In briefQuantum batteries whose storage is controlled by waveguide geometry
SummaryThis paper studies quantum batteries made of several emitters coupled to a one-dimensional waveguide driven by a broadband squeezed-vacuum reservoir. It shows how the waveguide geometry controls battery performance, including the nonpassivity of the steady state and the extractable part of the stored energy. For two emitters, geometry alone can switch the battery between a passive steady state and one where all stored energy is unitarily extractable.
Luis D. Zambrano-Palma, Yusef Maleki, M. Suhail Zubairy
In briefQuantum Submodular Maximization: quantum queries for approximately maximizing non-negative submodular functions
SummaryThis paper studies how many quantum queries are needed to maximize a non-negative submodular function, both without constraints and, for monotone functions, under a cardinality limit k. In the exact reversible digital value-oracle model, the unconstrained algorithm reaches an expected (1/2-ε) approximation with O(log n) queries. This is exponentially fewer than the Ω(n/log n) queries that classical randomized algorithms need for ratios above 1/4. For the cardinality-constrained case, the algorithm achieves a (1-1/e-ε) approximation and gives at least a quadratic speedup over classical methods when k=o(n), up to logarithmic factors.
WhyGives quantum query algorithms and lower bounds for submodular maximization, achieving an exponential separation in the unconstrained setting with a rigorous theoretical treatment.
In briefCollapse time of weak measurement across N entangled sites
SummaryThis paper studies how long local weak measurements take to collapse an initial superposition of N alternatives onto a single occupied site. For equal initial probabilities and a fixed confidence threshold, the authors prove that the ratio of collapse time to ln N converges to 1/2 in L¹, with time measured in units of each detector's characteristic measurement time. They also show that the first site to reach the threshold is the eventual outcome, with conditional probability exactly equal to the threshold, and correct a previously proposed double-logarithmic scaling.
In briefBeyond Ideal Cavities: How Cavity Loss Affects Strong Light-Matter Coupling
SummaryThis paper extends the Pauli-Fierz Hamiltonian to include cavity dissipation, described by the experimentally measurable cavity quality factor Q, and combines it with the QED-CCSD method. The authors compute the optical spectrum of a p-nitroaniline molecule under strong coupling. For realistic Q values, cavity dissipation reduces the Rabi splitting by more than 20% relative to the ideal-cavity limit, while the system remains in the strong-coupling regime. Approaching the ideal-cavity limit requires much higher Q values than those needed to establish strong coupling.
Giovanna Bruno, Enrico Busani, Lorenzo Gialli et al.
In briefSymmetry-resolved entanglement in Schwinger pair production: how entanglement is split across charge sectors
SummaryThis paper studies how the entanglement between particle pairs created by the Schwinger effect is distributed across electric charge sectors, using the U(1) charge of quantum electrodynamics. For a constant electric field, it gives closed-form results for each mode pairing, with all field dependence controlled by the pair production probability |β|²=e^(-πμ). The authors report that for particle-particle and antiparticle-antiparticle pairs the entropy within each charge sector does not depend on the field, while for vacuum-created pairs the negativity moves between charge imbalance sectors as the field increases.
In briefOptimal interferometer geometry for gravity-induced quantum entanglement
SummaryThis paper studies how gravity can entangle two massive particles in an interferometer, a possible experimental signature of the quantum nature of gravity. The authors show that the interferometer's geometry strongly affects entanglement generation. Geometric optimization can substantially enhance the gravitationally induced phase shift. The authors also argue that standard approximations used in earlier proposals may severely limit predictive accuracy.
In briefStudies imaginarity of quantum channels as a resource in Shor's order-finding algorithm.
SummaryThis paper examines the sequential version of Shor's order-finding algorithm through the imaginarity of quantum channels. By fixing an eigenbranch of the modular multiplication unitary and a target output path, the process is split into a real diagonal factor and a residual phase channel. For the ideal residual phase channel, the three trace-norm induced imaginarity measures are shown to be equal, enabling exact and bounded expressions for the success probability. The analysis is then extended to noisy residual phase channels.
In briefProof that collapse of nonuniform quantum polynomial-time hierarchy implies collapse of QCPH
SummaryThe paper introduces the non-uniform computational Quantum Polynomial-Time Hierarchy (QCPH/mpoly), a quantum analogue of the classical PH/poly. It shows that QCPH/mpoly collapses if and only if QCPH, the quantum polynomial-time hierarchy of Gharibian et al., collapses. The authors also show that QCPH collapses if coQCMA is contained in QCMA/mpoly.
In briefStructural conditions for distributed quantum advantage
SummaryCircuit cutting runs quantum computations on processors smaller than the circuit, but classical knitting cost grows exponentially with the number of cut gates. The paper states three requirements for distributed quantum advantage: affordable knitting, classical difficulty surviving the cut, and resolvable gradients for variational circuits. Under stated assumptions, the authors prove knitting stays affordable when subcircuits grow behind a bounded interface and becomes exponentially expensive when fixed-width subcircuits multiply. As a proof of principle on an IBM Nighthawk processor, they knit one gate joining two toric-code patches for up to 142 spins, resolving contact correlations beyond independent execution for up to 98 qubits.
In briefState-dependent entanglement and point-gap topology in a unidirectional Bose-Hubbard chain
SummaryThis paper studies how repulsive interactions affect skin modes and entanglement in the unidirectional Bose-Hubbard model. The ground state undergoes a superfluid-to-Mott transition that suppresses skin accumulation, but the entanglement change depends on which many-body state is chosen. For sixteen sites at unit filling, ground-state entanglement decreases toward the Mott limit, while steady states show a nonmonotonic crossover. The authors also find the many-body winding number stays nonzero at strong interaction.
In briefExactly Solvable Generalized Dunkl Quantum Systems with Energy-Dependent Interactions
SummaryThis paper studies a class of exactly solvable quantum systems described by a generalized Dunkl-Schrödinger equation with energy-dependent interactions. It introduces a two-parameter extension of the Dunkl operator that adds a derivative-reflection coupling to the usual reflection term. Using an energy-dependent harmonic oscillator as an example, the authors obtain exact eigenfunctions and spectra in terms of associated Laguerre polynomials, and analyze the partition function, internal energy, entropy and specific heat.
In briefCalculating Molecular Absorption Spectra from Ground States Using Neural Quantum States (Aurora)
SummaryThe paper introduces Aurora, a method combining neural quantum states with continued-fraction memory-kernel coupling theory to reconstruct molecular absorption spectra directly from variational ground states. It avoids explicitly constructing excited states or performing time propagation. Electronic spectra closely match full-configuration-interaction and conventional MKCT references for tractable molecules. For electron-phonon Hamiltonians, the authors add local SVD phonon encoders and report vibronic spectra for H2, N2, H2O, H2S, NH3, C6H6, and a C10H8 active space.
In briefExact distances and measurement allocation for logical Pauli readout (how many measurements a fault-tolerant logical readout needs)
SummaryThis paper studies how the minimum fault weight of a logical Pauli readout depends on data-error persistence, check redundancy, and time-boundary constraints. It proves an exact distance formula for a repeated-readout model and gives the minimum repetition count needed for each adjacent-column check in square Bacon-Shor and generalized Shor readouts. Combining these with redundant Gauss-check pair products yields an exact joint distance and an optimal outcome count within the specified gauged-readout family.
In briefPolynomial Gap Between One-Way and Two-Way LOCC for Distinguishing Maximally Entangled States
SummaryThe paper studies how well local operations and classical communication (LOCC) can tell apart maximally entangled states. One-way LOCC cannot always distinguish four orthogonal maximally entangled states in local dimensions of at least four. The authors show that, for sufficiently large dimensions, a protocol with a single feedback message (Alice to Bob to Alice) can perfectly distinguish any set of k pairwise orthogonal maximally entangled states. This yields a polynomial separation between one-way and two-way LOCC.
WhyProves polynomial separation between one-way and two-way LOCC, raising distinguishable candidate count from constant to d^{1/4} order, with a rigorous proof.
In briefAmenable groups and quantum channels needing near-linear memory
SummaryThe paper constructs a finitely presented elementary amenable group having a finite piece whose sofic profile grows nearly exponentially, close to the limit detectable by Cornulier's counting method. From this group it derives an explicit quantum channel on C^873 that is cheap to use once but needs roughly n/B qubits of memory to be applied n times. The construction also embeds in Brin's group 3V.
WhyConstructs a finitely presented elementary amenable group whose sofic profile is nearly exponential, sharply extending known counting limits, with quantum channel memory bounds.
In briefQ-MERGE: Splitting Large Quantum State Preparation into Parallel Parts
SummaryThe paper introduces Q-MERGE, which splits a large target quantum state into M n-qubit segments, prepares them in parallel, and coherently merges them into one amplitude-encoded state. On a real 128×256 ultrasound dataset, it reaches an infidelity of 1.066×10^-8, versus 3.413×10^-1 for direct preparation with the same method. The authors also report experiments on a Quantinuum H2 trapped-ion quantum computer.
In briefOptimal phase control for a measurement-assisted quantum refrigerator
SummaryThe paper studies a three-level quantum refrigerator in which a tilted nonselective measurement closes the upper transition but also creates coherence that suppresses the cooling current. The authors propose randomized open-loop control of the measurement's azimuthal phase and show that two equally weighted phases separated by π cancel the coherence source and maximize stationary cooling power. For one representative parameter set, phase cycling raises cooling power at fixed gap by about 32% over a fixed-phase measurement, with the ratio of extracted cold heat to measurement energy unchanged.
In briefQuantum sensing for consumer electronics: new methods and near-term use cases
SummaryThis paper reviews the near-term applicability of quantum sensing in consumer electronics, covering four platforms: nitrogen-vacancy centers, atomic vapor cells, Rydberg atomic sensors, and photonic quantum sensors. Case studies span navigation, healthcare and wearables, radio-frequency systems, IoT, and imaging. The authors argue that quantum sensing is more likely to enter products by upgrading specific measurement components within hybrid classical-quantum systems than by replacing devices outright. The clearest near-term opportunities identified are weak-field detection, compact RF reception, and noise-robust sensing.
In briefWhy the solid-state 229Th:CaF2 nuclear clock has broad transition lines
SummaryThis paper investigates why transition linewidths in solid-state 229Th:CaF2 nuclear clocks are far wider than the radiative lifetime of the nuclear isomer would predict. The authors measured linewidths against temperature, thorium concentration, and quadrupole state, combined with theory and simulations. They find the linewidth is temperature-independent, rises linearly with thorium concentration, and depends strongly on quadrupole state, with local electric-field gradient variations identified as the dominant broadening source.
In briefTelling chaotic from integrable systems using OTOCs
SummaryThe paper notes that out-of-time-ordered correlators (OTOCs) decay to a small value in both chaotic and interacting integrable many-body systems, so they cannot alone distinguish the two. The authors analytically study the late-time saturation of operator purity and show its system-size scaling robustly separates chaotic from integrable systems. The approach uses the Mazur bound and is supported by numerical simulations of one-dimensional spin chains.
In briefLower-Cost Quantum Kernel Training for Anomaly Detection
SummaryThis paper studies one-class anomaly detection as a resource-efficient way to train non-variational quantum kernel models, tested on the ULB credit card fraud dataset. Models trained on 500 samples retained about 90–93% of their fitted asymptotic average precision. Nyström approximation reduced kernel construction from O(N²) to O(Nm) evaluations, cutting required kernel evaluations by over 3,200-fold for one configuration with a modest drop in precision.
Daniel R. Germain, Benjamin Goldweber, Kayla J. Rodriguez et al.
In briefParallelizing Dissipative Quantum Algorithms: Reducing Circuit Depth by Running Jump Operators Simultaneously
SummaryThis paper studies dissipative quantum algorithms, inspired by classical Markov Chain Monte Carlo, for preparing quantum states on quantum computers. It proposes a parallel scheme that implements the jump operators of the Lindbladian simultaneously, using geometric locality to show these operators remain spatially localized. The authors report that this exponentially reduces circuit depth per time step, giving an overall polynomial improvement. Numerical experiments on a 100-qubit 1D benchmark show a 53x reduction in query depth.
In briefExact finite-channel Schur moments of the Wigner–Smith matrix with a tunnel barrier
SummaryThis paper studies the Wigner–Smith time-delay matrix of a chaotic cavity with broken time-reversal symmetry, M equivalent open channels, and a uniform tunnel barrier of reflection probability R. The authors show that each Schur moment for nonideal coupling factorizes into the ideal-coupling inverse-Laguerre value times a barrier factor given by a CUE average, and give a closed generating function for one-row partitions. The exact formula contains an extra term proportional to R^{M+1} that is invisible to every algebraic order in 1/M, and for the second moment it reproduces the exponentially small term in the random-matrix expression for ⟨τ_W²⟩ that is missing from the semiclassical expansion.
In briefExchange-controlled quantum beats and entanglement in an exciton–bimodal-cavity system
SummaryThis theoretical paper studies two excitons coupled to a bimodal optical cavity, including an exciton-exciton exchange interaction, showing tunable population transfer and entanglement generation. Parameterized with first-principles data for graphene nanoribbon excitons, it finds that in the large-exchange regime nearly complete transfer between excitonic states occurs over many coherent cycles. The authors provide analytical design rules linking beat period, transfer amplitude and coherent-cycle number to exchange, cavity detuning and light–matter coupling.
Cesar E. P. Villegas, Victor P. Brasil, Pedro A. S. Contri et al.
In briefPyCC: A Python Quantum Chemistry Package for Teaching, Validation and Prototyping
SummaryPyCC is a Python quantum chemistry package focused on coupled cluster and related methods, developed over five years. It is designed as a clear reference implementation that can validate production code, serve as a platform for prototyping new methods, and teach newcomers the field. The package covers a range of methods and molecular properties and is fully open source under the BSD 3-clause license on GitHub.
T. Daniel Crawford, Benjamin G. Peyton, Zhe Wang et al.
In briefFinite-temperature open-system quantum simulation via post-processing for collision models
SummaryThis paper studies simulating open quantum system dynamics on gate-based quantum computers, where collision models represent the environment through sequential system-ancilla collisions. For a broad class of U(1)-symmetric interactions, the authors show that finite-temperature dynamics can be reconstructed from simulations using pure ancillas in orthogonal basis states. The target temperature is introduced only through classical post-processing, so the same data can be reused across temperatures. This avoids repeated thermal ancilla preparation, reducing circuit overhead and preparation-induced errors.
In briefOptimizing atom placement so neutral-atom quantum computers can encode problems
SummaryNeutral-atom quantum computers can reshape their qubit layout between runs, allowing problems to be mapped onto the hardware. The paper introduces a force-directed method that places atoms to realize target pairwise interactions, encoding the input problem. Numerical results indicate the method improves embedding feasibility and solution quality by orders of magnitude and stays reliable on the largest instances.
Cl\'ement de Terrasson de Montleau, Victor Drouin-Touchette, Wesley Coelho
In briefEnergy-filtered readout keeps gap-enhanced sensing in interacting quantum dots
SummaryThis paper studies whether a small excitation gap in an interacting two-electron quantum dot, used as a weak electric-field probe, still boosts sensitivity under continuous charge readout. It finds that a quantum point contact detector can excite the probe once its bias exceeds the gap, so the information rate scales only as the inverse gap. A narrow-level sensor dot instead reaches full measurement strength below the gap, preserving the inverse-square gap dependence of the quantum Fisher information.
In briefQuantum input-output theory for nanophotonics using first-order Maxwell operators
SummaryThis paper develops a quantum input-output theory for open photonic systems using macroscopic quantum electrodynamics and the first-order electromagnetic Green's function. Quantum fields enter and leave through waveguide ports, and a Langevin-noise term from material absorption preserves bosonic output commutation relations. For embedded emitters, the single-excitation response is derived from port-emitter Green's functions, retaining non-Markovian effects. Finite-difference time-domain simulations compute emitter-modified transmission for a nanophotonic cavity and an inverse-designed coupler, linking electromagnetic response to a quantum input-output model.
Ankit Kundu, Ishita Agarwal, Adhyyan S. Mansukhani et al.
In briefFaster quantum search for global extremes in structured signals
SummaryThe paper introduces a quantum algorithm for finding the global extremum in amplitude-encoded signals by exploiting their structure. A nonlinear amplitude transformation lets it identify and certify the extremum while exponentially shrinking the effective search space for structured signals. The authors report polylogarithmic query complexity in data size N and demonstrate the method on turbulence simulation data.
In briefMulti-indexed Schatten quasi- and anti-norms, and additivity of conditional Rényi entropies
SummaryThe paper introduces multi-indexed Schatten spaces that extend commutative ℓ-spaces to quantum operators, generalizing Pisier's Schatten norms and earlier two-indexed Schatten quasi-norms. It establishes properties of these quasi-norms and anti-norms and lifts key tools from Devetak, Junge, King and Ruskai to this setting. It also proves that completely bounded minimal and maximal output conditional entropies are additive under tensor products of quantum channels for α ≥ 1/2.
WhyIntroduces multi-indexed Schatten quasi-norms, extends DJKR tools, and rigorously proves additivity of conditional Rényi entropies for alpha at least 1/2.
In briefVariational-principle observables can fail certification even when energy converges
SummaryThe paper examines whether a well-converged ground-state energy from variational methods guarantees accurate observables. The authors show that an energy error within ε can coincide with observable errors of about √(2εχ_O), where χ_O is the observable's static susceptibility, so observable errors can be much larger than energy errors. They test this on three algorithms: the variational quantum eigensolver on the transverse-field Ising chain, DMRG on weakly coupled hydrogen chains, and Krylov quantum diagonalisation on lithium fluoride.
In briefFoundational puzzles in quantum theory, from Wigner's friend to black holes
SummaryThis thesis examines two foundational paradoxes in physics: the quantum measurement problem, explored through extended Wigner's friend scenarios, and the black hole information paradox at the boundary of quantum theory and general relativity. Part I introduces new extended Wigner's friend arguments and links them to nonclassicality, including a refined Frauchiger–Renner paradox and contextuality-based scenarios. Part II combines these arguments with black hole puzzles and analyzes detector responses near a superposed black hole using quantum reference frames.
In briefTunable-bandwidth microwave-to-optical transduction via Rydberg excitation
SummaryThis paper proposes a cavity-based microwave-to-optical transducer that uses a collective Rydberg excitation. External driving fields adjust the conversion bandwidth in situ, from narrowband to broadband operation, without changing cavity parameters. Under impedance-matching conditions, the system works as a continuous-wave, phase-preserving linear transducer with near-unit efficiency and quantum-limited added noise across the tunable range.
Iason Tsiamis, David Petrosyan, Anders S. S{\o}rensen
In briefComparing circuit designs for encoding a graph problem on quantum hardware
SummaryThis paper benchmarks Pauli Correlation Encoding, a method that uses fewer qubits for quantum optimization, on Maximum Independent Set problems. The authors test several ansatz designs and compression ratios. They find that ansatz choice strongly affects solution quality and feasibility, with two families reaching approximation ratios near 0.9. Increasing compression weakens representability, while using more qubits improves raw solution quality.
Cian C. Reeves, Aaron C. Kemp, Richard Padbury et al.
In briefMagic quantum code surgery: a general method for fault-tolerantly measuring logical Clifford operators in quantum LDPC codes
SummaryThe paper presents a general framework for fault-tolerantly measuring transversal Clifford logical operators in quantum low-density parity check (QLDPC) codes. It deforms a given code using additional ancillary qubits so that a product of stabilizers measures the desired logical Clifford operator. The authors prove the deformed code remains LDPC with its distance preserved up to a constant factor, and that the measurement's fault distance grows linearly with the original code distance. The methods are applied to logical non-Clifford gates and magic state preparation.
WhyA general framework for fault-tolerant Clifford measurement in QLDPC codes, with proven distance preservation and linearly growing fault distance.
In briefQuantum query complexity and span programs via matroid structure
SummaryThis paper studies span programs as a method for designing quantum query algorithms, separating query-determined dependence data from the dependence structure chosen by a program using matroids. It gives exact reductions and certificates for adversary bounds, including estimates for a pointed R10 closure. Through recursive self-composition, it constructs a family of functions on N input bits with stated randomized and quantum query bounds and an asymptotic exponent range for Q(F).
WhyUnifies span programs and adversary bounds via matroids, and recursive constructions yield new quantum query complexity exponents with exact certificates.
In briefFaster quantum Monte Carlo by sampling cluster expansions instead of enumerating them
SummaryThe paper addresses the sign problem in quantum many-body simulations by introducing a Markov chain algorithm that samples cluster expansions directly in the space of connected clusters. Replacing exhaustive enumeration with Monte Carlo sampling avoids the conventional exponential sign problem within the convergence regime. The authors give an FPRAS runtime for general polymer models and improved bounds for quantum partition functions and long-range interacting systems.
WhyReplaces exhaustive cluster enumeration with Markov chain sampling, avoiding the sign problem and giving polynomial-time FPRAS guarantees for long-range systems.
In briefQuantum-assisted drone surveillance route planning using machine-learned risk maps
SummaryThis paper proposes a framework that combines classical machine learning forecasts with quantum annealing to select the best combination of drone surveillance tours. Machine-learned risk maps generate candidate tours, and a quantum-assisted heuristic chooses the best combination to form a full surveillance plan. The drone path problem is modelled as a Team Orienteering Problem with additional constraints, and the framework is applied to wildfire prevention, comparing the effect of larger quantum resources with classical resources.
Dorian Lauwerier, Alexis Vieloszynski, Yves B\'erub\'e-Lauzi\`ere et al.
In briefExact Timing of Entanglement and Negativity Criticalities in Open Fermion Chains
SummaryThis paper studies when the two largest eigenvalues of entanglement and negativity spectra in open fermionic systems, including Kitaev chains, become degenerate, closing the gap of the corresponding Hamiltonian while entropies remain smooth. The authors call this a temporal criticality and compare Gaussian loss and gain with non-Gaussian density dephasing. They find that Gaussianity, rather than the symmetry type, determines the criterion for criticality. Exact solutions are given at a point where the chain's bond terms commute, showing how dephasing shifts the criticalities.
Shrey Chowdhary, Sanket Chirame, Stephan Haas et al.
In briefRobustness of Quantum Signal Processing and Resource-aware Polynomial Design
SummaryThis paper analyzes end-to-end errors in quantum signal processing (QSP), showing that input error propagation is governed by the operator-Lipschitz constant of the implemented function. It presents an efficient classical algorithm for computing tight bounds on this constant and uses them to estimate the quantum resource cost, such as T-gate count, needed to meet a target total error. The authors also propose a method to find minimum-cost polynomials from their coefficients, and for ground state energy estimation of the H6 molecule, the resulting polynomials reduce modeled T-gate count by 51.9% to 56.7% compared with a standard error-function-based polynomial.
Thiago O. Maciel, Giancarlo Camilo, Allan Tosta et al.
In briefALPS Project 3.0: open-source software for simulating strongly correlated quantum systems
SummaryALPS is an open-source project providing libraries and programs for simulating strongly correlated quantum lattice models, such as quantum magnets and lattice bosons. Release 3.0 adds distribution via pip and Spack, moves development to GitHub with continuous integration, switches to the MIT license, and rebuilds documentation and tutorials. It also modernizes the C++ codebase, updates the DMRG code, and removes legacy components.
In briefInformation spread in Krylov subspaces: mapping quantum dynamics to a 1D chain and bounding its speed
SummaryThe paper uses Krylov subspace methods to map a quantum initial value problem onto a one-dimensional chain, and derives a speed limit within these dynamical subspaces using a time-ordered path formulation. For Lanczos coefficients growing as a power law, it finds super-ballistic lightcones, with exponential spreading for maximal growth. It further argues that causality in the Krylov chain limits Lanczos coefficients to grow at most linearly, and illustrates this in several algebras and models.
Pablo Martinez-Azcona, Maximilian Meyer-Moelleringhof, Adolfo del Campo et al.
In briefTime-dependent integrable quantum field theories with dynamical boundaries: a method for building and solving such theories on finite intervals
SummaryThe paper presents a general method to construct and solve time-dependent integrable chiral quantum field theories on finite intervals, starting from autonomous scattering and reflection data. It derives boundary quantum Knizhnik–Zamolodchikov equations, with local and global consistency ensured by the Yang–Baxter and reflection equations and boundary-qKZ flatness, and reconstructs the local Hamiltonian via Cayley inversion. The construction is applied to rational SU(N) scattering with boundary impurities and to an O(3) model with a spin-1/2 impurity. For the SU(2) impurity, explicit boundary-qKZ solutions are given, recovering static open-chain Bethe equations when the drive rate vanishes.
In briefModular neural decoder for surface code memory and logic on superconducting chips
SummaryThe paper presents a modular graph-recurrent neural decoder built from reusable local syndrome encoders, pretrained in simulation and fine-tuned to hardware. On IBM hardware it outperforms minimum-weight perfect matching (MWPM) at distances 3 and 5 and closely approaches AlphaQubit on Google's hardware data. The authors also apply it to an X-type stability experiment with tunable measurement error, where one decoder matches or beats MWPM across the noise range, and to a ZZ lattice-surgery merge, where it improves correlation with the final ZZ parity over MWPM.
Moritz Lange, Ole Fjelds{\aa}, Gustaf Jonasson Johansson et al.
In briefMixed-state 3D topological orders from braided fusion 2-categories
SummaryThe paper constructs large families of (3+1)D mixed-state topological orders, including intrinsically mixed-state ones. It links the data of braided fusion 2-categories to strong higher-form symmetries and their anomalies, and gives concrete lattice models. It shows every braided fusion 2-category arises from decoherence followed by strong and weak gauging, and identifies a new (3+1)D mechanism with no (2+1)D counterpart, involving a gravitational anomaly.
In briefSpiderCSS: A Scalable Fault-Tolerant CSS State Preparation Method
SummaryThis paper presents SpiderCSS, a compilation pipeline that generates optimized fault-tolerant circuits for preparing states of arbitrary CSS codes. It uses the ZX-calculus and fault-equivalent rewrites, so the resulting circuits are provably fault-tolerant without costly verification. Monte Carlo simulations on CSS codes up to distance 15 report reduced depth and qubit footprint, a 33.7% average decrease in logical error rate, and a 9.5% increase in acceptance rate compared with existing methods.
Boldizs\'ar Po\'or, Andrey Boris Khesin, Sarah Meng Li et al.
In briefHow to build pseudorandom unitaries in Microcrypt
SummaryThe paper shows that a circuit made of five independent random diagonal phase layers interleaved with Hadamard transforms is a strong pseudorandom unitary (PRU), secure under adaptive, controlled access to the unitary, its inverse, transpose, and complex conjugate. When the phase layers use a classical random oracle, the construction stays secure against uniform BQP adversaries aided by QMA-type access. This gives classical-oracle evidence that PRUs do not imply quantum-computable one-way functions, strengthening prior work by Kretschmer, Qian, and Tal (STOC 2025).
WhyProves a five-layer phase-Hadamard construction is a strong PRU and gives a classical-oracle black-box separation from quantum-computable one-way functions, strengthening prior work.
In briefQuantum estimation, channel orders, and private capacity: comparing quantum channels and their private capacity
SummaryThe paper studies the private capacity of quantum channels, showing that zero private capacity does not imply antidegradability and that two zero-private-capacity channels can jointly transmit private information. Using the link between binary estimation error and measured χ² divergence, the authors establish complete comparison criteria connected to entropic channel orders. They apply these results to noisy Werner–Holevo channels and Pauli half-erasure activation constructions.
WhyLinks measured χ² divergence to channel orders and private capacity, with a new integral representation and sharp thresholds, giving strong theoretical advances.
In briefScalable Passive QRAM: a blueprint for physically implementing quantum random-access memory
SummaryThe paper presents a blueprint for implementing the physical QRAM operation in a scalable, passive way and argues it is feasible in principle. Each query costs O(log N) energy and takes O(log² N) runtime, which the authors say is the first construction to use polylog N energy. It works by evolving a pre-manufactured, time-independent 4-local Hamiltonian with O(N) terms, where each qubit appears in at most 4 terms.
Siddhartha Jain, Alexander M. Dalzell, Connor T. Hann
In briefDriven-dissipative ground state preparation: mixing time and randomness
SummaryThis paper studies driven-dissipative protocols for preparing ground states in which the generator changes over time. The authors build a family of randomized Lindbladians whose jump operators come from averaging the unitary evolution of random matrices under a fixed target Hamiltonian. They show that empirical averages of these Lindbladians drive arbitrary initial density matrices to low-energy states. The mixing time bounds depend on the Hamiltonian only through its eigenvalue distribution and hold even for cold starts.
In briefExponential lower bounds on fermionic Gaussian rank of magic states and coherent state rank of Fock states
SummaryThe paper studies how many free states are needed to write tensor products of magic states as superpositions, a quantity that governs the runtime of certain classical quantum simulation algorithms. The authors prove that any fermionic Gaussian decomposition of the k-fold tensor power of the standard fermionic-linear-optics magic state has $\Omega(1.4^k)$ terms, with matching-order bounds for approximate rank. They also show that the coherent state border rank of an n-mode bosonic Fock state equals the product of (1 + m_j), confirming a conjecture from prior work.
WhyProves exponential lower bounds on fermionic Gaussian rank and exactly determines coherent state border rank of Fock states, resolving a conjecture.
In briefComplexity of Redundancy-Free Quantum Hamiltonians
SummaryThis paper studies a class of redundancy-free Hamiltonians, where the trace vanishes for any product of terms in which some term appears an odd number of times. Such Hamiltonians arise in Hamiltonian Decoded Quantum Interferometry. The authors show the problem becomes easy at quadratically lower temperatures than general Hamiltonians, give an efficient classical approximation algorithm for small β²d and NP-hardness for large β²d, and provide quantum state preparation algorithms. They also show estimating the ground state energy is QMA-complete.
WhyCharacterizes redundancy-free Hamiltonian complexity via a β²d threshold, with approximation algorithms, NP-hardness, and QMA-completeness; novel theory but largely analytic with limited empirical sup
In briefExtending short quantum correlation time series to spectra via maximum entropy
SummaryThe paper proposes a method that extends time series of quantum correlation functions and reconstructs their spectral densities, using the link between these functions and covariance sequences of stationary stochastic processes. Burg's maximum-entropy principle yields an all-pole autoregressive model compatible with the measured values, which is positive semi-definite by construction, guaranteeing spectral positivity and the total spectral weight sum rule. The approach applies to scalar and matrix-valued correlation functions and enables spectral reconstruction from short-time data, even with noise.
Filippo Maria Gambetta, Sabrina Yue Wang, Raul A. Santos
In briefAn operational characterization of finite-dimensional quantum theory
SummaryThe paper constructs a finite set of two-body correlations such that the only probabilistic theory that realizes them and stays stable under iterated teleportation is quantum theory. For n systems of dimension d, the first condition can be checked with poly(d,n) measurement settings. The second condition is a hierarchy of tests, one per teleportation step count N, so finite-dimensional quantum theory can be self-tested.
WhyProposes uniquely characterizing finite-dimensional quantum theory via finitely many two-body correlations and teleportation stability, a novel conceptual approach; rigor is not fully verifiable from
Lionel J. Dmello, Xiangling Xu, Marc-Olivier Renou et al.
In briefUniversal Bounds for Learning Quantum Unitaries Beyond the Training Distribution
SummaryThis paper asks how much learning an unknown unitary's action on one family of states reveals about its action on other states. The authors build a framework based on the first and second moments of the input distribution, defining the bias and expressivity of an ensemble that govern generalization between arbitrary pure-state training and testing distributions. They show, among other results, that studying random real states suffices to learn action on random complex states, and they derive tight product-to-Haar bounds. The paper also includes no-go results and limited generalization bounds for certain channels.
WhyProposes a moment-based framework yielding tight out-of-distribution generalization bounds for unitary learning, a clear theoretical advance with impact mainly in quantum learning theory.
In briefEfficient block encoding of structured Hamiltonians by separating where operators act from what they do
SummaryThe paper constructs permute-act-unpermute circuits for fault-tolerant block encodings of structured Hamiltonians, using a CSWAP network fixed by the support geometry to move a selected support to a fixed target register. A shared local circuit acts there, and the permutation is then undone. For Pauli terms the circuits use 8SN+o(N) T gates, where S depends on the support geometry (1 for nearest-neighbour, 3/2 for all-to-all). A bridged CSWAP variant is also introduced to reduce the T count.
In briefSingle-shot error correction achieving optimal spacetime cost for quantum memory
SummaryThe paper studies the cost of reliably storing logical qubits over many time steps in a quantum computer. It shows that, under independent erasures, an explicit noisy error-correction circuit with efficient decoding achieves the same scaling as the known lower bound, up to constant factors, when all operations are counted. The construction uses quantum Tanner codes, with each memory step consisting of one syndrome-extraction round and a fixed number of parallel classical decoding steps.
WhyAchieves matching spacetime lower bound under noisy circuits using quantum Tanner codes and parallel decoding; strong theory, no experiments.
In briefA modified log-Sobolev inequality for non-commuting 1D spin chains
SummaryThis paper studies finite-range, non-commuting Hamiltonians on a one-dimensional chain of finite spins. It proves a modified logarithmic Sobolev inequality with constant Ω(1/log n) for heat-bath dynamics, a quasi-local Gibbs sampler, and regularised heat-bath dynamics. The result implies rapid mixing toward the Gibbs state in relative entropy and trace norm, with mixing times of order O(log n·log(n/ε)). The authors state this is the first such proof in the non-commuting regime.
WhyFirst proof of a modified log-Sobolev inequality for 1D non-commuting Hamiltonians, yielding rapid mixing via a complete technical argument.
\'Angela Capel, David P\'erez-Garc\'ia, Matteo Scandi
In briefLow-overhead quantum error correction using modular planar blocks linked at their edges
SummaryThe paper proposes splitting a quantum processor into flat planar modules joined by sparse, fixed connections between their boundaries, forming modular hyperbolic surface and color codes. Circuit-level simulations report a physical qubit overhead reduction of tenfold or more relative to the surface code, even with elevated inter-module seam error rates. Projections suggest codes with rate 1/16 and distance at least 22, along with fault-tolerant walking circuits for logic operations.
WhyProposes modular high-rate quantum codes from boundary-connected planar modules, with circuit simulations and extrapolation showing over 30x overhead reduction.
Oscar Higgott, Hasan Sayginel, Francisco J.H. Heras et al.
In briefExact error recovery for non-Abelian surface codes built on any finite group
SummaryThis paper studies exact error recovery for topological surface codes based on the quantum double D(G) of any finite group G, including non-Abelian groups. The authors define an orthogonal error basis made of group multiplication and irreducible representation operators, and introduce a gauge-fixing to remove redundancy from errors supported on closed loops. Assuming predetermined neutral correctable error clusters, they build charge and flux transfer circuits that move errors onto ancillas, which are then projected out. The result is an exact, deterministic recovery protocol applicable to any finite group.
In briefMaking the Redfield Equation Safe: Positive Resummation for Non-Markovian Quantum Dynamics
SummaryThis paper examines the time-dependent Redfield (TCL2) equation, a simple perturbative description of open quantum systems derived from a microscopic theory. It compares Redfield evolution with a Magnus exponential resummation of the same second-order map, which is completely positive and trace preserving under broad conditions, and constructs another such resummation. The authors give a weak-coupling criterion under which Redfield evolution stays close to a completely positive map even when non-Markovian, illustrated with qubit examples.
In briefEfficient capacity-achieving entanglement generation and its use for pure-loss bosonic channels
SummaryThis paper addresses efficient coding for quantum communication over noisy channels, where few practical schemes reach the known limits. The authors build an efficient entanglement generation scheme that achieves coherent information for a broad class of channels. For degradable channels, including truncated pure-loss bosonic channels, it reaches the quantum capacity, using polar codes and belief propagation with quantum messages for decoding.
WhyConstructs an efficiently decodable entanglement scheme reaching the energy-constrained quantum capacity of pure-loss bosonic channels, a notable theoretical advance with mainly theoretical impact.
Avijit Mandal, Christophe Piveteau, Henry D. Pfister et al.
In briefQuantum simulation on curved spaces: quantum algorithms for the Schrödinger equation on Riemannian manifolds
SummaryThis paper studies quantum algorithms for simulating the Schrödinger equation on Riemannian manifolds, where the kinetic term is defined by the Laplace–Beltrami operator of the metric. The authors present a global spectral method for specific manifolds such as tori, spheres, and simplices, and a coherent local spectral method applicable in principle to any compact manifold. The methods are also applied to optimization, including Quantum Hamiltonian Descent, and to simulating spatially discretized field theories such as a nonlinear sigma model.
Dylan Herman, Jacob Watkins, Guneykan Ozgul et al.
SummaryThis paper studies how the ordering of Hamiltonian terms affects the accuracy of product-formula simulations of quantum many-body dynamics. The authors derive an efficiently computable, ordering-sensitive bound on the finite-step-size Trotter error for geometrically local Hamiltonians and arbitrarily high-order formulas. For translation-invariant one-dimensional chains, the bounds track exact errors closely in small systems and improve on earlier higher-order analytical bounds by orders of magnitude on large systems. The optimization of ordering is reduced to a minimum-mean-weight-cycle problem on a weighted de Bruijn graph, and sequential orderings are found to outperform standard brickwall circuits for random chains.
WhyProposes an efficiently computable, ordering-sensitive Trotter error bound, reduces ordering optimization to a cycle problem, and validates against exact small-system errors.
Zhenning Liu, Zhi-Yuan Wei, Michael Foss-Feig et al.
In briefSimulating field-tunable spin excitations of the quantum magnet Cs2CoCl4 on a trapped-ion quantum computer
SummaryThis paper uses IonQ's 36-qubit Forte Enterprise processor to simulate magnetic excitation spectra and spin dynamics of the quantum magnet Cs2CoCl4, modeled as a 36-site Heisenberg XXZ chain. The circuits use 420 two-qubit gates and combine an ancilla-free local kick protocol with classical tensor network compression. The reconstructed spectra closely match DMRG calculations and are compared with inelastic neutron scattering measurements.
In briefClassical Algorithms for Bipartite Quantum Max-Cut on Dense Expanders
SummaryThis paper studies the bipartite case of Quantum Max-Cut, whose classical complexity was previously open. The authors give a polynomial-time classical randomized algorithm for dense balanced bipartite expanders, a class that includes G(n,n,p) with high probability. The algorithm estimates the ground energy and ground state edge correlations to additive error ε. It uses a Markov chain on perfect matchings of the complete bipartite graph, and the graph's expansion is used to show that polynomially many steps and samples suffice for convergence to the ground state.
WhyGives a polynomial-time classical randomized algorithm for dense bipartite expanders, advancing an open problem via a rigorous Markov-chain analysis using expansion.
In briefOptimal kernel functions for simulating linear non-unitary quantum dynamics
SummaryThis paper studies linear combination of Hamiltonian simulation (LCHS), a quantum method for simulating linear non-unitary dynamics via an integral representation controlled by a kernel function. The authors construct, for each target error, the kernel that minimizes a query-cost functional and show the minimum has an asymptotic expansion with leading coefficient 2e/π. This improves on the empirical coefficient of Low and Somma by about a factor of 2.1. They also build a spectrally convergent quadrature with explicit error and subnormalization bounds that preserves this improvement after discretization.
WhyProves an optimal kernel and asymptotic constant 2e/π via Hardy space and convex analysis, improving prior empirical coefficient by about 2.1x.
In briefBARC codes: a general polynomial framework for quantum codes built from coherent-state superpositions
SummaryThe paper introduces an algebraic framework for a new class of quantum error-correcting codes, called bosonic algebraically-restricted constellation (BARC) codes. Code states are finite superpositions of coherent-state constellations, constrained by symmetries of solution sets of multivariate complex polynomial systems, and are designed to approximately satisfy Knill-Laflamme conditions for photon-gain and photon-loss errors. The authors derive upper bounds on the minimum geometric separation between equally weighted constellation points. In the single-mode case, they construct explicit ellipsoidal and hexagonal BARC codes and benchmark them against spherical and cubature codes under pure-loss noise.
Praneel Gore, Davit Aghamalyan, Varun Narasimhachar et al.
In briefLie Algebra Uncertainty Relations: Representation Theory Quantifies Quantum Incompatibility
SummaryThe paper introduces a covariance-matrix framework that yields infinitely many uncertainty relations for both Hermitian and non-Hermitian operators, with the variance sum as a special case. For simple and semisimple Lie algebras, it gives an exact, basis-independent optimal state-independent bound, expressed as an explicit pairing of the root system with the representation's highest weight. This minimum is attained by a highest-weight state, and uncertainty is shown to be constant within each weight space, giving a conservation law.
WhyLinks uncertainty relations to Lie algebra representation theory, giving an explicit optimal state-independent bound attained by highest-weight states.
In briefQuantum Codeword Sensing: Identifying a sent classical codeword with persistent quantum memory
SummaryThe paper studies identifying an unknown classical codeword that is delivered to sensor qubits through weak phase interactions, one bit at a time. It shows that a receiver with persistent quantum memory can identify the codeword more reliably than a receiver with only classical memory, even when bit flips occur. For a family of simplex codes, the scheme corrects up to a stated number of transmission errors exactly.
In briefA note on reconstructing quantum states with low stabilizer rank
SummaryThis note studies tomography, or full state reconstruction, for n-qubit states that can be written as a sum of k stabilizer states. The authors give a protocol that reaches trace distance ε in time poly(n, 2^k, 1/ε), so states with k = O(log n) can be handled efficiently. The result rests on bounding the stabilizer extent by 2^{O(k)}, improving the earlier k^{O(k)} bound.
In briefSqueezed light gives super-exponential gains in phase estimation with random phase offsets
SummaryThis paper studies phase estimation in quantum metrology using a channel with a random integer phase shift of 2πk/M plus a small unknown phase. Under a fixed mean photon number per channel use, squeezed vacuum states are shown to outperform coherent states in quantum Fisher information by a super-exponential factor. The authors also give explicit non-asymptotic estimation protocols and show the advantage persists under optical loss and thermal noise.
WhyProves super-exponential QFI advantage of squeezed vacuum over coherent states under discrete phase randomisation, with non-asymptotic estimation and noise analysis, overturning the quadratic-advantag
In briefFaster inverse-free Solovay-Kitaev compilation beats the cubic barrier
SummaryThe Solovay-Kitaev algorithm compiles unitaries to accuracy ε in polylog(1/ε) time using any universal gate set. This paper improves the exponent of inverse-free compilation, the setting where gate inverses are unavailable, and identifies cases with exponent below 3, surpassing information-theoretic bounds. For a qubit, the authors give an exponent of at most about 2.138 for Pauli gates plus an irrational rotation, and at most 2.988 for the general inverse-free case.
WhyImproves the inverse-free compilation exponent below the information-theoretic bound for qubit cases, with solid analysis but limited to single-qubit settings.
In briefA basis-aware method for quantum sampling of the Fermi-Hubbard ladder
SummaryThis paper studies sample-based Krylov quantum diagonalization (SKQD) for the half-filled Fermi-Hubbard ladder, comparing how compactly the target state can be represented under different one-body orbital rotations. The most compressible basis changes systematically with interaction strength and hopping anisotropy, and at intermediate interaction with isotropic hopping no representation compresses well. Hardware runs on up to 120 qubits show the same basis dependence, along with growing particle-number leakage as system size increases.
In briefApproaching ultimate ground-state metrology limits with many-body probes
SummaryThe paper studies how many-body probes with short-range or long-range interactions can estimate a Hamiltonian parameter by measuring its ground state, approaching the quantum Fisher information limits. It derives conditions for saturating the static ground-state bound and the dynamical Heisenberg limit. Paradigmatic models, including the transverse-field Ising chain, XXZ chain, squeezing Hamiltonian, and two-mode Bose-Hubbard model, are analyzed to identify suitable probes.
WhyDerives conditions saturating static and dynamical ground-state metrology bounds, including a universal critical-exponent condition, with analysis across several paradigmatic models.
Erik L. Andr\'e, V\'ictor Izquierdo, Ricard Puig et al.
In briefQuantum memory advantage for processing randomly ordered data streams
SummaryThe paper proves two unconditional quantum space advantages in a streaming model where data arrives in random order. First, the Yamakawa–Zhandry Code Intersection problem shows exponential quantum advantage even when the stream carries pairs (x, f(x)) for a random function. Second, a streaming version of the Decoded Quantum Interferometry algorithm yields provable quantum advantage for the Optimal Polynomial Intersection problem in certain regimes.
WhyGives unconditional exponential quantum space advantage in random-order streaming via density-restoring partitions and convex potentials, with a fairly narrow scope.
In briefClarifications on the Experimental Status of Real Quantum Theory
SummaryThe authors previously showed that real quantum theory cannot be experimentally falsified without also falsifying quantum theory. This note challenges the claim by Renou et al. in Nature that a bilocal network experiment falsified real quantum theory alone. It argues that the experiment relies on an premise about independent preparations being product states, which cannot be experimentally tested.
In briefPolynomial-time algorithms for tensor nuclear norms and multipartite quantum separability at constant accuracy
SummaryThe paper studies a multilinear optimization problem over tensors with bounded Frobenius norm, where each local factor is drawn from a convex set. The authors give a deterministic algorithm running in time d^{O(k)} that achieves constant additive approximation. Applying it, they obtain the first polynomial-time algorithms at constant accuracy for weak membership in the nuclear-norm unit ball of high-order tensors and for multipartite quantum separability in Frobenius norm. When the input state is given through copies, a quantum implementation solves separability testing using poly(k) copies and poly(k log d) time.
WhyGives a deterministic d^O(k) algorithm for constant additive error, yielding first polynomial-time results for high-order tensor nuclear norm and multipartite separability.
In briefPurification entanglement of Werner states: canonical purification and nonadditivity
SummaryThe paper proves that von Neumann entanglement of purification is nonadditive. For two-qubit Werner states with singlet weight between 1/64 and 1/4, canonical purification is shown to be globally optimal, so its entanglement (reflected entropy) equals the exact entanglement of purification. For small singlet weights below about 0.017, the regularized entanglement of purification is strictly smaller than the reflected entropy, establishing nonadditivity on that range.
WhyProves nonadditivity of von Neumann entanglement of purification, extending prior Rényi results to alpha=1 with a rigorous canonical-optimality argument.
In briefTelling apart two quantum Markovian dynamics over time
SummaryThe paper studies how well two quantum Markovian dynamics, each generated by a Lindbladian, can be told apart, focusing on total exposure time and temporal resolution. It characterises the optimal type-II error exponent (Stein exponent) and gives an algebraic criterion for when it is infinite. Using quantum Zeno protocols, it shows that finer temporal resolution can itself serve as a resource for discrimination.
WhyCharacterises the Stein exponent for Lindbladian discrimination via instantaneous relative entropy growth, with an algebraic criterion and proofs that temporal resolution is a resource.
Robert Salzmann, Ludovico Lami, Martin B. Plenio et al.
In briefSymmetry-preserving quantum compilation for fault-tolerant simulation
SummaryThis paper presents a fault-tolerant compilation framework that compiles time evolutions preserving SU(2) symmetry into discrete gate sets without breaking that symmetry. It uses measurement and feed-forward to circumvent a number-theoretic obstruction that limits symmetry-preserving Clifford+T circuits. In a one-dimensional Heisenberg model transport simulation, the method gives the expected transport exponent at matched T-count where standard synthesis fails, and reduces T-count by about a factor of five at equal accuracy. The framework is also extended to gauge symmetries and to fermionic particle-number and spin symmetries.
Maryam Mudassar, Zhi-Yuan Wei, Alexander Schuckert et al.
In briefDecoherence of Kitaev's sixteenfold way via a holographic approach
SummaryThis paper studies anyon decoherence in 2D topological order, using fermion decoherence in Kitaev's sixteenfold way as examples. The authors conjecture that the resulting density matrix can be obtained by lifting to a Walker-Wang model, transitioning to another Walker-Wang model, and tracing out bulk degrees of freedom. They show that decohering the fermion in each of the sixteen states yields an intrinsically mixed-state topological order, since the 3D bulk transitions into the 3D fermionic toric code.
In briefFast fidelity simulation for high-rate magic state distillation circuits
SummaryThis paper presents exact and efficient classical methods for benchmarking quantum circuits that include non-Clifford gates and their fault-tolerant error correction. The methods scale polynomially with the number of physical qubits and circuit depth, independent of the number of logical qubits. The authors use these algorithms to optimize high-rate magic state distillation factories built from three copies of a [[27,3,3]] tricycle code.
Xiao Xiao, Dominik Hangleiter, J. Pablo Bonilla Ataides et al.
In briefExact LCU sampling cost for collective phase gates, governed by continued fractions
SummaryThe paper studies the minimal sampling overhead for the quadratic collective phase gate e^{-iγK²} over one layer of single-qubit rotations, showing it is determined by the continued fraction of γ/π. It develops an optimality theory for this overhead, with different results for rational and badly approximable angles. It also gives a lower bound for Fourier-based squaring without permutation symmetry.
WhyGives an exact optimality theory via continued fractions, with new rational-angle and certificate-lifting lower bounds that are rigorously proved for quantum optimization and squeezing settings.
In briefFault-tolerant, fully addressable logical gates for qLDPC codes via round-robin sparsification
SummaryThis paper addresses quantum low-density parity check (qLDPC) codes, where operating on individual logical qubits is needed to exploit their efficient encoding. The authors present low-depth unitary circuits implementing fully addressable, fault-tolerant two-qubit Clifford gates for a subset of two-dimensional translationally invariant qLDPC codes. These transversal unitaries are built by applying a geometrically structured sparsification to round-robin circuits. Numerical simulations of addressable CZ gates across toric, cyclic hypergraph-product, color, gross, and directional codes show memory-like logical error rate scaling.
In briefA new method for randomized benchmarking that handles group multiplicity without multi-exponential fitting.
SummaryRandomized benchmarking is a standard set of techniques for measuring how accurately quantum processors perform operations. Many groups formed from native gates have multiplicity, which makes the resulting data hard to interpret reliably. This paper proposes lifted randomized benchmarking, which combines key ideas from character and synthetic randomized benchmarking to avoid fitting multi-exponential decays while staying robust to state preparation and measurement errors. Numerical examples show it can efficiently and reliably estimate the fidelity of two-qubit gates relevant to trapped-ion systems.
In briefComplete proof that weighted gapped clique homology is QMA₁-hard
SummaryThis paper studies the computational complexity of simplicial homology and proves that the weighted, spectrally gapped version of clique homology is QMA₁-hard. It identifies a gap in an earlier King–Kohler reduction concerning folded local gadgets and re-establishes the needed topological and spectral properties on the clique complexes the reduction actually produces. The authors also derive a quantitative global estimate that carries the source Hamiltonian's promise gap over to the final weighted Hodge Laplacian.
WhyRepairs a gap in a prior reduction with new local topology and spectral analysis, giving a complete QMA1-hardness proof with solid rigorous support and notable subfield impact.
In briefRobustness of quantum spectrum estimation when input copies are noisy
SummaryThis paper studies weak Schur sampling (WSS), a measurement underlying optimal quantum spectrum estimation and state tomography, under noisy inputs whose copies are not identical. For noisy product states, the authors show the expected total-variation estimation error is at most ε plus the noiseless error O(d/√n), so the output error does not grow with the number of copies. They also give a bound for arbitrary inputs using the quantum Wasserstein distance.
WhyFirst study of weak Schur sampling under noisy inputs, proving output error stays independent of n with optimal additive noise term.
In briefQuantum algorithms that efficiently map superpositions to orthogonal polynomial bases
SummaryThe paper presents quantum orthogonal polynomial transforms (QOPTs) for discrete Charlier, Meixner and Krawtchouk transforms and for integer-order continuous Laguerre transforms, with runtime polylogarithmic in grid size and inverse error. It reduces the continuous Jacobi transform to a discrete Hahn transform and gives a quadratic speedup over the naive approach via a more efficient Clebsch–Gordan compilation. It also introduces a framework for Laguerre transforms of all orders ν>0.
WhyUnifies Askey-scheme orthogonal polynomial transforms via optical gate compilation and reduces Jacobi to Hahn, gaining a quadratic speedup.
Anupam Prakash, Shree Hari Sureshbabu, Dylan Herman et al.
In briefFrom Symmetry to Secrecy: Covariant Classical–Quantum Wiretap Channels
SummaryThis paper studies classical–quantum wiretap channels with a transitive covariant input action, showing that both output ensembles are unitary group orbits of fixed seed states. This structure is used to build finite-block preprocessing schemes, with rates and trace-distance leakage bounds expressed through sandwiched Rényi information. For the hybrid binary channel studied by Tikku, Berta and Renes, numerical optimization at three and four channel uses reports rates above an estimated noisy-repetition benchmark, and the authors prove nonadditivity at an explicit channel parameter.
In briefFast mixing of quantum Gibbs samplers under a Dobrushin–Shlosman-type condition
SummaryThe paper extends classical Dobrushin–Shlosman theory to noncommuting quantum lattice systems by introducing a quantum condition for finite-block dynamics called smoothed heat-bath dynamics. For finite-range quantum spin chains at fixed finite temperature, the authors prove logarithmic trace-norm mixing in system size. They also prove stability under small local perturbations on graphs of polynomial volume growth.
WhyExtends classical Dobrushin-Shlosman conditions to noncommuting quantum lattices, proving logarithmic mixing at fixed temperatures, a notable theoretical advance with mainly theoretical impact.
In briefPreparing Gibbs states by quantum decoding of error-correcting codes
SummaryThis paper proposes a Gibbs state preparation algorithm that uses algebraic structure in the Hamiltonian, improving on the earlier HDQI method by replacing its classical decoder with a quantum decoder. For commuting Pauli Hamiltonians, the decoding task corresponds to transmitting a symplectic code over i.i.d. classical-quantum channels. The authors study two quantum decoders, and for certain dilute spin glasses they report that belief propagation with quantum messages reaches temperatures that no classical decoder can within their framework.
Christophe Piveteau, Yihui Quek, M. Isabel Franco Garrido
In briefGraph-based analysis of non-generic free-fermion solvability via Krylov decompositions
SummaryThis paper studies spin models that can be solved exactly as free fermions only at finely tuned couplings, characterizing them through the frustration graph of anticommuting Pauli terms. For Fendley's free-fermions-in-disguise chain, the authors construct Krylov currents that are exactly quadratic in effective fermionic modes, extending it to a linear family of free-fermion solvable Hamiltonians. They prove that each Krylov current expands in induced paths of the frustration graph, and identify path support as a signature of non-generic solvability.
WhyExtends the FFD chain to a linear free-fermion family via Krylov currents, with a proof of induced-path expansions; theoretically novel and rigorous.
In briefWhat information about time-correlated noise must a quantum memory decoder have?
SummaryThis paper studies what a quantum error-correction decoder must know about temporally correlated noise and what it costs to learn that information. Using weak coherent X rotations as the main example, it compares two noise models: one with a sign fixed throughout a run and one redrawn independently each interval. The models share identical syndrome statistics and the same spatiotemporal Pauli process, yet require different logical corrections at suitable storage times. The authors prove matching calibration bounds for a fixed code and target fidelity loss.
WhyProves matching calibration bounds showing identical SPP models require different corrections, a strong theoretical result with clear relevance to quantum memory decoding.
Danesh Morales-Hashemi, Graeme Smith, Ningping Cao
In briefASPIRE: a geometry-based method for preparing quantum states with shallower circuits
SummaryThis paper presents ASPIRE, an algorithm that approximately compiles quantum circuits for preparing states such as matrix product states. It selects gates according to the state's entanglement geometry and the target processor's connectivity, choosing parallel long-range gates that remove the most entanglement. The authors report that for states with long-ranged entanglement, ASPIRE typically achieves higher fidelities and shallower circuits than existing methods.
In briefComment on a paper on chiral electromagnetic surface waves at Chern-Simons interfaces
SummaryThis comment responds to a paper on chiral electromagnetic surface waves on Chern-Simons interfaces and a related preprint. The authors show that Maxwell electrodynamics coupled to a planar Chern-Simons interface has no plane wave solutions localized on the interface. They argue that an intermediate equation in the original derivation omitted certain terms, and that including them changes the original paper's final conclusion. They also state that the method used in the related preprint is not consistent.
In briefBorn rule in self-gravitating wave packet scenarios
SummaryThis paper studies how particle ensembles relax to the Born rule in a semiclassical gravity model described by the Schrödinger-Newton equations. It combines a Gaussian variational solution for a self-gravitating wave packet with Nelson's stochastic representation of quantum dynamics. Relaxation to quantum equilibrium occurs when the wave packet stays bounded or grows slowly, while rapidly expanding solutions can keep deviations from the Born rule indefinitely. Numerical simulations support this analysis.
In briefFull reconstruction of 100-dimensional frequency-bin quantum states with adaptive measurements
SummaryThe paper presents threshold quantum state tomography for entangled frequency-bin qudits, using adaptive measurements that exploit the sparsity of biphoton frequency combs together with Bayesian inference. The authors experimentally estimate the full state of biphoton frequency combs with Hilbert space dimension up to d²=100, a 56% increase over the previous record. This uses only 1.9% of the measurements required by conventional tomographically complete methods.
Hanson H. Nguyen, Zachary Goisman, Chen-You Su et al.
