In briefQTN-RQNN: A Recurrent Quantum Neural Network Using Tensor Networks for Near-Term Quantum Fault Diagnosis
SummaryThis paper proposes QTN-RQNN, a recurrent quantum neural network that combines tensor-network-inspired nearest-neighbor interactions with recurrent quantum processing and uses QSMOTE for class balancing. Tested on four heterogeneous fault-diagnosis datasets against QNN, QTN-QNN, and RQNN baselines, the results show that greater quantum architectural complexity does not universally improve classification. On SPID, the F1-score rises from 0.3077 to 0.4516 relative to RQNN, while two-qubit gates per sample drop from 32 to 24, a 25% reduction without increasing the four-qubit requirement.
Amit S. Patel, Himanshu R. Patel, Bikash K. Behera et al.
In briefEuropium molecular complexes studied by Judd-Ofelt analysis and coherent spectroscopy for quantum information use
SummaryThis paper provides an optical characterisation of twelve Eu3+-based molecular complexes, focusing on the coherent 5D0→7F0 transition near 580 nm. Judd-Ofelt analysis links ligand-field environments and local point-group symmetry to branching ratios, with lower-symmetry complexes showing higher ratios, some exceeding 1%. For complex 5-Eu, the optical coherence time at 4.2 K is 2.3 μs, comparable to the best reported molecular systems.
Nicholas Lester Jobbitt, Sascha Weis, Timo Schweizer et al.
In briefFinite-Size Limits of Adaptive Pauli Prediction
SummaryThis paper asks whether quantum data can reliably answer questions chosen based on earlier results. The authors prove that M adaptive Pauli predictions on n qubits need Ω(√min{n,M}) copies at fixed accuracy. Known upper bounds make this tight for M≤n, so n adaptive predictions cost Θ(√n) copies, versus O(log n) for a fixed list.
WhyProves a tight Ω(√min{n,M}) copy lower bound for adaptive Pauli prediction, sharply separating it from the logarithmic cost of fixed lists.
In briefElectric-dipole-induced nuclear electric resonance in silicon: a theory for controlling phosphorus nuclear spins with electric fields
SummaryThis paper theoretically proposes electric-dipole-induced nuclear electric resonance (EDNER) for controlling the nuclear spin of phosphorus atoms in silicon using electric fields. Using hyperfine interactions and magnetic field gradients to couple electron spin and charge, it claims faster control than conventional nuclear magnetic resonance. At specific working points, the nuclear-spin splitting is less sensitive to electrical noise, which the authors say could enable long coherence times and high-fidelity operations.
In briefMeasurable signatures of exceptional quantum channels
SummaryExceptional points are usually described as defective degeneracies of non-Hermitian Hamiltonians or Liouvillian generators. This paper instead builds an operational theory based on completely positive trace-preserving quantum channels, without relying on a Hamiltonian or master equation. Exceptional channels are defined through nontrivial Jordan chains of the channel. The authors show that a Jordan block of order m produces discrete polynomial-exponential terms with maximal degree m-1, linking exceptional-point physics to directly measurable probabilities.
In briefSmarter encoding for fewer qubits in quantum resilient routing
SummaryThis paper presents a structure-aware encoding method that maps logistics and routing problems onto qubits more efficiently. It is demonstrated on a benchmark of latency-resilient routing under dual-link failures, where the reduced formulation lowers qubit count and compiled circuit complexity while preserving the original optimization task. Running the reduced model on the same trapped-ion quantum computer yielded a 100X improvement in success probability.
Emanuele G. Dalla Torre, Bat-El Friedman, Daniel Porat
In briefDetecting genuine multipartite nonlocality in graph states (a stricter test of quantum nonlocal correlations)
SummaryThis paper introduces two classes of multipartite Bell inequalities that can detect genuine multipartite nonlocality (GMNL) in graph states. The first class needs a number of correlators that grows linearly with the number of parties, while the second class uses more correlators to gain higher noise robustness. Both classes can also be used to self-test graph states and the measurements performed.
In briefEntanglement catalysis that improves finite-size yield beyond asymptotic rates
SummaryThis paper asks whether the finite-size yield penalty in entanglement concentration can be reduced using an entanglement catalyst, an auxiliary state that helps the transformation and is returned unchanged. The authors show that a catalyst cannot raise the leading asymptotic yield but does change how the yield scales at finite sizes. For every bipartite pure state with nonuniform Schmidt coefficients, they exactly determine the optimal second-order yield correction and show that catalysis completely overcomes this finite-size penalty.
WhyProves catalysis fully removes the second-order finite-size yield penalty, with exact optimal corrections for all nonuniform pure states.
In briefA framework for optimizing Clifford-deformed quantum error-correcting codes, accounting for decoder and noise
SummaryThe paper addresses how to tune Clifford deformations, which modify a quantum error-correcting code's stabilizers to lower its logical error rate without extra qubits. The authors show the optimal deformation depends on the noise model and decoder, and introduce EBBI, an evolution-based best-arm identification search that treats the circuit, noise and decoder as a black box. On the rotated surface code, EBBI finds the optimal deformation at distance 3 with far fewer shots than random search and discovers a new code, B-XZZX, whose advantage over XZZX grows with code distance.
Julius Rye B{\o}nnelykke, Benjamin Joecker, Peter Krogstrup et al.
In briefMeasuring Entanglement in Rank-2 Mixed States Using Correlations
SummaryThis paper studies how to estimate entanglement in rank-2 mixed states of two- and multi-qubit systems using correlation-based measurements. The relevant two-dimensional subspace is treated as a logical qubit embedded in the physical Hilbert space, and closed-form expressions for concurrence and generalized concurrence are derived. Noisy simulations on the IBM Quantum FakeKingston backend, with readout-error mitigation and zero-noise extrapolation, agree with the analytical results up to 10 qubits.
In briefKrylov complexity of confined holographic systems for particles and strings
SummaryThe paper studies holographic Krylov complexity in bottom-up holographic QCD models of the confined phase, using the proposed link between Krylov complexity growth and the proper radial momentum of probes. Two horizonless backgrounds from Einstein-dilaton gravity are considered. For a massive particle in the Einstein frame, complexity oscillates in the deformed AdS-soliton but grows exponentially at late times in the deformed thermal-AdS. In the string frame, both backgrounds show oscillatory behavior, which the authors trace to an extra turning point in the infrared.
Jasper Nongmaithem, Deepak Kumar Kar, Ayush Kumar et al.
In briefBuilding quantum graphs with equal scattering but different spectra using germ graphs
SummaryThis paper uses the recently introduced germ graph concept to construct families of graphs that show dissipation, have identical scattering behavior, and differ in their spectra. The authors attach two previously known isoscattering, non-isospectral graphs to different contact vertices of a germ graph, producing two new graphs. Non-isospectrality is verified using Euler characteristics, and isoscattering is examined by numerically computing one-port scattering matrices.
Omer Farooq, Micha{\l} {\L}awniczak, and Leszek Sirko
In briefFinite Quantum Engineering Thermodynamics: a compact, measurable thermodynamic description of finite quantum working media
SummaryThe paper proposes a task-based method that keeps exact energy accounting separate from calibrated macroscopic prediction. Operator geometry is used to determine what a measured record fixes and how much uncertainty remains. It compares direct measurement of dynamical observables with measurement of a coarse record taken earlier, weighing each representation against its measurement cost. A Bose–Hubbard example gives a compact response table tested over a continuous operating region and on unseen microscopic trajectories, while a driven Ising chain shows that using history is not always the cheaper option.
In briefApproximating Sobolev functions on quantum state and unitary spaces via harmonic analysis and circuits
SummaryThis paper studies Sobolev functions on spaces representing quantum states (the complex unit sphere and complex projective space) and quantum unitary operations (the special and projective unitary groups). Using harmonic analysis on compact groups and homogeneous spaces, it characterizes the Peter-Weyl decompositions and Sobolev spaces through irreducible representations and the Laplace-Beltrami operator. It combines spectral truncation with finite-depth quantum-circuit approximation, invoking the Solovay-Kitaev theorem, to give quantitative rates that separate the spectral truncation error from the circuit approximation error.
In briefModelling Josephson junctions with boundary conditions for higher-fidelity superconducting qubit models
SummaryThe paper proposes a purely quantum-mechanical model of a Josephson junction, in which a charged particle moves on a one-dimensional loop and the junction is a point with self-adjoint boundary conditions set by a coupling strength and a phase jump. For a single-junction loop, the authors solve the spectral problem and obtain the ground-state supercurrent in exact factorised form. For more transparent junctions, the model predicts deviations from the pure sine law, and it reproduces both Josephson relations from first principles.
In briefQuantum extreme learning for predicting real chaotic circuit signals
SummaryThis paper applies quantum extreme learning, a special case of quantum reservoir computing, to forecast continuous time-series signals. The authors experimentally generated four signals from a chaotic electronic circuit and compared two discretization methods: sampling local peaks and troughs, and uniform sampling at the autocorrelation timescale. The algorithm achieved high forecasting accuracy on both simulated and experimental signals and stayed robust against moderate decoherence.
Mohammad Sharifian, Qingyu Li, Chiranjib Mukhopadhyay et al.
In briefBroadband microwave resonator for diamond NV vector magnetometry
SummaryThe paper proposes a planar microwave resonator that efficiently drives all four orientations of nitrogen-vacancy (NV) centers in diamond over a 100 MHz range. It uses 0.5 W of microwave power and 250 mW of laser power to enable vector magnetic field measurements. The authors built and tested a compact vector magnetometer with a sensitivity of about 1.2 nT/√Hz. They note this is not a record for diamond magnetometers but targets a compact hand-held niche.
S.V. Bolshedvorskii, E.A. Koreshin, V.V. Soshenko et al.
In briefA method for shortening quantum circuits while keeping their physical behavior, tested on 80-qubit hardware
SummaryThis paper studies approximate quantum compilation using tensor networks (AQCtensor) on an 80-qubit one-dimensional anisotropic XYZ Heisenberg chain starting from a Néel state. It finds that compressibility varies systematically with exchange anisotropy and field orientation, and is associated with a nested-commutator measure of second-order Trotter error and the target-state MPS bond dimension. On quantum hardware, a 10-repetition evolution was compressed to 5 repetitions with a target-state fidelity of 0.995474, reducing circuit depth by 45.9% and two-qubit gates by 47.6%, while measured observables remained comparable.
In briefShared-fiber QKD and classical communication link design optimization
SummaryThis paper studies how to share one transmitter and one fiber between continuous-variable QKD (CV-QKD) and classical signals, reducing duplicated optical hardware. The authors define a secure communication rate (SCR) that jointly reflects secret-key generation and classical transport, and optimize it for a 25 km link. The shared design reaches 12.079 Mbps, close to 12.095 Mbps for a separated-link reference, while cutting transmitters and fibers from two to one. Increasing usable receiver bandwidth raises the projected rate further.
Shivang Srivastava, Guillaume Ricard, Yves Jaou\"en et al.
In briefCompactness of Gaussian quantum Markov semigroups via second quantization
SummaryThis paper characterizes when the Hilbert-Schmidt semigroups induced by finite-mode Gaussian quantum Markov semigroups with a faithful normal invariant state are compact. Using a unitary second-quantization representation for each s-embedding, it shows that compactness at one positive time, compact resolvent, drift stability, and uniqueness of the normal invariant state are equivalent. The authors also derive trace-norm and Hilbert-Schmidt norm formulas and the generator spectrum, and give examples showing compactness does not require a spectral gap, and a gap need not imply compactness when the invariant state is not unique.
WhyProves equivalence of compactness, compact resolvent, drift stability and uniqueness with exact trace-norm formulas; a substantive theoretical advance with narrow applicability.
In briefA general method for extending quantum graphs that scatter identically but have different spectra
SummaryThe paper presents a general method for extending isoscattering, non-isospectral quantum graphs. Two graphs with the same total length but different topologies are used as examples; their scattering matrices are identical, yet their eigenvalues and Euler characteristics differ. Attaching the same star graph to each one, the authors use the Titchmarsh-Weyl M-function formalism to prove that the extended graphs remain isoscattering and non-isospectral.
In briefCircuit Design in Binary Polynomial Quantum Optimization: How to build the shallowest quantum circuit for a given polynomial form.
SummaryQuantum computers solving combinatorial optimization problems face extra circuit depth when using higher-degree binary polynomial formulations. The paper frames finding the shallowest circuit as a classical binary linear problem and proves NP-completeness for a variant of it. The authors introduce Tempura, a scalable heuristic, and faster binary linear formulations, showing much shorter circuits than state-of-the-art methods with Tempura's runtime mostly comparable to them.
Dylan Laplace Mermoud, Dimitri Watel, Sourour Elloumi et al.
In briefZak Phase Quantization Without Global Symmetry via Destructive Interference
SummaryThis paper examines whether the Zak phase of a one-dimensional band structure stays exactly quantized when the global symmetry protecting it is broken. The authors propose a mechanism based on local support symmetry and destructive interference, in which symmetry-breaking degrees of freedom are coupled to a topological parent system so that the relevant Bloch states cannot leak into them. They demonstrate quantized π Zak phases and boundary-localized states in an inversion-broken minimal model and a reflection-broken armchair nanoribbon. Perturbations that violate the interference condition continuously dequantize the phase, though a finite regime with a near-π phase and boundary response can survive.
In briefA theory of how excitons interact with each other in semiconductors with complex electronic bands
SummaryThis paper presents a general microscopic theory of interactions between excitons, which are bound electron-hole pairs in semiconductors, extending the authors' earlier work. The theory accounts for the full composite nature of excitons and applies to crystalline semiconductors where band topology, quantum geometry, and moiré effects matter. The authors also show results for simple flat-band systems with a nontrivial quantum metric, finding that the biexciton spectrum differs strongly from the case without quantum geometry.
In briefHow Data Constraints Percolate and Reshape Boolean Function States in Parity Learning
SummaryThe paper studies how a neural network reorganizes the Boolean function it learns as training proceeds and as unseen parity data accumulate. It treats the model's full sign table as a normalized function-state and uses inverse subsystem purity as an effective Schmidt rank. The authors report that small data additions broaden the Schmidt spectrum while larger additions refocus it on the target rule, and they examine how constraint-graph connectivity relates to learning stages.
In briefBlock encoding of semiseparable matrices via their generators: a quantum circuit that builds a block encoding of a semiseparable matrix from its two generators.
SummaryThe paper presents an explicit quantum circuit that constructs a block encoding of a one-pair semiseparable matrix directly from its two generators. For an N×N matrix with N=2^n, the circuit uses 2n+2 ancilla qubits and has O(polylog N) depth, realizing a (2√N, 2n+2, 2√2 ε)-block encoding. The accuracy parameter ε depends on the state-preparation routines that load the generators, and the circuit is built from cyclic shifts, swaps, and Hadamard gates.
Giacomo Antonioli, Gianna M. Del Corso, Roel Van Beeumen
In briefVerifiable, Private Sampling for Outsourced Quantum Generative Models
SummaryThe paper proposes a blind and verifiable sampling protocol for running inference on quantum generative models on a remote quantum server, so that the server learns nothing about the inputs and the results can be checked. Blindness is inherited from Universal Blind Quantum Computing, and verifiability uses trapification schemes. The authors also discuss extending a previously proposed verifiable delegated variational quantum algorithm to the training phase. Even against a malicious server, the protocol estimates the fraction of corrupted generated samples, beyond a simple accept or abort outcome.
In briefReal fiducial vectors exist only in dimensions d≡3 (mod 4)
SummaryThis paper studies restrictions on the dimensions and coordinate fields of real Weyl-Heisenberg fiducial vectors. The main result is that such vectors can exist only in dimensions d≡3 (mod 4). The authors further narrow the possible dimensions when the coordinate field is a totally real number field, an odd or even degree extension of the rationals, a real quadratic field, or a maximal real subfield of a cyclotomic field. They also establish non-existence over odd-degree number fields under certain conditions.
In briefContinuous-wave magnetometry of AC fields up to hundreds of MHz using NV centers in a strong transverse field
SummaryThis paper presents an AC magnetometry method using nitrogen-vacancy centers in diamond, based on continuous-wave optically detected magnetic resonance, which avoids high-power pulsed microwaves. A strong static magnetic field transverse to the NV axis resonantly couples electron-spin states with the target RF field. The method demonstrated frequency-tunable detection from 14.4 to 632 MHz, with sensitivities of 0.558 μT/Hz^0.5 at 14.4 MHz and 24.4 μT/Hz^0.5 at 632 MHz.
Ryusei Okaniwa, Rui Suzuki, Yuichiro Matsuzaki et al.
In briefPulsed control of entanglement-breaking index with thermal valleys and a switch
SummaryThe paper studies the entanglement-breaking index of quantum channels in thermal qubit collision loops, finding that some circuits show thermal valleys where the index drops on an interior polarisation window. By applying pulsed polarisation schedules, the authors report that an eight-round centred pulse restores entanglement at a reference target, and that closing this switch takes 21 to 35 rounds. The asymmetry is attributed to differences in entanglement margin distance and response rather than local rates.
In briefTime-resolved resource theory for quantum processes beyond endpoint channels
SummaryThis paper develops a fixed-task resource theory for continuous quantum process tensors, measuring how well a process can protect a logical task under time-resolved control. It shows that two processes with the same endpoint channel can have different optimal errors at the same pulse budget, so endpoint-only characterization is insufficient. The authors also give implementation bounds for coherent and dissipative control imperfections and apply randomized compilation to obtain achievable guarantees.
WhyProposes a fixed-task resource theory for continuous process tensors, with exact baselines and error bounds showing endpoint channels cannot distinguish processes.
In briefA robust digital receiver for continuous-variable quantum key distribution
SummaryThis paper examines the quantum security implications of digital down-conversion receivers used in continuous-variable quantum key distribution. It shows that frequency folding during down-conversion mixes image-frequency information into the baseband signal. The authors propose a dual-path digital heterodyne receiver that combines the two optical-path outputs with unequal weights to cancel the image-frequency component. Experiments validate the architecture's feasibility, reporting 11.4 Mbps over 42 km.
In briefHow chiral anomaly in tellurium, a Weyl semiconductor, changes and breaks down
SummaryDoped tellurium shows a large negative longitudinal magnetoresistance that can be tuned by the Fermi level and magnetic field. Moving the Fermi level toward the Weyl point strengthens this negative effect, which persists up to room temperature. At cryogenic temperatures in the extreme quantum limit, magnetoresistance reverses from negative to positive, which the authors suggest may indicate a field-induced phase transition driven by electron-electron interactions.
In briefAll-optical deconvolution for spectroscopy using bright twin beams
SummaryThis paper proposes quantum cross-correlation spectroscopy (QCCS), which uses macroscopic twin beams to overcome the convolution limit in coherent anti-Stokes Raman scattering. A correlation-enhanced sum-frequency channel and a 500-femtosecond temporal window remove uncorrelated background. The method recovers narrow Raman bands of 8 cm^-1 and 15 cm^-1 hidden by a 75 cm^-1 probe bandwidth, without numerical deconvolution.
In briefZero-noise extrapolation for error mitigation in indirect-control quantum systems
SummaryThis paper studies whether zero-noise extrapolation (ZNE), a common error mitigation method, can be applied to variational quantum eigensolver (VQE) computations in an indirect-control quantum architecture. Because operations in this setting are governed mainly by continuous time evolution under the system Hamiltonian, standard unitary folding for noise amplification is difficult to realize. The authors address these challenges and, with a minimal relaxation of the indirect-control constraint, propose a ZNE-based strategy that exploits the symmetry of the one-dimensional XY spin chain.
In briefQuantum-circuit residuals for predicting receptor drug potency, and their quadratic structure
SummaryThe paper jointly trains a classical molecular encoder with a linear base head and a shallow quantum-circuit residual head to predict GLP-1R cAMP-related pEC50, and extends the evaluation to ADRB2 and MC4R. Under the GLP-1R structure-group split, the quantum-residual models lower mean absolute error relative to the base models. A parameter-matched real-orthogonal control performs similarly, suggesting some gains may stem from structured quadratic feature interactions.
In briefWhen irrelevant terms dominate: a dissipation-regression scaling in open quantum criticality
SummaryThis paper studies real-time quantum phase transition dynamics in open systems coupled to finite-temperature environments, using the Schwinger-Keldysh formalism. In the coherence-dominated regime, it finds that a dissipative coupling naively considered irrelevant sets the longest timescale. This leads to a dissipation-regression scaling that reproduces unusual Kibble-Zurek scaling and relaxation seen in recent numerical studies.
In briefUsing Unruh-DeWitt detectors to tell flat from warped extra dimensions
SummaryThis paper studies how a two-level Unruh-DeWitt detector responds when it interacts with Kaluza-Klein mass modes of a bulk scalar field in extra-dimensional models. It compares large flat extra dimensions in the ADD framework with warped extra dimensions in the Randall-Sundrum scenario, and extends the calculation to a six-dimensional doubly compactified spacetime. The detector's response pattern depends on the spacing of the KK mass spectrum and the detector's resolution. The authors conclude that the two geometries produce qualitatively different response patterns, offering a way to distinguish flat from warped extra dimensions.
In briefQuantum information theory analysis of fiber sensing using stimulated Brillouin scattering
SummaryThis paper studies distributed sensing in optical fibers using stimulated Brillouin scattering (SBS), assuming the input probe is a quantum state. The authors derive an input-output relation for short fiber segments from a linearized opto-acoustic Hamiltonian and model the fiber as a cascade of bosonic Gaussian channels. They compute the quantum Fisher information for general SBS-dependent parameters and propose an adaptive approach. The framework is applied to fiber-tapping detection.
In briefQuantum-assisted meeting of two agents on hypercubes using quantum Bernoulli noise
SummaryThe paper studies two agents that use a quantum-walk framework to meet at a common midpoint on a d-dimensional hypercube, moving equal Hamming distances. It characterizes when finite-dimensional quantum strategies exactly reach the no-signalling benchmark, using a projective t-sphere resolution, and proves a rigidity theorem for optimal strategies. Quantum advantage can arise for nearest-neighbor updates, but for higher-cardinality updates the geometry of Hamming spheres rules out exact attainment.
In briefInstability of the Quantum Markov Length under Weak Channels
SummaryThe paper shows that the Markov length of a quantum many-body state, which governs the decay of conditional mutual information, is not generally stable under weak local channels, and that the failure already occurs for a pure product state. In a one-dimensional fermionic chain, a fine-tuned depth-two circuit of nearest-neighbor Gaussian channels maps the vacuum to a state with algebraically decaying CMI and infinite Markov length, even with channels arbitrarily close to the identity. The authors further argue that any translation-invariant state with a single rank-deficient reduced density operator can exhibit this instability, challenging recent Markov-length-based definitions of mixed-state phase equivalence.
WhyShows Markov length instability under weak local channels, with explicit fermionic chain construction and generalization, challenging recent mixed-state phase definitions.
In briefClassification of bipartite observables II: NIP observables and the Todorcevic trichotomy
SummaryThis is the second of three papers bringing model theory into quantum information. It studies observables lacking Shelah's independence property (NIP), whose idealized responses are of the first Baire class. Todorcevic's trichotomy for Rosenthal compacta divides these observables into three classes, each containing a physical order. In the transverse-field Ising model, spontaneous magnetization decides whether the family of magnetizations is stable or lies in the second class.
In briefImproved classical algorithm for optimizing fermionic Hamiltonians beyond Gaussian states
SummaryThis paper presents a polynomial-time randomized classical algorithm that approximates the largest eigenvalue of a traceless quartic fermionic Hamiltonian on n modes. The algorithm reaches energy at least λ_max/O(√n) and outputs either a fermionic Gaussian state or a polynomially sparse state in the Fock basis. It relies on a new upper bound on λ_max expressed through the maximum energy of a Gaussian state and √(2^{-n}Tr(H²)).
In briefComment on a paper linking Landau levels to Riemann zeros
SummaryThis comment responds to Sierra and Townsend's paper on Landau levels and Riemann zeros. Within the approximation they used, the authors construct eigenfunctions for an arbitrary Landau level and derive their asymptotics at the two box boundaries. They conclude that the boundary condition matches the lowest level up to an energy-independent phase, so no ln E term appears for any fixed level. They also note that the ln E term in the original semiclassical equation is a first-order shift of the smooth lowest-level counting function.
In briefTrainable Quantum-Native Language Models: Dissipative Memory, Capacity Limits, and Hardware Validation
SummaryThe paper studies byte-level language models whose hidden state is a small quantum register and whose next-byte probabilities come directly from Born-rule measurements. Learned, token-conditioned dissipative gating gives useful memory beyond one token, while a key-value recall benchmark shows a width-dependent capacity threshold. The tested models run on IBM Heron hardware but are classically simulable and perform substantially worse than classical n-gram baselines. The authors claim no computational quantum advantage.
In briefSimulating frustrated magnet behavior with Rydberg atom arrays under quantum fluctuations
SummaryThe study realizes a transverse- and longitudinal-field Ising model on the Shastry-Sutherland lattice using programmable Rydberg atoms, motivated by materials such as TmB4 and ErB4. Density matrix renormalization group calculations map the quantum phase diagram, and experiments on arrays of more than 110 atoms probe its signatures. Two regimes absent in the classical limit appear at finite transverse field: a 2/5 filling plateau and a quantum-dimer regime, with experimental response maps qualitatively agreeing with the calculations.
Vahagn Mkhitaryan, Milan Kornja\v{c}a, Mao Lin et al.
In briefCoset lifted product codes: quantum error-correcting codes built from non-normal subgroup actions
SummaryThe paper introduces coset lifted product (CLP) codes, a family of quantum LDPC codes combining lifted product protograph structure with coset actions, where the subgroup need not be normal. For groups of odd order, it gives an explicit dimension formula as a sum over irreducible representations. A search over 14,843 group-subgroup pairs reports certified codes exceeding the best published Q=kd²/n at several check weights, such as [[360,20,20]].
Rajendra Prasad Rajpurohit, V. Lalitha, Shayan Srinivasa Garani
In briefLieb-Robinson bounds for irreversible dynamics via adaptive Dyson expansion
SummaryThis paper studies a broad class of time-dependent, irreversible dynamics for quantum spin systems in finite and infinite volume. It introduces a flexible method that expands commutators of local operators with time evolution into self-avoiding paths of sets, without needing backward time evolution. This expansion directly yields Lieb-Robinson bounds that do not depend on the Hamiltonian or dissipative on-site terms of the generator.
In briefAn elementary derivation of the Szegő theorems via boundary leakage
SummaryThe paper studies the strong Szegő theorem and Fisher-Hartwig formula, which describe asymptotics of determinants of translationally invariant operators restricted to large finite regions. It proposes an elementary picture in which the strong Szegő correction arises from boundary leakage, where matrix-exponential paths leave the interval and return. It shows that an isolated boundary contributes half of the correction, and gives a rigorous derivation for finite-range matrices, with numerical examples including disordered and slowly decaying cases.
In briefFast computational primitives for La-cross quantum LDPC codes
SummaryThis paper builds a complete set of computational primitives for La-cross hypergraph product quantum codes. For one subclass, the authors show that seed automorphisms and fold-transversal gates generate the full logical Clifford group up to Pauli corrections. They also prove that every rank-one logical operator has D pairwise disjoint physical representatives, enabling parallel gauging, and they construct an addressable surface code interface for injecting external resource states.
Andrea Di Fini, Tom Hartweg, Laura Pecorari et al.
In briefA catalytic algorithm for transposing unknown qutrit unitaries with tight query bounds
SummaryThe paper constructs exact deterministic circuits that transpose and invert an unknown qutrit unitary in SU(3) using only forward queries. The authors prove that exact transposition and inversion of an unknown SU(d) unitary require at least d+1 and d²−1 processing queries, respectively. Both catalytic qutrit algorithms are shown to attain these bounds.
WhyGives catalytic exact transposition and inversion of unknown qutrit unitaries with proven matching tight query lower bounds, a clear theoretical advance with narrow scope.
In briefHidden Symmetry Linking Quantum Zeno Subspaces: Exact Relations Between Geometrically Inequivalent Subspaces
SummaryThis paper studies quantum Zeno dynamics, where continuous monitoring confines a system to measurement-selected subspaces. The authors use a circuit-QED network of coupled microwave resonators in which two geometrically inequivalent resonators are exactly exchanged by a latent symmetry. This symmetry gives the two corresponding Zeno subspaces identical escape and residence statistics. In the strong-measurement regime, residence times grow linearly with measurement strength and diverge in the ideal Zeno limit.
In briefOptimal linear-optical interferometers for building unitary t-designs with multi-photon light
SummaryThis paper studies how to construct approximate unitary t-designs in multi-photon Fock space using programmable linear-optical interferometers. Using the frame potential as the optimization target, the authors identify architectures needing far fewer controllable parameters than universal linear optics. Numerical evidence suggests the parameter count for unitary 1-designs scales empirically as 2d with the number of modes d.
Robert A. Grinshtein, Ivan V. Dyakonov, Stanislav S. Straupe
In briefDissipative Majorana Chain: Anomalies and Non-Invertible Symmetries
SummaryThis paper studies symmetries and anomalies of dissipative Majorana chains described by Lindblad dynamics. The Lindbladian is mapped to a non-Hermitian operator on a doubled Hilbert space, and anomalies are diagnosed by comparing symmetry algebras with and without weak fermion-parity defects for even and odd chain lengths. The authors connect the lattice algebras to the doubled Majorana CFT and use lattice bosonization to obtain an Ising Lindbladian with non-invertible Kramers–Wannier symmetries for even length, and a Kramers–Wannier duality defect for odd length.
In briefQuantum error correction and information spreading on sparse random graph structures
SummaryThis paper studies building quantum error-correcting codes on sparse graphs beyond regular lattices, and identifies the spectral dimension d_s, derived from the low-energy spectrum of the graph Laplacian, as the parameter linking quantum information spreading to code performance. The authors use Floquet random Clifford circuits on two sparse graph architectures with tunable spectral dimension to show that d_s governs both spreading and code distance scaling. They also report a geometry-induced transition from localized area-law to ergodic volume-law entanglement.
In briefPaired particle creation in trapped-ion simulators with opposite-sign mode frequencies
SummaryThis paper studies a trapped-ion spin-boson simulator in which spin-dependent forces set the signs of motional mode frequencies. Changing two modes from same-sign to opposite-sign frequencies shifts the dominant resonant process from excitation exchange to correlated pair creation. In the dispersive regime this realizes a two-mode parametric amplifier that generates squeezing and motional entanglement. The authors also report tripartite spin-boson entanglement and non-Gaussian entangled states via spin superposition and postselection.
In briefFrustrated Topological Orbital Magnetism: Semimetallic Ground States from Geometric Frustration and Aharonov-Bohm Fluxes
SummaryThis paper studies how geometric frustration combined with Aharonov-Bohm fluxes in three dimensions produces topological semimetal ground states with orbital magnetic dipole, quadrupole and ferrotoroidic orders, resembling spin patterns in classical spin ice. The authors argue that toroidization of these ground states, supported by non-Abelian topological nodal lines, induces measurable current-induced Hall effects. They also link distinct frustrated orbital current patterns to Weyl node charges and anisotropic linear and nonlinear Hall effects, and propose experimental signatures for validating these orders in candidate materials.
Sergio Garrido Bourkhaeva, Claudio Castelnovo, Wojciech J. Jankowski
In briefStudy of two-level-system loss in superconducting resonators on epitaxial hBN films
SummaryThis paper fabricates niobium resonators on few-layer epitaxial hexagonal boron nitride (hBN) grown by molecular beam epitaxy on sapphire, and compares them with a control without hBN. Radiofrequency measurements show the hBN-integrated resonators keep low dielectric loss, with a low-power internal loss tangent of order 10^-6 and minimal quality-factor degradation. The authors present this as a first step toward suppressing phonon-mediated correlated errors in solid-state quantum systems.
J. Christiansen-Salameh, D.J. Temples, R. Linehan et al.
In briefEngineering Ergodicity Breaking and Stable Emergent Conservation Laws in Quantum Many-Body Systems Under Strong Drive
SummaryThis paper studies periodically driven quantum many-body systems, which can break ergodicity when the drive is strong, leading to dynamical freezing. The authors identify the condition for ergodicity breaking under strong drive and show how exact, local engineering can stabilize dynamical freezing. They also find that the effective Floquet Hamiltonian becomes quasi-local under this engineering, unlike in a non-freezing system where it is non-local.
In briefExact solutions for spin systems with non-Markovian and Markovian dissipation
SummaryThis paper studies a class of exactly solvable many-body quantum systems in which spins couple to lossy bosonic modes that mediate Ising-type interactions. The systems exhibit both non-Markovian dynamics and Markovian dissipation on the spins. Using an exact stochastic representation, the authors decouple the many-body dynamics into the evolution of individual spins, obtaining exact spin observables and correlations without adiabatically eliminating the bosons. In an example of spin squeezing, the achievable squeezing and its optimal preparation time are shown to depend strongly on the interplay between the two types of dynamics.
In briefA paper on entanglement distillation under PPT operations
SummaryThe paper studies entanglement distillation using PPT channels, operations that stay completely positive under partial-transpose conjugation, in the asymptotic regime where the error vanishes but is nonzero. It gives a regularised formula for PPT distillable entanglement in terms of a measured-relative-entropy-like quantity, along with two single-letter converses. The authors show that PPT distillable entanglement can be strictly smaller than the regularised Rains bound, resolving an open problem.
WhyGives a regularised PPT distillable entanglement formula and two single-letter converses, resolving an open problem via rigorous proofs and a Werner-state numerical gap.
In briefEntanglement entropy and magic in ZX-diagrams: estimating entanglement and non-stabilizerness directly from graphical quantum circuit representations
SummaryThis paper shows how entanglement and non-stabilizerness ("magic"), two resources behind quantum state complexity, can be estimated directly from ZX-diagrams without costly tensor contractions. Using flow, the authors extract a normal form that separates a graph-state backbone from non-Clifford Pauli gadgets, yielding additive upper and lower bounds on bipartite entanglement entropy. A preprocessing step tightens these bounds, and the normal form also gives an upper bound on logarithmic stabilizer extent. Benchmarks on random unitary, monitored, and Trotterized Hamiltonian circuits indicate the bounds remain informative at large system sizes.
Marcin Szyniszewski, Razin A. Shaikh, Aleks Kissinger
In briefJoint tuning of circuit depth and training data size in adaptive quantum classifiers
SummaryThis paper asks whether adaptively grown quantum classifiers follow a predictable relationship between circuit size and training data size. The authors reimplement Q-FLAIR's gate-by-gate growth and test it on full-resolution MNIST 3-vs-5 classification across five training-set sizes. They find no predictable trend, with seed variance nearly as large as any change across sizes. The generalization gap stays within Caro et al.'s bound in 14 of 15 runs, but correlates only weakly with the bound's value (r = 0.12).
Saeefa Rubaiyet Nowmi, Md Mahmuduzzaman Kamol, Mohammad Saidur Rahman
In briefLocal polarization control for optical tweezer arrays, enabling precise manipulation of trapped atoms
SummaryThis paper presents a method for independently rotating the linear polarization at each site of an optical tweezer array, using the tunable local birefringence of a spatial light modulator. Applied to an array of 88Sr atoms, it homogenizes differential light shifts from 813-nm tweezers on a narrow transition, enabling sideband cooling under the magic-angle condition. The authors also demonstrate atom transport across polarization zones with high survival and preserved coherence, and closed-loop stabilization of tweezer polarization referenced to the atomic transition, reaching milliradian-level stability.
Xiangkai Sun, Richard Bing-Shiun Tsai, Andrew Winnicki et al.
In briefMeasure Now, Mitigate Later: Virtual Error Cancellation for Logical Quantum Circuits
SummaryThis paper addresses residual uncorrectable logical errors in early fault-tolerant quantum computing. It introduces virtual error cancellation, which uses only syndrome records and runs entirely in classical post-processing, without noise learning or modified circuits. A dual-decoder scheme is numerically tested on a distance-7 rotated surface code, where the error decreases as samples increase, reaching over three orders of magnitude suppression relative to the decoded logical error rate.
In briefHow long is a photon? A quantum theory paper on reconciling photon timing with relativity
SummaryA photon travels along a null interval with zero proper time, so its emission and absorption points are treated as a singular event, while those processes have finite duration that sets the photon's spectrum. The paper argues that a previously developed quantum wavefunction propagation model, using recursive Fourier transforms on dual spaces, can describe the photon's full life cycle and resolve this conflict. The author suggests the model could make quantum mechanics compatible with relativity and serve as an improved Klein-Gordon or relativistic replacement for the Schrödinger equation.
In briefTwo-way capacities of the pure-loss channel under an energy constraint
SummaryThe paper determines the two-way quantum and secret-key capacities of the pure-loss channel when the average input photon number is constrained. For transmissivity η and photon budget N, both capacities equal g(N) minus g((1−η)N), where g is the entropy of a thermal state. This matches the known reverse coherent information rate of a two-mode squeezed vacuum and supplies the last missing capacity formula for this channel.
WhyProves exact two-way capacity formulas for the pure-loss channel under photon constraints, matching known reverse coherent information rates and closing a long-standing gap.
Alessandro Falco, Francesco Anna Mele, Ludovico Lami et al.
In briefBuilding Large Structured Quantum Subspaces Shielded from Decoherence in Hybrid Systems
SummaryThe paper presents a framework for constructing large decoherence-free subspaces with nontrivial structure, using hybrid systems where quantum matter couples to a dissipative bosonic mode. Dissipation selects matter null states in the long-time limit, which span these subspaces. The authors illustrate the approach with a lossy optical cavity coupled to a one-dimensional directed tunneling operator, whose symmetries arise from an sl(2,C) algebra. They characterize the null states for both fermionic and bosonic particles, analytically and numerically.
In briefQuantum co-design for simulating dense neutrino fast flavor transformation
SummaryThe paper presents the QCNO code, which maps an inhomogeneous neutrino Hamiltonian with advection and finite-range interactions onto TEBD2 quantum circuits, linking ideal simulation, hardware execution, and fault-tolerant resource estimates. It reproduces the exact many-body evolution of a suppressed mean-field-like transverse fast flavor instability up to N=30. Circuit depth and T-gate costs are estimated up to N=50 for both NISQ and fault-tolerant approaches.
Zoha Laraib, Sherwood Richers, Alessandro Baroni et al.
In briefQuartic Uniqueness Certificates for Pure-State Tomography from Pauli Measurements
SummaryThe paper studies when a pure quantum state can be uniquely determined from expectation values of Pauli observables, leaving some of them out. Quartic certificates are derived from the fourth elementary symmetric polynomial of operators in the real span of the omitted observables. For three qubits, the condition exactly characterizes uniqueness among pure states and among all states. The authors also show these two notions coincide when the omitted observables commute pairwise.
WhyDerives quartic uniqueness certificates giving exact UDP/UDA characterization for three qubits, a notable theoretical advance confined to quantum tomography theory.
In briefResidual-guided design of global drives for trapped-ion quantum simulators
SummaryThis paper proposes a residual-guided optimization method for systematically designing multi-tone global drive spectra in trapped-ion quantum simulators, aiming to program arbitrary interaction graphs. The authors report that the method reaches the theoretical fidelity limit set by the motional modes, using a number of laser tones that scales nearly linearly with system size. It can synthesize both long-range and difficult short-range couplings, and it penalizes residual motional excitation to reduce errors from incomplete phase-space trajectory closure.
In briefDetecting electron entanglement with photo-assisted two-electron tomography
SummaryThis paper proposes photo-assisted two-electron tomography, a protocol that reconstructs two-electron coherences from dc currents and time-averaged current correlations routinely measured in electron quantum optics experiments. Driving an energy filter with a small rf tone enables single-electron tomography without current-noise measurements, and extending to two channels reconstructs the two-electron Wigner distribution. Applied to Coulomb-coupled quantum Hall edge channels, the method reveals interaction-induced energy entanglement.
In briefTheory of the CH$_\text{S}^-$ Defect in MoS$_2$ Confirming Quantum Emission Origin
SummaryThis paper develops a theoretical description of the negatively charged CH$_\text{S}^-$ defect, which is linked to an emission near 1.8 eV in monolayer MoS$_2$. It compares four environments: a monolayer, two bilayer configurations, and a MoS$_2$/hBN heterostructure. Adjacent layers strongly affect the emitter's electronic, vibronic, and optical properties. The MoS$_2$/hBN model shows a weak phonon sideband and closely reproduces the experimental photoluminescence lineshape.
In briefMultipartite entanglement spreads: generalizing a bipartite entanglement-flatness measure to many parties and studying hypergraph-tensor states.
SummaryThe paper generalizes the bipartite entanglement spread, a measure that vanishes exactly when the entanglement spectrum is flat, to multipartite pure states, yielding quantities that are monotonous under local operations. For three parties, it proves that hypergraph-tensor (HT) states are exactly the minimizers of a particular infinite family of entanglement spreads. It also introduces the larger family of spectral hypergraph-tensor (SHT) states, shows HT states are uniquely the minimizers of a fixed spread within SHT states for any number of parties, and characterizes SHT orbits under local unitaries. Asymptotic large-dimension values of several spreads for Haar-random states are also computed.
In briefExperimental generation of asymmetric keys from a six-qubit two-photon entangled state
SummaryThis paper proposes and experimentally demonstrates an asymmetric key-generation scheme in which public and private keys are derived from the parity structure of a six-qubit photonic entangled state. The state is produced with a Sagnac-based type-II SPDC source, reporting a Bell-CHSH parameter S = 2.798 ± 0.008. The authors present it as a physics-based alternative to public-key cryptosystems that rely on computational hardness assumptions.
Sanchari Chakraborti, Soumya Asokan, Sunita Khoth et al.
In briefA superconducting qubit protected from quasiparticles by gap engineering beyond the junction
SummarySuperconducting qubits are vulnerable to quasiparticles created by radiation and optical fields. The authors extend gap engineering beyond the Josephson junction, building a flux-tunable transmon with a gold-on-niobium ground plane and gap-engineered aluminum junctions. Compared with an all-aluminum transmon, the niobium device tolerated more than an order of magnitude higher near-infrared optical power before excess relaxation appeared, with no resolvable quasiparticle-induced frequency shift. However, dephasing and measurement infidelity still increased with optical power.
Trond Hjerpekj{\o}n Haug, Johan Kolvik, Joey Frey et al.
In briefSecure Quantum Handshakes: Verifying Quantum Clients in Networks Using Simon's Algorithm
SummaryThis paper introduces a client-validation protocol that works as a proof-of-quantum-capability handshake for quantum networks. It is designed to check whether clients joining the network truly have quantum computing capability and connect over robust channels. The protocol aims to protect against classical spoofers, noisy quantum computers, and genuine quantum devices connecting over noisy or insecure channels. The authors validate it through numerical simulations under erasure, dephasing, and depolarizing noise models.
In briefAutonomous code migration for quantum languages: a QED-C benchmark case study
SummaryThis paper studies autonomous coding agents porting the QED-C Application-Oriented Benchmarks from Qiskit to CUDA-Q. Three AI models each ported thirteen benchmark methods, taking far less time than a human engineer, though the agents took shortcuts when challenges arose and needed multiple prompts to stay on course. The authors released near-complete CUDA-Q support and model-generated skills that reduced agent turns and token use on an unseen benchmark.
W. Michael Brown, Thien Nguyen, Avimita Chatterjee et al.
In briefMutually unbiased bases: shared states, completion, and extension limits
SummaryThe paper studies pure states that give uniform outcomes in several mutually unbiased measurements and asks when such states can form another measurement basis. It distinguishes common unbiased states, their orthonormal completion, and further extension, giving an explicit completion for a phase-deformed Fourier pair in dimension 2m. In dimension six, it proves that a given mutually unbiased triple cannot be extended under a stated symmetry condition. The results do not determine the global maximum number of mutually unbiased bases or classify all triples.
In briefLarge-Scale Benchmark of Quantum Neural Network Configurations for Financial Forecasting
SummaryThis paper systematically compares quantum neural network (QNN) configurations, including encoding methods, ansatz designs, qubit counts, layer depths, and cost functions, for forecasting the GBP/USD exchange rate. A grid search yields 1,368 model configurations evaluated on accuracy, cost, and convergence. The best configuration reaches an R² of 0.985, outperforming a classical BiLSTM baseline. Tests on the IQM Emerald quantum device show that gate errors and decoherence are significant barriers to practical deployment.
In briefImaginary part of weak momentum: spectral vanishing and gauge invariance
SummaryThe paper builds a rigorous functional-analytic framework for the imaginary part p_I of the complex weak momentum. It proves that the expectation of p_I vanishes for every wavefunction in H^1, including those with nodes. The Bohm quantum potential is shown to arise entirely from p_I, and the decomposition is gauge-invariant under magnetic minimal coupling.
In briefNearly Optimal T-Count for Symmetry-Based Quantum State Purification
SummaryQuantum state purification improves the fidelity of an unknown quantum state by processing several noisy copies of it. The paper builds a Clifford+T circuit that block-encodes the symmetric projector for the symmetric-projection protocol using Õ(n) T gates. Using stabilizer nullity, it proves that any such implementation with small error requires at least 2n−2 T gates, showing near-optimal scaling in the number of copies.
WhyEstablishes nearly tight T-count upper and lower bounds for symmetric-projection purification with rigorous stabilizer-nullity proof, mainly impacting a quantum subfield.
