In briefDetuned cavity boosts spectroscopy precision for dipole moment estimation
SummaryThis paper studies cavity-enhanced spectroscopy with the cavity frequency deliberately detuned from the transition of interest. The authors report that detuning can improve dipole moment estimation precision by up to two orders of magnitude compared with resonant operation, including in the presence of losses. They attribute the gain to a detuning-controlled redistribution of information between light- and matter-like polaritons, and note it is accessible with conventional photodetection and time-correlated single-photon counting.
Subhasish Guha, Sourav Das, Francesco Albarelli et al.
In briefA density calculus for quantum field theory: an introduction to Haagerup L^p spaces
SummaryThese notes introduce Haagerup noncommutative L^p spaces for quantum field theorists, extending density matrix calculus to type III algebras where no intrinsic trace exists. The authors construct the spaces first for matrices, via crossed products and dual actions, then for general von Neumann algebras, discussing how normal states are represented by Haagerup densities. As an application, they compute the sandwiched Rényi divergence for a coherent excitation of a chiral current, checking monotonicity under restriction and the Rényi quantum null energy condition for all real orders α>1.
In briefWhy the Petz transpose map is the unique quantum analogue of Bayes' rule
SummaryThe paper asks whether quantum theory has a general retrodiction rule analogous to classical Bayes' rule, and whether such a rule is unique. The authors prove that a retrodiction assignment that is involutive, respects sequential and parallel composition, and agrees with unitary inversion must coincide with the Petz transpose map. The result applies to channels between finite-dimensional full matrix algebras.
WhyThe authors prove Petz transpose map is uniquely forced by consistency axioms, axiomatically characterizing quantum Bayes' rule and a family of doubly rotated maps.
In briefExperimental study of a reversible light-induced attack on quantum key distribution transmitters
SummaryThis paper experimentally studies a reversible photorefractive attack on a continuous-variable quantum key distribution system. Moderate blue-light illumination lowers the modulation variance of a lithium-niobate IQ modulator to a stable value, and the variance recovers once the light is removed. The authors exploit this recovery to compromise modulation calibration, which leads to overestimated channel transmittance and underestimated excess noise. Key rates computed from the measured parameters can be positive when the correctly calibrated rate is nonpositive.
WhyThe authors report a reversible photorefractive attack that exploits recovery to miscalibrate modulation in CV-QKD, turning a nonpositive key rate positive.
In briefEstimating how alike two unknown continuous-variable quantum states are, across separate quantum platforms
SummaryThis paper proposes a CV-DIPE protocol that estimates the inner product between two unknown quantum states prepared on distributed platforms. It uses only local homodyne measurements at shared phase settings and classical communication. Under a known bound on mean energy per mode, the authors derive explicit finite-sample guarantees and sufficient copy counts for a prescribed accuracy and confidence. Numerical simulations with Gaussian and non-Gaussian states show the trade-off between truncation bias and statistical error.
In briefA dissipative controller as a hidden source of quantum gate errors
SummaryQuantum systems are usually controlled by classical devices that inevitably dissipate energy into their surroundings. Using the fluctuation-dissipation theorem, the paper studies how the noise in the control field relates to the entropy produced by the macroscopic controller, working with a minimal model. In the fast-control, high-fidelity regime, it finds a tradeoff between dissipation and control errors. Perturbative calculations of gate fidelity and of state-transfer fidelity via shortcuts to adiabaticity in the Landau-Zener model illustrate this tradeoff.
Serhat C. Kad{\i}o\u{g}lu, Saulo V. Moreira, Mark T. Mitchison et al.
In briefIdentifying Executed Logical Operations from Syndrome Histories in qLDPC Codes
SummaryThis paper shows that syndrome histories, normally used for error correction in fault-tolerant quantum computation, can also reveal which logical operations were executed. The authors develop an exact inference method and a scalable approximation that account for unknown faults and measurement randomness. Evaluated on [[18,4,2]] and [[72,12,6]] bivariate bicycle codes, single logical instructions are identified with over 94% accuracy under circuit-level noise.
In briefNon-Bloch dynamical quantum phase transitions in chains with memory
SummaryDynamical quantum phase transitions in periodic chains are governed by real Bloch momenta. This paper identifies non-Bloch transitions that appear only in open chains and are governed by complex momenta, arising in a Hermitian chain coupled to a simple substrate with exactly treated memory. The effect stems from the point-gap winding number W of the projected propagator. For nonzero W, open boundaries alter both the dynamical free energy and critical times, even in the thermodynamic limit, and both follow from analytic continuation to complex momenta. The authors also show that W can be measured by particle counting.
Zhesen Yang, Wei-Wei Yang, Henning Schomerus et al.
In briefNonequilibrium thermodynamics of a small quantum system linked to quantum heat reservoirs
SummaryThis paper uses a statistical mechanical framework in which nonequilibrium averages of selected quantum observables are expressed exactly as averages over local density operators, to describe a small quantum system coupled to reservoirs. It focuses on how the system's average internal energy evolves, including under external autonomous driving that does work on it, and on entropy production within the system. When the system couples to large quantum reservoirs, its effect on them is captured by boundary conditions on the reservoir equations, which the authors derive. The framework is illustrated with heat transfer through a quantum system connected to two heat reservoirs at different temperatures.
In briefWhether a quantum system's memory measures depend on its surrounding environment's state
SummaryThis paper studies a fermionic quadratic open quantum system. It shows that the Breuer-Laine-Piilo and Lorenzo-Plastina-Paternostro non-Markovianity measures are independent of the bath state. In contrast, the Rivas-Huelga-Plenio measures and the Megier-Smirne-Vacchini entropic measure remain sensitive to the reservoir's temperature and chemical potential.
Mirko Consiglio, Ilia Khomchenko, Tony J. G. Apollaro
In briefEstimating Inner Products of Distributed Continuous-Variable Quantum States
SummaryThis paper studies continuous-variable distributed inner product estimation (CV-DIPE), which compares unknown states prepared by distant bosonic and quantum optical systems without requiring efficient classical descriptions or joint measurements. The authors develop three protocols for energy-constrained continuous-variable states, based on coordinated displaced parity, coordinated Haar measurements, and independent homodyne shadows. For arbitrary multimode inputs, including entangled and non-Gaussian states, they establish truncation error bounds and worst-case sample complexity guarantees. The leading terms favor coordinated Haar measurements, which are experimentally challenging to implement globally.
In briefKelvin-wave multiplication through sound emission
SummaryThe paper studies how a subsonic Kelvin quantum can emit a phonon and split into two lower-energy quanta, increasing Kelvin population while losing energy. In the soft-phonon limit, rotational invariance links the leading acoustic shear amplitude to the released energy, and microscopic calculations support this dispersion dependence. In a reflecting cavity with coherent sound and Kelvin seeds, Gross-Pitaevskii simulations show Kelvin gain, and shifting the initial sound phase by π reverses these changes.
In briefQuantum neural network combining digital and analog operations using long-range interactions
SummaryThe paper proposes a digital-analog quantum neural network (DA-QNN) whose analog blocks use an Ising model with power-law long-range interactions to generate entanglement, reducing the number of two-qubit entangling gates. It is benchmarked on supervised and unsupervised learning tasks. For image classification and many-body phase detection, the long-range ansatz matches short-range performance with fewer layers or shorter evolution times. In unsupervised phase detection, the two ansatzes give complementary signatures that together reconstruct the full phase diagram.
In briefNon-asymptotic bounds for quantum hypothesis testing via the Nussbaum-Szkoła mapping
SummaryThis paper studies quantum hypothesis testing, which distinguishes between quantum states. Using the Nussbaum-Szkoła mapping, the authors propose new lower and upper bounds for asymmetric quantum hypothesis testing. These bounds unify converse and achievability results across large-, moderate-, and small-deviation regimes. Numerical comparisons indicate that they approximate the optimal quantum error trade-off function more accurately at small blocklengths.
WhyThe authors derive unified non-asymptotic lower and upper bounds via the Nussbaum-Szkoła mapping, with numerical comparisons against existing bounds.
In briefEntropy-maximizing mixed quantum states with a fixed average
SummaryThis paper studies the maximum-entropy distribution of mixed quantum states under a fixed ensemble average. Its eigenvalue density is argued to converge asymptotically to that of the correlated Wishart ensemble (CWE), obtained via a free multiplicative convolution formula. Applied to the transverse-field Ising model with a thermal average state, it yields a high-temperature correction to the Marchenko-Pastur law. The authors also show, with numerical support, that the ensemble after random POVM measurement is asymptotically equivalent to the CWE, and compute finite-temperature Page curves for average entanglement entropy.
Charlie Shakeshaft, Christopher David White, Harry J. D. Miller
In briefQuantum query cost of finding tournament winners
SummaryThis paper studies how many quantum queries are needed to compute tournament solutions, which pick winners from the results of all pairwise comparisons among N alternatives. Classically these problems need Θ(N²) queries. The authors show the top cycle can be computed with Θ̃(N) quantum queries and a Condorcet winner found with Θ̃(√N), while finding a strong king needs Θ(N^{3/2}) queries.
In briefOptimized dynamical decoupling for spin ensembles with large inhomogeneities
SummaryThis paper compares many dynamical decoupling (DD) protocols for protecting coherence and enabling quantum sensing in an ensemble of negatively charged NV centers in diamond under ambient conditions. The authors identify an optimal approach that uses rapid adiabatic passage pulses, which are robust to amplitude and frequency inhomogeneity, combined with varying their phases. Experiments show improved signal contrast and an order-of-magnitude longer memory time compared to XY8 with standard rectangular pulses, and the method is also applied to sensing a weak oscillating field.
In briefError-Corrected Quantum Optimization with Rydberg Atom Array Embeddings: Using Embedding Ancillary Atoms for Error Correction
SummaryThis paper studies how Rydberg atom arrays solve combinatorial optimization on complex graphs through embeddings that add ancillary atoms. The authors show that the embedding structure naturally forms a classical error-correcting code and introduce a Cluster decoder to correct bit-flip errors. On the QuEra Aquila device, the decoder recovered exact optimization solutions with an average success rate of at least 8% for systems of up to 107 atoms.
In briefA method for detecting and suppressing quantum decoherence caused by collisions with the environment.
SummaryThe paper proposes two protocols for protecting quantum states from noise without needing full knowledge of the noise dynamics, based on a collisional model. The first preserves the states of qubits, and the second protects a logical qubit under similar conditions. According to the paper, the protocols protect arbitrary single-qubit and entangled states against general noise and scale to any number of qubits.
Sagnik Chakraborty, Srijon Ghosh, Federico Amato et al.
In briefProbabilistic imaginary-time evolution using precompiled diagonal Hamiltonian representations
SummaryThe paper proposes a probabilistic imaginary-time evolution method that uses a compiled approximate diagonal representation of the Hamiltonian, with the basis transformation optimized offline. For a fixed compiled representation, the online circuit structure and gate count per attempt do not depend on imaginary time, and the representation can be reused across input states and evolution times. The authors derive a condition for enhanced success probability and report numerical tests showing lower online cost than termwise Pauli-based methods at a common accuracy threshold. They also examine how approximation errors and offline preparation costs affect the overall benefit.
In briefSharp Tilting Inequalities: An Optimal Bound on the Directional Derivative of the Logarithm and Fractional Powers
SummaryThis paper studies a trace inequality for positive semidefinite matrices A and B, involving the directional derivative of the logarithm and fractional powers, with parameter 1/2≤α≤1. The authors prove an upper bound with the optimal coefficient. The result extends to positive trace-class A and positive, possibly unbounded, self-adjoint B on a separable Hilbert space. The proof uses a superoperator representation of the logarithm's directional derivative and an Araki-type estimate for the derivative of a fractional power.
In briefTraining quantum algorithms with adiabatic methods to detect entanglement
SummaryThis paper proposes a hybrid quantum framework that trains Variational Quantum Algorithms with an adiabatic-inspired optimization strategy to detect entanglement. The method combines parameter-space discretization with a hierarchical segmentation scheme and formulates the problem as a QUBO model for quantum annealing. Preliminary results are compared against classical neural networks and conventional VQA training techniques.
In briefOptimal Linear Combination of Hamiltonian Simulation for Simulating Dissipative Quantum Dynamics
SummaryLinear combination of Hamiltonian simulation (LCHS) is an efficient quantum-computing method for simulating dissipative dynamics, and its cost depends on the choice of kernel. The paper proves that the kernel family proposed by Ni and Ying minimizes LCHS query cost in the minimax sense. For target accuracy ε, the minimum cost is asymptotically (2e/π)(ln(1/ε) − ln ln(1/ε) + o(1)), with optimal leading constant 2e/π. The lower-bound proof combines weak duality with a realization lemma.
WhyThe authors prove the Ni-Ying LCHS kernel family is minimax optimal, with leading constant 2e/π, via weak duality and a realization lemma.
In briefAutomated Verification of Hamiltonian Simulation Using Quantum Signal Processing
SummaryThis paper presents what the authors believe is the first fully automated verification framework for Hamiltonian simulation based on quantum signal processing (QSP). The framework exploits the algorithm's structure, proving that the all-zero ancilla block is proportional to the target Hamiltonian and inferring the subnormalization factor automatically. It then verifies the QSP layer by extracting the implemented polynomial and certifying its approximation error. The implementation handles block encodings of Pauli-sum Hamiltonians with up to 256 system qubits.
In briefSeQUeNCe.DQC: A Full-Stack Simulator for Distributed Quantum Computing
SummaryThis paper presents SeQUeNCe.DQC, a new top-level module in the SeQUeNCe package that compiles quantum circuits into network-aware execution plans and runs them using existing quantum-network modules. The authors validate it by reproducing a two-node trapped-ion Grover experiment and comparing success probabilities with a reported 71% benchmark. They also study how compiler strategy, topology, and memory capacity affect execution time and success rate, finding that hybrid compilers mixing TeleGate and TeleData outperform pure gate-teleportation strategies.
In briefQSoftCore: A Conceptual Model for Quantum Software Engineering
SummaryThis paper presents QSoftCore, a conceptual model that reorganizes established quantum computing concepts from a software engineering perspective. It links quantum applications, computational problems, algorithms, configurations, programs, and paradigm-specific computation specifications with state evolution, execution results, and backends. The authors report that the model provides shared referents for computations, executions, deployment configurations, backends, and measurement evidence across the quantum software engineering lifecycle.
In briefPöschl-Teller-type Jaynes-Cummings Hamiltonians via supersymmetric transformations
SummaryThis paper uses supersymmetric quantum mechanics to define and study generalized Jaynes-Cummings (JC) Hamiltonians. Trigonometric and hyperbolic Pöschl-Teller potentials are used to modify the standard JC model. The generalized Hamiltonians share several features with the standard JC model, including matrix intertwining, excitation number symmetry, Rabi frequency, atomic inversion formulas, and classical and revival times. The authors conclude that the JC Hamiltonian is one example of a wider class of generalized Hamiltonians.
\.{I}smail Burak Ate\c{s}, \c{S}eng\"ul Kuru, Javier Negro et al.
In briefConditional Information Flow in Rotated Cluster States and Neural Learnability
SummaryThis paper studies how measurement outcomes in one-dimensional rotated cluster states stay conditionally dependent over long distances, despite an exact matrix product state bond dimension of 2. It compares the conditional mutual information of an entanglement-swapping endpoint readout with a bulk readout of the locally equivalent conventional cluster state, using the spin-1 AKLT chain as an exact control. The paper also benchmarks several neural learners on the same target, finding that building the small virtual memory into the architecture greatly eases optimization.
In briefClosed-form solutions for fully quantized parametric amplification
SummaryThis paper derives analytic expressions for how observables evolve under the fully quantized trilinear Hamiltonian that describes quantum three-wave mixing and parametric amplification. Starting from a coherent pump and vacuum signal and idler, the authors reorganize the Heisenberg expansion into resummed depletion and return profiles, giving directly evaluable expressions for correlations up to third order. Numerical benchmarks reported in the paper show errors around 10^-12 across the full pump depletion and below 10^-3 over dozens of depletion-and-back-conversion cycles.
In briefComposable device-independent quantum digital signatures for verifying message integrity and authenticity
SummaryThis paper establishes a composable security framework for quantum digital signatures within constructive cryptography. It presents a device-independent protocol using one-time universal hashing and multi-channel multiplexing. The authors also derive a related-key security bound for LFSR-based Toeplitz authentication, and numerical simulations indicate efficient signing of multibit documents over metropolitan distances.
WhyThe authors build the first composable security framework for QDS, propose a DI-QDS protocol, derive a related-key bound for LFSR-based Toeplitz authentication, and report finite-size simulations.
In briefEfficient experimental classification of quantum data using quantum kernels
SummaryThe paper proposes a framework for efficient quantum-state classification that reduces the number of measurements needed, deriving conditions under which the measurement count grows polynomially with system size. It applies this to classifying stellar rank, a measure of non-Gaussianity, in continuous-variable quantum computing. The authors experimentally classify single-mode states with stellar rank zero and one on a programmable photonic processor, reporting accurate results despite experimental imperfections.
Keitaro Anai, Akimoto Nakayama, Shintaro Ooka et al.
In briefA family of fermionic relative Rényi negativities in Sachdev-Ye-Kitaev models
SummaryThis paper introduces relative Rényi negativities as entanglement witnesses for mixed fermionic states. The authors relate fermionic partial time reversal to the size superoperator to obtain a path-integral representation. They evaluate these quantities in thermal states of the SYK model and the Maldacena-Qi coupled SYK model using a large-N expansion. The study identifies a class that plausibly approximates logarithmic negativity and finds first-order entanglement transitions not visible in simple observables.
In briefNAKO: A Benchmark for Testing and Diagnosing Compilers for Neutral-Atom Quantum Computers
SummaryNeutral-atom quantum processors must jointly schedule gates, place atoms, and move them in parallel, so compiler choices drive physical costs. This paper introduces NAKO, a benchmarking framework that pairs each benchmark with an executable reference schedule to measure resource gaps in compiler outputs. Controlled interventions on reference mappings and intermediate states trace excess costs to specific compiler decisions. In a 648-run evaluation of Enola and OLSQ-DPQA, NAKO identifies distinct bottlenecks in each compiler and validates resource savings from targeted fixes.
In briefQuantum field theory with scale-dependent weighted measures in momentum space
SummaryThe paper revisits constructing free quantum fields using weighted measures in momentum space, adding an independent energy scale that recovers the conventional theory at low momenta. The resulting family is described by a dimensionless spectral function, with the spatial weight linked to the Euclidean Snyder algebra as one special case. It also examines connections to modified dispersion relations and nonlinear momentum coordinates, and analyzes equal-time algebra, vacuum fluctuations, two-point functions and nonlocal causal structure for the complex Klein-Gordon field.
In briefDissipation dilution boosts SiV coupling to diamond nanomechanical beams
SummaryThis paper experimentally studies a tensioned diamond nanobeam platform where strain couples negatively charged silicon vacancy centers to a mechanical resonator. By monitoring the SiVs' optical response, the authors observe that dynamical strain localizes near the clamps under static strain. This enhances both SiV-mechanical coupling and mechanical coherence, and yields a strain sensitivity with much better accuracy than prior literature values.
In briefQuantum Optimization Using Cavity Dissipation to Escape Local Minima
SummaryThis paper proposes a cavity-based dissipative quantum solver for a class of NP-hard combinatorial optimization problems encoded as atomic-spin Hamiltonians. The method uses dissipative false-vacuum decay in configuration space to escape metastable local minima in rugged energy landscapes. Numerical studies on MaxCut and Maximum Independent Set identify favorable parameter regions, and time complexity estimates based on finite-size scaling are reported as more favorable than standard Grover search.
In briefA design and verification flow for quantum circuits modeled on VLSI practice, tested on pi estimation
SummaryThis paper proposes a four-level design and verification flow for quantum circuits, adapted from conventional VLSI digital design, covering behavioral modeling, register-transfer level, gate level, and integration with quantum algorithms. It uses quantum Monte Carlo pi estimation as a case study to show a path from specifications to large-scale circuit implementation. Classical simulations indicate that replacing random sampling with grid sampling yields a quadratic improvement in this case without any quantum computation, suggesting the speedup may come from the sampling strategy rather than the quantum amplitude estimation circuit.
In briefBeyond Direct Imaging: Quantum Measurement Design for Small-Target Detection in UAV Hyperspectral Sensing
SummaryThe paper proposes a quantum-assisted framework for detecting small targets in UAV hyperspectral sensing by comparing direct imaging with spatial-mode measurements. Simulations based on measured mineral spectra and published UAV acquisition scales, at a shared active-exposure budget, show it outperforms complete direct imaging. At an empirical 1% region-level false alarm rate, detection for a representative target rises from 62.95% to 69.65%.
In briefSpatial-mode selection for measuring mineral absorption in small regions
SummaryThis paper proposes a quantum-inspired measurement framework that uses spatial-mode demultiplexing (SPADE) to keep the absorption response of a small mineral region while reducing background light before detection. In equal-time simulations that include localization uncertainty, alignment time, calibration, and detector costs, it reduces absorption-depth root-mean-square error by 14% to 26% across five absorption strengths compared with all-pixel direct imaging using the same background freedom.
In briefQuantum processes without definite causal order: a limit on how distinguishable and how precisely measurable their outputs can be
SummaryThe paper studies quantum processes without a definite causal order and proves that the geometric Rényi divergence at the output of a deterministic completely positive process cannot exceed the sum of the divergences of its individual channel uses. It also proves an additive bound on the RLD Fisher information of parameter-dependent channels, which yields a Cramér–Rao bound on locally unbiased estimation precision. An erasure-probability example attains this bound.
WhyThe authors extend additive divergence and RLD Fisher information bounds to processes without definite causal order, proving a tight bound, an attaining example, and a Cramér-Rao consequence.
In briefForce sensing in a recoverable bosonic quantum memory, a paper on sensing an external force while protecting quantum information
SummaryThe paper constructs finite-energy bosonic codes that let a single oscillator sense an external force while actively protecting an unknown logical qubit. Logical amplitudes are encoded across discrete wave-packet sites, and the force signal is captured in a shared internal coordinate, enabling a probe readout independent of the logical state under continuous photon loss. Binomial site recovery is shown to suppress memory infidelity and memory-probe correlations at stated orders, and superconducting circuit benchmarks identify preferred encoding regimes for hardware.
In briefCompetition Between Resonance and Transition Channels in Cavity-Assisted Floquet-State Stabilization
SummaryThis paper studies coupling a driven quantum system to a dissipative cavity to autonomously stabilize Floquet eigenstates. At intermediate driving frequencies, meeting the resonance condition alone is shown to be insufficient, because the steady state depends on the interplay between resonance selection and cavity-induced transition strengths. This interplay can yield successful stabilization, mixed steady states despite resonance, or complete breakdown near Floquet-zone hybridization. The authors state that the same mechanism extends to multilevel spin-S systems.
In briefNarrowband and ultrashort-pulse-like probing in CARS using twin beams and SFG readout
SummaryThis paper theoretically studies coherent anti-Stokes Raman scattering (CARS) driven by bright twin beams, with sum-frequency generation (SFG) as the readout. Expressing the SFG output through quantum-field correlation functions reveals several correlation structures tied to different interaction pathways on the bra and ket sides. Frequency correlations between the CARS probe and SFG gating fields let the two fields act together as an effective narrowband probe, avoiding probe-induced spectral convolution.
In briefBeyond energy bounds: comparing Schrödinger eigenstates
SummaryThe paper derives comparisons between eigenstates of ordered Schrödinger operators, extending energy bounds to ground-state overlaps, spatial distributions and nodes. In one dimension and radially, a single crossing condition on the potential difference orders ground-state likelihood ratios and monotone observables. For Yukawa ground states, Hulthén comparison functions bound overlaps, radial moments and the density at the nucleus, yielding a lower bound of about 1.13611 on the scaled critical screening parameter.
In briefReverse quantum annealing to compute molecular ground-state energies
SummaryThis paper reports reverse quantum annealing calculations of ground-state energies for alkaline-earth monofluoride molecules. The Dirac-Coulomb electronic Hamiltonian is split into sub-QUBOs, and forward-annealing solutions are refined with optimized reverse-annealing schedules to systematically reduce residual configuration errors. Electronic ground-state wave functions and energies are obtained with the Quantum Annealing Eigensolver algorithm, and the authors present this as a route toward sub-milliHartree chemical accuracy.
In briefQuantum relay optical link using squeezed signals and energy harvesting
SummaryThis paper studies a quantum relay-assisted free-space optical link in which a decode-and-forward relay is powered by time-switching optical energy harvesting and forwards data using displaced squeezed signaling. Turbulence-induced loss is modeled as a pure-loss bosonic channel with a truncated Gamma-Gamma transmissivity distribution. The authors derive error and fidelity expressions for coherent and squeezed hops and analyze when squeezing improves throughput.
Nizar Khalfet, Francisco A. Monteiro, and Ioannis Krikidis
In briefA rhombic spin-1 model explaining a room-temperature GaN emitter's magnetic resonance lines
SummaryThis paper studies optically detected magnetic resonance from single defects in GaN at room temperature. It argues that a minimal S=3/2 model cannot explain a g≈4 line in a common defect class, and proposes a rhombic S=1 model that reproduces three line positions with rms errors of 8.1-9.8 MHz. The authors state that existing data cannot uniquely establish the S=1 assignment and propose a zero-field sweep to test it directly.
In briefThe Fate of Quantum Magic: How a Non-Entanglement Quantum Resource Dies or Persists Under Thermal and Dynamical Evolution
SummaryThis paper studies quantum magic, a quantum resource distinct from entanglement that measures how far a state departs from states stabilized by products of Pauli operators. The authors develop a framework to evaluate magic in generic many-body states and examine how it changes under thermal and dynamical evolution. They report a thermal sudden death of magic in the transverse field Ising model, generic spin chains, and the Kitaev spin liquid, and discuss how magic equilibrates after quantum quenches. The paper also introduces non-local magic and proposes a way to witness volume-law frame-robust magic in quantum materials using neutron scattering.
Liuke Lyu, Erik S. S{\o}rensen, William Witczak-Krempa
In briefHigh-bandwidth magnetic sensing with bulk diamond NV centers
SummaryThe paper presents a magnetic quantum sensor that uses heterodyne mixing under strong optical and microwave driving, reaching MHz-scale instantaneous bandwidth with 548 pT/√Hz sensitivity in bulk nitrogen-vacancy diamond. The authors then extend the bandwidth of a single resonance to 48 MHz using a strong magnetic gradient and many individually modulated microwave control fields. The peak sensitivity in this configuration is 8.5 nT/√Hz.
In briefFully quantum diffusion model generating synthetic malware records, with limited utility and costly sampling
SummaryThis paper introduces a fully quantum latent diffusion model that generates synthetic malware opcode-sequence records, using a parameterized circuit with one mid-circuit measurement and no classical neural layers. Across 17 malware families, the circuit cut denoising infidelity by 63%, yet classifiers trained on its records scored a macro-F1 of 0.11 on real records, below 0.44 for a classical diffusion model. The authors conclude that quantum generators of shareable security data need joint evaluation of utility, privacy, and sampling cost.
In briefAdaptive local measurements can beat fixed global measurements exponentially in quantum learning
SummaryThis paper asks whether measurements chosen adaptively, based on earlier outcomes, can be exponentially more informative than measurements fixed in advance. The authors construct multi-qubit states that encode a scalar parameter in one of exponentially many candidate observables, indicated by an auxiliary marker. An adaptive protocol using only single-qubit measurements and one round of adaptation needs logarithmically many copies, while every nonadaptive protocol needs exponentially many. The gap arises from measurement incompatibility, and the states are separable.
WhyThe authors show that adaptive single-copy local measurements achieve an exponential advantage over nonadaptive global measurements, with tight bounds up to the exponential base.
In briefHigh-threshold fusion-based quantum computing with optical hybrid qubits
SummaryThis paper proposes hybrid fusion-based quantum computation using small optical resource states that combine discrete- and continuous-variable encodings, connected through hybrid fusions. The authors present methods to generate these resource states directly, without local hybrid logic gates, and a decoding strategy that uses error information from individual fusion outcomes. They report a photon loss threshold of 2.231% using 12 hybrid fusions per surface-code unit cell, improving on a previous hybrid measurement-based scheme with a 0.89% threshold and 60 fusions.
WhyThe authors report a hybrid DV-CV fusion-based scheme with a 2.231% loss threshold and 12 fusions per unit cell.
In briefReducing Errors in Quantum Eigensolver Molecular Calculations Using Extended Random Phase Approximation
SummaryThis paper proposes an error-mitigation method based on the extended random phase approximation (ERPA) to reduce hardware noise in variational quantum eigensolver (VQE) molecular simulations. It reconstructs the two-particle reduced density matrix from approximate transition density matrices, with a DMRG calculation supplying a noise-free one-particle density matrix. Benchmarks on IBM quantum hardware for water double-bond stretching and cyclobutadiene automerization show energy errors reduced by orders of magnitude, and adding multireference adiabatic connection corrections recovers dynamical correlation.
Michael Wagner, Pavel Begy, Ji\v{r}\'i Brabec et al.
In briefExecution bias and repeatability in molecular VQE energy evaluation on quantum hardware
SummaryThis paper tests molecular energy estimates from variational quantum eigensolver states on two 156-qubit IBM Heron processors, Aachen and Pittsburgh, with parameters and circuits frozen. It compares raw measurements against zero-noise extrapolation and readout error mitigation in terms of residual error, cost, and repeatability. The authors find that a smaller statistical error bar does not guarantee a more accurate energy. They recommend workload checks and repeated measurements before taking additional samples.
In briefTunable Floquet exchange spectroscopy using Hong–Ou–Mandel interference
SummaryThis theoretical study shows that delay-resolved Hong–Ou–Mandel (HOM) coincidence measurements can probe how Floquet driving changes two-photon exchange in a collectively coupled cavity. A frequency-entangled signal photon scatters from the driven cavity while its idler serves as a delayed reference, and averaging over an unsynchronized drive phase preserves exchange interference within each output order. Fourier transforming the coincidence trace reveals two drive-dependent exchange branches tied to the Floquet-polariton spectrum.
In briefLocal quantum fault tolerance without expansion arguments
SummaryThis paper studies fault-tolerant quantum computation using a fixed local error-correction rule and the cubical (d,d')-Toric code, including the 4D Toric code. Under sufficiently weak local-stochastic Pauli noise, the correction cycle acts only on the current syndrome, has constant depth, and needs no multiscale decoder or scale-dependent delays. The authors give a local higher-dimensional sweep rule, prove a circuit-level threshold theorem for noisy sweep cycles interleaved with logical gates, and bound the probability of ideal decoding under local-stochastic noise.
WhyThe authors give a local higher-dimensional sweep rule and a circuit-level threshold theorem without expansion, covering the 4D Toric code.
In briefThe geometry of Floquet states: a study of the moduli space of periodic Hamiltonians
SummaryThis paper studies the moduli space of periodic Hamiltonians with nondegenerate Floquet spectrum, called "good" Hamiltonians. The corresponding Floquet states give a geometric model of this space, expressed using configuration spaces, flag manifolds, and principal bundles. A corollary of the main result is the complete determination of the rational cohomology ring of the space of good periodic Hamiltonians. The paper also considers adiabatic driving of a one-parameter family of such Hamiltonians and proposes two conjectures describing the resulting asymptotic quantum evolution, as Floquet analogues of the adiabatic theorem.
In briefUsing neural networks to infer how many times a quantum channel has been used
SummaryThis paper studies repeated-use quantum state transfer, where memory builds up in the channel between uses because it is not reset. The authors train a simple feed-forward neural network that takes only the Bloch vectors sent and received in a single use of an XX spin-chain channel and identifies the use number with over 90% accuracy. Using the channel's U(1) symmetry to form a reduced two-component representation raises accuracy to about 95%.
Hayden Zammit, Tony J. G. Apollaro, Gianluca Valentino et al.
In briefGravity-mediated entanglement in interferometers with repeated splitting
SummaryThis paper proposes and analyses protocols with repeated splitting stages, each doubling the occupied paths, to generate entanglement between spatially separated masses mediated by gravity. The authors derive an exact lower bound on the change in negativity and an explicit condition for when an additional splitting stage improves readout. Numerical simulations show an advantage in positional negativity over the parameter ranges considered.
In briefGravity Between Nuclear Clocks: Using Quantum Nuclear Energy Superpositions to Probe Short-Range Gravity
SummaryThis paper studies whether the mutual gravitational interaction among a large ensemble of nuclear clock nuclei could be observed. The authors analyze the gravitational redshift caused by neighboring nuclei and treat nuclear energy superpositions as gravitational sources, producing a quantum gravitational interaction between pairs of nuclei. They find that for a macroscopic number of nuclei, such as in a solid-state thorium clock, the resulting frequency shift may become non-negligible.
Konstantin Beyer, Niklas E. \"Onne, Shimon Kolkowitz et al.
In briefFrom entanglement bootstrap to DHR theory: linking anyon descriptions
SummaryThis paper directly connects the entanglement bootstrap with the Doplicher–Haag–Roberts theory of superselection sectors for two-dimensional quantum spin systems. Under the entanglement-bootstrap assumptions, it proves Haag duality and shows a one-to-one correspondence between simple entanglement-bootstrap anyon types and irreducible superselection sectors. For each fusion channel, it constructs an affine bijection between density matrices on the fusion space and normalized positive intertwiners in the operator-algebraic channel.
WhyThe authors link entanglement bootstrap to DHR superselection theory, proving Haag duality and a one-to-one anyon-sector correspondence.
In briefMemory Effects Limiting Repeated Entanglement Distribution
SummaryThis paper studies the practical limits of distributing entanglement through quantum channels reused without reinitialization. It shows that excitations left in the channel by earlier uses act as a memory source that progressively suppresses coherent quantum transmission. The authors derive an analytical lower bound on quantum capacity and combine it with a Holevo-Werner semidefinite-programming upper bound to define a capacity window.
Roberto Benjamin Salazar Vargas, Hayden Zammit, Trevor Spiteri et al.
In briefKey Performance Evaluation of Relativistic Quantum Key Distribution Through Turbulent Free-Space Optical Channels
SummaryThis paper examines how atmospheric turbulence affects relativistic quantum key distribution (RQKD) over free-space optical links, for both single-photon and coherent-state versions. The authors build a model that adds turbulence-induced phase fluctuations to the key-rate analysis and run numerical simulations under realistic channel conditions. Turbulence lowers interference visibility and degrades performance, with the severity depending on the ratio of interferometer separation or time separation to Fried's parameter.
In briefEngineering Baths to Generate Multipartite Entanglement
SummaryThis paper proposes a dissipative method for preparing genuinely multipartite-entangled steady states using independent local reservoirs, an Abelian strong symmetry, and temporal bath correlations. In interacting Ising chains, flat baths are shown to erase Ising-axis correlations exponentially, while structured baths convert temporal correlations into classical spatial ones that strong symmetry lifts into quantum entanglement. Engineering the bath spectrum lengthens the correlation length, enabling GHZ-like states to be prepared from separable initial states.
Baptiste Debecker, Philipp Westhoff, Visal So et al.
In briefA benchmark family of Ising models that can be solved exactly.
SummaryThe paper introduces the Generalized Mean-Field Ising (GMFI) family, a class of densely connected, inhomogeneous Ising Hamiltonians whose ground states can be obtained exactly. The exact solution reveals hidden low-dimensional structure and allows a number-theoretic classification of system sizes and degenerate ground states. The family is used to benchmark quantum and classical optimization methods, including quantum annealing, D-Wave experiments, QAOA, and several classical algorithms. The authors report unexpected system-size-dependent oscillations in the quantum-annealing gap.
Madita Willsch, Gopal Chandra Santra, Dennis Willsch et al.
In briefEigenvector-Continued Green's Function Method: A Fast Reduced-Order Approximation of Many-Body Green's Functions
SummaryThe paper notes that emulating the Green's function with reduced-order equations is difficult because it contains a large amount of information, including one-particle spectra, the one-body density matrix, and the ground-state energy. The authors introduce a systematically improvable emulator based on eigenvector continuation and moment-matching. The resulting approximation is obtained by solving linear equations, which separates the computation into offline and online stages.
In briefMixed-state topological transition in a non-Abelian Kitaev spin liquid with emergent supersymmetry
SummaryThis paper studies a topological transition in a mixed quantum state of the non-Abelian Kitaev spin liquid, driven by bond dephasing noise. The noise maps onto interacting fractionalized Majorana systems, allowing sign-problem-free Monte Carlo simulations. At an interface between topological and trivial Kitaev states, a gapless Majorana mode appears, and at the dephasing-driven transition this mode gains emergent N=1 supersymmetry. Simulation results agree with the exact supersymmetric values.
In briefA Primer on Instanton Physics: A Short Course
SummaryThese six lectures were given at the University of New Brunswick from 6 to 21 October 2026 for senior undergraduates and beginning graduate students. They introduce instantons in quantum mechanics and quantum field theory. The first four lectures cover particle mechanics as background, and the last two cover applications in semi-classical field theory.
In briefComputing quenched thermodynamics of disordered spin models with a quantum circuit that uses an ancilla and imaginary-time evolution
SummaryThis paper presents a quantum algorithm for computing quenched disorder averages in the transverse-field Ising model, with coupling configurations grouped into gauge classes. Approximate Gibbs states are prepared through ancilla-assisted imaginary-time evolution, and the ancilla measurement record indicates which gauge class each energy estimate belongs to. On a 3×3 open lattice, a one-step circuit resolves all sixteen flux classes, and thermodynamic integration yields a quenched free-energy estimate.
In briefMeasuring the edge heat-transport constant of a Kitaev spin liquid from spectra
SummaryThis paper proposes measuring the chiral central charge c of a two-dimensional topological phase from the spectrum of edge response to weak modulations of edge couplings, rather than through thermal transport. Using the Virasoro algebra, the authors derive absorption weights that depend on c and the mean edge energy, and build a combination equal to c. Numerical results for the Kitaev honeycomb spin liquid are reported, along with robustness tests under coupling errors, interacting edges, and a quantum-processor protocol.
In briefQuantum algorithm for molecular geometries and reaction pathways on a quantum processor
SummaryThis paper introduces VGSQD, a variable-geometry extension of sample-based quantum diagonalization that reuses quantum samples from a reference geometry for displaced geometries, reducing quantum cost. Using circuits of up to 124 qubits on the IBM Heron r2 processor ibm-quebec, the authors determine the equilibrium geometry and energy of the beryllium dimer and water. They also compute the minimum energy path and energy barrier of a hydrogen exchange reaction, with results comparable to CCSD(T) and DMRG.
In briefQuantum observables of nonperturbative superradiant scattering, a theory of how many coherent spins scatter particles collectively.
SummaryThe paper studies inelastic scattering from N coherent spins or any two-state system, showing the scattering scales as N², so the Born approximation fails at large N even when coupling is weak. The authors develop a nonperturbative theory of this superradiant scattering and its backreaction on the spins. The theory is said to apply to searches for millicharged particles and to neutron and charged-particle beams that could test quantum protocols for detecting cosmic relics.
Asimina Arvanitaki, Savas Dimopoulos, Marios Galanis et al.
In briefGoldbach representations in quantum optics and metrology: linking prime-number splittings to photon statistics and precision limits
SummaryThe paper links Goldbach representations to photon-number statistics in a quantum-optical setup. An even-number Fock state is sent into a stochastic beam splitter with uniformly distributed transmissivity, and the two outputs are projected onto prime subspaces. Each successful outcome corresponds to a Goldbach representation, and the averaged detection probability is proportional to their number. Using the Hardy–Littlewood asymptotic formula, the authors show that fixed transmissivity yields standard quantum limit scaling, while an equal superposition of representations yields Heisenberg scaling in phase estimation.
In briefComparing homodyne and heterodyne detection for classifying optical quantum state families from finite detection records
SummaryThe paper compares heterodyne detection with homodyne detection (using filtered back-projection to reconstruct the Wigner function) for identifying one of seven optical quantum state families, including GKP states, from finite detection records. With convolutional networks at N=100 events and 20% dephasing in the first family set, heterodyne detection outperformed homodyne by 14.1 percentage points, a difference that remains significant after multiple-comparison adjustment. At N=10^3 and 10^4 no significant difference was found, and the results concern a reconstruction-based pipeline rather than homodyne detection in general.
Franciszek Grzywa, Sebastian Dolata, Karol Bartkiewicz
In briefUsing cold atoms in optical tweezers to search for micron-scale fifth forces
SummaryThis paper proposes a new method for searching for fifth forces at micron scales by resonantly exciting the motion of ground-state-cooled atoms held in optical tweezer arrays. The authors develop a homodyne readout protocol based on sideband thermometry that can approach the Standard Quantum Limit. According to the paper, this raises the discovery reach for fifth forces by up to four orders of magnitude over existing constraints, and can also probe extra-dimension models beyond the current tabletop state of the art through the parametric enhancement of higher-dimensional gravity.
