacitive-feedback transimpedance amplifier with a custom photonic chip made on imec's iSiPP200 silicon photonics platform. The receiver achieves a 7.6 GHz 3-dB bandwidth, up to 27 dB shot noise clearance, a 13.7 GHz shot noise-limited bandwidth, and common-mode rejection up to 54.8 dB. The authors state these results support use in continuous-variable quantum key distribution, quantum random number generation, and optical coherence tomography.
Sarah Bastiaens, Cedric Bruynsteen, Simone Cammarata et al.
In briefLoss of resonance in noisy Shor's algorithm
SummaryThis paper argues that the exponential quantum advantage of Shor's algorithm is broken by even small one-layer depolarizing noise, based on a resonance breaking effect in noisy circuits. The authors write the measurement distribution as a superposition of 4^n wave functions using the Pauli path integral. They bound the measurement success rate when depolarizing noise is applied to the middle layer of the circuit. They also propose a polynomial-time classical factoring algorithm to replace the low-frequency contribution.
In briefAdaptive decoding of quantum LDPC codes using decoder disagreement
SummaryAccurate decoding of quantum LDPC codes often needs costly post-processing search, yet decoding difficulty varies widely between syndromes. The paper introduces an adaptive decoder combining belief propagation and ordered-statistics decoding, using the disagreement between the BP hard decision and the order-zero OSD solution as a risk signal. On a [[144,12,12]] bivariate bicycle code under circuit-level noise, escalating only the highest-risk 20% of instances recovers 85% to 92% of the full search's logical error rate gain while cutting mean serial decoding cost by a factor of 3.6.
In briefA general framework for photonic circuits beyond quantum theory
SummaryThe paper uses the analogy between quantum-optical quadrature operators and mechanical harmonic oscillator phase-space coordinates to extend linear optics into generalised probabilistic theories. It tests whether the Hong-Ou-Mandel effect and Mach-Zehnder interferometry are unique to quantum theory. The authors find that the vanishing coincidences at a beam splitter also occur for classical light and a modified quantised light, and that Mach-Zehnder interferometry shows no qualitative difference between quantum theory and these alternatives. The framework is proposed as a basis for studying generalised photonic set-ups and photonic quantum computers.
Isma\"el Septembre, Matthias Kleinmann, Martin Pl\'avala
In briefOptimal interferometric certification of how indistinguishable multiple photons are
SummaryThis paper presents two efficient, experimentally friendly protocols for estimating or bounding the fidelity of an N-photon state to the closest perfectly indistinguishable state. The first protocol applies to sources preparing separable states and yields tight two-sided bounds using a single Fourier interferometer with photon-number-resolving detection. The second combines randomized linear-optical interferometers with photon counting to directly estimate fidelity for arbitrary N-photon states. Both methods, based on a multiphoton generalization of the Hong-Ou-Mandel test, can certify fidelity 1 − O(ε) with provably optimal O(1/ε) samples.
Marco Robbio, Micha\l{} Oszmaniec, Nicolas J. Cerf et al.
In briefSemiclassical spin-bath study of how nitrogen isotopes affect NV⁻ coherence in diamond
SummaryThis paper examines the ratio of Hahn-echo to Ramsey coherence times for nitrogen-vacancy ensembles in diamond, comparing natural ¹⁴N with ¹⁵N-doped samples. Using a semiclassical spin-bath model, the authors find that the nitrogen nuclear isotope alone shortens T₂ by a ratio of about 1.118 while leaving T₂* unchanged. The measured effect is larger, so the isotope effect is a real but partial contribution.
Chikara Shinei (University of Tsukuba, J-FAST, CNRS / University Grenoble Alpes / Grenoble INP / University of Tsukuba)
In briefQuantum heat engine using pairing correlations across the BCS-BEC crossover
SummaryThe paper proposes a quantum heat engine based on a two-component Fermi gas with s-wave contact interaction operating across the BCS-BEC crossover. Work is extracted from the gas's interaction-controlled statistical properties, using a non-perturbative equation of state obtained via functional renormalization group methods. In the absence of density variations, the cycle acts as a statistical Stirling-like engine with efficiencies up to 38%.
Santiago Henr\'iquez Lira, Felipe Isaule, Mart\'in HvE Groves et al.
In briefPreparing quantum states on digital computers by growing a lattice from a small seed
SummaryThis paper proposes a state preparation method, inspired by nucleation, for lattice Hamiltonians on digital quantum computers. It prepares the exact ground state of a small lattice in a circuit, then grows the lattice to the target size through Trotterized adiabatic evolution stages. The authors give sufficient conditions on total evolution time and Trotter steps for a desired fidelity, and add an optimized variant using variational optimization. For a two-dimensional Ising model, the optimized method is shown to outperform a current leading digital state preparation method.
Jean Paul Sadia, Morten Hjorth-Jensen, Dean Lee et al.
In briefAsymptotic pseudospectra in driven open quantum systems: geometry and observable dynamics
SummaryThe paper studies periodically driven open quantum systems, where nonnormality makes the Floquet spectrum insufficient near the thermodynamic limit and pseudospectra are needed. The authors classify the unit disk into exponential, algebraic, and bounded accuracy domains using size-scaling laws of pseudospectral residuals, revealing a geometric structure. Its physical consequences are illustrated in two exactly solvable models, a dissipative shift chain and a chiral XY model.
In briefError-Resistant Entangled Photon Generation Using SU(1,1) Composite Segmentation
SummaryThis paper studies how composite segmentation, governed by SU(1,1) spatial dynamics, can reduce errors in spontaneous parametric down-conversion, a common source of non-classical light. The authors address phase mismatch caused by temperature drift, angular misalignment, and fabrication flaws in domains. They report that odd spatial Fourier harmonics preserve error cancellation, that a design rule helps adapt setups to several wavelengths, and that an open-loop thermo-optic bias widens the angular acceptance range. Over a 5°C thermal window, the reported relative conversion efficiency stays at or above 0.954, with phase coherence above 0.95.
In briefExact anomalous spin-current fluctuations in the strong-anisotropy limit of the XXZ chain
SummaryThis paper studies spin-current fluctuations in the folded XXZ chain, a model describing the strong-anisotropy limit of the XXZ chain. At infinite temperature, the authors derive an exact expression for the moment-generating function of the time-integrated spin current. Long-time asymptotic analysis shows that the rescaled integrated current converges to a non-Gaussian distribution described by the M-Wright function. The derivation uses a nonlocal map to the one-dimensional t-0 model and its exact spin-charge separation. The authors also show that the dynamical correlation of spins summed over two adjacent sites develops a diffusive Gaussian profile at long times.
WhyDerives an exact moment-generating function for folded XXZ spin current and proves a non-Gaussian M-Wright limit, a substantive new result.
Taiki Ishiyama, Taiga Kurose, Kazuya Fujimoto et al.
In briefExperimentally checking multipartite Bell correlations using only few-body symmetric measurements
SummaryThe authors show that multipartite Bell correlations can be certified using only few-body permutation-invariant correlations of fixed maximal order, avoiding full many-body measurements. They test witnesses for six- and eight-photon postselected Dicke states, finding that adding a few four-body correlators markedly improves noise tolerance over two-body witnesses. The observed violations exceed the witness bounds by 32 and 8.9 standard deviations.
WhyCertifies multipartite Bell correlations using few-body symmetric correlators, adding four-body terms boosts noise tolerance, with large observed violations in six and eight photons.
Jiacheng Sun, Mengyao Hu, Pawe\l{} Cie\'{s}li\'{n}ski et al.
In briefConsistent histories and an ultrametric on infinite tensor products
SummaryThe paper studies the consistent histories formulation of quantum mechanics for sequences of events that accumulate quantum records. It shows that when interference decays with accumulated squared Bures distance, the Kakutani–von Neumann dichotomy separates weakly equivalent record sequences from orthogonal superselection sectors. The convergence exponent of the Bures defect defines a complete ultrametric on histories after quotienting zero-distance degeneracy.
In briefA paper on the trade-off between classical memory and magic-state cost when phases arrive in pieces during Clifford+T compilation
SummaryThe paper studies a trade-off in fault-tolerant processors: a phase delivered in additive pieces can either be stored in classical memory until all pieces arrive, or executed on arrival, which commits magic states (T gates) before the phase is known. The authors give bounds on the exchange rate α, the number of committed T gates per bit of memory forgone, for ancilla-free coordinatewise Clifford+T compilation. They show the rate is at least about 3 in the Clifford-framed case, with some results conditional on an equidistribution conjecture.
WhyA new elementary determinant method with sphere decomposition yields improved exchange-rate bounds for ancilla-free Clifford+T compilation, verified by exact SMT checks; impact is confined to quantum
In briefA magnetic-field insensitive gate set for trapped-ion nuclear spin qubits
SummaryThis paper outlines a complete set of operations for manipulating nuclear spin qubits of trapped ions in high magnetic fields, such as those used in Penning traps. Nuclear spins are largely decoupled from electron spins there, making them insensitive to external fields but slow to manipulate. The authors propose a two-qubit phase gate that uses the electron spin while keeping the qubit protected by its nuclear encoding. The method also works at lower fields and with both microwave and laser field gradients.
Jonathan Paul Home, Jeremy Flannery, Matteo Mazzanti et al.
In briefParametric DRAG pulses that suppress leakage in superconducting qubit exchange gates
SummaryThe paper introduces parametric derivative removal by adiabatic gate (PDRAG), a pulse method that suppresses two leakage pathways in superconducting transmon qubits while preserving the target exchange interaction. In Duffing simulations at a coupling of 100 MHz, calibrated PDRAG reduces leakage by a geometric-mean factor of 5.27×10^5 relative to the base pulse over 12.5–35 ns. Transferring the derivative coefficients to a charge Hamiltonian yields a mean 893-fold reduction over 12.5–22 ns after recalibration.
In briefFast, scan-free quantum mid-infrared spectroscopy for analyzing solids and surfaces
SummaryThis paper presents a scanless quantum Fourier-transform mid-infrared microspectrometer that uses spectral-domain acquisition without scanning an optical delay. It can acquire spectra in about 100 ms across 3000 to 2400 cm⁻¹. The authors demonstrate hyperspectral imaging of dried insulin on gold, analysis of a banknote security feature, and imaging through a turbid ceramic medium.
Paul Gattinger, Michela Conti, Franziska Dietz et al.
In briefCoherence-to-polarization transfer and algebraic storage in a glassy-environment transmon
SummaryThe paper presents a non-Markovian transmon qubit model combining longitudinal Markovian dephasing with transverse renewal events from a glassy two-level-system environment. Without energy relaxation, coherence and longitudinal polarization exchange directionally. For heavy-tailed waiting times with 0<α<1, the longitudinal polarization shows a t^(-α) storage tail. For the studied parameters, the Prabhakar renewal model yields larger forward-transfer magnitudes than Poisson reference models.
In briefSingle-photon source in silicon's telecom L-band via cavity coupling
SummaryResearchers isolated a single silicon C-center and coupled it to a nanophotonic crystal cavity. This enhanced the zero-phonon line emission rate, shortening the excited-state lifetime about fivefold compared with bulk conditions. Second-order autocorrelation confirmed single-photon emission, with g(2)(0)=0.23 without background correction.
WhyDemonstrates isolating a single silicon C-center coupled to a cavity, with Purcell factor ≥33 and g2(0)=0.23 for L-band single photons.
Carolina Crosta, Kyu-Young Kim, Purbita Purkayastha et al.
In briefApproximate majorization and higher-order capacity of quantum depolarizing channels
SummaryThis paper examines whether entanglement can help classical communication over quantum depolarizing channels when coherent operations span multiple channel uses. The authors conjecture a majorization relation for depolarizing channel outputs and prove an approximate version. From this they derive a tight third-order expansion of the classical capacity, showing entangled codewords with collective decoding improve message size over product coding by at most O(log log n) bits.
WhyConjectures and approximately proves majorization for depolarizing channel outputs, yielding a tight third-order classical capacity expansion via anti-concentration bounds.
In briefUltra-high-distance quantum memories built by amplifying qLDPC codes
SummaryThis paper introduces distance amplifiers, a modular method that tensors a base quantum LDPC code with an amplifier to increase code distance and certified circuit-level protection. The authors prove that for flagged [[4,2,2]], hypergraph-product, and rotated surface code amplifiers, the circuit distance multiplies exactly. Applying the flagged [[4,2,2]] amplifier four times to a [[18,4,4]] seed gives a [[13320,64,64]] code with circuit distance at least 48.
WhyIntroduces a recursive modular amplification with proven multiplicative circuit-distance relations and concrete code examples, giving strong novelty and rigorous support.
In briefChoosing Codes and Nodes for Fault-Tolerant Distributed Quantum Computing
SummaryThis paper compares different Bivariate-Bicycle (BB) encodings and node choices for distributed quantum operations such as transversal non-local CNOTs. It finds that minimizing ebit consumption alone may not be the best criterion for reducing logical error rates, since encodings with larger distance can be preferable despite using more physical qubits. The authors use distributed CNOTs and the global CZ gate (GCZ) as examples. They show that a transversal physical GCZ on a self-dual [[120,8,12]] BB code can realize eight concurrent logical GCZ operations after accounting for the logical permutation induced by transversal Hadamard.
In briefA quantum algorithm for solving Riccati equations, with near-optimal complexity analysis
SummaryThis paper develops quantum algorithms that build block-encodings of solution matrices for algebraic, differential, and finite-horizon Riccati problems. A unified Quantum Weighted Riesz Method is used, and under stated assumptions the algebraic cases achieve near-optimal query complexity up to logarithmic factors. The authors also prove lower bounds and BQP-completeness results for certain promise problems. Applications include linear-quadratic control, quantum chemistry, and heated boundary control with numerical validation.
WhyUnifies four Riccati problem types with a weighted Riesz quantum method, giving near-optimal query bounds, product lower bounds, and BQP-completeness; numerical validation is limited.
In briefOptimal entanglement routing in quantum repeater chains beyond fixed operation order and purification schedule
SummaryThis paper studies entanglement routing in quantum networks, where distant nodes share entangled pairs created by purification and swapping. The authors relax the usual restrictions on operation order and per-link purification schedules, and maximize expected end-to-end throughput under a fidelity threshold in linear repeater chains with finite link capacities. Under symmetric Pauli noise, they prove feasibility bounds for pumping-based and tree-based purification schedules. Numerical results show tree schedules serve over 90% of requests that pumping cannot at moderate fidelity thresholds.
Aikaterini Mandilara, Antonia Tsili, Dimitris Syvridis et al.
In briefEncoding universal quantum computation into quantized Berry phases: hardness and classical algorithms
SummaryThis paper studies the computational complexity of estimating quantized Berry phases. It proves that deciding whether the Berry phase is exactly 0 or π is BQP-complete when the spectral gap is inverse-polynomially small, implying a super-polynomial quantum advantage assuming BPP≠BQP. The hardness is extended to physically motivated Hamiltonians on a 2D square lattice, such as Heisenberg and XY models. The authors also give a classical polynomial-time algorithm for geometrically local Hamiltonians with constant spectral gaps, identifying the spectral gap rather than precision as the key factor for classical tractability.
WhyProves quantized Berry phase decision is BQP-complete via a new encoding and gives a classical algorithm for constant gaps, sharpening the quantum advantage boundary; theory-focused.
In briefNon-Canonical Quantum Otto Engine: Studying Quantum Heat Engines Beyond Weak Coupling
SummaryThis paper studies the statistics of efficiency and power in a finite-time quantum Otto cycle heat engine. Conventional analyses assume canonical thermalization, which holds only under weak coupling. The authors show that engineering the energy spectrum of the combined working substance and bath allows control over both the average values and variances of efficiency and power. Near a quantum critical point caused by a bound state in the spectrum, average efficiency and power can rise together while their variances decrease.
In briefAdaptive rotation for iSOMA: a method that reduces coordinate sensitivity in a population-based optimizer, tested on benchmarks, real-world problems, and quantum objectives
SummaryThe paper introduces iSOMA-AR, a variant of the improved Self-Organizing Migrating Algorithm that learns a rotated basis from successful migration moves to reduce coordinate dependence. On the noiseless BBOB suite it significantly outperformed baseline iSOMA, with the largest gains on geometrically difficult landscapes. On frustrated-spin variational quantum objectives it improved most transverse-field conditions, while under strong sampling noise the SOMA variants were the most robust, though iSOMA-AR was not significantly better than baseline iSOMA.
In briefLight-controlled modulation and tuning of diamond photonic cavities: green light shifts near-infrared cavity resonances quickly and reversibly, and produces long-lived wavelength tuning
SummaryResearchers illuminated suspended diamond nanobeam cavities containing nitrogen-vacancy centres with 532 nm green light to achieve all-optical modulation and long-lived tuning. The infrared cavity response is governed by a thermo-optic red-shift and a charge-mediated blue-shift attributed to the free-carrier plasma dispersion effect. With 10 mW of 20 kHz-modulated green light, an infrared modulation depth of about 45% of the available reflection contrast was achieved. A maximum tuning of 3.15 nm (0.87 THz) was observed without measurable loss of linewidth or contrast.
Yuchun Zhu, Amirali Arabmoheghi, Nicolas Le Thomas et al.
In briefA quantum heat engine beating the classical thermodynamic precision limit
SummaryThis paper reports an experiment on a superconducting quantum thermal machine showing that steady-state quantum transport can exceed the precision allowed by the canonical thermodynamic uncertainty relation (TUR). The measured TUR ratio is Q = 1.71 ± 0.17, violating the classical bound Q ≥ 2. The authors argue this reveals a fundamental difference between classical and quantum thermodynamics.
WhyExperimentally shows a superconducting quantum heat engine violating the classical TUR bound, with measured Q=1.71±0.17, impacting quantum thermodynamics foundations.
Simon Sundelin, Ludvig Nordqvist, Khalak Mahadeviya et al.
In briefMargenau-Hill Distribution as an Indicator of Measurement Incompatibility
SummaryThis paper links measurement incompatibility to the Margenau-Hill (MH) quasi-probability distribution for two dichotomic observables. It derives a joint measurability condition for such observables in arbitrary finite dimension and proves that, for unsharp dichotomic measurements, the MH distribution is positive if and only if the measurements are jointly measurable. The authors also introduce an MH-like distribution for n unsharp observables and give a sufficient joint-measurability condition for mutually anticommuting observables, along with an interferometric setup for reconstructing the distribution.](Note)
WhyProves an exact equivalence between joint measurability and MH distribution positivity for dichotomic observables, extended to n observables with rigorous derivations.
In briefUltrafast polariton coherence in plasmonic lattices: a second-order measurement study
SummaryThis paper measures the second-order coherence of polariton emission from a plasmonic lattice, separately for Γ-point (ground state) and non-Γ-point (high-energy tail) radiation. The authors report a high degree of coherence, with g(2)(τ=0)-1 below 10^-4, and ultrafast dynamics above 1 THz. They interpret the process as a Bose-Einstein condensate with sub-50-fs thermalization, and also propose superradiance in emitters with vibrational degrees of freedom as an alternative explanation.
Evgeny A. Mamonov, Lukas Freter, Sioneh Eyvazi et al.
In briefPurifying high-dimensional entanglement using path superposition
SummaryThis paper proposes a scalable method for an arbitrary high-dimensional entanglement purification protocol (HDEPP) using path superposition. Suitable single-qudit gates can purify both qudit-flip and phase-flip errors. The protocol becomes more robust and achieves higher purification fidelity as the dimension increases. The authors also outline feasible optical schemes for purifying photon frequency degrees of freedom using hyperentanglement.
In briefSQUARE: Compact quadratic feature maps for frozen language models using quantum circuit adapters
SummaryThis paper proposes SQUARE, an adapter that amplitude-encodes a low-dimensional bottleneck vector from a frozen language model, runs it through a parameterized quantum circuit, and measures the output state to capture pairwise feature interactions. On eight GLUE-derived controlled interaction tasks, it reports an average test accuracy of 0.7565, higher than an affine normalized-quadratic predictor (0.7355) and an MLP (0.6817). The circuit experiments use simulation, and the learned feature map can be evaluated exactly in batched PyTorch without quantum hardware.
In briefStability of quantum state isometries under small distortions
SummaryThe paper proves dimension-independent Hyers–Ulam stability for surjective approximate isometries of the positive trace-class cone in the trace and Bures metrics. Such maps are uniformly approximated by Wigner symmetries, with error at most 9ε/2 in trace distance and 2√2ε in Bures distance. In infinite dimensions, the authors construct spectrum-preserving homeomorphisms whose distortions vanish yet remain a fixed distance from every Wigner symmetry.
WhyGives dimension-independent Hyers-Ulam stability with sharp constants and infinite-dimensional counterexamples showing dimension-independent moduli are impossible.
In briefMinimal building blocks for exact-spin molecular quantum circuits
SummaryThe paper determines which extra operations, combined with spin-preserving orbital rotations, can generate every real state rotation within each fixed particle-number, total-spin, and spin-projection subspace. Below the maximal-spin limits, repeated singlet-pair transfer between two spatial orbitals suffices. On nontrivial maximal-spin boundaries, an additional generator of one- and two-electron terms is needed, with minimum orbital counts given. Molecular benchmarks show this operation removes boundary energy-error plateaus, and some sparse constructions reach the target accuracy with fewer CNOT gates.
WhyGives necessary and sufficient conditions and minimal orbital counts for complete spin-symmetric generators, with proofs plus molecular benchmarks removing boundary plateaus.
In briefConstructing and probing three-boundary booklet geometries (bulk shell states linking three boundaries).
SummaryThis paper extends partially entangled thermal states (PETS) to three boundaries, replacing two-index insertion data with a trivalent junction tensor to define PETS$_3$. The bulk three-boundary booklet geometry is constrained semiclassically by the Israel junction condition, yielding candidate symmetric and mixed-orientation branches. The authors check self-consistency by counting states in the symmetric all-black-hole sector and estimate a detection-to-universal ratio of about 3 using a heavy-operator probe, twice the two-boundary value of 3/2. They suggest a fine-tuned probe on one boundary could test the proposed state and distinguish it from the two-boundary case.
In briefA quantum algorithm that makes imaginary-time evolution much shallower
SummaryThis paper introduces a probabilistic variant of double-bracket quantum imaginary-time evolution (PDBQITE) for preparing ground states of target Hamiltonians. It needs only one ancilla qubit and one controlled real-time evolution plus one mid-circuit measurement per iteration, giving an exponential reduction in circuit depth. The total success probability decays exponentially with iteration count, and the authors derive a lower bound independent of system size. Simulations show the per-step success probability stays close to one.
In briefQuantum query lower bounds for finding triangles and building spanners
SummaryThis paper proves quantum query lower bounds for two graph problems, triangle listing and constructing multiplicative spanners, in the general graph query model. The authors extend the quantum query recording framework to bidirectional oracles and use intermediate multi-block search problems to obtain their reductions. Listing a constant fraction of the triangles in certain n-vertex graphs requires Ω(n^{3/2-o(1)}) quantum queries. For multiplicative k-spanners with k≥7, the paper gives lower bounds of Ω(n^{1+1/(2μ_k)}) queries.
WhyIntroduces a bidirectional-oracle quantum recording framework and reductions, giving the first nontrivial quantum lower bound for triangle listing and improved spanner bounds, with rigorous proofs.
In briefQuantum simulation of detuning-controlled localization and re-entrant delocalization in coupled quasiperiodic chains
SummaryThis paper studies a two-leg quasiperiodic ladder in which detuning is applied to only one leg. In the weak quasiperiodic regime, this staggered detuning localizes the neighboring leg through inter-leg hybridization, and larger detuning makes the pure chain delocalize again. The authors report dynamical signatures of this delocalized-localized-delocalized sequence on IBM Quantum hardware. They present leg-selective detuning as a programmable way to induce and reverse localization.
Mrinal Kanti Giri, Shih Tai-Ming, Pinaki Sengupta et al.
In briefCavity-QED boosts entanglement and battery performance in double quantum dots
SummaryThe paper theoretically studies quantum correlations and energy storage in a silicon double quantum dot coupled to a microwave cavity. Rashba spin-orbit coupling hybridizes charge and spin, and the authors quantify spin-charge entanglement and coherence at low temperature. The cavity produces a nonlinear crossover between dot-dominated and photon-dressed regimes, which also changes the quantum battery's stored energy and ergotropy.
Hamid Arian Zad, Usama Shoukat, Michal Ja\v{s}\v{c}ur et al.
In briefScalable quantum optimisation for power-system unit commitment, with qubit reduction and hybrid refinement
SummaryThis paper proposes a quantum optimisation framework for power-system unit commitment (UC), which decides which generators run and when. It uses Pauli Correlation Encoding (PCE) to reduce the number of qubits and Sample-based Quantum Diagonalisation (SQD) as a hybrid post-processing step. The authors study how these techniques affect scalability, computational effort, feasibility, and the chance of finding the optimal solution as the number of generators grows. They report that combining both methods gives more reliable solutions at lower effective computational cost than the unreduced formulation in several scalable case studies.
Marc Carrillo-Mu\~Noz, Sergio Mart\'Inez-Hermida, Sara Barja-Mart\'Inez et al.
In briefUniversal Inductive Inference of Quantum States: a framework for learning and predicting quantum sources from measurement data
SummaryThe paper extends Solomonoff's universal inductive inference to quantum systems, introducing a framework for learning and predicting quantum sources that may have arbitrary correlations and entanglement across time. Given past measurement outcomes and post-measurement systems, the learner outputs a joint state predicting the next outcome while preserving correlations with past systems. The authors give an information-theoretic inference algorithm with round complexity O(sε⁻²δ⁻¹), prove a matching lower bound in the relevant regime, and construct a non-i.i.d. state tomography algorithm. They also investigate computational hardness under quantum cryptographic assumptions.
WhyExtends Solomonoff universal induction to quantum sources with a matching lower bound; theoretically novel and rigorous, but impact remains largely theoretical.
In briefAn exact quantum algorithm for searching the intersection of multiple sets
SummaryThis paper builds on Long's modified Grover search, which uses a phase-matching condition to find the target with zero failure rate. The authors extend it to find the intersection of multiple constrained sets exactly, deriving and proving the required phase-matching condition. They also present a quantum circuit implementing the exact intersection search, with numerical simulations supporting the results.
In briefDevice-independent measure of steering in three-party systems
SummaryQuantum steering is the ability of one party's local measurements on a shared entangled state to affect distant parties' conditional states in a way no local model can explain. The authors extend the assemblage moment matrix framework, previously used for two parties, to tripartite cases where two parties steer a third or one party steers two others. For each case they build a semidefinite program that yields lower bounds on the steering robustness from observed correlations or even Bell inequality violations. The bounds also certify, device-independently, that the steering parties' measurements are incompatible.
In briefDigital twin of quantum dynamics using dissipative quantum reservoir computing
SummaryThe paper introduces dissipative quantum reservoir computing (DQRC), a framework that learns the input-output behavior of driven quantum many-body systems while keeping a small open quantum reservoir fixed and training only a classical readout. Applied to high-harmonic generation, the authors report that a single-qubit reservoir reproduces the response of a larger Ising spin chain. On a representative benchmark, they state the model matches and on several metrics surpasses prior temporal convolutional and Kolmogorov-Arnold network models.
Abhijit Sen, Bikram Keshari Parida, Shital Chauhan et al.
In briefTwo-copy measurements close the single-copy gap to the Holevo bound
SummaryThis paper studies whether the Holevo Cramér-Rao bound for quantum multiparameter estimation can be attained with finite copies of a state. The authors construct a three-parameter rank-two model whose Holevo bound cannot be reached with one copy but is attained exactly with two, and they prove that full-rank models retain a finite-copy gap for any number of parameters. They also experimentally implement the two-copy collective measurement on superconducting qubits, observing error below single-copy and separate-measurement bounds, with this advantage persisting over a finite range of depolarizing noise.
WhyConstructs a three-parameter rank-two model where two copies attain the Holevo bound but one copy cannot, and proves finite-copy gap persistence for full-rank models.
In briefExact Trotter error analysis for the degenerate quantum Rabi model
SummaryThis paper studies digital quantum simulation of the quantum Rabi model in the deep strong coupling regime, where Trotterization errors were previously known only through qualitative bounds. In the exactly solvable degenerate limit, the authors show that the first-order Trotter operator has a closed form and that the generated phase-space trajectory lies exactly on a rescaled, rotated circle. This yields a closed-form expression for state fidelity. They also report that promoting the Trotter-step coupling to a complex amplitude corrects this geometric error without additional circuit cost.
In briefMeasurement-feedback interval can induce order in quantum Boltzmann samplers
SummaryThis paper studies whether changing only the measurement-feedback interval, with fixed couplings and a fixed local dissipative rule, can induce ordering in a quantum Boltzmann sampler. At zero environmental dephasing, repeated projective measurements remove transverse coherence regenerated during relaxation, enhancing the local longitudinal response. In the Curie–Weiss limit, for couplings below the equilibrium threshold, shortening the readout interval drives a continuous transition to an ordered stationary state even though the programmed Boltzmann distribution remains disordered.
In briefQuantum States and Spectra of Small Cylindrical and Toroidal Lattices
SummaryThis paper studies the spectra and quantum states of small cylindrical and toroidal lattices under a scalar gauge potential that adds a position-dependent phase to inter-site coupling. Periodic boundary conditions generally break the gauge equivalence assumed for infinite lattices, and the authors identify conditions that restore it. They report gauge-dependent avoided crossings and persistent degeneracies, and examine the effects of boundary conditions, coupling strengths, and an axial field.
In briefBlock-wise quantum algorithm for PDEs with interface penalties
SummaryThis paper proposes a block-wise variational quantum algorithm for solving partial differential equations whose solutions vary in complexity across space. The domain is split into local quantum subproblems, with grid sizes and circuit designs assigned according to a computable difficulty indicator. Neighboring blocks are coupled through jump penalties on state values, derivatives, and fluxes, and the rough regions are adaptively tracked. Simulations on elliptic, advection-diffusion, and Burgers problems show lower errors and smaller peak local circuit width than global variational quantum approaches.
In briefQuantum-Selected Configuration Interaction for Benzene Dimer Stacking Energies
SummaryThis paper proposes Divide-and-Conquer Quantum-Selected Configuration Interaction (Deep QSCI) to evaluate π-π stacking interaction energies in the sandwich benzene dimer. QSCI is run on one monomer, and a reduced local basis built from its ground state is used to diagonalize an effective dimer Hamiltonian, reusing monomer results across monomers and distances to cut the required qubits from 40 to 20. With 6-31G**, the minimum is -0.91 kcal/mol at 4.0 Å, compared with -1.14 kcal/mol from counterpoise-corrected CCSD(T). With cc-pVDZ, large cancellations appear, which the authors suggest may stem from insufficient consistency of active orbitals and local bases between monomers.
In briefCalibrating quantum priors with fidelity structure for single-circuit QGAN image generation
SummaryThis paper studies pixel-level, end-to-end image generation with a single-quantum-circuit Quantum Generative Adversarial Network (QGAN), avoiding patch-based decomposition. The authors introduce the Quantum Fidelity Landscape (QFL) and use it to calibrate the quantum prior before adversarial training, in a framework called BasicQGAN. On small grayscale image datasets, the method achieves stable generation while requiring fewer qubits and trainable parameters than representative patch-based quantum generators.
In briefOptimizing randomized quantum simulation of Hamiltonians by minimizing average error
SummaryThe paper presents a framework for randomized Hamiltonian simulation that samples terms with arbitrary probabilities and implements their short-time evolutions in sequence. It shows that sampling in proportion to Hilbert-Schmidt norms, derived from Haar-averaged error bounds, can give smaller average-error bounds than the standard qDRIFT method. For Pauli-string Hamiltonians, combining this with commuting Pauli grouping further reduces error bounds at fixed depth.
In briefSingle-photon nonlinearity from a quantum dot in a nanobeam cavity
SummaryThis paper reports a single-photon nonlinearity built from a nanobeam cavity coupled to one quantum dot. The device couples directly to a single-mode fiber with 60% efficiency and reaches the nonlinearity at a threshold of 0.24 incident photons per resonant picosecond pulse. The system operates in the strong-coupling regime, with a coupling rate g/2π of 29.1 GHz and cooperativity C of 3.98. The authors present it as a compact, chip-integrable, fiber-compatible building block for photonic quantum technologies.
Abhijit Biswas, Neelesh Kumar Vij, Allan S. Bracker et al.
In briefSynchronizing quantum devices over lossy channels using polarization assistance
SummaryThis paper proposes and experimentally demonstrates a polarization-assisted protocol that uses entangled photon pairs to keep quantum devices synchronized under high channel loss, such as satellite-to-ground links. The experiments show reliable synchronization at higher losses and up to a 40% increase in satellite-to-ground distance. Monte Carlo simulations indicate the improvement holds across a wide range of photon-starved conditions.
In briefRoot-system structure of sloppiness in passive Gaussian metrology
SummaryThe paper studies when passive transformations of squeezed Gaussian probes become locally unidentifiable because the quantum Fisher matrix loses rank. It shows that the C_n restricted-root system of Sp(2n,R)/U(n) governs this exact sloppiness for pure zero-mean Gaussian probes. It also solves the E-optimal probe-design problem of maximizing the smallest passive Fisher eigenvalue at fixed mean photon number.
In briefShared phase arithmetic: applying a layer of diagonal quantum rotations at once
SummaryThe paper proposes parallel phase kickback (PPK), which coherently computes a weighted sum of several rotation parameters, adds it once to a phase-gradient state, and then uncomputes it. This separates the cost of representing a phase function from the cost of applying it. The authors prove correctness, give explicit error bounds, and analyze logical gate counts for general weights, pairs of rotations, and weights with disjoint binary support. The bounds show when shared phase arithmetic reduces amortized rotation cost and when encoding overhead limits that advantage.
In briefA paper on how quantum Fisher information and quantum coherence factorize over time
SummaryThis paper studies the factorization relationship between quantum Fisher information, which measures how sensitive a quantum state is to parameter changes, and quantum coherence. The authors prepared pure states in qubit and qutrit systems, applied unitary evolution, and confirmed the factorization law both theoretically and experimentally. They also derived a lower bound on the variance of the estimated parameter that does not require final-state information.
In briefA general spin-chain method for multicomponent anyons in 1D optical lattices
SummaryThis paper introduces a generalized effective spin-chain (GESC) framework for strongly interacting multicomponent anyons in one-dimensional optical lattices. It maps particle motion to spinless fermions and spin states to an ordered chain, separating spin and charge degrees of freedom. The authors report that in the strong-interaction regime the fractional exchange phase appears in spin-exchange coefficients through virtual tunneling. They also describe how direction-dependent phases affect non-equilibrium impurity transport.
In briefMulticomponent anyons in one-dimensional optical lattices: a study of how particles with fractional exchange statistics behave in a 1D lattice
SummaryThis paper studies the ground-state and dynamical behavior of multicomponent interacting anyons confined in a one-dimensional optical lattice, using the Anyon-Hubbard model. It shows that fractional exchange statistics combined with multicomponent effects reshape charge and spin correlations, including asymmetric momentum-distribution shells and new peaks. The authors report antiferromagnetic spin ordering and find that the statistical phase parameter can switch dipole oscillations between underdamped and overdamped regimes.
In briefEmergent symmetries after ensemble averaging: a review of how global symmetries can arise in quantum gravity.
SummaryThe paper reviews work showing that global symmetries, believed absent in quantum gravity, can emerge after ensemble averages of theories as encountered in holography. Its case study is the ensemble average of two-dimensional Narain-type conformal field theories with an even quadratic form, computed by the Siegel-Weil formula and interpreted as a sum over geometries in a three-dimensional Abelian Chern-Simons theory. The authors also relate this to the Swampland program and recast strong-to-weak spontaneous symmetry breaking of mixed states as symmetry emergence in ensemble averages, motivating a new Swampland conjecture.
In briefQuantum References Beat Classical Ones for Leakage Detection
SummaryThe paper shows that leakage from an encoding subspace can be detected using independent quantum reference states prepared by the same encoder, without a classical description of the encoding. For orthogonal leakage, the miss probability is asymptotically 4/M, independent of the ambient dimension. Measuring all references first yields zero detection under the same zero-false-alarm requirement. For one logical qubit in three physical qubits, seven coherent references achieve at least 50% detection, while a measurement-first receiver needs at least 588.
WhyProposes coherent quantum references for leakage detection without classical encoding description, with optimality proofs and exponential sample advantage shown.
In briefFactorization of driven anisotropic Rabi–Stark Hamiltonians via affine spin pencils
SummaryThe paper constructs a supersymmetric factorization of generalized driven anisotropic Rabi–Stark Hamiltonians using an affine factor in an inhomogeneous orthosymplectic superalgebra. The normal product has an exact zero-energy ground doublet and a Witten index of two. It also covers a Bargmann hierarchy, endpoint conditions for exceptional finite-polynomial states, several limiting cases, and an interior example with additional drives, Stark deformation and intensity-dependent coupling.
B. M. Rodriguez-Lara, F. H. Maldonado-Villamizar, A. Kafuri et al.
In briefEvanescent-wave Johnson noise from superconductors, explained
SummaryThis paper calculates evanescent-wave Johnson noise above a superconductor's surface and the resulting relaxation time T1 of spin and charge qubits placed nanometers away. It uses a microscopic current-response kernel for a BCS superconductor, together with the fluctuation-dissipation theorem and nonlocal surface impedances. Magnetic noise is enhanced just below Tc by the coherence peak and falls exponentially at lower temperatures, while magnetic impurities produce a zero-temperature noise floor.
WhyDevelops a full theory of evanescent-wave Johnson noise and qubit T1 near superconductors, predicting coherence peaks and a zero-temperature noise floor.
Hruday Mallubhotla, Gustav Romare, Ilya Esterlis et al.
In briefImproved quantum algorithms for decomposing black-box Abelian groups into cyclic factors
SummaryThis paper presents a quantum algorithm that decomposes finite Abelian black-box groups into cyclic factors. It adapts quantum sampling and classical lattice reduction from Regev's factoring algorithm to compute an invariant-factor decomposition with high probability. Compared with the Cheung-Mosca approach, the authors report lower total gate counts, quantum time bounds, and qubit requirements.
In briefQuantum Computing for Network Security Classification: Near-Term and Long-Term Memory Efficiency
SummaryThis paper examines how quantum computing may help network-security classification through two experiments. First, quantum-kernel SVMs are compared with classical SVM baselines on KDD Cup 1999, CICIDS2017, and BoT-IoT, finding quantum kernels competitive in some settings while classical RBF kernels remain stronger in others. Second, quantum oracle sketching is used to study memory efficiency for classifying streaming data, showing that comparable accuracy requires a much smaller effective memory size than explicit sparse or QRAM-style storage. The authors suggest the long-term value may lie in memory-efficient data access rather than immediate runtime speedup.
Yuqing Li, Poonam Bala Nehru, Yunpeng Zhang et al.
In briefHow work cumulants scale when a driven Gaussian field crosses over between regimes
SummaryThe paper derives the finite-temperature characteristic function of work for a driven O(N) Gaussian field theory and gives closed-form expressions for all zero-temperature excess-work cumulants. For gapped protocols, adiabatic perturbation theory yields a τ_Q^-2 scaling, where τ_Q is the protocol duration. For power-law protocols approaching criticality, the authors analyze the competition between critical excitations and regular contributions, identifying Kibble–Zurek-type scaling and a logarithmic correction at a specific threshold.
In briefDegree balance sets a fine-grained complexity boundary for quantum SAT
SummaryThis paper studies the local Hamiltonian problem, a QMA-complete problem, under fine-grained complexity. Assuming the Hamiltonian is frustration-free on YES instances and approximately regular, the authors give classical and quantum algorithms that are exponentially faster than brute force. Assuming (Q)SETH, they show quantum 5-SAT has no non-trivial worst-case speedup, even when only O(√n) qubits have high degree. Reducing that high-degree set or its degrees by a factor of n^δ yields an O(2^{(1-ε)n}) algorithm.
WhyGives exponential speedups under frustration-freeness and regularity, plus a near-tight (Q)SETH lower bound forming a fine-grained dichotomy.
Atsuya Hasegawa, Jonas Kamminga, Fran\c{c}ois Le Gall et al.
In briefTransverse momentum as the counter-diabatic generator in bent waveguide couplers
SummaryThis paper studies bent mode-evolution couplers, where bending the waveguide axis suppresses coupling between supermodes. The authors identify transverse momentum as the operator that generates the required counter-diabatic term. They derive a closed-form expression for the axis slope and compare the design with a straight coupler using a unitary transformation, reporting supermode fidelities of 0.994 and 1.000.
In briefDynamical resource theory of time-reversal symmetry breaking
SummaryThe paper proposes an operationally meaningful framework for quantifying the intrinsic time-reversal symmetry breaking (T-violation) of quantum channels, treating it as a resource within dynamical resource theory. T-violation is split into kinematic T-violation, arising from antiunitary motion-reversal, and nonunitality driven purely by thermodynamics. The authors also analyze the resulting resource theory of kinematic T-violation and report a universal golden unit, including for classical channels.
In briefA rigidity theorem: Gaussian states dominating separable operators are separable
SummaryThe paper proves that a finite-mode Gaussian state is separable across a fixed mode partition if it dominates a nonzero positive operator that is separable across that partition. Three consequences follow: a Gaussian channel with a nonzero entanglement-breaking subchannel is entanglement breaking, and a connected graph of entangled two-mode Gaussian marginals certifies genuine multipartite entanglement. The authors also show full inseparability and genuine multipartite entanglement coincide for finite-mode Gaussian states.
WhyProves a separability rigidity theorem for finite-mode Gaussian states with several applications, offering substantive theoretical novelty and a rigorous argument.
In briefPuncturing method for adaptive entanglement-assisted quantum error-correcting codes
SummaryThis paper extends a puncturing construction for standard stabilizer codes to entanglement-assisted codes, so that one mother code can be adjusted to different numbers of available pre-shared Bell pairs. The three-step procedure treats the code as unassisted, punctures one receiver-side qubit, and recovers an entanglement-assisted form, reducing the required Bell pairs by one while keeping transmitted and logical qubit counts. The authors derive a bound on the resulting distance loss and give conditions for preserving the original distance. In an analysis of random codes with five to eight transmitted qubits, 14.75% had greater distance than their unassisted counterparts, and 81.4% of those admitted a puncturing choice that keeps the original distance.
Nicolai Peder B\"ulow Pedersen, Jakob Kaltoft S{\o}ndergaard, Jaron Skovsted Gundersen et al.
In briefEstimating teleportation costs for distributed quantum chemistry circuits
SummaryThis paper estimates the resources needed to run unitary coupled-cluster circuits for hydrogen chains across distributed quantum processors using teleportation. It compares a naive distribution method with the TeleSABRE algorithm, counting Bell pairs and classical communication for nonlocal two-qubit gates. The authors find that UpCCD with spin-blocked Jordan-Wigner ordering scales most favorably, while UCCSD requires substantially more distributed resources.
Grier M. Jones, Hassan Tariq Shafi, Zixuan Wang et al.
In briefBivariate bicycle codes over group algebras: quantum codes built from weighted shifts
SummaryThis paper studies bivariate bicycle group-algebra (BBGA) quantum error-correcting codes built from weighted shift operators over finite group algebras. The authors give sparsity bounds and present computer-verified examples, including a [[144,16,12]] code over a nonabelian group and a [[18,4,3]] code. They show these examples are inequivalent to ordinary abelian realizations.
In briefWhat physics is for: why classical physics is not the limit of quantum mechanics
SummaryThis paper examines the claim that classical physics is the low-action limit of quantum mechanics. It argues that interpretive problems such as the measurement problem, the subject-object divide, and the nature of scientific representation were already present in classical physics. The authors contend quantum mechanics exposes long-unacknowledged philosophical assumptions rather than breaking cleanly from classical physics. The London-Bauer interpretation and QBism are discussed as examples of this broader reconceptualisation.
Adam Frank, Jacques L. Pienaar, Michel Bitbol et al.
In briefNear-optimal quantum simulation of open-system lattice dynamics, explained
SummaryThis paper studies how to simulate time evolution under geometrically local Lindbladians on a lattice of qudits. The authors present an algorithm that approximates this evolution for time t on N qudits, with diamond-norm error ε, using geometrically local circuits of depth O(t polylog(Nt/ε)). The authors state that this performance is comparable to the HHKL algorithm for lattice Hamiltonian simulation.
WhyExtends HHKL lattice Hamiltonian simulation to local Lindbladians, giving near-optimal circuit depth with rigorous error analysis.
In briefMASH-PLDM: a partially linearized surface hopping method for nonadiabatic dynamics and nonlinear spectroscopy
SummaryThis paper introduces MASH-PLDM, a partially linearized version of the mapping approach to surface hopping for simulating nonadiabatic dynamics in molecules. It uses two spin vectors, based on the partially linearized density matrix, to describe either electronic population on one adiabatic surface or coherence on the average surface. The method gives improved results over the original MASH for various scattering problems and spin-boson models, especially where coherences matter. It can also compute multi-time correlation functions, which is demonstrated with a proof-of-principle simulation of time-resolved pump-probe spectroscopy.
Jan Obermeier, Kasra Asnaashari, Jeremy O. Richardson
In briefFrom Classical to Quantum Channels: Positive Covert Communication Rates
SummaryThis paper examines when covert communication at positive rates is possible over discrete memoryless classical, classical-quantum, and quantum channels. For classical point-to-point channels, positive covert rates are achievable for certain channel classes when the input alphabet is larger than the output alphabet. For quantum channels, if the innocent state is mixed, a non-trivial input ensemble can always satisfy the covertness constraint.
WhyDerives new conditions for positive covert rates across classical, cq, and quantum channels, extending prior results with rigorous proofs.
Hassan ZivariFard, Xiaodong Wang, and Alexei Ashikhmin
In briefNear-optimal parallel quantum gate learning with low diamond-distance error
SummaryThis paper studies how to learn an unknown quantum gate (unitary process tomography), a key step toward working quantum computers. Sequential circuits were already known to achieve optimal query complexity under diamond-distance error, but it was unclear whether parallel circuits could match this. The authors introduce a new explicit parallel procedure and prove that near-optimal query complexity is achievable with parallel circuits. The gap between parallel and sequential approaches is thus closed up to a logarithmic factor.
WhyIntroduces an explicit parallel procedure achieving near-optimal query complexity in diamond distance, nearly closing the gap with sequential circuits.
In briefCollectivity: a mechanism that limits quantum entanglement even with long-range interactions
SummaryThis paper studies how ground-state quantum entanglement is limited in gapped many-body systems with long-range power-law interactions. The authors show that many weak interactions produce fluctuations controlled by their square-summed strength, a mechanism they call collectivity. They derive logarithmic or subextensive entanglement bounds for arbitrary bipartitions and polylogarithmic bounds for regular bipartitions, and show several of these scalings are optimal.
WhyProves collectivity, not locality, constrains entanglement for power-law interactions, with rigorous bounds and matching optimality results advancing long-range many-body theory.
In briefMeasuring non-Markovianity via witnesses, avoiding full Choi state reconstruction
SummaryThis paper proposes a witness-based framework for quantifying non-Markovianity in open quantum systems that avoids fully reconstructing the Choi state of the intermediate dynamical map. It shows that every witness gives a certifiable lower bound on a geometric resource measure, and that positive-semidefinite witnesses also bound the RHP measure. For amplitude-damping and Pauli dynamics, the optimal positive witnesses reduce to Bell-parity projectors whose values come from a few experimentally accessible correlation measurements.
In briefChecking whether projected and full-space open-shell ADAPT-VQE states match
SummaryThe paper examines whether a state optimized in a symmetry-projected space equals the state from exponentiating the unprojected parent generators. It proposes the target-space invariance condition QAP=0 as an equivalence audit and applies it to a Cu(II) CAS(15e,9o) Hamiltonian, where most Hartree–Fock-origin excitations violate it. The work presents a validation framework rather than a new spin-adapted ADAPT algorithm.
In briefQuantum parameter estimation under decoherence in neutrino oscillations
SummaryThis paper studies neutrino oscillations as an interferometric system for open-system dynamics, quantum resources and parameter estimation. It distinguishes two decoherence models, propagation-basis dephasing and effective flavor-mode dephasing, and derives concurrence, entanglement of formation and local quantum uncertainty for the two-flavor mode state. A monochromatic three-flavor benchmark compares the quantum Fisher information matrix with flavor Fisher information, and the results are state-level information-geometric benchmarks rather than event-level sensitivity forecasts.
Jilali Loulijat, Abdallah Slaoui, Mohamed Gouighri et al.
In briefStudying Quantum Chaos Measures Beyond the Standard Lindblad Approach
SummaryThis paper examines out-of-time-ordered correlators (OTOCs), which measure quantum chaos and information scrambling. Starting from a microscopic model of a subsystem coupled to a random bath, the authors find that OTOC dynamics includes an extra contribution, arising from correlations between replicas, beyond the standard Lindblad approach. This extended formalism better preserves properties such as long-time freeness and captures scrambling more faithfully. The authors also show it can be used to numerically study OTOCs in large closed systems by replacing part of the system with a dissipative boundary.
In briefIndependent density and coherence skin effects in adaptive fermion circuits
SummaryThis paper studies adaptive quantum circuits that use measurements and outcome-conditioned feedback to produce nonreciprocal dynamics without postselection. The authors show that density and coherence skin effects in fermion circuits can be tuned independently. The stationary density tilt depends only on measurement strength and feedback displacement, while bulk coherences follow an effective Hatano-Nelson generator set by the conditioned gates through a relative occupation phase. Tuning this phase drives a point-gap topological transition and reverses coherence localization.
In briefIs rapid mixing stable? A study of whether fast relaxation in open quantum systems survives local perturbations
SummaryMany open quantum systems governed by Lindbladians relax to steady states quickly, in polylogarithmic time in system size. The paper questions whether local perturbations leave this fast mixing intact. It gives counterexamples showing rapid mixing is not stable in general, even when the steady state is unchanged, and shows arbitrarily weak local Hamiltonian perturbations can destroy it. It also provides sufficient conditions guaranteeing stable rapid mixing for several classes of systems.
WhyShows rapid mixing is generally unstable via counterexamples and gives several sufficient conditions for stability, with strong theoretical support and clear relevance to the subfield.
Jordi A. Monta\~n\`a-L\'opez, Barbara Roos, Sebastian Stengele et al.
In briefEntanglement spectrum and magic in higher-dimensional free-fermion systems
SummaryThis paper studies fermionic non-local magic in higher-dimensional free-fermion systems using the entanglement spectrum. For translationally invariant Gaussian states in strip geometries, dimensional reduction reduces the problem to independent lower-dimensional momentum sectors, giving a logarithmic violation of the boundary law in two dimensions. The authors show that second Rényi fermionic non-local magic is bounded by entanglement capacity and introduce an entanglement-temperature deformation. Applied to the Kitaev model, the response is exponentially suppressed in the Abelian phase and algebraic in the non-Abelian phase. For quenches, random Gaussian circuits are shown to spread diffusively in two spatial dimensions.
In briefFast Hamiltonian engineering via cut polytope geometry
SummaryThis paper presents a unified framework for Hamiltonian engineering, which simulates a target Hamiltonian's quantum dynamics using a native entangling system and restricted controls, across 2-local qubit, qudit, and fermionic systems. The authors recast time-optimal engineering as a k-cut polytope problem, prove it NP-complete, and relax it to an elliptope with Krivine-type rounding to generate pulses for a linear program. On Ising, chiral clock, and fermionic Harper-Hofstadter benchmarks, the method achieves near-optimal run times and outperforms state-of-the-art approaches, with an O(√m) approximation ratio.
WhyReduces time-optimal Hamiltonian engineering to a k-cut polytope, proves NP-completeness, and gives an O(√m) approximation via elliptope relaxation, outperforming baselines on several benchmark models
Thomas Joachim Friese, \"Ozg\"un Kum, Aram W. Harrow et al.
In briefDigital quantum algorithms for creating and using spin squeezed states
SummaryThis paper presents algorithms for efficiently generating and using spin squeezed states on digital quantum computers. The authors introduce an adaptive local-circuit protocol that prepares states with squeezing parameter ξ in depth O(log 1/ξ), which they prove is optimal for permutation symmetric states. Classical simulations under realistic noise models predict a metrological gain of 4.2 dB beyond the standard quantum limit using 55 superconducting qubits including ancillae.
WhyAn adaptive local circuit achieves exponential depth improvement for spin squeezing, with a matching entanglement lower bound and noisy simulations supporting feasibility.
In briefOut-of-time-order correlators in tunable Volcano potentials
SummaryThis paper studies out-of-time-order correlators (OTOCs), a diagnostic of quantum scrambling and chaos, for Volcano potentials. This family interpolates between bounded wells and confining walls and includes the Pöschl-Teller potential. Using numerical diagonalization and semiclassical analysis, the authors examine parameter regimes with both positive and negative curvature. They find that short-time exponential OTOC growth does not necessarily indicate global quantum chaos, but correlates with excited states sampling negative-curvature regions.
In briefAsymptotically Optimal Mixed-State Cloning (theory of copying quantum mixed states at scale)
SummaryThe paper determines the asymptotic global fidelity of cloning generic mixed states with simple full-rank spectra, with n inputs and m_n outputs such that m_n/n tends to γ>1 in fixed dimension d. It gives an optimal fidelity formula when the spectrum is known and a spectrum-independent cloner when it is unknown, shown to be minimax optimal. For flat projector states, the optimum is also derived, and the proposed cloners are shown to strictly outperform the purify–clone–trace (PCT) method for simple full-rank spectra and rank-r projectors with 1<r<d.
In briefMeasuring quantum gains in joint current precision in open systems
SummaryThe paper derives a multi-current kinetic uncertainty relation (MKUR) that bounds the precision of multiple currents in classical nonequilibrium steady states. It compares a quantum system with a classical emulator having the same average currents to identify when quantum coherence reduces joint current fluctuations below the classical limit. The approach is illustrated with a coherently driven two-level system and a three-level heat engine with parasitic environmental couplings.
Khalak Mahadeviya, Sheikh Parvez Mandal, Mahasweta Pandit et al.
In briefChern-number estimation: near-optimal quantum algorithm with provable speedup
SummaryThis paper presents a quantum algorithm for estimating the Chern number, a topological invariant, of a smooth Hamiltonian family over a two-dimensional parameter torus with a unique gapped ground state, including interacting many-body systems. Its Hamiltonian-oracle evolution time is Õ(L_xL_y/Δ_min³), and the authors prove a matching worst-case oracle lower bound, even when the Chern number is promised to be zero or one, so the algorithm is optimal up to polylogarithmic factors. They also show that exact Chern-number computation for local Hamiltonian families is in FBQP and BQP-hard.
WhyGives a nearly optimal Chern-number algorithm with matching lower bound and BQP-completeness results, a strong theoretical advance with notable impact on topological phases.
Soichiro Imamura, Shintaro Ae, Kazuki Sakamoto et al.
In briefTopological band theory for quantum Hall systems with high-dimensional flux parameter spaces.
SummaryThis paper studies topological band theory for quantum Hall systems whose adiabatic flux parameters form a high-dimensional manifold. Such settings arise for strongly correlated matter on Riemann surfaces of genus greater than one and for matter on compact oriented manifolds coupled to p-form gauge potentials. The topological invariants on the parameter space include higher-order curvature terms beyond the first Chern class, which contribute topologically protected terms to Kubo-like formulae. The authors illustrate these ideas with a hyperbolic band theory example based on the genus-two Bolza Riemann surface, a case recently simulated on a synthetic-dimension platform.
Vivek Chakrabhavi, Walt Chavarria, Jonathan J. Heckman et al.
In briefProving that deciding whether the multiparameter quantum Fisher information is attainable is NP-hard
SummaryThe quantum Fisher information sets a bound on the precision of estimating several parameters at once, but a general condition for reaching this bound with measurements on single copies of a state has been missing. This paper proves that deciding exact attainability is NP-hard, even for a restricted class of real, constant-rank quantum models. The proof reduces from deciding whether a bipartite density matrix is separable. Unless P=NP, no efficiently computable necessary and sufficient criterion exists in general.
WhyReduces QFI attainability to separability and proves NP-hardness, resolving a long-open question with a rigorous argument, significant for the subfield.
In briefConstant-depth circuits that prepare 1D quantum Gibbs states
SummaryThe paper proves that the Gibbs state of any spin chain at any constant temperature is exactly a mixture of product states over bounded-length blocks of qubits. This implies such states can be prepared by constant-depth local unitary circuits with efficient classical preprocessing. The authors also obtain analogous results for 1D local fermionic Hamiltonians.
WhyProves exact decomposition of any 1D spin-chain Gibbs state into bounded-block product mixtures, yielding constant-depth preparation and tight entanglement bounds.
Sa\'ul Pilatowsky-Cameo, Georgios Styliaris, Ainesh Bakshi et al.
In briefDetecting Low-Frequency Gravitational Waves via Gravito-Magnetism
SummaryThis paper proposes a method to detect low-frequency gravitational waves (10 nHz to 1 µHz) that separates the signal from asteroid-belt gravity gradient noise. It exploits the gravito-magnetic component of gravitational waves, measured through the Lorentz-type acceleration of test masses. The authors argue this is metrologically feasible and show it allows unambiguous signal extraction in a three-satellite constellation. Atom interferometers are proposed as the isolated inertial reference.
