In briefMeasurement incompatibility and noiseless quantum codes: a theory paper on whether quantum channels can preserve measurement incompatibility
SummaryThe paper studies when a quantum channel universally preserves the incompatibility of measurements. The authors construct a rank-one minimal informationally complete measurement and prove that such preservation holds if and only if the input space contains a noiseless code subspace of full output dimension. They also give an explicit construction of exact encodings and connect the results to quantum steering and quantum error correction.
WhyConstructs a rank-one MIC and proves equivalence with noiseless codes, resolving a conjecture with thorough proofs; impact mainly within quantum information theory.
In briefSecurity analysis of an Ekert-type QKD protocol under cloning attacks
SummaryThis paper analyzes the security of an Ekert-type bipartite key distribution protocol when an untrusted observer performs cloning attacks. An eavesdropper intercepts qubits sent over a public channel and applies an asymmetric, phase-variant cloner to one or both of them. The authors partially characterize two-qubit states and use the Devetak-Winter framework to compute key rates, identifying states from which a secret key can still be distilled under such attacks.
In briefQuantum key distribution secured by a bound on information leakage
SummaryThis paper examines whether, in prepare-and-measure quantum key distribution, a single bound on information leakage from the sender's source can replace a detailed model of the source. The authors show that this bound, quantified by the probability of guessing the input from everything the source emits, suffices to prove security against collective attacks, with no assumptions on the form, dimension, energy or purity of the emitted states. They note that the standard B92 and BB84 protocols cannot certify a key under this assumption, whereas closely related protocols can reach one secret bit per round in the ideal limit. For noisy implementations, key rates are computed with semidefinite programming relaxations, and the best protocols tolerate visibilities down to 0.84, corresponding to an 8% quantum bit error rate, versus the 11% threshold of device-dependent BB84.
WhyProves security from a single leakage bound without device modeling, reaching near-ideal key rates; validation rests mainly on theory and SDP computations.
Abhishek Mishra, Michele Masini, Maria Balanz\'o-Juand\'o et al.
In briefExperimental evidence that quantum Brownian motion drives electron decoherence in metals
SummaryThis paper reports experiments showing that quantum Brownian motion plays a key role in the decoherence of electron motion. The authors observe clear signatures of electron-metal decoherence for the first time and show it can be continuously tuned. Agreement between experiment and theory is quantitative, which the authors say paves the way for testing the Caldeira-Leggett dissipation theory with free electrons.
Wayne Cheng-Wei Huang, Zilin Chen, Herman Batelaan
In briefField-deployed entanglement-based BBM92 quantum key distribution using quantum-dot photons converted to telecom wavelengths
SummaryThis paper uses a quantum dot to generate polarization-entangled photon pairs at a 1 GHz excitation rate, then converts them to telecom wavelengths while preserving entanglement. The researchers ran BBM92 quantum key distribution over a 1.59 km field-deployed fibre link at the University of Stuttgart's Vaihingen campus. Over 19 hours of stable operation they achieved a secure key rate of 206 Hz and a total secure key length of 14.2 Mbit, which was used to encrypt and decrypt a colour image.
Michal Vyvlecka, Raphael Joos, Benjamin Breiholz et al.
In briefHTM: A Hybrid Model Combining Classical and Quantum Computing
SummaryThis paper addresses the lack of a unified hybrid model for collaborative classical and quantum computation. It proposes HTM, a hybrid classical-quantum computation model built on unified state sets and transition function representations. The model clarifies hybrid control logic, implements a control-sharing mechanism, and introduces a complexity calculation method based on entanglement and superposition to support task partitioning and resource scheduling.
In briefQuantum circuits for elastic wave equations using Schrödingerisation
SummaryThis paper builds explicit quantum circuits for the velocity-stress form of elastic wave equations in homogeneous media, using Schrödingerisation. The equations are rewritten in symmetric matrix form, with Fourier spectral discretization for periodic problems and staggered-grid finite differences for physical boundaries. The authors analyze splitting errors and CNOT-gate counts for higher-order Trotter-Suzuki formulas and compare with classical partitioned splitting, finding a polynomial improvement in spatial-resolution dependence. Noiseless circuit simulations illustrate the constructions and quantify errors against exact and classical reference solutions.
In briefQNETSIM: A Simulator for Designing Satellite and Hybrid Quantum Networks with Memory
SummaryThe paper introduces QNETSIM, a modular discrete-event simulator for designing and evaluating satellite and hybrid space-ground quantum networks. It combines orbital geometry, free-space optical and fiber channels, quantum memories, entanglement generation, and Bell-state measurements in one event-driven framework. The simulator models optical loss, atmospheric turbulence, detector imperfections, finite memory capacity, and storage decoherence. It links these components to entanglement fidelity, throughput, latency, availability, and memory utilization.
In briefThreshold conditions for boson and fermion three-body bound states on a square lattice
SummaryThe paper compares two three-particle models on a square lattice at zero total quasimomentum: three identical bosons with attractive contact interactions, and two fermions plus one distinguishable particle with attractive interspecies contact. It uses the Birman–Schwinger principle with symmetry reduction and strong-coupling asymptotics to separate shared methods from model-specific spectral results. For bosons, exactly two bound states lie below threshold at large coupling, the second being a true eigenvalue 0.03542 below threshold. For fermions, the critical mass ratio is π/(π−2), about 2.75194, above which a doubly degenerate level appears at strong coupling.
In briefMatrix samplers and quantum-proof extractors: equivalence and near-optimal constructions
SummaryThe paper establishes an equivalence between matrix samplers and quantum-proof randomness extractors, extending Zuckerman's classical sampler-extractor correspondence. Using this equivalence, the authors construct explicit strong matrix samplers with optimal randomness overhead and near-optimal sample complexity. They also obtain strong quantum-proof extractors with improved seed and output lengths.
WhyEstablishes equivalence between matrix samplers and quantum-proof extractors, improving sample complexity and seed length over prior matrix samplers.
In briefQuantum generative model that trains only a linear output layer, not the circuit
SummaryThe paper proposes a quantum generative method that encodes a random latent vector into a quantum state, applies a fixed unitary and measures, training only a linear output layer so the circuit itself is never trained. Using Pauli propagation, the authors show that Clifford circuits do not create new functions, while Haar-random brickwork circuits have features whose variation with the latent variable decreases with depth. Across one- and two-dimensional distributions, entangling reservoirs do not systematically improve the generator, and a reservoir with no gates performs competitively.
In briefTime needed to confirm weak-force entanglement between levitated particles
SummaryThis paper studies how to certify motional entanglement generated by weak forces between levitated nanoparticles using finite, noisy measurement records. The authors derive a lower bound on the number of measurements needed to certify Gaussian entanglement and translate it into certification time. They compare release-recapture and continuous monitoring protocols, finding that release-recapture enables certification at interaction strengths several orders of magnitude weaker.
Yao-Tong Chen, Salambo Dago, Oriol Romero-Isart et al.
In briefQuantum Fisher information deficit as a geometric sign of strong-to-weak symmetry breaking
SummaryThe paper studies strong-to-weak spontaneous symmetry breaking (SW-SSB), a phase of open quantum systems that conventional charged two-point correlators cannot detect. For strongly Z2-symmetric states with local charged involutions, the authors show that SW-SSB appears as a persistent gap between the quantum Fisher information and its maximum under symmetry-neutral pair rotations. This deficit is shown to be equivalent to fidelity and Rényi-1 correlator diagnostics of asymptotic long-range order, and a lower bound is derived for symmetry-projected Gibbs states.
In briefExact decoherence of a detector in bounded vacuum geometries
SummaryThis paper studies how a two-level detector coupled to a vacuum scalar field loses coherence over time in three settings: free space, a single perfectly reflecting boundary, and a cavity between two parallel reflecting boundaries. The authors derive an exact decoherence function for the detector. Coherence decays monotonically in free space, partially persists with one boundary, and oscillates with a larger surviving fraction inside the cavity. The results suggest that boundary conditions can be used to engineer quantum coherence.
In briefMaking the TEMPO network independent of system size
SummaryThe TEMPO method simulates non-Markovian open quantum system dynamics by contracting a two-dimensional tensor network. The paper shows that, within the usual second-order time-step error, all internal bond dimensions can be reduced to (2m+1)(m+1), where m is the number of independent coupling channels. This dimension does not depend on the number of distinct eigenvalues of the coupling operators. System size enters only through the final boundary layer, making large systems accessible to TEMPO.
In briefQuantum entanglement in momentum space after Kaluza-Klein reduction
SummaryThis paper studies how a four-dimensional observer's reduced state, obtained by tracing out massive Kaluza-Klein modes of a five-dimensional scalar with cubic or quartic self-interaction, is entangled in momentum space. At leading order in the coupling, it computes the mutual information between low-energy zero modes and a single Kaluza-Klein level, finding a tail that falls as one over the level mass in the cubic theory. The authors conclude that the local four-dimensional effective theory describes low-energy observables but not the state of the reduced system.
In briefQuantum evolution kernel for embedding attributed graphs on neutral-atom computers
SummaryThis paper proposes a way to embed node-attributed graphs on neutral-atom quantum computers and applies it to digit recognition. It extends PASQAL's quantum evolution kernel with a node-level encoding based on three-level quantum states, and uses the resulting correlation-based information for classification. The quantum process is simulated with the Pulser library, which limits dataset size. On digit recognition, the method using the Wasserstein distance achieves higher mean accuracy than commonly used Jensen-Shannon distance-based methods.
Manuel Padovani, Alessandra Di Pierro, Claudia Daffara
In briefCircuit-aware mutation testing for quantum programs: exact visibility and execution planning
SummaryThis paper proposes a circuit-aware framework for mutation testing of quantum programs, distinguishing whether surviving mutants leave behavior unchanged, are hidden by input or measurement choices, or lack sufficient statistical evidence. It targets ideal, noiseless programs with mutations that replace one gate or subcircuit, combining mathematical checks with statistical estimates. For supported cases, it gives conditions under which a test cannot reveal a mutation and exact effect formulas, along with a decision procedure, guarantees, and a small-circuit reference implementation.
In briefQuantum and Classical Memory Needed to Store and Retrieve Quantum Measurements
SummaryThis paper studies how much persistent quantum and classical memory is needed to store and retrieve quantum measurements exactly and with heralding. Assuming only black-box access to the measurement channel, the authors compress a port-based program into an outcome-type record and a quantum register whose total dimension grows polynomially with the number of queries. For n-outcome POVMs on C^d with d ≥ 2, they prove lower bounds Q+C ≥ log₂n and 2Q+C ≥ log₂((n−1)d²+1) on the qubits Q and bits C of any retrieval program.
Filip Turobo\'s, Ludmi{\l}a Marcinkowska, Zbigniew Pucha{\l}a
In briefFrom QCCD trapped-ion hardware to quantum compilers: architectures and compilation methods
SummaryThis paper examines shuttling-based trapped-ion quantum computers (QCCD) and their compilers, abstracting QCCD architectures and native operations so that computer scientists can address compilation problems without deep knowledge of the platform's physics. The design space is organized into a few architectural archetypes, and compilation methods are applied to one- and two-dimensional QCCD architectures. Routing overhead is found to scale roughly cubically with qubit number in one dimension and roughly quadratically in two dimensions. The authors also compare physical and logical levels when a quantum error-correction layer is added, and conclude that hardware-software co-design is required.
Ludwig Schmid, Jurek Eisinger, Daniel Schoenberger et al.
In briefCorrelation-sensitive magic-state distillation from spin-squeezed neutral atoms
SummaryThe paper shows that correlations between blocks can reverse magic-state distillation gain even when each input exceeds the independent-state threshold. Using the five-to-one Bravyi-Kitaev protocol, it expresses the output through measurable target-axis moments and gives a direct sign test for gain. It links this mechanism to neutral-atom resource preparation via finite-range Ising dynamics.
In briefEntanglement between a qubit and its environment during pure dephasing when the qubit starts mixed
SummaryThe paper studies entanglement between a qubit and its environment under interactions that cause pure dephasing, allowing the qubit's initial state to be mixed. The authors find that separability criteria valid for pure initial states reduce to entanglement witnesses in this setting. Using a spin qubit coupled to a sparse spin environment as an example, they illustrate the evolution of entanglement and note that witnesses are numerically more practical for large environments.
Ma{\l}gorzata Strza{\l}ka, Nico Peters, Laura Ares et al.
In briefOpen effective field theories: a framework for noisy, dissipative environments in gravity and cosmology
SummaryThese are lecture notes on Open Effective Field Theories, based on lectures given at the La Ricotta Summer School "The Disordered Universe 2025". The text notes that traditional effective field theories were developed for particle physics with clean, isolated initial states, while realistic environments are often noisy and dissipative. It presents an approach that models the gravitational sector as evolving in the presence of an unobservable medium, and uses the Schwinger-Keldysh formalism to show how unknown environments appear as dissipation and noise in observational probes.
Alessandro Fumagalli, Francesco Paronetto, Leonardo Stanzani et al.
In briefA unified six-step protocol for arbitrary Z rotations on a class of bosonic cQED qubits
SummaryThis paper examines a class of bosonic Fock-based qubits in circuit QED and shows that different ways of implementing arbitrary Z rotations on them share a common structure. The authors formulate this structure as a six-step protocol that gives a unified procedure for arbitrary Z rotations across this qubit class. Whether the protocol applies depends on a specific condition on the encoding, which serves as a criterion for identifying which bosonic Fock-based cQED qubits admit this common implementation.
In briefStoring and extracting energy in V-type quantum batteries via dark states
SummaryThis paper studies a quantum battery made of V-type qutrits coupled to a lossy cavity. A finite splitting pulse converts cavity-bright excitations into atomic dark states, which keep their stored energy even after degeneracy is restored. The authors also bound the passive energy in the symmetric atomic subspace and compare coherent and Fock initial states for finite-time ergotropy and extractable work.
In briefLifting Quasi-Cyclic Additive Codes to Certified Quantum Codes
SummaryThis paper studies additive codes over F4 that correspond to binary quantum stabilizer codes, focusing on 1-generator (1,2)-quasi-cyclic additive codes. It gives an ancestor-lifting theorem for composite lengths, dimension laws, and a palindromic criterion for symplectic self-orthogonality. Exact quantum distances are determined through information-set decoding screening, Brouwer–Zimmermann computation, and independent witness verification. The authors certify a set of record-breaking binary quantum codes and report further propagated entries and upper bounds.
In briefQuantum state preparation for complex amplitudes
SummaryThis paper presents a procedure that prepares a quantum amplitude approximating z/α for a complex number z=x+iy, starting from registers holding its real and imaginary parts, with α a normalization constant. It computes the magnitude and argument with the CORDIC algorithm, encodes the magnitude into an amplitude, and applies phase gates for the argument. The method uses O(n²) T gates and O(n) extra qubits. Compared with encoding real and imaginary parts separately and combining them via LCU, it can allow a smaller normalization and reduce amplitude-amplification costs.
In briefDiagnostic-dependent lasting Mpemba effect in a parametrically driven oscillator
SummaryThis paper studies relaxation of two Gaussian states in a detuned degenerate parametric amplifier below threshold. The trace distance shows a lasting Mpemba reversal, while relative entropy eventually restores the initial order and Hilbert-Schmidt distance alternates indefinitely. The three diagnostics agree on the initial order but can disagree because a real mode and a complex pair share the leading decay rate.
In briefKinetic Slush in Dissipative Rydberg Arrays: a nonequilibrium soft-matter state in driven atom arrays
SummaryThe paper studies a kinetic slush state in a two-dimensional dissipative Rydberg atom array, where excitations are facilitated by neighboring atoms. Using kinetic Monte Carlo simulations in the strong dephasing regime, the authors show that detuning compensates nearest-neighbor interactions, while residual next-nearest-neighbor interactions create kinetic frustration. The competition yields a slush phase with liquid- and solid-like configurations and strong dynamical heterogeneity.
In briefNoise thresholds for reliable quantum approximate optimisation under noise
SummaryThis paper studies how much noise the quantum approximate optimisation algorithm (QAOA) can tolerate at each circuit depth. The authors run GPU-accelerated noisy simulations on MaxCut for three graph families and fit approximation ratios with a generalised logistic surface. They define an effective noise threshold, which generally decreases as depth increases, and use it to separate reliable from unreliable noise regimes.
Yozef Tjandra, Hendrik Santoso Sugiarto, Celine Vania Setiadi et al.
In briefMeasurement-induced entanglement phases in hyperbolic gauge-Higgs models
SummaryThis paper studies entanglement phases of gauge-Higgs models on hyperbolic lattices, described by measurement-only dynamics. The authors map two-dimensional phase diagrams using topological entanglement entropy and a generalized measurement-induced entanglement suited to hyperbolic Higgs phases. They identify an "archipelago" phase absent in Euclidean space, where separated clusters of symmetry-protected topological order exist, and its transitions have mean-field critical exponents.
Cole Kelson-Packer, Hiroki Sukeno, and Akimasa Miyake
In briefFewest Measurement Settings for Estimating Several Quantum Observables
SummaryThis paper studies the minimum number of orthogonal projective measurement settings needed to estimate several observables without bias for any input state. The authors derive structural lower bounds beyond dimension counting and give explicit constructions that certify minimum setting counts for chosen target spaces. A classical variational algorithm searches for shared measurement bases and optimizes readout coefficients and sample allocation. For the collective first and second moments of two qubits, four projective settings are shown to be both necessary and sufficient.
In briefUnusual shapes of Fisher zero lines in biorthogonal dynamical quantum phase transitions
SummaryThis paper studies how Fisher zero lines of the Loschmidt amplitude in non-Hermitian quenches can form unusual patterns in the complex time plane, such as divergence, separation, or branches lying on the real or imaginary axis. It uses a biorthogonal framework to explain these patterns and sets critical momentum conditions based on the dot product of normalized prequench and postquench complex Bloch vectors. The results are verified in a generalized non-Hermitian SSH model, and Jordan form is used to analyze dynamics at postquench exceptional points.
In briefDynamical behaviour of the mass tensor in the lattice
SummaryThis paper studies, with a semiclassical model, how a particle hopping through an orthorhombic lattice moves under a static Coulomb field and a rapidly oscillating homogeneous field. Applying the oscillating field reparameterizes the effective masses so they become equal in both directions, turning a chaotic trajectory into an elliptic one in the continuum limit, as confirmed by Lyapunov exponents. The authors also show that an external magnetic field along the Z direction can control chaos, and extend the scheme to three-dimensional trajectories.
In briefCoherent optical control of a single donor electron spin
SummaryThis paper demonstrates optical initialization, coherent control, and readout of a single donor-bound electron spin in ZnSe. Using spin-selective donor-bound exciton transitions and off-resonant picosecond pulses, the authors observe spin Rabi oscillations, Ramsey interference, and high-contrast coherent population trapping. At higher driving strengths, multiple dark resonances reveal the hyperfine interaction with the I = 3/2 Cl nucleus, and the authors identify isolated optical donors as a promising platform for solid-state optically active qubits.
WhyFirst coherent optical control of a single donor electron spin in a II-VI semiconductor, with coherent population trapping and hyperfine resolution.
Yuxi Jiang, Amirehsan Alizadehherfati, Christine Falter et al.
In briefAnalytic energy formulas for radial power-like potentials via new Bohr-Sommerfeld quantization conditions
SummaryThe paper proposes two new Bohr-Sommerfeld type quantization conditions for d-dimensional radial singular and non-singular potentials. It studies power-like potentials and the logarithmic potential across many radial quantum numbers and angular momenta in dimensions two and three. For large radial quantum numbers the approximate energies approach the exact ones, and a dimensionless WKB correction reproduces exact energies within the cases examined.
In briefSideways position shift of a spinning particle's wave packet under Lorentz boosts
SummaryThis paper studies how spin-orbit coupling makes the average position of a spinning particle shift unusually under a Lorentz boost, an effect called a side jump. The authors develop a trace method that yields an exact, compact transformation kernel for the probability center of a general three-dimensional Dirac wave packet under any finite boost, without a semiclassical expansion. They find that side jumps depend on the wave packet's internal structure and that, for Gaussian packets, they show a non-monotonic dependence on mass.
In briefConsensus and information spreading in quantum networks: how nodes learn global quantum information from local measurements
SummaryThis paper studies decentralized quantum consensus in qudit networks evolving under discrete random unitary dynamics. The authors analyze asymptotic behavior, identify global information preserved by the evolution, and give conditions under which different forms of quantum consensus arise. They present a general theorem for extracting globally encoded information from local measurements, examine CNOT networks, and identify two-qubit interactions that asymptotically reach consensus on average excitation number.
In briefFinite-temperature quantum theory of lossy magnon-cavity resonators
SummaryThis paper develops a finite-temperature quantum quasinormal mode (QNM) theory for cavity magnonic systems containing non-reciprocal magnetic media, material dissipation, open-cavity radiation losses and thermal fluctuations. It uses macroscopic quantum electrodynamics and complex coordinate transformations to quantize the QNMs. The authors apply the theory to hybrid dielectric-magnonic resonators coupled to spin and superconducting qubits, showing modal interference, a transition from coherent to dissipative coupling, and magnon-mediated qubit synchronization.
In briefSuppressing microwave crosstalk in superconducting quantum processors by designing parasitic capacitances
SummaryThis paper studies how unwanted microwave drive crosstalk between qubits in a superconducting quantum processor can be reduced. The authors build a detailed circuit model of a processor with two fixed-frequency transmon qubits and a tunable coupler, and experimentally show that crosstalk can be suppressed. They find the suppression comes not only from cancelling the effective qubit-qubit coupling but also from interference among other coupling paths. The authors conclude that choosing suitable parasitic capacitances can suppress crosstalk, suggesting that parasitic coupling paths should be engineered rather than simply minimized.
Anuj Aggarwal, Jorge Fern\'andez-Pend\'as, Simon Pettersson Fors et al.
In briefMulti-day magnetic imaging of single living cancer cells using a quantum sensor
SummaryThis paper presents Quantum Cell Monitoring (QCM), a widefield nitrogen-vacancy magnetometry platform that records single-cell information from stray magnetic fields instead of emitted photons, at subcellular resolution. Combined with a live-cell incubator, it tracks magnetically labeled living cancer cells for up to 72 hours. The authors report observing mitosis, morphological changes, and cluster formation, splitting, and migration.
Andre Pointner, Sarah Belasi, Regine Schneider-Stock et al.
In briefUpper bounds on how often feedback-controlled quantum trajectories exceed quantum speed limits
SummaryThis paper studies the probability that a single conditioned quantum trajectory, under continuous measurement feedback, exceeds a quantum speed limit (QSL) velocity derived from an ensemble. Using the finite-time average fidelity velocity, the authors bound this exceedance probability in terms of its mean and variance, and obtain state-independent bounds, including an exponential concentration bound. For a feedback-controlled qubit they give explicit model-specific bounds that are nontrivial at short times. They also identify a finite-time regime where the exceedance probability is exactly zero because the conditioned dynamics have restricted support. Monte Carlo simulations confirm the analytical bounds and show their tightness.
In briefPreparing Geometric States on the Bloch Sphere with a Linear Mechanical Resonator
SummaryThis paper applies the Bloch sphere representation, familiar from quantum two-level systems, to a linear two-mass, three-spring mechanical system. The system is driven from both ends at a fixed frequency between its two resonances, producing tunable superpositions of its symmetric and antisymmetric modes. Laser vibrometer measurements and frequency-domain analysis are used to extract the modal coefficients and map them onto Bloch sphere coordinates. The results show planar rotations under phase sweeps and continuous steering between eigenstates under amplitude-ratio tuning.
Abrar N-E Faiaz, Donte McMullen, Kazi T Mahmood et al.
In briefQuantum fluid dynamics built on Nambu's unpublished fluid notes
SummaryThis paper develops a quantum hydrodynamic theory based on an unpublished note by Nambu on fluid dynamics. Tracing out unobserved fluid modes yields a quantum channel for an observed cyclic deformation, and a criterion is given for exact preservation of coherence between opposite momenta. Using two shear flows as an example, the authors identify an exact noiseless sign subsystem and show that a preparation with smaller initial decoherence can still suffer larger maximum loss over a finite readout interval.
In briefQuantum computing study of bulk FeO ground-state properties
SummaryThis paper studies the ground-state properties of molecular FeO and Fe2O2 model Hamiltonians using classical exact diagonalization, the Variational Quantum Eigensolver (VQE), and Sample-based Quantum Diagonalization (SQD). The experimentally known quintet ground state of FeO is recovered both classically and with quantum algorithms, and a nonet ground state is found for Fe2O2. Raw VQE does not reach chemical accuracy, but SQD with two connectivity shells recovers the exact ground energy for both molecules using very few quantum resources.
Daniel Staros, Federico Petrovich, Ammar Kirmani et al.
In briefTensor-train method for simulating quantum system dynamics in phase space
SummaryThis paper presents a dynamical tensor-train method for solving the Wigner–Fokker–Planck equation, which describes continuous-variable open quantum systems. The Wigner function is evolved directly in tensor-train form using a projector-splitting integrator, and the nonlocal Wigner pseudo-differential operator is handled with low-rank representations and matrix-free exponential actions. Numerical experiments in one, two, and three spatial dimensions show the method's accuracy and scalability, including simulations in a six-dimensional phase space.
In briefSemiconductor quantum dot produces quantum light with adjustable Wigner negativity
SummaryThis study uses a single semiconductor quantum dot inside a cavity to generate quantum light states with tunable Wigner negativity. Optical coherent control of the dot's transition creates a superposition of zero and one photon, which is characterized point by point in phase space via homodyne measurement. Wigner-function negativity appears as excitation power increases. After correcting for collection and propagation losses, fidelities to the ideal state and quantum purities exceed 95%.
In briefUltrafast light-electron modulation for free-electron quantum optics
SummaryThis paper proposes a unified Light-Electron Modulation (LEM) framework that treats optical near fields as programmable phase modulators for free-electron wavepackets. It identifies longitudinal energy and transverse momentum modulation channels and describes how their operation depends on wavepacket extent, recoil, phase matching, and field geometry. The authors show that PINEM, Raman-Nath and Bragg diffraction, DLA-like acceleration, and anomalous PINEM can be organized as limiting regimes of one modulation picture, and they derive design principles for free-electron modulators.
In briefOptical tensor processing for simulating quantum circuits
SummaryThis paper presents a classical optical architecture for quantum circuit simulation that treats gates and input-state batches as independent tensor dimensions and maps eligible tensor network contractions onto the same processor. Using multidimensional encoding and readout across spatial and wavelength degrees of freedom, the authors experimentally realize high-order tensor-matrix multiplication in a single propagation for all computational-basis inputs of a 4-qubit gate. A physics-based optical propagation model is used to numerically evaluate the approach for the Deutsch algorithm and a tensor network covering all 128 target instances of a 7-qubit Grover algorithm.
In briefAnalog quantum experiments with automatic differentiation: from programs to atoms
SummaryThis paper introduces DiffSimuQ, a method that applies automatic differentiation to a broad class of open-loop analog quantum experiments. It transforms an experiment program into a derivative program whose expected outcome equals the gradient. For continuous evolution it gives two realizations, the Nyquist shift rule for general time-dependent evolution and a parameter-shift realization for involutory generators. In noisy emulation, both avoid the finite-difference error floor and improve closed-loop optimization.
In briefEstimating entanglement in many-body states from partial-transpose moments
SummaryThis paper shows how the logarithmic negativity, a measure of entanglement, can be estimated for an arbitrary many-body state without reconstructing the state. It uses a finite number of even partial transpose moments and solves a truncated Hausdorff moment problem with Gauss and Gauss-Radau quadrature. The resulting lower bounds improve as the moment order increases and are illustrated on ground states of three interacting spin models and a thermal state, with an error analysis for finite statistics.
WhyDerives a hierarchy of converging lower bounds on logarithmic negativity from finite partial-transpose moments, validated on several many-body ground and thermal states with error analysis.
In briefScaling and renormalization theory applied to grokking in neural networks
SummaryThis paper examines whether scaling and renormalization group theories can describe grokking, the delayed shift from memorization to generalization in deep neural networks. Using a two-layer network trained on modular addition, the authors define an order parameter and fluctuation measures, then apply real-space renormalization with a coupling matrix to derive five critical exponents. The reported direct empirical estimates match the theoretical predictions within 1 to 10 percent, and the authors propose this formalism as a tool for studying neural network dynamics.
In briefNon-Hermitian Schwinger effect in imaginary magnetic fields
SummaryThe authors analyze the one-loop effective Lagrangian of scalar and Dirac QED in a real electric field combined with a parallel imaginary magnetic field. They show that the imaginary magnetic field adds an extra pole family to the proper-time integrand and can produce a nonzero imaginary part even without an electric field. When the field-strength ratio is rational, some poles coincide and require careful treatment.
In briefAlgebraic characterisation of invariants for n-qubit pure states
SummaryThis paper studies n-qubit pure quantum states written as density matrices in Bloch representation. The authors define a family of quadratic functions of Pauli expectation values and fully determine which choices yield state-independent purity constraints. The resulting invariants are closely tied to the geometry of symplectic polar spaces. A subfamily stable under state updates is shown to correspond to symplectic Lie algebras generated by Pauli operators.
In briefTraining quantum circuits by learning from equilibrium states of a physical model
SummaryThis paper extends equilibrium learning, which trains physical systems using observables of their relaxed states, to gate-based quantum circuits. A parametrized circuit is embedded in a Feynman-Kitaev Hamiltonian, and the compilation target is imposed via an output clamping term or a target-dependent cyclic condition on the clock register. Cost functions for unitary and state compilation are defined using ground state energies and overlaps with the free history state. In two-qubit benchmarks, optimization with these equilibrium costs reaches a fixed fidelity threshold in fewer sweeps than the standard compilation infidelity cost for many instances.
Frank Barrows, Touheed Atif, Yi\u{g}it Suba\c{s}\i et al.
In briefDiagonal, Switching, and Locally Optimal Unraveling: an efficient method for quantum trajectories in metastable open systems
SummaryThis paper introduces DiSLOU, a method for efficiently simulating quantum trajectories in open quantum systems that exhibit metastability. It combines three optimization layers: switching among locally optimal unravelings that minimize quantum jumps, diagonalizing the non-Hermitian effective Hamiltonian once per attractor to speed up no-jump evolution, and propagating states in a truncated subspace of slowly decaying eigenmodes. The method is tested on a driven-dissipative Kerr resonator, with the largest speedup in the bistable regime, and applied to rare bit-flip events in the cat manifold of a dissipatively stabilized parametric oscillator, where it gives over an order of magnitude improvement.
Pietro Pacchioni, Alberto Mercurio, Patrick Winkel et al.
In briefInteractions between spin-like states in ultracold molecules, a step toward precision tests of physics
SummaryThis paper reports observing and controlling resonant dipolar exchange interactions between parity-doublet states in ultracold polyatomic CaOH molecules held in an optical trap. The researchers encode a pseudospin in these states and detect density-dependent loss of Ramsey contrast and a mean-field precession whose sign reverses with the initial population imbalance. Floquet engineering of the interaction anisotropy suppresses many-body dephasing near the SU(2)-symmetric Heisenberg point.
WhyFirst observation and control of resonant dipolar exchange in polyatomic parity doublets, with a unified truncated Wigner model explaining two signatures; evidence is fairly solid.
Junheng Tao, Paige Robichaud, Christian Hallas et al.
In briefScaling Laws for Conditional Mutual Information in Random Classical Systems
SummaryThis paper studies how conditional mutual information (CMI), which measures dependence between two regions given an intervening buffer, evolves in one-dimensional classical stochastic models. The authors propose a universal scaling form for systems whose Markov length grows with time and derive it in the inactive phase of parity-conserving directed percolation. A Hankel-based truncation scheme enables matrix-product-state simulations that verify the scaling. The CMI between fixed microscopic regions is found to share a common scaling dimension of two.
In briefMesons, Confinement, and Krylov Complexity in a Long-Range Ising Chain
SummaryThis paper studies how confinement and Krylov complexity are linked in a long-range transverse-field Ising chain, where power-law interactions create an effective confining potential between domain walls. Using the time-averaged Krylov state complexity after a quench as a diagnostic, the complexity is strongly suppressed at small α and small transverse field, and grows rapidly at larger α. In the confined regime, the oscillation frequencies match the meson masses of an effective two-kink model.
In briefTypical entanglement growth and transport fluctuations in a quantum exclusion model
SummaryThis paper studies the quantum symmetric exclusion process, a model of randomly hopping free fermions with diffusive transport and long-range quantum coherence, using macroscopic fluctuation theory. The authors show that charge-transfer statistics for individual noise realizations almost surely match those of the classical symmetric exclusion process at long times, both in equilibrium and after quenches from diagonal product states. They also derive asymptotically exact predictions for entanglement growth from domain-wall and Néel initial states, which agree well with numerical simulations.
In briefSymmetry-resolved fermionic correlations in iron-oxide ground spaces
SummaryThis paper studies how symmetries organize degenerate ground states in many-body electronic models of FeO and Fe2O2. Resolving the same degenerate ground space with different symmetry operators yields states with very different correlation properties. With density-density Hund interactions added, the FeO ground space reduces to a spin-reversal pair with maximal magnetization.
Federico Petrovich, Daniel Staros, Daniel N. Blaschke et al.
In briefAn open effective field theory for dark matter searches with matter-wave interferometers
SummaryThis paper treats matter-wave interferometers as open quantum systems coupled to a dark matter environment and derives an open effective field theory using the Schwinger-Keldysh formalism. The framework describes two signatures, dark matter-induced phase shifts and loss of contrast. The authors analyze elastic spin-independent sub-GeV dark matter scattering off nucleons and discuss the regions of parameter space that composite-particle interferometers could probe for Higgs-portal and light hadrophilic scalar mediated dark matter.
In briefAn analytic bootstrap method for solving quantum mechanics of a particle on a circle
SummaryThe paper solves the Schrödinger equation for a particle on a circle using a quantum mechanical bootstrap approach. It requires the solutions of recursion relations for Fourier coefficients to vanish exponentially fast, yielding a generalized continued fraction representation that is analytic in the couplings and energy. The authors show how to compute the density of states, reconstruct the wave function, and extract quasimomentum versus energy. Applied to the Mathieu equation, the method resolves exponentially small bands in the spectrum.
In briefAlgebrasTQD: A Tool for Computing Algebras and Interfaces in Twisted Quantum Doubles
SummaryThis paper presents AlgebrasTQD, an open-source GAP program for computing condensable algebras and their topological boundaries and interfaces in twisted quantum doubles. It can classify 1+1d gapped and gapless phases related to a finite group by gauging, study 2+1d anyon proliferation, and construct logical gates in non-Abelian topological codes. The paper illustrates its use with several Abelian and non-Abelian groups and states that all arithmetic is exact.
In briefA paper linking qubit- and boson-based quantum sensing methods for detecting new physics
SummaryThe paper uses the Holstein–Primakoff transformation to unify qubit-based and boson-based sensing proposals within one framework. It introduces a novel generalization of GHZ states that performs better at detecting rare interactions, and states these states can be readily prepared while combining GHZ coherence with improved error rejection. It also extends the Hamiltonian-Not-in-Lindblad-Span theorem to collections of bosonic modes.
In briefComplete entropy contraction from conditional hyperboundedness
SummaryThe paper studies finite-dimensional quantum channels with a faithful conditional expectation and shows that conditional hyperboundedness together with strict GNS contraction yields relative entropy contraction. For KMS-symmetric quantum Markov semigroups, it gives a formula for a modified logarithmic Sobolev constant. Completely bounded hyperboundedness over auxiliary systems then produces complete versions of entropy contraction at the same rates.
In briefNetwork nonlocality from three-qubit entangled sources
SummaryQuantum networks are built from independent sources, and most nonlocality studies have used sources emitting two-party entangled states. This paper studies sources emitting three entangled qubits and asks how network nonlocality relates to the single-source Mermin and Svetlichny inequalities. The answer depends on the wiring: when two input-free central nodes share every source, any Svetlichny violation yields a network violation, while sharing a single central node requires the source to violate the Mermin inequality.
In briefInterference-driven transport crossovers in quantum walks on disordered square lattices
SummaryThis paper studies discrete-time quantum walks with Fourier, Grover, and Hadamard coins on disordered square lattices, compared with classical random walks. It considers two models: edges that are fully absent, and edges that partially transmit with coefficient f. Quantum walks prove highly sensitive to the coin symmetry and walk protocol, while the classical anomalous diffusion exponent stays asymptotically stable. The authors map the subdiffusive and superdiffusive regimes in the (f,p) plane, finding no quantum diffusion in two dimensions.
Ramnarayan Bera, Arijit Roy, Soumyadip Ghosh et al.
In briefSparse Carleman embeddings for nonlinear discrete systems, applied to quantum state preparation
SummaryThe paper studies Carleman embedding for forced quadratic discrete nonlinear systems and applies it to quantum state preparation. Under explicit stability and initial-state assumptions, the truncation error is shown to decrease geometrically with the embedding degree, uniformly over all iterations. An exact auxiliary linear system with bounded sparsity avoids the density problem of the lifted update. The authors present a quantum algorithm that prepares an approximation to the normalized nth iterate with constant success probability.
In briefε-smoothed Entanglement of Formation and Its Link to Moreau-Yosida Approximation
SummaryThe paper defines a family of convex continuous functions E_{F,ε} on bipartite quantum states by applying the Mora-Piani-Briegel ε-measure construction, using trace norm distance, to the Entanglement of Formation (EoF). These functions decrease in ε and converge pointwise to the EoF as ε tends to zero. The authors study their variational expression, weak subadditivity and continuity, relate them to Moreau-Yosida approximations of the EoF, and derive computable bounds on the rate of uniform convergence. They also show that a nearest separable state in trace norm exists for infinite-dimensional bipartite systems.
In briefControlling a Mpemba-type faster-relaxation effect in quantum spin systems by spatial twists
SummaryThe paper builds a controllable imaginary-time Mpemba effect in quantum spin systems using spatially modulated local rotations that leave the initial entanglement spectra and correlation magnitudes unchanged. Using a compact-boson description, higher-harmonic twists are shown to select high-energy modes and speed convergence, with exact analytical crossing times derived. The mechanism is checked on XXZ chains and ladders, and a twelve-qubit variational imaginary-time simulation reproduces the reversals and their controlled delay.
In briefGrowth phase map of α and β tantalum versus growth temperature and oxygen pressure
SummaryThis paper reports sputtered 100 nm tantalum films on sapphire, grown from 300 to 900 °C with varying oxygen partial pressure. The authors map which phase and orientation forms (α-Ta(110), α-Ta(111), or metastable β-Ta) under each condition. Without added oxygen α-Ta(110) dominates, a small oxygen dose favors α-Ta(111), and β-Ta appears only at the highest oxygen dose. The reported phase-selection energy is close to the oxygen diffusion activation energy in Ta, suggesting oxygen transport influences phase selection.
Marius O. Eji, Tyler J. Kirkpatrick, Ty J. Cawein et al.
In briefCompositional operational rank and when dimensional reduction preserves it
SummaryThe paper studies how the dimension of a microscopic description in higher-dimensional theories relates to the number of directions a physical observer can access. It gives sufficient conditions under which a compositional operational rank is preserved, first as a smooth integral leaf dimension and then as an observable Fisher-information rank. For rank four, it offers a conditional criterion: a viable dimensional reduction must preserve the relevant operational dependency structure, not merely yield four coordinates.
In briefCompeting coherence patterns in positive maps: positivity, atomicity and optimal entanglement witnesses
SummaryThe paper introduces a family of positive maps on qudits whose Choi operators mix independent exchange couplings with collective diagonal couplings. It derives exact conditions for positivity, complete positivity and all k-positivity levels, and maps the phase structure of decomposability and atomicity. At maximal coherence, an explicit positive subtraction yields an atomic optimal entanglement witness with a larger PPT-detection set.
In briefDAWG: a low-cost belief-propagation decoder for quantum LDPC codes using alternating graph sparsification
SummaryThis paper proposes DAWG, an ensemble decoder that combines Tanner graph sparsification with belief-propagation (BP) decoders. It runs BP on the full detector error model graph, then transfers posteriors to a sparsified graph for further BP rounds. Numerical tests on bivariate bicycle codes and superdense color code circuits show that DAWG with an LSD-0 post-processor performs similarly to Relay-BP and Vibe decoding. The post-processor is called about an order of magnitude less often than in Vibe, and it operates on a much smaller sparsified graph.
Josu Etxezarreta Martinez, Francisco Garcia-Herrero, Ruben M. Otxoa et al.
In briefParametrically Boosted Ergotropy and Charging Power in a Three-Mode Bosonic Quantum Battery
SummaryThis paper proposes a scheme using squeezed light to increase the extractable work (ergotropy) and charging power of a quantum battery. The system has a coherently driven charger cavity, a strongly dissipative mediator cavity, and a battery cavity, with directional energy flow arising from destructive quantum interference. Analysis based on the Lindblad master equation shows that active parametric driving substantially raises stored energy and peak charging power. Two-photon pumping, however, adds photon-number fluctuations that slightly reduce the fraction of stored energy that is extractable.
In briefProof that distillable entanglement varies continuously with the state
SummaryThe paper proves that distillable entanglement, the optimal asymptotic rate of converting bipartite states into maximally entangled pairs via LOCC, is continuous. It gives an explicit asymptotic continuity bound valid for arbitrary bipartite states that depends logarithmically on system dimension. The proof builds an explicit LOCC protocol whose ebit cost vanishes as the trace distance between the two states goes to zero.
WhyProves continuity of distillable entanglement with an explicit asymptotic bound, resolving a basic open question via rigorous proof, without experiments.
In briefBell-pair distillation under imperfect operations: how robust a quantum entanglement protocol is to real hardware errors
SummaryThis paper examines how well an entanglement distillation protocol works when its operations are imperfect. The protocol probabilistically produces a maximally entangled Bell pair from multiple copies of an unknown two-qubit state, using local operations and classical communication. The authors test several gate-error models, both incoherent and coherent, along with measurement readout errors, and identify when distillation still raises fidelity with the target Bell state. They find the protocol stays effective over substantial error ranges, though its robustness depends strongly on error type, and they also analyze asymmetric errors between the two parties.
In briefSampling Boltzmann distributions with a κ-parameterized quantum optimization algorithm
SummaryRestricted Boltzmann Machines are generative models whose training requires sampling an unknown Boltzmann distribution, which is computationally hard. This study uses Qiskit's Aer Simulator to evaluate QAOA-assisted sampling by analysing the inverse effective temperature κ on tractable problem sizes. Simulation results indicate that parameterized annealing-scheduled QAOA (PAQ-QAOA) can approximate RBM Boltzmann sampling for the instances considered. Hardware performance and scaling remain open questions.
Jo\~ao Marcos Cavalcanti de Albuquerque Neto, Gustavo Castro do Amaral, Guilherme Penello Tempor\~ao
In briefQuantum computing method for energy degeneracy and thermodynamics of spin systems
SummaryThe paper proposes a hybrid quantum-classical method that uses one ancilla qubit to measure the partition function at imaginary inverse temperatures, reconstructing energy-level degeneracies and thermodynamic properties of spin systems. For spectra on a known equally spaced energy grid, the inverse discrete Fourier transform gives exact degeneracies without noise. The authors demonstrate the method on frustrated Ising antiferromagnets on periodic Kagome graphs with up to 36 spins using the ibm_kingston processor. Despite deep circuits and hardware noise, the reconstructed spectra keep their dominant features and the heat capacities reproduce the main temperature dependence of exact results.
In briefImproving quantum-optimization CT image reconstruction with spin-error mitigation
SummaryThis paper studies CT image reconstruction using quantum optimization, where the underlying QUBO model needs rapidly growing numbers of binary variables as images get larger. The authors keep the CT-QUBO objective unchanged and apply simulated annealing followed by spin-error mitigation for optimisation (SEMO). They test 54-view region-of-interest reconstructions and nine-view reconstructions with detector-row corruption. SEMO reduced incorrectly reconstructed pixels in many cases, and at the tested sizes the results matched or exceeded selected unmitigated hybrid-solver results.
Hyunju Lee, Jeonghwa Lee, Yushuang Sam Yang et al.
In briefQuantum-enhanced metrology using classical shadows
SummaryThe paper proposes a metrology protocol that combines Pauli moments, estimated from a fixed set of randomized local measurements, into an optimized method-of-moments estimator without choosing an observable in advance. The authors derive guarantees on estimator variance and sample complexity. They show that entanglement can yield a constant-factor sensitivity enhancement, illustrated with one-axis-twisted probes.
In briefDid the Gran Sasso experiment rule out Diósi-Penrose theory? Reviewing the 2021 result and current experimental status
SummaryIn 2021, a low-background experiment at Italy's Gran Sasso lab searched for spontaneous radiation predicted by standard Markovian Diósi-Penrose dynamics and set a new lower bound on the short-length cutoff parameter R0. The paper argues this excluded one specific combination of Diósi's stochastic dynamics with Penrose's mass-density resolution. Later searches, including Majorana and XENONnT, tightened the bound. The authors stress that these conclusions apply only to Markovian white-noise dynamics, not to all colored-noise or gravity-modified collapse theories.
Catalina Curceanu, Nicola Bortolotti, Lajos Di\'osi et al.
In briefTraining quantum systems out of equilibrium with equilibrium propagation
SummaryThis paper extends equilibrium propagation, a training method for self-learning physical systems, to many-body driven-dissipative quantum systems. These systems naturally relax to a parameter-dependent non-equilibrium steady state, so they need not return to the ground state after each parameter update. For a class of open systems, the authors show that a quantum detailed balance symmetry still enables an efficient training strategy, supported by newly derived non-equilibrium static susceptibility relations. The approach is illustrated on a driven-dissipative transverse field Ising model and a parametrically driven bosonic lattice.
Aditya Gandotra, David D. Noachtar, Aashish A. Clerk
