In briefQuantum mutual information in the spin-1/2 J1-J2 Heisenberg chain near its commensurate–incommensurate and Kosterlitz–Thouless crossovers
SummaryThis paper uses DMRG on the spin-1/2 J1-J2 Heisenberg chain to decompose block mutual information into SU(2) correlation channels. In the dimerized phase, blocks capture bond-energy correlations, and the scalar channel dominates at large distances in the commensurate regime up to J2/J1=0.40, dropping to a few percent beyond the Majumdar-Ghosh point. On the gapless side, ring results are compared with the two-interval prediction of SU(2)₁ conformal field theory near the Kosterlitz-Thouless point at J2/J1=0.241167.
In briefThermal aliases in quantum noise: sampling clocks and pulse widths
SummaryThe paper asks whether collective quantum-noise measurements can tell apart different mode temperatures from a single common temperature when the coupling spectrum is unknown. For stationary Gaussian oscillator environments, it derives a bandwidth threshold for an exact thermal alias on an integer-time sampling lattice, and proposes a fractional-time fluctuation observation and a calibrated second pulse width as ways to exclude common-temperature fits. It reports outcome counts for two designs and states that the guarantees assume independently validated preparation, spectral and control specifications.
In briefGeomagic square picture of a real six-level four-party entangled state
SummaryThe paper builds a real four-party absolutely maximally entangled state with local dimension six from a table of signed Pauli matrices. Its two-unitary matrix has 60 nonzero entries, each equal to 1 or ±1/√2. A locally equivalent version gives a genuine geomagic square in which every row, column and main diagonal tiles a hexagon, and all 36 pieces are pairwise non-congruent. Colours, shapes and hatching encode the full tensor, so the state can be reconstructed from the picture.
In briefDirect polarisation-state reconstruction using a temporal pointer: reconstructable states, resolution and optimal coupling
SummaryThe paper studies direct reconstruction of polarisation states from weak measurements using a temporal pointer, where the weak value is read from the mean arrival time and mean frequency of the postselected pulse. For a Gaussian pointer and arbitrary postselection state, it shows that unreconstructable states form a spherical cap centred on the state orthogonal to the postselection, with a half-angle set by three thresholds. It also derives an optimal coupling for first-order inversion that scales as the inverse sixth root of the incident photon number, and shows that exact inversion at finite coupling removes systematic error but leaves a bound from the two-centroid readout.
In briefExact Gaussian-Hermite closure for the mapping quantum-classical Liouville equation
SummaryThis paper studies the exact form of the quantum-classical Liouville equation in the Meyer-Miller-Stock-Thoss mapping representation. The authors expand the mapping density in Hermite functions and show that the excess coupling term cancels the raising contribution from the back-reaction force, so exact dynamics closes on a finite, sparse set of equations. Using Tully's dual avoided crossing model, they report that the Poisson bracket mapping equation (PBME) is less accurate than the quantum-classical description for populations, coherences, and momentum distributions across all regimes examined.
In briefGeodesic steering: a control method that speeds up entanglement creation in open quantum systems
SummaryThe paper presents an optimal-control strategy to accelerate the dissipative preparation of highly entangled many-body quantum states. Control pulses guide the open system along trajectories of instantaneous steady states while minimizing leakage from non-adiabatic transitions. Applied to qubits coupled to a photonic waveguide or a distributed squeezed reservoir, the method reduces preparation times for near-maximally entangled states by orders of magnitude compared with bare relaxation dynamics.
Keshav Venkataraman, Pablo Martinez-Azcona, Marko Ljubotina et al.
In briefThe Quantum Character Transform: Quantum Algorithms Exploiting Group Symmetry
SummaryThis paper discusses the discrete character transform, the group Fourier transform restricted to the center of the group algebra, where class functions form a commutative convolution algebra and irreducible characters serve as the spectral basis. The author states that, via a restriction operator, an efficient quantum Fourier transform yields an efficient quantum character transform for any finite group. Two quantum algorithms for class convolution are presented, based on direct class-sum block encoding and spectral implementation in the character basis. The paper covers applications to symmetry-adapted many-body dynamics, molecular symmetry analysis, quantum walks, and hidden-subgroup problems, including limitations for graph isomorphism.
In briefQMBL: A Live Leaderboard of Published Ground-State Energies for Lattice Models and the Electron Gas
SummaryThis paper presents QMBL, an interactive, maintained web record of published ground-state energies for lattice Hamiltonians and the homogeneous electron gas. The latest release, v0.5.0, contains 2,511 energies across 532 instances. Of these, 285 instances have no exact solution and serve as targets for a companion benchmark, QMBL: Open Problems.
In briefRealistic simulation of lossy multiport interferometers using a Gaussian model
SummaryThis paper addresses photon losses, a major obstacle to fault-tolerant optical quantum computing, by proposing a Gaussian model. The model reproduces lossy dynamics from experimental characterization of imperfect interferometers, yielding a mean vector and covariance matrix. The authors also use numerical simulation to quantify how optical losses deviate from being uniform across a multiport interferometer.
Sebastiano Corli, Dario Chemoli, Samuele Altilia et al.
In briefFisher-Information Certification from Bell Statistics: CHSH Bounds and Finite-Data Guarantees
SummaryThis paper derives lower bounds on classical Fisher information directly from Bell scores and their parameter dependence, using only experimentally accessible Bell statistics and without full state tomography. For CHSH measurements, it establishes a hierarchy of information among the full outcome record, individual correlators, and the compressed Bell parameter, quantifying the metrological cost of data compression. It also gives finite-sample lower-confidence bounds from coincidence counts and analyzes the effects of biased marginals, accidental coincidences, visibility loss, and multipair emission.
Juan Sumaya-Mart\'inez, Omar Olmos-L\'opez, Jorge Mulia Rodr\'iguez
In briefEuler's 36 officers need not all be entangled: real AME(4,6) states, families and classification
SummaryThis paper studies absolutely maximally entangled states of four six-level systems, AME(4,6), the quantum solutions of Euler's thirty-six officers problem. The authors give real solutions with only 60 non-zero coefficients and derive two closed-form families. These fall into exactly 20 classes under local unitaries and permutations.
In briefReverse quantum aging: restoring rhythmic oscillations in quantum networks
SummaryThe study explores how rhythmic oscillations can return in a network of globally coupled quantum oscillators that has entered an aged, degraded state. The authors add a controlled incoherent single-boson pumping channel and use a Lindblad master equation to model the system. They report that stronger pumping progressively suppresses and eventually eliminates the aging transition, even when all oscillators are inactive, and that full compensation of dissipative loss is not needed.
Bulti Paul, Biswabibek Bandyopadhyay, and Tanmoy Banerjee
In briefBosonic Quantum Conditional Mutual Information and Bose-Einstein Condensation: A theory paper using quantum information to characterize condensation
SummaryThe paper rigorously defines bosonic quantum conditional mutual information for infinite-dimensional Fock spaces via quantum instruments. It proves that Bose-Einstein condensation induces a logarithmic divergence, positioning this quantity as an order parameter for condensation. Applications discussed include composite bosons, the BEC-BCS crossover, and a quantum-gas-microscope protocol, with the reduced quantity proposed as a finite-size scaling probe analogous to the Binder cumulant.
In briefClosed-form exceptional points in a two-parameter PT-symmetric matrix model
SummaryThe paper studies stable bound states on a discrete one-dimensional N-point lattice, assumed to be generated by a two-parameter PT-symmetric potential V=V(A,B). It defines the coordinates A and B of Kato's exceptional point, which marks the instant of stability loss, exactly. These coordinates are obtained from the roots of an elementary quartic polynomial.
In briefEmergent quantum algebras in dissipative time crystals
SummaryThis paper studies persistent oscillations in open quantum systems described by the Lindblad equation, using an algebraic framework. For a single spin in a magnetic field under linear dissipation, it identifies the conditions under which non-decaying oscillatory modes appear as the spin size grows large. It gives a closed-form symmetry operator that, applied to the steady state, builds these modes up to O(1/S) corrections. The approach extends to two interacting spins sharing a reservoir, making entanglement during a quench analytically accessible.
In briefGeometry of quantum optical measurements: Kraus trajectories on a twelve-dimensional Lie group
SummaryThe paper uses Lie group geometry to study single-mode quantum optical measurements, whose Kraus operators lie in a twelve-dimensional group (IWH^12) that includes all diffusive 'dyne' measurements. It develops two more general dyne classes: slomodyne, which interpolates between diffusive homodyne and heterodyne, and a class adding adaptive squeezing and displacement. Using the Instrument Manifold Program and a Harish-Chandra-like decomposition, the authors track the Kraus operator as it evolves along the measurement record.
In briefBell's go theorem: a new realism that restores local causality
SummaryThe paper argues that Bell's theorem is usually read as showing quantum theory is incompatible with local realism, but this relies on the standard ontological models framework. The authors replace classical point-like elements of reality with point-free "records" (sublocales of a locale) and generalize Kolmogorov probability so that modularity fails across incompatible contexts. They claim locally causal models in this framework reproduce several quantum strategies, including the optimal CHSH violation, and attain every Bell-CHSH value up to the algebraic maximum.
WhyRedefines realism via point-free sublocales, showing local causality can coexist with quantum statistics; explicit models reproduce optimal CHSH violation, challenging the standard reading of Bell's t
Lorenzo Catani, Nesta van der Schaaf, Rui Soares Barbosa
In briefQuantum state texture of maximal-resource Fourier states under Hawking radiation
SummaryThis paper studies how quantum state texture (QST), a measure of a density matrix's nonuniformity in a computational basis, changes when Hawking radiation from a Schwarzschild black hole affects a two-mode Dirac field. It examines three maximally resourceful Fourier states under single-mode and two-mode radiation. When the unaffected mode is orthogonal to the textureless single-mode state, the output QST stays maximal regardless of Hawking temperature, a effect called orthogonality protection. Under simultaneous two-mode radiation this protection disappears and QST decreases as temperature rises, with QST partly redistributed between modes.
In briefPrecise placement of single-photon emitters in hBN using electron beam irradiation
SummaryThis paper studies how accurately B centers, single-photon emitters in hexagonal boron nitride that emit at 436 nm, can be created at chosen positions using an electron beam in a scanning electron microscope. Using in-situ cathodoluminescence mapping, the authors measure the electron beam-to-emitter distance at creation, finding a standard deviation of 27 nm. Including contributions such as the density of carbon dimer precursors raises the overall positional standard deviation to 40 nm. The authors suggest the technique could be improved to sub-10 nm accuracy.
In briefCertifying logical error rates in fault-tolerant quantum circuits without consuming magic states
SummaryThe paper proposes a certification protocol that checks whether a fault-tolerant quantum device runs a target circuit below a set logical error rate, without consuming magic states. It is independent of the code and decoder, runs alongside the target circuit, and its sample complexity grows linearly with logical qubits and non-Clifford gates. The authors illustrate the method with Steane-code simulations of a magic state injection gadget and a quantum Fourier transform.
In briefQBFF: Deep Quantum Bottleneck for Speaker Verification Anti-Spoofing
SummaryThis paper introduces QBFF, which passes a compressed speech representation through a small 8-qubit variational quantum circuit acting as a bottleneck, compared against a matched classical bottleneck. The quantum version gives better-calibrated confidence in most comparisons, including out-of-distribution evaluation, though its deployment-cost benefit depends on the model. The same circuit was also run on a real IBM quantum processor, described as the first anti-spoofing pipeline on a QPU, with lower subset EER and C_llr but higher mean actDCF than the classical reference.
Anton Firc, Nouhaila Innan, Vojt\v{e}ch Stan\v{e}k et al.
In briefQuantum entanglement and parametric resonance in coupled oscillators
SummaryThis paper studies two quadratically coupled harmonic oscillators, one in the ground state and one in a coherent state, as a toy model for a quantum field mode in an oscillating classical background. Using the Feynman-Vernon influence functional, the authors perturbatively compute the purity of the mixed state obtained by tracing out one oscillator. They find runaway growth of entanglement between the oscillators and rapid breakdown of perturbation theory in regions of parametric instability.
In briefBenchmarking a randomized quantum algorithm for estimating molecular expectation values
SummaryThis paper benchmarks the randomized sampling quantum algorithm of Wang et al. through numerical simulations on a hydrogen molecule and resource estimates for several active spaces of cytochrome P450, a pharmaceutical-industry system. The analytical error bounds were found to significantly overestimate the actual sampling error, while the imaginary evolution time bound was comparatively tight. However, the measurement overhead remains prohibitively high, requiring around 10^10 samples even for the smallest active spaces and over 10^15 for the largest, so substantial improvements are needed before the approach becomes competitive for industrial applications.
Anna Schroeder, Gian-Luca R. Anselmetti, Matthias Degroote et al.
In briefPathfinder-BP: A Low-Latency Recursive Decoder for Topological Codes
SummaryThis paper proposes Pathfinder-BP, a recursive decoder for topological quantum codes that combines belief propagation with controlled bit-flipping. It first fixes high-confidence errors in an initial belief propagation pass, then tentatively flips low-confidence variables to explore alternative error patterns when convergence fails. On surface codes, it reaches a noise threshold and logical error rate comparable to minimum-weight perfect matching (MWPM). Its highly parallel structure gives worst-case decoding latency that is quasi-linear in code distance, making it a candidate for low-latency hardware.
Stefano Tinelli, Francisco L\'azaro, Francisco Garc\'ia Herrero
In briefFinite-time quantum equilibration derived from local correlations
SummaryAn isolated quantum system evolves reversibly, yet a small subsystem can lose almost all information about its initial state. The paper considers a subsystem coupled to a maximally mixed bath and shows that the worst-case mean-square equilibration error is bounded above and below by the mean square of a local autocorrelation with the stationary part removed. A finite-interval correlation record thus controls errors on every interval of the same length. The result allows arbitrary energy degeneracies and is illustrated with two static Hamiltonian families.
In briefExact energy spectrum of a 3D oscillator with two spins
SummaryThe paper builds representations of the symmetry algebra of a three-dimensional oscillator with two spin-1/2 degrees of freedom and derives its exact spectrum. Finite modules at fixed total angular momentum describe angular and spin multiplicities, while a positive discrete series su(1,1) representation of the radial Hamiltonian yields the energy sequence. The authors provide explicit matrices, eigenfunctions, ladder actions and energy-shell multiplicities.
In briefMetasurface-based quantum graphs for polarization-independent certified randomness
SummaryThis paper presents a compact metasurface platform that achieves polarization-independent certified randomness using a quantum graph framework. The authors map multi-channel nanophotonic responses onto graph vertices and link weighted graph degrees to conditional min-entropy estimation. Experiments with fabricated 4- and 6-channel dielectric metasurfaces certify randomness using heralded single photons and Poissonian light.
In briefContinuity of Certain Quantum Channel Divergences (whether standard distance-like measures between quantum channels change smoothly)
SummaryThis paper studies the continuity of the geometric channel fidelity, geometric Rényi divergences, and Belavkin–Staszewski relative entropy, which give converse bounds for channel capacities, discrimination, and estimation. The authors introduce the Arveson–Radon–Nikodym derivative with respect to the sum of two maps to restore continuity, obtaining dimension-free continuity moduli. For two pairs of channels with the same sum, the fidelities differ by at most a bound involving the derivative difference, yielding Hölder continuity in the diamond norm.
WhyUses the Arveson–Radon–Nikodym derivative to establish dimension-free explicit continuity moduli for channel divergences, a substantive theoretical advance with impact mainly in quantum information th
In briefAxiomatic study of information measures for classical and quantum state convertibility
SummaryThis PhD thesis takes an axiomatic approach to multivariate divergences, which measure the information content of tuples of classical or quantum states. It studies these divergences in large-sample and catalytic convertibility of state tuples. The classical case yields generalizations of bivariate Rényi divergences that do not require equal supports. In the quantum case for classical-quantum state pairs with pure components, majorization is characterized by all α-z relative entropies with α<1.
In briefMinimal Subsystems for Measuring Genuine Multipartite Entanglement
SummaryThis paper examines how to quantify genuine multipartite entanglement (GME), a useful resource for quantum technologies, in many-body systems at lower measurement cost. It introduces two concepts, GME evaluation length and GME evaluation number, which measure the largest subsystem that must be jointly measured and how many distinct subsystems must be measured. Using the genuine multipartite concurrence as an example, the authors show that for N-qubit Haar-random pure states, it can be evaluated with only N single-qubit purity measurements.
In briefCollective Floquet engineering of photon-mediated coupling between two distant superconducting qubits
SummaryThis paper demonstrates dynamical control of photon-mediated interactions between two superconducting qubits coupled to a waveguide with a capacitive mirror. Periodic flux driving (Floquet engineering) of the qubit frequencies, with qubits placed at antinodes or nodes of a standing wave, realizes Hermitian or non-Hermitian coupling. The authors show on-demand control of coherent energy splitting and collective decay between remote emitters.
In briefStronger Classical and Quantum Query Lower Bounds for Tarski Fixed Points
SummaryThis paper studies the Tarski fixed-point problem, which seeks a fixed point of a monotone map on a k-dimensional grid of width n, with uses in game theory, economics, and verification. The authors prove two bootstrapping theorems that strengthen quantum query lower bounds starting from a known hard instance family. These yield improved classical and quantum lower bounds, including an Ω(k log² n) bound for k≥4 and bounds linear in dimension and polynomial in width. The paper also gives a superpolynomial lower bound for exponentially wide grids, suggesting generic polynomial-query black-box solvers cannot yield polynomial-time algorithms for simple stochastic games and ARRIVAL.
WhyBootstrapping theorems substantially improve known quantum query lower bounds and rule out a black-box route, with rigorous proofs.
In briefDeterministic preparation of squeezed and non-Gaussian quantum states using coupled qubit-boson systems
SummaryThis paper proposes a measurement-based imaginary time evolution (MITE) protocol for preparing squeezed and non-Gaussian bosonic states. It combines ancilla-mediated weak measurements of the Hamiltonian with a conditional phase rotation that helps the system converge to the ground state. The authors report deterministic convergence over a broad parameter range and extend the framework to Schrödinger cat states and excited states with Wigner negativity. The squeezed states are shown to remain robust under bosonic loss in experimentally relevant regimes.
In briefSingle-photon time-frequency continuous-variable quantum teleportation protocol
SummaryThis paper proposes a quantum teleportation protocol for single photons using time-frequency continuous variables, with time defined as the photon's arrival time at a detector. It details the nonlinear interactions required and shows that fidelity falls short of unity unless the receiver corrects for detector-position mismatch, creating a trade-off with the input photon's temporal bandwidth. The protocol can also be used for remote detector synchronization.
In briefUsing quantum sensing to probe signatures of quantum chaos
SummaryThis paper studies how quantum sensing protocols can detect quantum chaos. The authors establish a relationship between the spectral form factor (SFF) and the quantum Fisher information (QFI). When the eigenvalues and eigenstates of a disordered Hamiltonian are statistically independent, they prove QFI is typical at short and long timescales, and numerics suggest the same at intermediate timescales. This self-averaging property makes measuring QFI less noisy than directly measuring the SFF.
In briefVariational quantum circuits for medical image classification with architectural robustness to label noise
SummaryMedical image datasets often contain label noise, which deep networks can memorize, hurting generalization. The paper feeds features from a frozen ViT-B/16 backbone through a bounded low-dimensional bottleneck into an eight-qubit variational quantum circuit for classification, without an explicit noise-handling component. With clean labels, it leads five of six MedMNISTv2 benchmarks against published hybrid quantum-classical models. At 30% and 50% symmetric noise, it outperforms many published baselines on all six datasets.
In briefSimulating spectrally resolved quantum photonic circuits from device physics to protocol performance
SummaryThe paper presents PhoQuS, a framework combining frequency-resolved source models, electromagnetic compact models, and spatially correlated fabrication variation to simulate quantum photonic circuits. A covariance-Gram reduction lowers readout cost while keeping dominant spectral correlations, accelerating photon counting by 60.4-fold in an approximate GKP circuit. For three-photon GHZ circuits, the authors report that component robustness alone does not predict circuit fidelity, which depends jointly on source spectra, architecture, and control.
Seongjin Jeon, Youngbin Kim, Joaquin Matres et al.
In briefTelling apart a set of orthogonal two-qubit states may need joint measurements on two copies
SummaryThe paper studies an orthogonal basis of two-qubit space containing three entangled states and one product state. With a single copy, this basis cannot be perfectly distinguished by LOCC or even by separable measurements. The authors show that no adaptive separable protocol measuring two copies one at a time can distinguish it perfectly. A collective separable measurement on the two copies, however, does succeed. Whether two copies suffice under LOCC remains open.
In briefFew-magnon universality with long-range interactions in spin chains
SummaryThis paper studies two- and three-magnon problems in long-range quantum spin chains, with magnons interacting through a model potential V(x)=V0/(1+|x|^β). The authors find that few-body universality persists for any β>1. Near a two-body resonance, the low-energy scattering matrix matches the universal form from contact-interaction theory. The three-magnon bound-state spectrum shows Efimov scaling, and the model can be realized in trapped-ion systems.
WhyExtends Efimov universality to long-range magnon interactions; two- and three-body results match contact-theory predictions, a clear novelty with solid evidence.
In briefQIAP: A quantum-inspired login protocol that also checks the quantum channel for eavesdropping
SummaryThis paper presents QIAP, a hybrid framework that pairs a classical commitment-based challenge-response login with BB84-based quantum channel monitoring. After successful authentication, the system estimates the quantum bit error rate and aborts the session if it reaches the configured threshold. In simulation, no wrong-secret attempts succeeded among 1,000 tries per branch, and mean QBER was about 0.25 under full intercept-resend versus about 0.02 at baseline. The authentication stage took about 0.6 ms and used about 113 bytes per round.
Owais Ishtiaq Siddiqui, Nouhaila Innan, Hira Zaheer et al.
In briefNMR experiment: noise-resistant off-resonance π-rotation for qubit control
SummaryThe paper proposes a double-pulse and an eighteen-pulse sequence to perform a single-spin π-rotation off resonance, suppressing dephasing and driving-field noise. In an NMR spin system with a polarized initial state, fidelities reached 0.9992 ± 0.0008 for the double-pulse and 0.9997 ± 0.0006 for the eighteen-pulse sequence. The eighteen-pulse sequence tolerates noise up to about 20 percent of the driving field strength, roughly three times the double-pulse range.
In briefFrom isolated singular wells to exact Bloch bands: a trigonometric Pöschl-Teller lattice
SummaryThis paper studies an exactly solvable one-dimensional lattice with periodic inverse-square singularities. Its model is based on the generalized trigonometric Pöschl-Teller potential, in a coupling range where both local solutions at each singularity are square-integrable, with neighboring cells joined by a current-preserving self-adjoint matching condition that yields a nontrivial Bloch spectrum. The paper identifies two distinct gap-closing mechanisms: one arising from equivalence of the two sublattices, which is an artifact of Brillouin-zone folding, and another at a critical asymmetric configuration that produces a massless Dirac-like cone at the zone center.
In briefPermanent Thermodynamic Mpemba Reversal via Quantum-Jump Feedback
SummaryThis paper shows that a common quantum-jump feedback protocol can permanently reverse the free-energy ordering of two chosen initial states while keeping their Gibbs equilibrium unchanged. The authors prove that removing the full slow-mode contribution of the higher-free-energy state, while keeping it for the other, yields different decay exponents so their free-energy ratio vanishes at long times. A thermal qutrit is used to illustrate the mechanism and its detection thresholds.
In briefQuantum Computer Study of Multipolar Nanophotonics
SummaryThis paper encodes the multipolar light responses of nanoparticles in qubits and uses quantum circuits to compute light scattering and the Purcell effect, where surroundings change an emitter's decay rate. The method is tested against classical theory on an ideal simulator and on real IBM and IonQ quantum computers. The authors also analyze how the number of multipoles and the required accuracy affect qubit and measurement demands.
In briefMeasuring hidden 3D topology of a quantum simulator's bulk
SummaryThe authors use up to 728 superconducting qubits to simulate one-, two-, and three-dimensional topological insulators. They reconstruct complex propagators from real-space measurements, revealing localized boundary modes through local densities of states and bulk invariants through band projectors. The study culminates in extracting a three-dimensional octupole moment via third nested Wilson loops.
Pratik Sathe, Niclas Heinsdorf, Majid Kheirkhah et al.
In briefGradient-free sequential orbital optimization for variational quantum eigensolvers
SummaryThis paper proposes sequential orbital-optimized unitary coupled cluster doubles (SOO-UCCD), a gradient-free and hyperparameter-free orbital optimization method for the variational quantum eigensolver. It extends sequential minimal optimization to orbital rotation parameters, determining each rotation angle from a nine-point energy profile without computing orbital gradients or Hessians. State-vector simulations of LiH in the STO-3G basis show that SOO-UCCD reproduces UCCSD-level accuracy along the bond-stretching curve. Its macro-iteration convergence is reported to be comparable to L-BFGS-based orbital optimization.
In briefAdaptive Entanglement Witnesses for Two-Qubit Systems: Detecting Entanglement Without Full Tomography
SummaryThis paper studies entanglement witnesses, tools for checking whether an unknown two-qubit system is entangled without full tomography. It adds a new witness set, W5, to the earlier three-basis set W3 from Riccardi et al., and uses an adaptive two-step method that chooses which W5 witnesses to evaluate based on W3 results. Computationally, the protocol identifies 72% of entangled states generated by the Roik et al. methods while using five of the nine bases needed for full tomography. Both witness sets were also checked experimentally with polarization-entangled photon pairs.
In briefFast exact simulation of realistic noise for fault-tolerant quantum error correction circuits
SummaryThis paper presents QuasiStim, a framework for exactly simulating realistic non-Pauli noise, such as coherent control errors, in fault-tolerant quantum error correction circuits instead of approximating it with Pauli twirling. It consists of QuasiFold, which merges equivalent non-Pauli noise sites to reduce the number of shots, and DeltaFrame, which samples from precomputed reference trajectories. The authors report over 100× fewer shots on bivariate-bicycle codes and 166× to 1331× speedups over a per-shot tableau simulator on rotated surface-code memory.
In briefQuantum simultaneous decoding using pretty-good measurements on tilted states
SummaryThis paper studies quantum multiple-access channels, where several senders transmit messages to one receiver. It presents a joint measurement that recovers all messages simultaneously at known achievable rates. The proof combines Sen's tilted-subspace method with Cheng's analysis of the pretty-good measurement. It yields a deterministic packing theorem for finite state ensembles and recovers known rates in several applications.
In briefQuantum limit cycles from phase coupling: a framework for NISQ thermodynamic devices
SummaryThe paper quantises the Kuramoto model and the van der Pol oscillator and couples them to one or more qubits, showing a robust limit cycle even in typical quantum thermodynamic settings. It reports novel effects including entanglement state revivals, Zeno locking, and thermal current interference. The authors also propose toy model devices that could exploit synchronisation between qubits and a nonlinear phase oscillator.
In briefQudit LDPC codes with lower dimension thresholds
SummaryThis paper studies how to convert qubit stabilizer codes into codes for qudits, systems with more than two basis states. It examines the large cutoff value required by the local-dimension-invariant (LDI) method to preserve code distance, and focuses on quantum low-density parity-check (qLDPC) codes to reduce that cutoff. In some cases it drops to the original local dimension, and for arbitrary CSS-derived qubit codes it becomes singly exponential in the distance d, independent of the number of logical qubits k.
Md. Shahinul Islam, Aaryan Reza, Lane G. Gunderman
In briefStabilizer entropy cones as self-dual slices of linear rank cones, with a five-party gap and dependence on local dimension
SummaryThis paper studies the linear inequalities that entanglement entropies of multipartite pure states satisfy, focusing on the entropy vectors achievable by stabilizer states, which underpin quantum error correction. After a linear lift, the closure of this cone is shown to be exactly the self-dual slice of a classical object with one more element than there are parties, built from rank functions of subspace arrangements over GF(d). For five parties the stabilizer cone is strictly smaller than the quantum linear rank cone, witnessed by an explicit six-variable inequality. The cone also depends on the local dimension, and for six parties the logical zero state of Steane's code lies outside the stabilizer cone for every odd local dimension.
In briefEnd-to-end fidelity and rate analysis for zero-added-loss multiplexing
SummaryThis paper analyzes a midpoint-source entanglement distribution scheme called zero-added-loss multiplexing (ZALM) for end-to-end fidelity and rate. The analysis covers multipair emissions and partial Bell-state measurement losses in the transmitter, propagation loss to receivers, and loss and mode mismatch in receiver mode converters. It also includes losses from loading quantum memories.
In briefQuantum Localization in Geometric Complex Networks: How Network Structure Can Halt Wave Spreading
SummaryThis paper studies how the structure of a complex network affects the localization of single-particle quantum states. It uses the geometric soft configuration model S¹ and tunes its temperature and heterogeneity parameters to move from small-world to non-small-world networks. The authors report that small-world networks tend to host extended states spreading across the whole system, while non-small-world networks tend to localize waves, suggesting connectivity can play the role of random energetic disorder.
Jan Lewenstein-Sanpera, Tobias Grass, M. \`Angeles Serrano et al.
In briefTransitions between eigenstates and critical transport in the 3D Aubry-André model
SummaryThis paper numerically studies spectral and wave-function properties, and time evolution, in finite-size commensurate approximations of the 3D Aubry-André model. Scaling analysis reveals two critical points: a real-space localization-delocalization transition similar to the 3D Anderson model, and a localization-delocalization transition in dual momentum space with no 3D Anderson analog. Both points show signatures of critical points between quantum ergodicity and localization, and the critical dynamical exponent is sub-diffusive with z=3.
In briefQuantum ordinal optimization with a fixed comparison budget: a paper on selecting good-enough designs more reliably using quantum comparisons when only a few comparisons are allowed
SummaryThis paper studies ordinal optimization, which selects designs that are good enough rather than optimal when evaluation is costly and the budget is small. The objective is the alignment probability, the chance that the selected set contains at least a prescribed number of truly good designs. The authors show that, for every classical comparison budget below the number of designs, a knockout among uniformly sampled designs attains the optimum. They also show that at the same budget the maximum quantum degree is at most twice the classical maximum. For selecting the best of n designs, one quantum comparison achieves an optimal success probability of about 3.30/n, versus 2/n for one classical comparison.
In briefBell-Type Inequality Violation in a Simplified HBT Model: Quantum Correlations Beyond Local Realism
SummaryThe paper proposes a simplified 4-mode toy model of the original 8-mode Hanbury Brown-Twiss (HBT) interferometer, retaining its essential physics while reducing analytical complexity. The authors formulate a Bell-type inequality suited to the model's measurement configuration. They report that the correlations produced by the toy model violate this inequality, indicating non-local features incompatible with classical hidden-variable descriptions.
In briefSpeed and depth of pair-exchange two-axis twisting under a self-Kerr constraint
SummaryThis paper studies two bosonic modes that exchange pairs of quanta, which within fixed particle number sectors equals the two-axis twisting generator. Real nonlinear media add a local Kerr nonlinearity, and the two combine into one twisting Hamiltonian set by the ratio r of Kerr to exchange strength. The squeezing rate vanishes at r=±1, while the attainable squeezing depth reaches the ideal two-axis twisting value at r=0 and r=±3.
In briefAn optimization problem for δ′ leaky star graphs
SummaryThe paper studies singular Schrödinger operators with an attractive δ′ interaction of strength β supported on a star graph. It proves that the ground-state eigenvalue is uniquely maximized by stars with maximum symmetry. Two proofs are given: one for an even number of edges, comparing with the δ interaction star, and a general one based on the Birman-Schwinger technique.
In briefNonperturbative optomechanics: thin dielectric plates reshape the cavity itself
SummaryThe paper studies a levitated dielectric sensor shaped as a plate wide enough to capture the full optical mode. Even a thin plate with modest refractive index strongly restructures the intracavity field, splitting the cavity into coupled subcavities with new resonances and trapping sites. The authors report that standard perturbative formulas deviate from the exact solution at thicknesses around λ/(10n), and that cavity locking reduces coupling while raising trap stiffness.
In briefVariational search for almost strong zero modes in parafermionic chains
SummaryThis paper studies strongly interacting fermionic chains with a Z_n symmetry, whose topological phases have highly degenerate ground states linked by strongly bound fractionalized edge modes called parafermionic zero modes. The authors propose a quantum-inspired variational algorithm to search for these almost strong zero modes in generic parafermionic chain models. They show that the ansatz reproduces exact results and finds strongly bound parafermionic operators in the non-integrable Kitaev-Hubbard chain and chiral Potts model. They also verify a true strong zero mode for Z_3 parafermions in the symmetric limit of the chiral Potts model.
In briefSpatial interference can change a Josephson junction's symmetry class, creating odd nonlinear terms in its effective potential.
SummaryThe paper shows that spatial interference in a laterally homogeneous Josephson junction can break inversion symmetry of the effective potential, even when the local energy is inversion-symmetric. It gives a criterion based on harmonic-dependent complex spatial form factors: a single harmonic stays a shifted cosine, while multiple harmonics can allow cubic interactions. For a capacitively shunted junction, phase reflection reverses the odd-order coefficients while preserving the full quantum spectrum. A centered cross junction is given as a concrete example.
In briefVibronic molecular complexity as a quantum resource: nonadiabatic mixing protects coherence in noisy environments
SummaryThis paper studies why electronic coherence in molecules decays within a few hundred femtoseconds, and argues that the type of coherence excited matters. Using gradient-based optimal control (GRAPE) with Redfield dynamics on a three-state model, the authors maximize vibronic coherence between the ground and optically bright excited states. They identify a picosecond-lived mode protected by mixing with a dark state, which GRAPE finds without prior information. At 800 fs, the optimized coherence exceeds that of a Gaussian pulse by more than two orders of magnitude at the weakest coupling.
