In briefEntanglement asymmetry and asymmetry contour when a boundary field breaks symmetry
SummaryThis paper studies how a boundary magnetic field that breaks symmetry affects magnetization and the Rényi-2 entanglement asymmetry (EA) in the transverse-field Ising model. It derives lower and upper bounds for EA and examines how magnetization spreads from the boundary into the bulk after a boundary quench. It also introduces the asymmetry contour, a finite-difference quantity that resolves the symmetry-breaking information spatially.
In briefBest probe states for measuring dephasing in a quantum spin system
SummaryThis paper studies how to estimate dephasing, the loss of quantum phase coherence, in finite-dimensional spin systems. The authors present an efficient numerical algorithm to find the optimal probe states and the best achievable precision. They analytically identify the dephasing range where the spin cat state stays optimal for spins J=1 and J=3/2, and compare several probes numerically. In a central-spin model with a nuclear-spin bath, they find that the best probe depends on both dephasing strength and the control dynamics.
Leonardo Ratini, Stefano Carretta, Francesco Albarelli
In briefDiscrete WKB method for density profiles in inhomogeneous two-band free-fermion chains
SummaryThe paper extends the discrete WKB method to one-dimensional bipartite tight-binding chains of free fermions whose hopping amplitudes and on-site potentials vary slowly. It focuses on the inhomogeneous Rice-Mele model and derives semiclassical expressions for wave functions, density of states, and sublattice-resolved densities. The authors show that the WKB density profiles agree with those from the local-density approximation.
In briefElementary proofs of quantum lower bounds for element distinctness and k-sum
SummaryThis paper gives elementary proofs of the Ω(n^{2/3}) quantum query lower bound for element distinctness and the Ω(n^{k/(k+1)}) lower bound for the k-sum problem, for fixed k and sufficiently large groups. The proofs rely only on basic properties of quantum states and linear algebra. They analyze how the algorithm's states differ on different inputs.
In briefStochastic and quantum autonomous information machines: fluctuations, precision and optimization
SummaryThe paper studies an autonomous machine that converts thermal and informational resources, coupled to thermal reservoirs and a tape acting as an information reservoir. The machine can erase information driven by heat and refrigerate driven by information, with suitable efficiency definitions introduced. The work focuses on fluctuations in currents and stochastic efficiencies, and on operation at optimal performance. The model is extended to include a coherent information reservoir that can modify operation and performance, offering insights for small-scale information-to-work devices.
In briefAn Introduction to Algebraic Methods for Analyzing Quantum Systems
SummaryThis paper examines several well-known quantum systems, including the harmonic oscillator, hydrogen-like atoms, optical components, and particle spin, and shows how they can be analyzed algebraically. It emphasizes that algebraic relationships between operators determine a system's physical character, and highlights the Lie algebra so(2,1) ≅ su(1,1) as a recurring spectrum-generating algebra. The authors aim to serve as a gentle introduction for readers interested in algebraic methods in quantum mechanics.
In briefForming and identifying high-quality oxygen-vacancy defects deep in silicon carbide
SummaryThis paper studies optically addressable paramagnetic defects PL5, PL6, and PL7 in silicon carbide, which are promising for quantum sensing. By decoupling oxygen incorporation from defect formation, the authors produce defects with highly homogeneous spin-resonance frequencies, narrow optical linewidths, and long T2* coherence times. They also show defect formation beyond the ion range using oxygen diffusion, and provide hyperfine statistics of 17O and host nuclei across many PL6 defects that identify the oxygen-vacancy origin.
Ryo Shiotani, Fu-Chieh Chuang, Mitsuaki Kaneko et al.
In briefFeasibility Framework for Deadline-Constrained Key Delivery in Mobile Free-Space QKD
SummaryThis technical note examines whether mobile free-space quantum key distribution links can deliver cryptographic keys at required times, separating optical feasibility, positive finite-key output, and on-time key service. It formalizes these distinctions using a time-indexed, security-qualified arrival process and a key-inventory model, with an elementary prefix-feasibility condition under stated assumptions. A stylized finite block model and two numerical examples show that positive long-run optical availability does not guarantee positive finite-key output when observations are fragmented. The work is a systems-level accounting and benchmarking framework rather than a new security proof or hardware demonstration.
In briefTrace-distance measure of recurrent pairwise synchronization in cavity-coupled superconducting qubits
SummaryThis paper theoretically studies recurrent pairwise synchronization among three superconducting qubits coupled indirectly through a shared single-mode microwave cavity and driven by a coherent microwave field. Synchronization is quantified by the trace distance between reduced single-qubit density matrices, with low-distance regions marking finite synchronization windows. An envelope-threshold procedure extracts the representative duration of these windows, which shrinks rapidly as the relative outer-qubit coupling increases and depends only weakly on the middle-qubit coupling in the stronger-coupling regime.
In briefOptimizing a Quantum Battery with Counterdiabatic Driving
SummaryThis paper studies how a quantum battery charges within an open quantum framework, using a driven qubit as the charger and an ancilla as a controllable switch. It uses an adiabatic protocol for lossless energy transfer and adds a counterdiabatic control field to suppress unwanted transitions and speed up charging. The authors report that charging efficiency improves under adiabatic evolution with stable, non-oscillatory behavior, and they identify an optimal operation time.
In briefQuantumBilliards.jl: A Julia library for large-scale computation of quantum billiard eigenstates
SummaryThis paper presents QuantumBilliards.jl, an open-source Julia library for solving the two-dimensional interior Helmholtz eigenproblem with Dirichlet boundary conditions, a standard model in quantum chaos. It includes conventional wavenumber-sweep methods along with accelerated eigensolvers such as the Vergini–Saraceno scaling method, EBIM, Beyn's contour-integral method, and the CORK method. The library also reconstructs eigenfunctions from boundary normal derivatives and computes Poincaré–Husimi phase-space representations.
In briefA Reference of Problems Where Quantum Computers May Beat Quadratic Speedups
SummaryThis compendium is a reference for non-quantum researchers and domain experts assessing whether quantum methods suit their real-world problems. It lists core computational problems with good evidence that quantum computers can achieve more than a quadratic speedup in offline, non-relativized time complexity. Rather than specific algorithms, it describes the problem characteristics and the structural constraints real instances must satisfy to realize these advantages in practice.
Philipp Kammerlander, Thomas E. O'Brien, Robbie King et al.
In briefA note on whether observational ergotropic advantage is monotonic
SummaryThis paper examines the observational ergotropic advantage, introduced by Mahanti et al., which measures the maximum extra work a measurement can extract compared with all incoherent measurements. The authors show that this quantity is monotonic under a suitable resource theory of measurement coherence, using energy-preserving channels and passive resets as free operations. They find monotonicity is necessary but not sufficient for measurement transformations, and that the measure is not convex.
Debanjan Dey Sarkar, Mallika Mondal, and Preeti Parashar
In briefClassically pre-training large quantum circuits with Pauli propagation, then running them on quantum hardware
SummaryThe paper uses Pauli propagation to convert the loss of a quantum machine learning model into an explicit parametric formula that can be minimized entirely on classical computers, avoiding costly parameter-shift gradients. It adds truncation and pruning strategies to make the method scale. The authors test it on 64-qubit circuits for a two-dimensional Ising model ground-state task and a binary image generative model, and report deploying the pre-trained parameters on the IBM processor ibm_berlin..
In briefPhoton pairs boost loss estimation in whispering-gallery resonator interferometers
SummaryThis paper studies estimating detuning and intrinsic loss in a lossy whispering-gallery-mode resonator placed in a balanced Mach-Zehnder interferometer. It compares indistinguishable photon-pair probes with coherent-state probes at equal mean photon number. The authors report that photon pairs give higher quantum Fisher information for dissipative parameters away from critical coupling, and that photon-number-resolved detection saturates this value.
Elnaz Darsheshdar, Callum Jones, Seyed Mostafa Moniri et al.
In briefLYNX: A trapped-ion quantum computer with 31 qubits
SummaryThis paper introduces LYNX, a quantum information processor built from trapped calcium-40 ions, using up to 31 qubits with all-to-all connectivity. The authors assess its performance with randomized benchmarking, GHZ state fidelity estimates, and quantum volume tests. They report average single-qubit gate errors of 8(5)×10⁻⁵ and average two-qubit gate errors of 2.84(8)×10⁻³ in a 24-qubit register. The device passes quantum volume tests up to 15 qubits, corresponding to a quantum volume of 2¹⁵.
Alexander Erhard, Georg Jacob, Max Hettrich et al.
In briefQuantum secret sharing built on CSS qLDPC codes, with computable access structures and network costs
SummaryThis paper studies quantum secret sharing schemes constructed from CSS quantum low-density parity-check (qLDPC) error-correcting codes. It presents an exact computational framework that classifies authorized, forbidden, and intermediate coalitions using parity-check matrices and binary linear algebra, and introduces an accessible logical dimension to refine intermediate cases. The authors also account for network embedding, routing, and scheduling costs, and verify the predicted properties through numerical experiments on four CSS qLDPC codes.
In briefQuantum Landau-Lifshitz-Gilbert equation for magnetic conductors and insulators
SummaryThis paper builds a microscopic framework that derives Gilbert damping terms from specific interactions in magnetic materials. In ferromagnetic conductors, damping is dominated by the s-d exchange interaction between localized moments and itinerant electrons, yielding a quantum LLG equation. In magnetic insulators without free electrons, spin-phonon interactions are the main source, and linear response theory gives an analytic quantum LLG equation with a Gilbert damping tensor. The results show that different interactions produce qualitatively different damping structures, which can depend on position and take tensor form rather than a single scalar.
In briefQuantum theory of how laser noise limits cooling of levitated particles by coherent scattering
SummaryThe paper studies how classical amplitude and phase fluctuations of the laser limit the state purity of a levitated nanoparticle cooled by coherent scattering. The authors derive a master equation that includes laser noise and quantify cooling performance at several noise levels in state-of-the-art experiments. They give approximate analytical expressions for noise-induced heating rates and excess phonon numbers in weak and strong coupling regimes. The model also applies to noise with generic power spectral densities and finite correlation times.
Davide Candoli, Andreu Riera-Campeny, Lorenzo Dania et al.
In briefEntangled logical qubits on a superconducting quantum processor
SummaryThis paper demonstrates high-fidelity logical qubit operations on ibm_phoenix, a 120-qubit superconducting processor with fast reset. The authors build distance-3 and distance-5 surface codes and entangle two logical qubits via lattice surgery, reporting Bell-state fidelities above 93%. They also report logical teleportation across three logical qubits with fidelities of 78% to 93%, and stability improvements of about 2·10⁻⁷ over 170 measurement rounds.
Robin Harper, Xanda C. Kolesnikow, Campbell K. McLauchlan et al.
In briefPaper showing finite nonsignalling resources can simulate entangled qubit measurement statistics
SummaryThe paper shows that for any fixed pure two-qubit state, all local projective-measurement statistics can be exactly simulated using shared randomness and finitely many PR boxes, without communication or postselection. The number of boxes has a worst-case bound independent of the measurement settings. The result reveals a separation between the continuity of quantum measurement correlations and the alphabet size of the resources needed to simulate them.
WhyExact simulation of partially entangled qubit measurement statistics with finitely many PR boxes resolves a longstanding open question in Bell nonlocality.
In briefA lower bound on how environmental collisions create Wigner negativity
SummaryThe paper studies when classical evolution laws can emerge exactly from quantum theory if the environment interacts with the system through collisions. The authors derive an inequality relating the distribution of environmental momentum kicks to the absolute value of the Fourier transform of the potential, and show that violating it is necessary and sufficient for a non-quadratic potential to generate Wigner negativity. They also obtain a lower bound on the heating rate needed for a quantum system to evolve effectively classically, illustrated with a levitated nanoparticle.
In briefHigh-resolution hyperspectral quantum infrared imaging using undetected photons
SummaryThis paper demonstrates spectrally resolved transmission imaging near 1550 nm using undetected photons with a folded nonlinear interferometer based on spontaneous parametric down-conversion. A zebrafish larva was imaged as a biological feasibility test. The authors report spectrally resolved interference fringes in the near-infrared with a maximum baseline visibility of about 74 percent.
Aadi Suketu Bharatia, Vidya Prakash Muppalla, Ananya Asthana et al.
In briefNear-field maps reveal edge states in molecular aggregates
SummaryThis paper studies topological edge states in two-dimensional self-assembled molecular aggregates built from two molecular sublattices. Because these states have weak far-field transitions and far-field spectra do not show whether excitations sit at the edge, the authors propose spatially resolved near-field spectroscopy to capture their full spatial structure. The resulting maps are strongly nonuniform and interference-like rather than mirroring site populations. The authors also report that a convolutional neural network can reconstruct the complex expansion coefficients of the eigenstates from these maps, and that the reconstruction holds up under substantial random noise.
In briefTwo-layer checks for reliable magic-state preparation in high-rate quantum codes
SummaryThis paper addresses the high resource cost of preparing magic states in high-rate quantum codes. It proposes two-layer verification, which checks independently prepared subblocks locally and then verifies them logically after embedding them into a target code. This detects harmful errors, such as even-parity logical-eigenvalue flips, that a collective product check alone cannot see. For a [[21,3,5]] code, the authors embed three verified Steane-code magic states, and circuit-level simulations of T- and S-state preparation show logical-error suppression consistent with the code distance.
In briefBose-Einstein condensate on a spherical shell: nonlinear wave patterns and symmetry breaking
SummaryThis study examines nonlinear wave patterns that form in a shell-shaped Bose-Einstein condensate, a cloud of ultracold atoms confined to a spherical surface, with both repulsive and attractive interactions. Several classes of modes are found, including analytical extensions of spherical harmonics, some of which match planar Townes solitons and vortices. Another class arises from symmetry-breaking bifurcations under repulsive interaction and has no linear counterpart. The authors also report a breathing dynamics oscillating between an unstable soliton and a stable vortex necklace state, showing curved-geometry behavior differs substantially from planar systems.
Alexander Wolf, Vladimir V. Konotop, and Maxim A. Efremov
In briefRunning a Quantum Subroutine on Cluster States: A Phase Oracle in Measurement-Based Computing
SummaryThis paper shows how a reusable phase oracle subroutine can be implemented within measurement-based quantum computation using experimentally feasible cluster states. Unlike earlier Grover's algorithm demonstrations in this model that leave out explicit oracle construction, it gives a transparent formulation of the oracle. The work covers measurement patterns, byproduct correlations, density-matrix simulations, and corresponding MBQC measurement circuits.
Sakibul Islam Rayhan, Karima Hassan, Md Rasedujjaman et al.
In briefTraceable quantum secret sharing that identifies leaked or forged shares
SummaryQuantum secret sharing protects distributed quantum information, but existing schemes cannot assign accountability when shares are leaked or forged. The paper proposes LVT-QSS, which attributes leaked shares through a leakage verification mechanism, and MTA-QSS, which identifies participants who submit forged shares during reconstruction. The authors give security definitions for both settings and prove the protocols meet the corresponding guarantees. Numerical simulations under per-share depolarizing noise show that the verification stage is the most noise-sensitive.
In briefBogoliubov Dynamics and Zitterbewegung in Optical Dirac Systems
SummaryThe paper develops a bosonic Bogoliubov description of Zitterbewegung in time-dependent optical-Dirac systems. When constitutive parameters vary in time, interbranch coupling and positive-negative-frequency coherence arise. Under periodic modulation near Ω≈2ω₀, this coupling becomes resonant, parametrically amplifying the coherence and enhancing the Zitterbewegung motion.
In briefSingle-step SU(3) Hahn echo for qutrit atom interferometry
SummaryThis paper generalizes the Hahn echo, a dephasing-refocusing technique, from two-level spins to three-level qutrits using single-step SU(3) gates. The gates, designed with optimal control theory, extend coherence time by more than an order of magnitude in an ultracold atomic ensemble in free fall. Process tomography gives fidelities near 93%, mainly limited by state preparation and measurement errors. The beam geometry also realizes a three-path Mach-Zehnder atom interferometer with two independent phase differences.
Chirantan Mitra, Lucas Gabardos, Fran\c{c}ois Impens et al.
In briefNeural Model Learns Long-Term Dynamics of Driven Three-Spin Quantum Systems
SummaryThe paper introduces Quantum Evolution Networks (QENs), which map physical parameters and time to full propagators for periodically driven three-spin registers. The networks learn one-period unitary propagators and within-period paths, so predictions are made by periodic composition rather than per-query numerical integration. For transverse driving, the fifth-percentile fidelity is 0.9947 over 24 periods on 256 held-out configurations. A leading-order analysis of spectrally resolved endpoint residuals is also presented, which predicts multicycle process error more accurately than simpler estimates.
In briefPhoton-number discrimination via arrival-time separation in wide superconducting microstrip detectors
SummaryThe authors measure photon-number-dependent arrival-time distributions in wide NbN superconducting microstrip single-photon detectors with 3.2 μm and 6.4 μm widths under pulsed 515 nm light. The wider device's histograms are fitted with exponentially modified Gaussian components up to n=8 photons. Adjacent peaks become more separable at higher photon numbers, unlike the compression seen in conventional narrow-wire SNSPDs.
In briefTrident: Efficient Load Verification for Yoked Surface Codes Using a Three-Level Memory Hierarchy
SummaryQuantum computers often encode qubits with surface codes, which have a low encoding rate. This paper addresses the verification delay when loading qubits from 2D Yoked Surface Codes, which are more storage-efficient but slow to verify. The authors propose Trident, which adds a small intermediate level built from a 1D Yoked Surface Code to reduce how often slow verification is needed. They report speedups of 2.8x (demand-driven) and 4.2x (prefetch-driven) with only a 4.9% increase in memory physical qubit cost.
Gunagya Singh Mamak, Suhas Vittal, Kabir Dubey et al.
In briefQuantum public-key encryption with classical communication that does not require quantum one-way functions
SummaryThe paper studies whether quantum public-key encryption with classical keys and ciphertexts (qPKE) requires quantum-computable one-way functions (qOWFs). The authors show a black-box separation: relative to a specific oracle, qPKE exists but qOWFs do not. They also construct qPKE from quantum indistinguishability obfuscation and efficiently verifiable one-way puzzles.](
WhyProves a black-box separation between qPKE and qOWF and constructs qPKE from quantum iO and one-way puzzles, a novel theoretical advance.
In briefKinetic competition decides whether loss-induced binding of Hubbard pairs forms exceptional points
SummaryThe paper studies how two-body loss can bind two fermions in a Hubbard lattice and whether the binding threshold is an exceptional point. At fixed total momentum, the two particles' hops interfere to give a relative-motion hopping that sets its kinetic energy. When one direction's maximum kinetic energy exceeds the sum of the transverse maxima, the threshold is an exceptional point where two scattering zeros coalesce. Without a dominant direction, binding occurs without coalescence or breaking of parity-time symmetry.
In briefMaterial conditions for transferring angular momentum from twisted photons to photoelectrons
SummaryThis paper studies which semiconductor materials can transfer a twisted photon's total angular momentum to the orbital angular momentum of photoelectrons emitted from an n-type surface. Using a single-valley effective-mass model, the authors compute angular-momentum-resolved spectra for several materials, including GaAs and InSb. They conclude that efficient transfer needs the electron's transverse momentum to be much smaller than the photon's, favoring low temperature, small effective mass and shallow donor levels. GaAs is less favorable in this model.
In briefConstructing center-of-mass momentum eigenstates in 2D lattices in real space, with selection rules
SummaryThe paper presents a framework for building center-of-mass momentum eigenstates of two-dimensional quantum many-body systems directly in real space. It accounts for uneven cyclic subspace dimensions caused by the spatial symmetries of many-body configurations and particle statistics. The authors report an anomalous coupling in highly symmetric particle distributions, where allowed momenta in one direction are constrained by the perpendicular direction, and argue that neglecting this coupling causes missing or duplicated basis states. Concrete examples are given.
In briefHow well quantum links keep their correlations and controlled teleportation working under noise
SummaryThe paper studies how a three-qubit GHZ resource holds up under bit-flip, phase-flip, depolarizing, and amplitude-damping noise. It characterizes the noisy resource using multipartite quantum discord, genuine multipartite concurrence, localizable entanglement, and controlled teleportation fidelity. It also outlines a photonic proof-of-concept setup for the protocol. Bit-flip and amplitude-damping noise generally preserve useful multipartite correlations over broader parameter ranges.
In briefLong-lived non-thermal states left behind by quantum phase transitions
SummaryThe paper shows that asymptotic quantum many-body scars (AQMBS), non-thermal states whose stability grows with system size, arise as remnants of certain quantum phase transitions. For a broad class of frustration-free Hamiltonians, the gapless excitations survive deformation into a scarred Hamiltonian with energy variance bounded by the gap. The authors model the critical Fredkin and Motzkin chains and the 2D PVBS model, finding that stability is set by the dynamic critical exponent, and exponentially stable states with volume-law entanglement in the Motzkin chain.
Leonard Logari\'c, Shane Dooley, Tsuyoshi Okubo et al.
In briefCan spontaneous time-translation symmetry breaking be quantized without keeping explicit Hamiltonian branches?
SummaryThe paper asks whether classically branched dynamics linked to spontaneous time-translation symmetry breaking can be quantized without explicitly keeping the Hamiltonian's branches. It uses a reduced phase space formulation in which the Hamiltonian is single-valued and the singular structure of the Legendre map is encoded in momentum-dependent symplectic geometry. Quantization yields a deformed position-momentum commutator, with a bounded central momentum sector and two unbounded outer sectors. In the central sector, states with zero mean momentum have a nonzero lower bound on position uncertainty, under operator-domain assumptions, and a possible link to k-essence is noted, while the relation to branch-matching quantization remains unresolved.
In briefAdditive uncertainty relations derived with pseudospectral methods
SummaryThe paper studies the sum of variances for finitely many Hermitian observables. For d observables, the authors show that this sum exceeds an expression built from the expectations of i[A_j,A_k], plus the square of the smallest singular value of the associated localizer. They also establish a containment between Clifford pseudospectra and quadratic pseudospectra for d observables.
In briefQuantumMatterExplorer: An Autonomous Agent for Discovering Quantum Many-Body Phases
SummaryThis paper presents an autonomous agent built on a large language model that takes only a Hamiltonian and its parameter ranges as input and produces a phase diagram from its own numerical simulations. It uses persistent planning, expert computational-physics tools, and density-matrix renormalization group calculations cross-checked against exact diagonalization. Tested on a recently published frustrated spin-1 chain without any hint about the physics, it identified candidate Néel, Haldane and dimerized phases, along with incommensurate correlations, within an eight-hour compute budget.
In briefRFSoC-based control of a fully connected exchange-only qubit
SummaryThe paper presents spinQICK, an open-source control package built on the Xilinx RFSoC for voltage control and readout of semiconductor spin qubits. The authors use it to demonstrate coherent control, state preparation, and readout on a fully connected triangular exchange-only triple-quantum-dot device. They also introduce and experimentally verify a new dynamical decoupling sequence and use it to characterize electrical noise.
Abigail L. Wessels, M. Garrett Bimstefer, Joseph D. Broz et al.
In briefNoise-Assisted Quantum Entanglement: How Environmental Memory Helps Qubits Stay Entangled
SummaryThis paper studies how entanglement between two qubits in a cavity evolves when their coupling strength fluctuates randomly. It compares white noise, which has no memory, with Ornstein-Uhlenbeck noise, which has memory, and solves the dynamics analytically for Fock and coherent cavity states. The authors show how initial qubit states and cavity photon statistics affect whether entanglement is generated and preserved. Under strong non-Markovian noise with long correlation times, entanglement shows notable resistance to sudden death and repeated revivals.
In briefFidelity Dynamics of a Jaynes–Cummings Qubit Under Markovian and Non-Markovian Coupling Noise
SummaryThis paper analytically studies the fidelity of a qubit coupled to a single-mode cavity when the qubit–cavity coupling strength fluctuates randomly. The authors model these fluctuations with Gaussian white noise and with Ornstein–Uhlenbeck noise of finite correlation time, and derive exact expressions for the noise-averaged density matrix and fidelity. They find that fidelity is governed by a single decoherence factor, decaying exponentially for white noise and non-exponentially for finite correlation times.
In briefRigidity of continuous-variable graph states under Gaussian local transformations
SummaryThis paper studies multimode entangled pure Gaussian states, described as continuous-variable graph states with complex adjacency matrices. It establishes, for finite squeezing, a criterion for when one such state can be converted into another by a Gaussian local unitary, including the case relating imaginary and real graph states. The authors find these graph states are too rigid to admit an exact qumode local-addition operation, but define an approximate version when squeezing is strong enough.
In briefOptimal control of a fluxonium qubit using the Q-PRONTO method
SummaryThis paper designs and benchmarks single-qubit gates for a fluxonium superconducting qubit, optimized with the Q-PRONTO trajectory-optimization method based on the circuit Hamiltonian. The authors modified the QICK firmware's memory allocation so that long strings of arbitrary pulses can be applied. Standard randomized benchmarking gives a total error of 6.6×10^-4 per gate.
John Barta, Brian D. Isakov, Pablo Aramburu Sanchez et al.
In briefTime Degeneracy Limits Decoding of Quantum Codes With Repeated Noisy Measurements
SummaryThis paper studies how repeated noisy syndrome measurements affect message-passing decoders for quantum LDPC codes. It shows that time degeneracy in the space-time decoding graph creates low-weight error patterns that cause local decoder failures depending on node degrees. The authors propose a space-time anisotropic min-sum decoder and report improved failure probabilities on bivariate bicycle codes compared with min-sum plus ordered statistics post-processing.
WhyCharacterizes temporal degeneracy kernel with counting bounds and degenerate error patterns, rigorous theory plus simulations on BB codes showing practical relevance to QLDPC decoding.
In briefA topology-aware quantum-classical method for choosing multiple space debris to remove, using Gaussian Boson Sampling
SummaryThe paper presents a framework that combines orbital mechanics, weighted orbital-transfer graphs, Gaussian Boson Sampling (GBS), and multi-objective evolutionary optimization to select several debris targets and plan their removal order. GBS first generates candidate target subsets, which are then evaluated with PyGMO-based optimization to minimize total velocity increment and mission duration. The authors test the approach on three benchmark environments: SOCRATES Minefield, Collision Cloud, and Random.
In briefPhotoelectrons reveal phase-dependent noise in bright squeezed light
SummaryThis paper shows that the variance of bright squeezed vacuum (BSV) depends on phase as well as strength, which earlier strong-field experiments did not record. Using coherent light of the same color as a phase reference, the authors ionize xenon and find that the photoelectron yield follows the BSV quadrature along the coherent field. Ionization nonlinearity amplifies this quadrature noise many times in the electron yield, and the noise differs by an order of magnitude between ionization channels.
In briefQuantum complexity of fermion systems: how pairing and deformation shape simulation resources
SummaryThis paper studies quantum complexity in a fermionic system showing deformation and pairing, using entanglement, non-stabilizerness, and fermionic non-Gaussianity. The deformed phase combines high entanglement with low non-stabilizerness, while the superfluid pairing phase shows substantial multipartite entanglement and non-stabilizerness. The authors combine stabilizer-state expansion with variational basis optimization to describe the phase diagram in a classically scalable, symmetry-preserving way.
In briefWhat quantum parameter estimation estimates: a no-go result for true values
SummaryThis paper examines when quantum parameter estimation is compatible with the idea of a unique "true" value of the estimated quantity that exists independently of measurement. The authors identify three assumptions common in quantum metrology and prove a no-go theorem showing they are jointly incompatible with the completeness of the quantum state (no hidden variables) and with entanglement between probes and the measured system. Since entanglement is a generic prediction of standard quantum theory, a realist account of estimation is impossible unless hidden variables are accepted or quantum theory is modified.
In briefScreening strongly correlated oxide-electrode materials using quantum simulation
SummaryThe paper presents an end-to-end framework for assessing quantum computing in screening strongly correlated oxygen-electrode materials for SOFCs and SOECs. It targets interface observables such as oxygen-vacancy formation energies, vacancy migration barriers, and electronic conductivity, obtained through GW-based embedding methods like GW+DMFT or SEET. The authors also identify benchmarks and resource costs needed to evaluate potential quantum advantage.
In briefUniversal mixed-state deep thermalization under generic quantum errors
SummaryThis paper studies deep thermalization of projected ensembles in mixed-state quantum dynamics containing local quantum channels (errors). The authors show that the late-time mixed-state projected ensemble is fully determined by the normalized Choi state of the error channel and is universal, independent of the microscopic details of the unitary dynamics. They prove this analytically for dual-unitary circuits, global Haar-random dynamics, and local Haar-random circuits at large local dimension, and verify it numerically in qubit circuits and kicked Ising dynamics.
WhyExtends deep thermalization to mixed states, showing the limiting ensemble is fixed by the error channel's Choi state, verified analytically and numerically.
In briefSize-independent log-Sobolev inequalities for quantum Gibbs samplers
SummaryThis paper proposes a method to prove L² and modified logarithmic Sobolev inequalities, with constants independent of system size, for quantum Gibbs samplers satisfying KMS detailed balance. The authors transport the inequality along a temperature-dependent path from the infinite-temperature product state to the Gibbs state, keeping a size-independent decay rate for the sandwiched Rényi-2 divergence. A tensor-power argument with the quantum asymptotic equipartition property then transfers this bound to relative entropy. The framework is applied to one-dimensional quantum spin chains at every finite temperature and to finite-range quantum spin systems at sufficiently high temperature in any fixed dimension.
WhyIntroduces a temperature-path transport framework with tensor powers and quantum AEP, yielding size-independent log-Sobolev bounds for 1D chains and high-temperature spin systems.
In briefArcTN: Efficient Tensor-Network Contraction Planning for Quantum Circuit Simulation
SummaryThis paper presents ArcTN, a framework for optimizing tensor-network contraction orders used in quantum circuit simulation, with Light and Heavy search presets. It combines randomized-greedy construction, subtree reconfiguration, and parallel tempering, and adds Fixed and Dynamic slicing to meet tensor-size limits. On the QC32 networks, Light reduces FLOPs by 61.32% relative to Cotengra Auto/CMA-ES while planning 1.62 times faster, and Heavy reduces FLOPs by 43.83% relative to Cotengra AutoHQ/Optuna while planning 7.21 times faster.
In briefProblem-aware sampling reduces bias and variance in randomised Hamiltonian simulation
SummaryThis paper introduces StateDRIFT, a variant of the qDRIFT quantum simulation algorithm that optimises its term-sampling distribution using the initial state and target observable. It aims to estimate time-evolved quantities more accurately while keeping qDRIFT's guarantees. Tests on short-time dynamics of lattice models and molecules up to 18 qubits show reduced estimator bias and variance, lowering the required circuit depth; for BeH2, the two-qubit gate count for a given accuracy falls from 11,201 to 983.
Brian Coyle, Jonathan H. Fetherolf, Antonio M\'arquez Romero et al.
In briefOne-shot quantum entanglement generation and distillation using hypothesis testing
SummaryThe paper studies how much entanglement two distant labs can share over a noisy connection, linking this to deciding which of two quantum hypotheses holds. Using Cheng's trace inequality, the authors bound the infidelity of a Petz decoder by a binary hypothesis testing cost, yielding one-shot bounds for entanglement generation over channels and one-way distillation from shared states. They also prove an error-preserving conversion from generation codes to transmission codes, and derive achievable coherent-information rates with logarithmic remainder terms.
WhyBounds Petz-decoder infidelity via binary hypothesis testing, using Cheng's trace inequality and random-subspace second moments, yielding explicit one-shot entanglement results; strong theory, mainly
In briefMarkovian Errors and Random Circuit Benchmarks: How Noise Shapes the Decay Parameter
SummaryThis paper studies randomized benchmarking (RB) and related random-circuit benchmarks under small gate-local Markovian noise. The authors factor each noisy gate into an ideal unitary times the exponential of a small error generator, and perturb the RB decay matrix accordingly. Pauli-stochastic errors contribute linearly to the decay parameter, while Hamiltonian errors contribute through a gauge-invariant quadratic form. For the single-qubit gate set of X and Y rotations by pi/2, the authors give an explicit formula in three first-order gauge-invariant coordinates.
WhyDerives explicit closed-form RB decay dependence on elementary Markovian error rates, with clear linear and quadratic structure; strong theory, though impact is confined to quantum benchmarking.
Anthony M. Polloreno, Timothy Proctor, Robin Blume-Kohout
In briefNanopillar metasurfaces combining high reflectivity with ultracoherent nanomechanics
SummaryThis paper proposes lightweight optomechanical mirrors made of high-refractive-index nanopillar metasurfaces on a thin membrane, avoiding the usual trade-off between optical reflectivity and mechanical performance. A 50-micrometer nanopillar array achieves 99.82(1)% reflectivity for a tightly focused 7-micrometer beam and a roughly 100-nanometer-wide high-reflectivity band near 1550 nanometers. The same patterning forms a phononic crystal that isolates an ultracoherent localized mechanical mode with a Q·f product of 2·10^14 Hz.
WhyNanopillar metasurface simultaneously achieves high reflectivity and ultracoherent mechanics, overcoming a known trade-off, with supporting measurements.
Alexander Jung, Anastasiia Ciers, Hannes Pfeifer et al.
In briefConQEC: Concolic Testing Framework for Quantum Error-Correcting Code Implementations
SummaryThis paper introduces ConQEC, described as the first concolic testing framework for quantum error-correcting code (QECC) implementations. It combines concrete Pauli fault replay with symbolic repair-path constraints to generate tests that reveal logical failures and show where the repair path first diverges. In evaluations on generated and public QECC artifacts, ConQEC detected the seeded bug in every case and produced a replay-valid, fault-localizing witness for each.
In briefMutual information between different quantum reference frame views
SummaryThe paper addresses how subsystems change when described relative to different quantum reference frames, so standard information measures that assume a fixed tensor product structure no longer directly apply. Using an algebraic definition of subsystems, the authors study the union and overlap of subsystem algebras across frames. They find that the usual chain law double-counts the information in the overlap, and propose a modified chain law. The resulting cross-frame mutual information satisfies subadditivity.
Leonardo Valente, Carla Ferradini, Flaminia Giacomini et al.
In briefA quantum theory of light in nonlinear media, showing non-Gaussian noise from nonlinear absorption.
SummaryThe paper builds a quantum theory of light in nonlinear materials that have dispersion and absorption. It uses a path-integral formulation of the microscopic Huttner-Barnett model with cubic self-interactions needed for chi(2) processes. The authors report that non-Gaussian noise linked to nonlinear absorption emerges from this framework, which they state is consistent with the nonlinear fluctuation-dissipation theorem.
