In briefMeasuring how faithfully a quantum memory stores quantum information
SummaryThe paper presents a general framework for certifying quantum memories and quantifying their performance efficiently, using tools from quantum channel theory. Fidelity is quantified as average channel fidelity, which can be estimated in experiments with a finite set of probe states forming a 2-design. The authors apply these methods to a solid-state quantum memory and certify an average channel fidelity of 98.6%.
Victor Barizien, Sophie Egelhaaf, Angelo Gelmini Rodriguez et al.
In briefUsing post-selected von Neumann measurements to boost entanglement and quantum features in coherent states
SummaryThis paper studies how post-selected von Neumann measurements change the nonclassical properties of two-mode entangled coherent states (ECSs). Using the conditional pointer state, the authors characterize squeezing, photon statistics, intermode correlations, entanglement, fidelity, and post-selection probability. They report that anomalous weak values at moderate coupling enhance squeezing, antibunching, sub-Poissonian statistics, intermode correlations, and bipartite entanglement, and that fidelity tracks the crossover from weak perturbation to strong distinguishability.}
Janarbek Yuanbek, Zelalem Abebe Bekele, and Zhi-qiang Liu
In briefA unified method for the (inverted) quantum harmonic oscillator and the Berry-Keating Hamiltonian
SummaryThis paper treats three common quadratic quantum Hamiltonians, the harmonic oscillator, the inverted harmonic oscillator, and the Berry-Keating Hamiltonian, within one framework. The authors describe a unified approach to find the discrete spectrum of these operators and derive their (generalized) eigenstates. They also view these Hamiltonians as generators of su(1,1), and of a generalized version relevant when non-Hermitian generators are present.
In brief3D-printed microwave-resonator Paul trap for electron confinement and millisecond spin-qubit coherence
SummaryThis paper reports a 3D-printed Paul trap built as a GHz microwave resonator that keeps an open geometry for laser access and imaging of ion Coulomb crystals. The resonator has a quality factor of about 1000 and agrees well with finite-element simulations despite manufacturing imperfections. Using the validated model and measured surface roughness, the authors estimate electron spin-qubit decoherence and predict coherence times on the order of 10 ms, assuming motional heating is dominated by Johnson noise.
In briefRelative entropy changes across the Page transition between competing gravity saddles
SummaryThe paper develops a replica-trick framework for computing quantum relative entropy and applies it to evaporating Jackiw-Teitelboim black holes. It compares the exact radiation state with the Hawking saddle state and the replica wormhole saddle state. The relative entropy for the Hawking saddle increases during evaporation, while that for the replica wormhole saddle decreases, and the sign of their difference reverses at the Page time.
In briefElectron wave packets with adjustable skyrmion textures
SummaryThis paper studies free-electron space-time wave packets (STWPs), which are propagation-invariant matter waves with tunable group velocities, built by constraining the spatiotemporal spectrum of the electron wavefunction. Owing to free-electron dispersion, these packets can host both meron and skyrmion topological textures in momentum space. The authors demonstrate topological phase transitions and tunable skyrmion numbers through spectral geometry tuning, and show that the electron pulses propagate with topological robustness.
In briefPerfect state transfer on mixed graphs: complete classes and transfer times
SummaryThis paper studies perfect state transfer (PST) on unweighted mixed graphs and classifies normalized transfer times of complete PST classes. It gives a condition for a finite set to occur at a nonstationary periodic vertex and examines return phases of oriented realizations. The authors construct complete classes of every finite size and characterize simultaneous realization in connected oriented graphs.
In briefStudy of quantum many-body scars protected by symmetry through half-gauging.
SummaryThis paper examines how inserting symmetry defects interacts with quantum many-body scarring. The authors use a class of models from an embedding mechanism, whose stochastic-matrix-form Hamiltonians host zero-energy scarred states. They identify conditions under which scarred states survive defect insertion and analyze half-gauging in these chains. The analysis shows that half-gauging creates a nontrivial interface that yields scarred states protected by the underlying symmetries.
Weslei B. Fontana, Fabrizio G. Oliviero, Yi-Ping Huang
In briefPauli Decomposition via Character Theory: A Memory-Bounded Method for Qubits and Qudits
SummaryThe paper presents a method for decomposing an n-qubit operator into Pauli terms by labeling Pauli strings with the configuration space (Z_2)^n, treating them as displacement operators. The operator is split into 2^n fibers, each transformed with a length-2^n Walsh–Hadamard transform, giving a total cost of O(n·4^n). The authors extend the same picture to (Z_p)^n for qudits and present paulikit, a qubit implementation that keeps peak memory bounded for matrix-sparse inputs. Performance is reported on a low-end GNU/Linux platform for a coupled-oscillator sweep with over a billion Pauli terms.
Mohammadreza Khellat, Mohammad Masoumi, Saman Nasoori et al.
In briefBoosting classical light's photon bunching with a modified Fabry-Pérot cavity
SummaryThe study replaces one cavity mirror of a Fabry-Pérot cavity with a spatial light modulator, cascading multiple transverse modulations that encode spatially correlated phases on the light's wavefront. The measured two-photon and three-photon bunching peaks of the resulting superbunching light are 36.9±2.0 and (2.46±0.12)×10³, improved by about one and three orders of magnitude over thermal light. Ghost images reconstructed with this light show about 40 times higher visibility than with pseudo-thermal light.
In briefMulti-time advantage for certifying quantum coherence
SummaryThis paper shows that non-classical dynamics in open quantum systems can hide in temporal correlations that standard state and channel tests miss. The authors define coherence for multi-time quantum processes and show that intermediate-time access can reveal coherence absent from every pairwise channel. In an Ising model example, all three pairwise channels are incoherent while the full three-time process remains coherent. This was observed on a superconducting quantum processor using a coherence witness and full process tomography.
In briefInertial Counterdiabatic Driving: A New Method for Shortcut-to-Adiabaticity Control
SummaryThis paper introduces an inertial counterdiabatic (CD) protocol that recasts shortcut-to-adiabaticity design as a moving-frame diagonalization problem. It uses the Magnus expansion to build a variational propagator from an accessible CD ansatz. Benchmarks on a two-qubit system and the one-dimensional quantum Ising chain show it consistently outperforms action-minimization-based variational CD protocols, with the largest gains near gap-closing regions.
Juli\'an Ferreiro-V\'elez, F. A. C\'ardenas-L\'opez, F. Motzoi et al.
In briefMeasurement Complexity of Quantum Compressed Sensing: Lower Bounds from Quantum Parallelism
SummaryThis paper studies lower bounds on the measurement complexity of quantum compressed sensing (QCS), comparing them with the classical bound of Ω(K log(N/K)) for non-adaptive compressed sensing. It argues that quantum parallelism lets a unitary evolution map the sparse basis onto the measurement basis one-to-one, with nonzero locations carried by measurement-index labels. Depending on the requirement, the effective index sample complexity is Ω(K) for basic statistics, Θ(K ln K) for exact support recovery, and Θ(K ln K + K/ε²) when amplitude relative error ε is also required. Multimode photon-number-resolving detection reduces experimental rounds but not the total effective index sample complexity.
In briefPost-Selection-Free Quantum Automated Learning: a quantum training method that builds the full training path into one coherent circuit and boosts success odds without post-selection.
SummaryThis paper presents a quantum automated learning algorithm that trains quantum models by directly updating quantum states rather than optimizing variational circuit parameters, and it avoids post-selection. The full training path is organized into one coherent quantum circuit, and fixed-point amplitude amplification increases the probability of obtaining the learned model. The authors provide theoretical guarantees on output error and learning loss, and identify conditions under which additional coherent resources reduce the cost of restarting failed trajectories.
In briefQuantum Entangled Multimodal Fusion Networks (QEMFN): a hybrid quantum-classical method that fuses image and text features using trainable entanglement.
SummaryQEMFN is a hybrid quantum-classical framework that fuses pretrained image and text features for retrieval using parameterized entangling circuits. Under matched parameter budgets and frozen CLIP backbones, it outperforms classical fusion baselines on COCO-5k and Flickr30k. The work is run on shot-based simulators and a real superconducting device, and explicitly does not claim quantum computational advantage.
In briefClassical checking of remote quantum processors via degenerate concordant computations, applied to randomness generation
SummaryThe paper proposes a protocol that lets a client renting a cloud quantum processor check, in O(n) time per round, whether its outputs came from a quantum device. It uses degenerate concordant ensembles, with the client keeping a secret parity and the server receiving only random inputs and returning samples. Completeness, client efficiency and soundness are proven in an ideal model, while soundness of the explicit construction remains conjectural.
In briefPolarization of two interacting identical spin-1/2 particles in a slowly varying magnetic field
SummaryThe paper derives the density matrix of a nonstationary system in the adiabatic representation and its corresponding Liouville equation, a approach suited to cases where the standard interaction representation fails. It illustrates the method with two spatially separated identical spin-1/2 particles coupled by magnetic dipole-dipole interaction in a slowly varying external field. The authors analyze spin polarization of pseudo-qutrit states in regimes where they become entangled. The results indicate that entangled states can significantly modify the time dependence of observables and offer additional opportunities for their control.
In briefQuasiprobability test of macrorealism using non-signaling in time
SummaryThe paper introduces quasi non-signaling in time (QNSIT), extending non-signaling in time to quasiprobability distributions. QNSIT requires that intermediate-time marginals are unaffected by the back-action of a sequence of quantum measurements. Based on this, it proposes a quasiprobabilistic characterization of macrorealism, MR_qp, which requires QNSIT and a positive quasiprobability distribution. The authors show MR_qp implies NSIT but not conversely, and that the two coincide for two-level systems.
In briefTotal Ordering of Resources: Quantum vs. Classical Divide
SummaryThis paper examines whether quantum states can be ranked so that higher-ranked states convert into lower-ranked ones. The authors prove that such a total ordering is impossible for any quantum system of dimension greater than 2, because some states are always incomparable. They also construct classical systems of any size that can be perfectly ranked, showing the limitation is uniquely quantum.
WhyProves quantum systems above dimension 2 admit no total resource ordering, while classical systems can be perfectly ranked, establishing a rigorous quantum-classical separation.
Jingsong Ao, Julio I. de Vicente, Alexander Streltsov
In briefQuantum register gives unbounded memory advantage over classical models
SummaryThe paper studies a spin-one-half system driven only by total-spin operators, which produces a renewal process in which one interevent time is forbidden. It shows that a classical hidden Markov model needs at least 1+√n* states to reproduce this process, a gap that is unbounded and relies only on a relative phase of π.
In briefBroadband telecom entanglement from a compact all-fiber source
SummaryThe authors present a compact, low-cost all-fiber source of polarization-entangled photon pairs in the telecom band, built from off-the-shelf components. Pairs are generated by type-0 spontaneous parametric down-conversion in a pigtailed periodically poled lithium-niobate waveguide inside a Sagnac interferometer. At 0.5 mW pump power, the source reaches a Bell-state fidelity of 0.850, purity of 0.836, concurrence of 0.782, and a CHSH value of 2.3301 ± 0.0075.
Alessandro Cestelli, Spyridon Grountas, Scott Mc Haffie et al.
In briefCyclic triorthogonal codes in prime dimension (quantum codes enabling logical non-Clifford gates)
SummaryThis paper studies cyclic triorthogonal codes in prime dimension p, where a transversal third-level diagonal gate acts as a logical non-Clifford gate. For cyclic codes of length coprime to p, triorthogonality reduces to a sumset condition on the spectral support, making exhaustive enumeration feasible. The authors give a complete description of triply-even cyclic qubit codes and present qudit codes that improve on shortest Reed-Muller and Reed-Solomon codes.
In briefSqueezed light generated by a semiconductor amplifier
SummaryThis paper theoretically analyzes whether a semiconductor amplifier can produce squeezed quantum light during saturated optical amplification. Four-wave mixing gives weak spontaneous emission components at symmetric frequency shifts from the strong wave two-mode squeezed quantum properties. Quadrature squeezing occurs over several GHz and can reach 10 dB or more under optimal conditions.
In briefA single conformal coordinate decodes entanglement left after measurement
SummaryThis paper studies how much entanglement remains between two unmeasured regions of a critical quantum many-body state after a local measurement, which yields exponentially many possible outcomes. The authors show that in critical quantum chains, the universal outcome-resolved Rényi entropy is asymptotically determined by a single compact conformal coordinate extracted from the measurement record. Compact-boson theory explains that the entropy depends only on one relative compact zero mode and is insensitive to spatially varying components of the boundary profile.
In briefScheduling entanglement swapping in quantum repeater chains under decoherence during classical communication
SummaryThis paper studies quantum repeater chains, which split long links into shorter segments to distribute entanglement over long distances. The authors develop an analytical model that estimates how memory decoherence during the classical heralding of swapping results affects a given protocol. They find a trade-off: more repeaters increase entanglement generation but also increase the cumulative impact of decoherence, so an optimal repeater count exists. The findings are presented as guidance for designing inter-repeater distances and swapping timings in future quantum networks.
Jorge Benito D\'iaz, Andr\'es Agust\'i, Jabier Faba et al.
In briefDivisibility of non-invertible quantum dynamics in the Heisenberg picture
SummaryThis paper studies whether finite-dimensional quantum dynamics divide into consistent steps in the Heisenberg picture when the dynamical maps are not invertible. The authors show that Heisenberg CP-divisibility is equivalent to operator-norm monotonicity, and that independently chosen extensions can fail to satisfy a composition law. They use generalized inverses and unital completely positive projections to restore this law, and show that for qubit dynamics a completely positive generalized-inverse propagator is always guaranteed. The paper also analyzes time-local generators at singular times and the gauge freedom on dynamically inaccessible directions.
In briefPolaron-like response of a fast impurity strongly coupled to a Bose condensate
SummaryThis paper studies a fast-moving fermionic potassium-40 impurity immersed in a sodium-23 Bose-Einstein condensate in an ultracold atom experiment. A Raman pulse sets the condensate in motion and tunes the interspecies scattering length, giving an initial relative speed 36 times the condensate sound speed. As the interaction is tuned toward resonance, the early-time impurity acceleration is strongly suppressed compared with a two-body collision model, indicating enhanced apparent inertia. The effect is observed near two Feshbach resonances and is presented as evidence for a polaronic response in the strongly coupled supersonic regime.
WhyObserves enhanced dynamical inertia near two Feshbach resonances, providing experimental evidence for a polaronic response in a supersonic Bose-Fermi mixture.
In briefHorizon-scale black hole geometry corrections from a conserved quantum atmosphere
SummaryThe paper introduces a conserved, anisotropic source at the horizon scale representing a coarse-grained near-horizon quantum atmosphere, and solves Einstein's equations for a static black hole at fixed ADM mass. The dressed geometry has a renormalized mass function, a shifted horizon, and a modified surface gravity, with the effective potential and ISCO also changing. The authors present this deterministic mean geometry as a controlled background for later stochastic treatments in the Einstein-Langevin framework.
In briefCharging quantum batteries in a balanced loss-gain cavity pair
SummaryThis paper studies how a parity-time-symmetric photonic environment affects charging of Dicke and Tavis-Cummings quantum batteries. Each cavity holds an identical battery to keep the symmetry intact. In the broken phase the gain-side battery stores more energy, while in the unbroken phase it stores less than the lossy-side battery. The optimum lies on the broken side, near but not at the exceptional point.
In briefQuantum Data Ruler: Reading Unknown Quantum State Matrix Elements Against a Known Reference
SummaryThe paper proposes a "quantum data ruler" that reads a matrix element of an unknown quantum state by comparing its signal with that of a known reference, using their ratio. The method is stated to be exact for any Hamiltonian and any time, and unbiased under dephasing and amplitude damping. It also recovers the coherent ergotropy of a quantum battery that two-point measurement erases.
In briefQuantum telescopy using realistic anti-correlated light as reference
SummaryThis paper studies quantum telescopy, which modifies HBT stellar interferometry using spatially entangled single-photon states. The authors generate these states by beam-splitting an anti-bunched source from resonance fluorescence, and include detector imperfections and finite celestial light bandwidth. They optimize source and detector parameters for the best signal-to-noise ratio. In the weak incoming field limit, the realistic anti-bunched source still outperforms the coherent-state scheme.
In briefHawking radiation emerging spontaneously from black-hole formation in quantum spin systems
SummaryThe paper shows that Hawking radiation produced by dynamical black-hole formation can be simulated in a local quantum spin model. Starting from the early-time vacuum ground state with no prepared excitations, the authors follow the dynamics driven by the evolving geometry. They derive a renormalized local energy density in the continuum field theory and identify a local spin observable whose expectation value matches that prediction, including its dependence on surface gravity. The agreement holds over a finite time window that grows logarithmically with system size.
Shunichiro Kinoshita, Keiju Murata, Daisuke Yamamoto et al.
In briefQuantum bootstrap that converges without becoming exact at any finite order
SummaryThe paper studies the eigenstate quantum bootstrap, whose moment bounds stay nonexact at every finite order while still converging to the physical moment set. The authors prove this for a one-dimensional quasi-exactly solvable sextic oscillator, including excited levels. They also prove convergence for polynomial Schrödinger operators under explicit sum-of-squares conditions. A four-mode extension yields nonphysical feasible points with strictly positive definite moment matrices.
In briefParallel quantum chemistry runs across three on-site quantum computers
SummaryThis paper demonstrates parallel fragment molecular orbital quantum chemistry calculations on three room-temperature diamond-based quantum computers at Oak Ridge Leadership Computing Facility. Helium clusters were used as a testbed to compute total energies with the Quantum Wave Function Sampler, comparing synchronous shot-parallel and asynchronous fragment-parallel execution. Both modes increased sampling throughput without systematic accuracy loss, with the shot-parallel workflow reaching 93.60% efficiency and the fragment-parallel workflow reaching 75.01% measured efficiency (95.17% excluding non-useful idle time).
Nils Herrmann, Mariam Akhtar, Luke W. Bertels et al.
In briefWhen Expressivity Is Not Enough: Routing Geometry in Quantum Circuits
SummaryThis paper studies how the discrete routing of CNOT gates in variational quantum circuits affects both overall expressive capacity and local accessibility during training. It derives capacity constraints and analyzes why gradients can vanish even when the objective gradient is nonzero. The authors propose inserting identity blocks that preserve the current circuit while adding new tangent directions, and test ranking criteria with exact-statevector experiments on Bell tasks, Heisenberg chains, and TFIM models.
In briefSparse qubit operation in a 6×6 quantum dot array
SummaryThis paper demonstrates a 6×6 quantum dot array defined by a shared barrier gate and individual plunger gates. Using coherent spin shuttling over distances up to 5.2 µm, the dots are arranged into a sparse configuration of 10 simultaneously operated qubits, leaving space for shuttling connections. The authors report a 42-fold crosstalk reduction in this separated regime, enabling high-fidelity simultaneous single-qubit control, and control-Z operations via shuttling and plunger-only control.
WhyDemonstrates a 6x6 spin-qubit array with coherent shuttling, operating 10 qubits and cutting crosstalk 42-fold; strong novelty and experiments, but limited to semiconductor platforms.
Alexader S. Ivlev, Harold L. Co, Damien R. Crielaard et al.
In briefMeasuring a molecular ion's energy splitting with dipole-phonon quantum logic
SummaryThis paper reports the first experimental demonstration of dipole-phonon quantum logic (DPQL) as a spectroscopic tool. Using the shared motional mode of a CaO⁺-Ca⁺ ion chain, the authors measure the frequency splitting of CaO⁺'s ground Ω-doublet. They find it to be 2π×454±1 kHz and set a lower bound on the effective dipole-phonon coupling. The observation rate is limited by the low thermal population of the molecular ground rotational state.
In briefExciting subradiant atom chain states with surface plasmon waves
SummaryThis paper studies subradiant states of finite subwavelength atom chains in free space, which can store photons but are hard to prepare selectively with conventional laser excitation. The authors propose coupling the atoms to a surface plasmon wave travelling along the interface with a metal film. By controlling the distance between the chain and the surface, photons can be loaded, stored and released, which the authors present as a promising tool for future quantum memories.
In briefQuantum Darwinism via environmental records formed through an intermediate apparatus
SummaryThis paper examines whether redundant environmental records of a system's pointer states can form when the environment interacts only with an intermediate measurement apparatus, not the system directly. Using exact analytical solutions of quantum circuit models, the authors compare system monitoring with apparatus monitoring. Without noise, both give identical accessible pointer information and redundancy, with differences in mutual information explained by discord. Apparatus bit flips limit recoverable information, while larger environment fragments can mitigate independent noise on environment qubits.
In briefAn X2C-style approximation of the Dirac coupling operator using multiwavelets
SummaryThis paper adapts the exact two-component (X2C) method, usually used with fixed Gaussian-type bases, to an adaptive non-uniform multiwavelet basis. X2C block-diagonalises the Dirac Hamiltonian restricted to the basis subspace in an energy-independent way. The approach builds on the success of atomic mean-field X2C on Gaussian bases, representing the coupling operator as a projector onto the small components of the constituent atoms' eigenstates.
In briefCoupled cluster method for molecules with multiple references and open shells
SummaryThe paper proposes a simple coupled cluster approach for systems with multireference character and open-shell electronic structure. Within a restricted active space framework, the cluster operator includes only excitations from doubly occupied to virtual orbitals, so the individual operators commute. The authors demonstrate the method with the RAS-CCSD model and a complete active space, treating open-shell systems in a spin-adapted manner. According to the paper, the approach captures significantly more dynamical correlation than calculations without the coupled cluster similarity transformation.
In briefQuantum algorithms for locating low-energy vacua in a string landscape toy model
SummaryThis paper studies quantum algorithms for finding vacua with a small cosmological constant in the ADK toy model of the string landscape. The authors build a function-value oracle and use Grover search, achieving query complexity O(2^{N/2}) for N scalar fields. By exploiting the linearity of vacuum energy, they reduce the task to a collision problem between two blocks of a bit string and construct algorithms with query complexity O(2^{N/3}). The authors report a large reduction in computational cost over the classical pseudo-polynomial algorithm of Denef and Douglas for physically motivated parameter values.
In briefWhite paper: A 1–10 Hz matter-wave interferometer to test quantum gravity's spin entanglement witness
SummaryThis white paper highlights the importance of the 1–10 Hz frequency band for laboratory tests of gravity's quantum nature via the quantum gravity-induced entanglement of masses (QGEM) protocol. QGEM requires matter-wave interferometers with masses near 10^-15 to 10^-14 kg, separations of 30–50 μm, and coherence over about 0.1–1 s, making low-frequency environmental noise a central challenge. The authors state that relative acceleration and gravity-gradient noise must be suppressed well below 10^-15 m s^-2/√Hz, a requirement closely related to the low-frequency noise goals of the Einstein Telescope and Cosmic Explorer.
Sougato Bose, Anupam Mazumdar, Marko Toro\v{s} et al.
In briefBenchmarking exchange-only control of a 48-spin singlet manifold
SummaryThis paper evaluates system-wide performance of exchange-only quantum computing using arrays of up to 48 electron spins. Measurements of out-of-time-order correlators reveal rich scrambling dynamics. Using generalized cross-entropy and mirror randomized benchmarking, the authors estimate an effective error of 3×10⁻⁴ per two-spin exchange operation.
HRL Quantum Team & Microsoft Collaborators: Stephen Carr, Matt Abbitt, Michael Abraham et al.
In briefClassical chaos signatures revealed in Krylov space
SummaryThis paper examines how Krylov space methods, used to characterize dynamical chaos, connect to the established structures of classical chaos, a link that has been largely unexplored. For quantum maps with a classical limit, the authors show that the two classical chaos signatures, stretching and mixing, are encoded in different Krylov space structures. Stretching appears in the geometry of Krylov operators as set by the Lyapunov exponent, while mixing appears as exponential decay of Arnoldi sequences consistent with Ruelle-Pollicott resonances.
Gast\'on F. Scialchi, Augusto J. Roncaglia, Diego A. Wisniacki
In briefEntangled Learning Rules Offer Advantage in Quantum Measurement Learning
SummaryThis paper studies quantum measurement PAC learning, where a learner selects a measurement from a hypothesis class using quantum states and classical labels. It examines learning rules based on entangled measurements that cannot be implemented with LOCC, compared with single-copy rules. The authors construct a scenario where single-copy rules are asymptotically suboptimal. They further show that, under a natural joint measurability covering assumption, entangled rules offer at most a polynomial sample complexity advantage.
In briefExplicit steering witnesses from generalized equiangular measurements in prime dimensions
SummaryThe paper constructs a family of generalized equiangular measurements (GEAMs) in every prime dimension d≥5, yielding explicit steering witnesses. The construction combines d-1 mutually unbiased measurements with a parameter-dependent family of Hermitian operators, and an analytically derived interval for the parameter τ guarantees a valid POVM. Using a maximally entangled realization and a previously derived local-hidden-state bound, it obtains an explicit steering inequality and a sufficient condition for quantum violation.
In briefSimulating spin-system quantum dynamics with quantum-like circuits
SummaryThis paper builds on a framework of quantum-like (QL) bits and gates derived from synchronized networks to simulate quantum dynamics. It focuses on the transverse field Ising model, showing how QL circuits can prepare arbitrary wavepackets and evolve them to extract observables such as magnetization. The authors also introduce graph-level metrics describing coupling, phase coherence, and inter-block coupling, which may serve as design targets for hardware implementations.
Debadrita Saha, Ethan Dickey, William Horvat et al.
In briefThe Parliament of Observers: Challenging the Quantum Axiom That Observables Are Self-Adjoint Operators
SummaryThis paper examines a core assumption of quantum mechanics: that observables correspond to self-adjoint operators. The authors argue that this premise fails under careful scrutiny, at least when considering all observables at once. They question whether the noncommutative algebra of bounded operators is an adequate formalisation of the algebra of observables.
In briefResource-aware Grover search for the minimum vertex cover problem
SummaryThis paper studies how to reduce the quantum resources needed to run Grover's search on the Minimum Vertex Cover problem. It proposes three formulations, Dicke-Parallel, Edge-Counting, and Edge-Centric, each with different oracle and encoding designs. The authors analyze trade-offs among qubit count, circuit depth, gate count, and Grover iterations to guide the choice of formulation under given hardware and graph conditions.
Beilei Jiang, Harry Fu, Pavan Krishna Yarlagadda et al.
In briefQuantum machine learning for detecting rare impersonation fraud in digital account opening
SummaryThis paper studies detecting identity impersonation fraud using behavioral and transactional signals shortly after digital account opening. It uses a 2025 cohort of 3,419 accounts from Banco de Creditos e Inversiones (Chile), including 8 confirmed fraud cases, to compare quantum one-class classifiers with classical methods. The best quantum configuration, using 2 qubits, reached 88% recall and 9.21% precision in 2025. On the independent 2026 cohort, it detected 20 of 31 frauds.
In briefProbe choice and optimal measurements for dispersive coupling metrology in open systems
SummaryThis paper studies how photon loss and environmental memory affect probe selection and sensitivity when estimating the dispersive coupling strength in a cavity qubit system. Using density operator and quantum state diffusion methods, it compares quantum Fisher information for separable and entangled initial states in Markovian and non-Markovian regimes. The authors find that closed-system generator variance alone does not determine open-system performance, and that finite environmental memory can enhance and prolong sensitivity for the parameters studied.
In briefLearning disentangled representations with quantum variational autoencoders
SummaryThis paper studies whether quantum variational autoencoders (QVAEs) can learn disentangled and interpretable latent factors. The authors examine what counts as an individual quantum latent dimension and test this on synthetic problems, including MNIST variants. Across three datasets, QVAEs yield factorized, semantically interpretable latent representations, with individual qubits acting as meaningful latent factors.
In briefGeneralised entanglement wedges in three dimensions: a study showing gravitating-region properties follow from boundary CFT entropy inequalities
SummaryThis paper studies generalised entanglement wedges (GWs), proposed by Bousso and Penington, in vacuum AdS3 at leading order in G. It shows that each GW on a static slice is a union of geodesically convex regions, built from unions and intersections of ordinary entanglement wedges. Using the Crofton formula, the perimeter of a convex region is written as a measure of intersecting geodesics, expressible via CFT interval entropies. Monotonicity and strong subadditivity of GWs therefore follow from boundary strong subadditivity.
In briefConnectivity Controls Variational Accessibility in Symmetry-Preserving Quantum Circuits
SummaryThis paper studies symmetry-preserving quantum circuits for the variational quantum eigensolver (VQE), used to simulate interacting many-body systems. For the XXZ and Hubbard models, circuits with only nearest-neighbor connections generate restricted dynamical Lie algebras that miss key many-body directions, limiting VQE performance even at large depth. Adding one next-to-nearest-neighbor single-excitation connection (XXZ) or one correlated double-excitation (Hubbard) reconstructs the full orthogonal algebra and yields near-unit ground-state fidelity.
In briefPauli-flat quantum states that mimic maximal magic
SummaryThis paper studies the Pauli correlation structure of quantum states that maximize Rényi stabiliser entropies, such as T-type and Hoggar states. It introduces Pauli flat states, N-qubit states whose Pauli expectation values all have equal absolute value. These states reproduce the correlation structure of highly magical states without necessarily possessing nontrivial magic. The authors examine their existence, constructions, entanglement, and Bell nonlocality.
In briefMagnus: a code for neutrino oscillation probabilities in any Hamiltonian, flavor number, and matter profile
SummaryThe paper presents Magnus, an open-source Python code that computes neutrino oscillation probabilities using the Magnus expansion. It accepts any matter density profile, any number of flavors, and any Hermitian Hamiltonian. Where density varies slowly, it switches automatically to instantaneous eigenstates and applies the expansion only at resonances. The authors report that it is the fastest of the public codes compared at high accuracy on varying profiles, taking a few milliseconds per probability.
In briefChiral parafermions in Floquet Z_N topological order (non-equilibrium topological states driven periodically)
SummaryThis paper realizes Z_N Floquet topological order in a generalized Kitaev honeycomb model with clock degrees of freedom, using a three-step periodic drive. The driven system is described by constrained parafermions coupled to conserved Z_N gauge fields, and chiral parafermionic Floquet edge modes appear at the boundary. The authors track their propagation with correlation functions, characterize fractional quantum-information transport with a chiral unitary index, and probe exchange statistics and bulk anyon transmutation.
In briefSpectral gaps and entanglement complexity decouple in quantum annealing
SummaryThis paper shows that exponentially small spectral gaps in quantum annealing do not necessarily require complex entanglement. The authors find first-order transitions with bounded Schmidt rank and continuous transitions with polynomially closing gaps alongside logarithmically growing entanglement entropy. They also construct a mirror-twin manifold model whose gap closes exponentially while entanglement entropy still grows logarithmically.
In briefKPZ superdiffusion in chaotic quantum circuits
SummaryThe authors build chaotic brickwork quantum circuits with superdiffusive transport (dynamical exponent z=3/2) in the full KPZ universality class. Using nonlinear fluctuating hydrodynamics, they derive the propagation velocity, broadening scale and universal scaling form of the charge correlation function from microscopic equilibrium properties. Tensor-network simulations of a qutrit circuit reproduce these predictions, and the paper concludes that KPZ superdiffusion in quantum systems is not limited to fine-tuned integrable models.
WhyConstructs chaotic circuits showing full KPZ superdiffusion, deriving parameter-free predictions via nonlinear fluctuating hydrodynamics confirmed by tensor-network simulations.
In briefProtecting bosonic codes from ancilla-induced errors using continuous-variable flags
SummaryThis paper introduces continuous-variable flags, auxiliary oscillators coupled to an ancilla qubit whose phase-space positions encode continuous errors on the storage mode. A heterodyne measurement followed by feedback corrects these errors. The scheme uses only the dispersive coupling, displacements and rotations already needed for the gates. Simulations with realistic circuit-QED parameters predict over three orders of magnitude fewer logical errors for parity measurement of a four-component cat code.
WhyProposes continuous-variable flags protecting gates from ancilla-induced continuous errors, with simulations showing orders-of-magnitude fewer logical errors under circuit-QED parameters.
Thomas D\'ecultot, Ronan Gautier, and Mazyar Mirrahimi
In briefBoundary-accessible work in a topological quantum battery charged by collisions
SummaryThis paper studies a quantum battery built as a dimerized SSH-type spin chain, charged at one end by repeated collisions with excited two-level ancillas and discharged by an initially empty two-level load at the same site. Using an exact free-fermion mapping, the authors derive a bound on the load work for all number-conserving quadratic extraction protocols. For representative parameters, a single boundary pulse exploiting the topological edge mode delivers 98.6% of this maximal bound.
Osman Or\c{c}un Keskin, \"Ozg\"ur E. M\"ustecapl{\i}o\u{g}lu
In briefRewiring and resetting: minimal resources for manipulating non-Abelian anyons
SummaryThe paper determines the minimal circuit resources needed to braid and fuse anyons in quantum double models of generic finite groups. It introduces graph rewiring, a diagrammatic method that braids anyons through a sequential unitary circuit without ancillas. For fusion, it proves that purely unitary protocols cannot fuse unknown anyon types without ancillas, but qudit reset enables such input-agnostic fusion.
WhyIntroduces graph rewiring and proves ancilla-free braiding plus reset-enabled fusion, overturning folklore; rigorous no-go and constructive proofs with notable impact on topological computation.
Chiu Fan Bowen Lo, Rohith Sajith, Anasuya Lyons et al.
In briefQuantum information processing under maximal distance measures: how stricter error metrics change task rates
SummaryThis paper examines how quantum information tasks change when standard distance measures such as trace distance and purified distance are replaced by maximal extensions of classical distances. Channel coding and quantum resource distillation are unaffected, while channel simulation and quantum resource dilution rates are instead governed by the Belavkin-Staszewski relative entropy rather than the Umegaki quantum relative entropy. The authors also show that known reversibility results, including the reverse Shannon theorem, no longer hold under these maximal measures.
WhyReanalyzes quantum tasks under maximal distances, showing Belavkin-Staszewski entropy replaces Umegaki and reversibility results fail, with rigorous proofs.
In briefA spectrum-based converse bound for quantum state discrimination and its use in classical-quantum channel coding
SummaryThe paper studies converse bounds on average decoding error probability in finite-blocklength classical-quantum channel coding. It gives a lower bound for multiple quantum hypothesis testing based on pairwise trace distances, along with a corresponding fidelity bound. A spectrum-based converse is then derived that depends only on a priori probabilities and state spectra, and is shown to be tight for the quantum depolarizing channel under suitable conditions. The bound is applied to binary codes over the quantum amplitude damping channel with inputs |+⟩ and |−⟩, and a normal approximation is discussed for large blocklengths. In the numerical examples considered, the spectrum-based converse is tighter than other converse bounds at low noise levels.
In briefSemi-Clifford Gates in the Single-Qudit Clifford Hierarchy for Composite Dimensions
SummaryThe paper studies whether every gate in the Clifford hierarchy is semi-Clifford, since such gates can be implemented efficiently via gate teleportation. It extends prior prime-dimension results to single qudits of arbitrary dimension d, proving that all hierarchy gates are semi-Clifford if and only if d is square-free. For composite dimensions, the authors distinguish four gate types and show that some equivalences between them fail when d is not square-free. The paper also proves that every third-level gate of the one-qudit Clifford hierarchy is generalized semi-Clifford in any dimension.
WhyExtends prime-dimension results to composite qudits, proving hierarchy gates are semi-Clifford exactly when d is square-free, with a four-way gate classification.
In briefDistributional Quantum Query Complexity: Lower bounds on quantum query cost under input distributions for composition, direct sum, and direct product problems.
SummaryThe paper notes that known quantum query complexity results for composition, direct sum, and direct product hold only in the worst case and do not account for input distributions. The authors prove distributional joint computation lower bounds for these three problems. To do so, they introduce a new multiplicative variant of the γ2 norm and a "Shaltiel-free" measure of quantum query complexity, which they show characterizes the composition behavior of distributional quantum query complexity.
WhyExtends quantum query composition, direct sum, and direct product theorems to distributional settings with new multiplicative gamma-2 norm and Shaltiel-free measure.
In briefEnergy-limited two-way capacities of pure-loss and quantum-limited amplifier channels
SummaryThe paper determines the two-way quantum, entanglement-distribution, private, and secret-key capacities of the pure-loss bosonic channel under a mean photon-number constraint. All four coincide and equal g(N)-g((1-η)N), where g is the thermal-mode entropy. The authors also find the energy-constrained capacities of the quantum-limited amplifier, showing classical assistance does not improve its unassisted rates.
WhyResolves a longstanding energy-constrained capacity problem, proving optimality of reverse coherent information rate via a new sector teleportation simulation technique with complete converse argument
In briefThe real cost of magic state cultivation without destructive measurement
SummaryThe paper examines magic state cultivation, a low-overhead method for preparing high-fidelity non-Clifford resource states for fault-tolerant quantum computing. Prior resource estimates assumed noiseless transversal measurement of the output state for postselection, which would destroy the state and is unavailable during computation. The authors introduce Caliper, an open-boundary postselection method using only nondestructive mid-circuit syndrome information, which substantially outperforms existing methods under these constraints. They find it recovers prior resource efficiency in some regimes, but at previously reported spacetime costs, achievable logical error rates can be orders of magnitude higher.
In briefNatural proofs barrier for quantum state preparation lower bounds
SummaryThis paper identifies a barrier explaining why stronger quantum state-preparation lower bounds are hard to prove. The authors establish a quantum analogue of the Razborov-Rudich natural proofs barrier. Under a standard cryptographic assumption, no natural property can prove superpolynomial state-preparation lower bounds, even against a fixed level of the Magic Hierarchy. The paper shows that several existing lower-bound techniques, including arguments based on approximate degree, non-unique ground states of local Hamiltonians, and mutual information, are natural in this sense.
WhyExtends the Razborov-Rudich natural proofs barrier to quantum state-preparation lower bounds, showing under cryptographic assumptions that superpolynomial bounds are unattainable by natural properties
In briefDesigning group-valued quantum codes with full regular low-weight logical bases
SummaryThe paper studies group-valued quantum error-correcting codes whose complete canonical logical bases consist of low-weight operators generated by translating seed operators, which matters for fault-tolerant quantum computing. It introduces frame width f as an additional code parameter alongside distance and check weight. Explicit high-rate examples are given, including a [[1088,128,22]] lifted-product code with f=22 and a [[1024,256,24]] pair-partition code with f≤27, and a method combining symmetry reduction with stabilizer-based pruning is used to certify distances exactly.
In briefTighter limits on how far quantum states are from stabilizer states
SummaryThe paper proves that pure states with stabilizer rank at most k have stabilizer extent at most 2^{O(√(k log(k+1)))}, with an analogous bound for Clifford-rank operators. This yields a stabilizer fidelity lower bound and an Ω(n²/log n) lower bound on the approximate stabilizer rank of tensor powers of any non-stabilizer qubit state. The authors also give tomography algorithms for low-stabilizer-rank states whose exponent is nearly square-root better than the best previous algorithm.
WhyImproves stabilizer extent from exponential to subexponential bound, with several new lower bounds and tomography algorithms, supported by rigorous proofs and resolving a conjecture.
In briefComplete phase diagram of detailed-balanced Gibbs samplers for a mean-field quantum spin model
SummaryThis paper studies the spectral gap of recently discovered families of Gibbs-sampler generators for the mean-field Heisenberg model on n spins, which satisfy KMS detailed balance. The authors show that all these families share one phase diagram: the gap is constant in the disordered phase above the critical temperature, scales as 1/√n at the critical temperature, and as 1/n in the ordered phase below it. The result extends earlier work by Basso et al. (2026), which covered one such family but only partly resolved the gap scaling at the critical temperature.
Levente Raikovich, J\'ozsef M\'ak, Csaba Czab\'an et al.
In briefCV-QAOA: A continuous-variable quantum algorithm for efficient low-depth continuous optimization
SummaryThis paper studies a continuous-variable quantum approximate optimization algorithm (CV-QAOA) for high-dimensional continuous optimization. It extends an earlier proposal with a variationally optimized initial state. The authors prove performance guarantees on several cost-function families, including convex quadratics and nonconvex rotated double-well functions. Numerical simulations on deflected corrugated spring and Easom functions illustrate its promising performance.
In briefLimiting quantum computers' cryptanalytic power while keeping them useful to public users
SummaryThe paper proposes a restricted model, 1/2BQP_1, where a quantum server gives random computational-basis inputs and reveals only one designated output bit after execution. The authors conjecture that a classical client making polynomially many adaptive requests cannot efficiently factor RSA moduli. They argue security by showing the quantum stages of standard factoring algorithms become classically simulable under this one-bit readout, and discuss rational reconstruction as a possible workaround.
Shiv Akshar Yadavalli, Joel Rajakumar, Alexander Schuckert et al.
In briefPolynomial-time simulation of non-Clifford quantum error correction circuits
SummaryThe paper shows that every intermediate state of a broad class of non-Clifford quantum error-correction circuits is a third-order phase-polynomial state, even under stochastic Pauli noise. It introduces a diagonal-Clifford-and-Pauli stabilizer formalism, proves these states are exactly its stabilizer states, and gives an exact polynomial-time simulation algorithm, implemented as the open-source tool merlin. Benchmarks report improved runtime and memory scaling in Bravyi-Haah distillation and simulation of a code switching circuit beyond the reach of other tested simulators.
WhyIntroduces third-order phase-polynomial states, proves equivalence to a new DCP stabilizer formalism, and gives polynomial-time simulation of non-Clifford QEC circuits.
In briefFinding Gaussian Structure in Bosonic States: Estimating the Closest Pure Gaussian State to an Arbitrary Quantum State
SummaryThis paper studies agnostic tomography of pure bosonic Gaussian states: given copies of an arbitrary n-mode bosonic state, it outputs a pure Gaussian state whose infidelity is within ε of the best achievable. The authors give efficient protocols for both high and low fidelity regimes, yielding the first truly tolerant Gaussianity testing protocol. They also prove that poly(n, 1/ε) runtime is impossible unless NP is contained in BQP.
WhyProves non-Gaussian measurements are necessary and gives strong agnostic tomography with a hardness result, a strong theoretical contribution with impact mainly within quantum information theory.
In briefQuantum 1-PCA using Pauli measurements in nearly linear time
SummaryThe paper studies quantum 1-PCA, which aims to recover a classical description of the leading eigenvector of an unknown n-qubit mixed state from copies of it. The algorithm uses only non-adaptive single-qubit Pauli measurements and recovers the eigenvector to fidelity at least 1 − ε under a spectral gap assumption, with explicit bounds on copies and runtime. When the gap is constant and ε is comparable to the noise level, the complexity is roughly 2^n/ε up to polylogarithmic factors, extending prior results that assumed pure states.
WhyExtends pure-state results to misspecified mixed states and introduces structured Pauli sampling for near-linear runtime, a clear but narrow theoretical advance.
In briefPolynomial-time classical algorithms for mean-field models up to the glass transition
SummaryThis paper studies the strongly interacting SYK fermionic model, which is highly quantum. The authors show that classical algorithms can estimate local observables at all constant temperatures in polynomial time, and extend the results to computing thermal expectations of classical spin glasses up to their phase transition. They develop a rigorous quantum cavity method and give a quantum algorithm that learns SYK Hamiltonians from Gibbs states at constant temperature with polynomial time and sample complexity.
WhyExtends polynomial-time classical thermal estimation to all constant temperatures via a rigorous quantum cavity method, resolving a spin glass open problem.
In briefTight limits on hybrid quantum-classical query algorithms
SummaryThis paper studies hybrid quantum-classical algorithms in the query model, where quantum subroutines each make at most q oracle queries and all qubits are measured between them. The authors prove matching upper and lower bounds for phase estimation, amplitude estimation, search among N items, and a two-level AND-OR tree. They also develop new methods for proving lower bounds on such hybrid algorithms.
WhyProves matching tight bounds for several hybrid query problems and introduces a general progress-measure framework for hybrid lower bounds, strong theory with broad subfield impact.
Andris Ambainis, Andr\'as Gily\'en, Martins Kokainis
In briefNonlocal behaviours that evade nonlocal games
SummaryThe paper examines whether nonlocal games fully capture Bell nonlocality. With the standard definition using a deterministic predicate, the authors prove that some nonlocal behaviours violate no such game. They further show that quantum mechanics can produce these game-classical nonlocal behaviours. The phenomenon holds in every bipartite scenario with X, Y ≥ 2 and A, B ≥ 4.
WhyProves deterministic-predicate nonlocal games are not complete witnesses of Bell nonlocality, holding for all bipartite scenarios with A,B≥4.
Ricardo Faleiro, Lucas E. A. Porto, Marco T\'ulio Quintino et al.
In briefFrom Quantum Tunneling to Classical Optimization via Instantons: How a classical algorithm can mimic quantum escape from local minima
SummaryThis paper uses an instanton analysis to show that Path Integral Stochastic Gradient Descent (PISGD), a classical optimizer derived from path integral Monte Carlo, can inherit the quantum tunneling mechanism. Its escape time scales exponentially with the bounce action rather than the barrier height, the same scaling as quantum tunneling, and this is confirmed numerically on separable and nonseparable potentials. However, PISGD only captures incoherent tunneling, so the authors do not rule out a quantum advantage for quantum-tunneling-based algorithms in general.
In briefTesting whether quantum states are Gaussian using a fixed number of copies
SummaryThis paper studies how to test whether a given quantum state is Gaussian, or has bounded overlap with any Gaussian state. Earlier tests needed a number of state copies that grew with the number of modes. The authors show that a constant number of copies is enough. They base this on symmetries of identical Gaussian state copies and on bounding the distance to Gaussian states using a gradient flow and a spectral bound previously studied for the Kac random walk on a sphere.
WhyReduces Gaussian state testing from system-size-dependent to constant copies using symmetry and gradient-flow arguments, a notable theoretical advance.
Jop Bri\"et, Davi Castro-Silva, Michael Walter et al.
In briefImaginary magnetic fields for ultracold atoms: a four-level scheme creating a uniform imaginary synthetic field
SummaryThe paper proposes a four-level scheme that uses Raman coupling and state-dependent particle losses to generate a uniform imaginary magnetic field for ultracold atoms. After eliminating two lossy auxiliary states and projecting onto one remaining Raman-dressed state, atomic motion is governed by an imaginary vector potential with constant curl. The authors analytically derive Gaussian wavepacket dynamics in this synthetic field and show numerical agreement between the two-level non-Hermitian Hamiltonian and the adiabatic projection description.
Saulius Alminas, Domantas Burba, Gediminas Juzeli\=unas
In briefError mitigation using syndrome data from one unmodified error-corrected circuit
SummaryThis paper introduces SOLEM, an offline logical error mitigation framework that uses syndrome data only in post-processing, without modifying the error-corrected circuit. It builds offline versions of probabilistic error cancellation and zero-noise extrapolation, plus a global-regression estimator. The authors report runtime overhead exponentially lower than external methods and comparable to syndrome-aware real-time approaches.
In briefShared geometric basis of non-local quantum resources in rotationally invariant scattering
SummaryThe paper studies entanglement and non-local magic generated between the spins of two outgoing particles in elastic scattering, encoded in the S-matrix. It gives a closed-form solution for the entanglement power for all spin values J. The authors prove that a broad class of non-local resources depend at leading order only on the squared projective Hilbert-Schmidt distance to the nearest non-entangling gate, with the resource choice only changing the normalization.
In briefCharacterizing quantum advantage in generalizations of the Boolean Hidden Matching problem
SummaryThis paper studies the one-way communication complexity of the f-Boolean Hidden Partition problem, where Alice holds an n-bit string and Bob must decide with one message from Alice whether f's values on his blocks agree with his labels. The authors give classical and quantum communication bounds in terms of the sign degree d of f, proving a conjecture of Doriguello and Montanaro. For every f with sign degree d ≥ 2, the randomized classical complexity is Θ(n^{1-1/d}), while the quantum complexity lies between Ω(n^{1-2/d}) and O(n^{1-1/⌈d/2⌉} log n). This identifies exactly the functions admitting polynomial quantum advantage.
Mark Bun, Joao F. Doriguello, John Kallaugher et al.
In briefComputational entanglement distillation from mixed states with limited resources
SummaryThis paper studies distilling entanglement from mixed quantum states under two resource limits: the number of input copies and computational efficiency. The authors show that the Rényi coherent information determines the optimal worst-case distillation rate. They present universal protocols that achieve this rate under polynomial rank constraints, and prove that no universal sample-efficient or efficient protocol can exceed it.
WhyIdentifies Rényi coherent information as the optimal distillation rate under limited resources, with matching universal and efficient protocol bounds; strong theory, narrower practical reach.
In briefQuantum-optimized phase closure: joint multi-photon measurements for robust interferometric imaging
SummaryClosure phase cancels telescope-dependent phase errors caused by atmospheric fluctuations in ground-based interferometric imaging. The paper shows that joint measurements on multiple photons can estimate closure phases more accurately with fewer photons than single-photon measurements. For large arrays, the required photon cost grows nearly linearly with array size, while sequential single-photon protocols need more photons. The authors also find a similar advantage for collective measurements in the high-precision regime, using multiparameter quantum metrology.
WhyProposes joint multiphoton measurements for closure phases, showing three-photon advantage and near-linear photon cost scaling versus quadratic for single-photon protocols.
Zhenning Liu, Emil T. Khabiboulline, Lorcan O. Conlon et al.
In briefPretty good shadow tomography: estimating many observables from fewer state copies
SummaryThis paper presents a shadow tomography algorithm that estimates the expectation values of m observables using O(log(m) log(m/δ)/ε²) copies of an unknown quantum state, with each estimate accurate to within ±ε except with probability at most δ. The approach first gives a constant-error guarantee in an average-case setting over a random prior state using a pretty good measurement, then boosts it and applies the minimax principle to obtain a worst-case existence result. The authors also show that this technique amplifies success over the prior's randomness but not over measurement randomness, which they argue leaves a remaining log(m) factor relative to the classical problem.
WhyImproves shadow tomography sample complexity via average-case and minimax arguments, with a clear analysis of an inherent barrier.
Sabee Grewal, Angelos Pelecanos, Jack Spilecki et al.
In briefInformed trading model using quantum walks
SummaryThis paper extends the classic Kyle model of informed trading by modeling the asset's future value as either a classical random walk or a continuous-time quantum walk. The authors analytically approximate and numerically identify the equilibrium between a risk-neutral market maker and an informed trader. In the classical case, the trader uses a linear strategy and the pricing rule resembles a logistic curve, with profit growing sub-linearly over time. In the quantum case, the trader's strategy forms multiple clusters and prices show multiple jumps, yet profit grows linearly with time.
In briefDesigning logical gates with irreducible-representation surface codes
SummaryThe paper introduces irrep surface codes (ISCs), two-dimensional topological quantum error-correcting codes designed to transversally implement a chosen set of logical gates. The target gates must generate a finite group and be irreducible. The authors also develop lattice-surgery protocols that transfer encoded information between standard surface codes and ISCs, allowing these gates to be integrated into conventional computations.
In briefFast convergence of propagation algorithms for open quantum systems: a method for efficiently computing local properties of noisy and thermal quantum many-body systems.
SummaryThe paper gives general conditions under which propagation algorithms converge rapidly when computing local observables in quantum many-body systems, including spin and fermionic systems. The results apply to sufficiently contractive evolutions, where contractivity controls growth from local interactions and enables efficient classical simulation. For noisy dynamics, the authors show efficient simulation when the noise strength is large relative to the interaction graph degree, and in the noiseless limit the efficiently simulable time scale extends to order 1/u. They also apply the framework to Gibbs states at sufficiently high temperature.
In briefFermions and the Tsirelson Problem in Real Quantum Theory
SummaryThis paper asks whether real quantum theory (RQT) stays experimentally indistinguishable from ordinary quantum theory when two extensions are added: commuting instead of tensor-product observables for separated measurements, and superselection rules as in fermionic information theory. The authors show that indistinguishability holds in both cases. They give a positive answer to the Tsirelson problem for RQT and build a real formulation of superselected theories, including a fermionic version whose predictions match fermionic information theory.
In briefComplexity gaps in optimal matchgate-Clifford circuit synthesis
SummaryThe paper studies optimal exact synthesis in the matchgate-Clifford group, the intersection of Clifford and matchgate circuits, finding that complexity depends strongly on the gate set. For path and complete connectivity graphs, it gives an O(n²) classical algorithm and gate-optimal compilers. For tree connectivity graphs, the decision version is shown to be NP-complete. On chains up to 80 qubits, the compiler reduces total gate counts by about 2.57× versus Qiskit and 2.28× versus Tket.
Berta Casas, Diego Garc\'ia-Mart\'in, Yuxuan Zhang
In briefExponential entropy decay for infinite-dimensional quantum Gibbs samplers
SummaryThe paper derives rates of exponential relative-entropy decay for a broad class of infinite-dimensional quantum Gibbs samplers. Its key tool is a perturbative stability theory for hypercontractive estimates and logarithmic Sobolev inequalities. It proves exponential entropy decay for multimode Bose-Hubbard samplers, harmonically confined quantum Coulomb gases, and molecular systems. It also presents a periodic charging model with a positive spectral gap but no finite-time L²-to-L^p bound for any p>2.
WhyGives entropy decay rates for infinite-dimensional quantum Gibbs samplers via a new perturbative stability theory; proofs are thorough, though applications are limited to specific models.
In briefA classical oracle separating QMA from QMA(2)
SummaryThis paper shows that QMA and QMA(2) are different relative to a classical oracle. The separation uses a separable Hamiltonian problem on a graph with signed edge constraints. YES instances have zero-energy product states, while NO instances have entangled zero-energy states but no low-energy product states. For the QMA lower bound, the authors use compressed-oracle techniques to track information gained from a few queries.
WhyGives a classical oracle separating QMA from QMA(2) via compressed-oracle techniques, a significant complexity-class separation result.
In briefNonadditivity in fermionic quantum information theory (shows that fermionic information measures do not add up across copies)
SummaryThe paper studies collective state preparation and channel encoding in fermionic systems under parity superselection and canonical anticommutation relations. For a two-mode Gaussian state, it gives the exact entanglement of formation for any number of copies, showing that two copies have the same value as one, which violates additivity. For an associated Gaussian channel, it determines the minimum output entropy and Holevo information and proves that both are nonadditive. The authors also derive exact capacities and a strong converse for these channels.
WhyGives exact answers to fermionic additivity questions with complete proofs of nonadditivity, a significant result for a specialized subfield.
Farzin Salek, Amir-Reza Negari, Graeme Smith et al.
In briefA game-based certification method for continuous families of quantum measurements
SummarySelf-testing certifies quantum states and measurements using only observed correlations, without a description of the devices. This paper shows that the Grothendieck game, a two-player nonlocal game where players receive directions on a sphere and return binary answers, self-tests Majorana observables. Near-optimal play therefore certifies an entire continuously parameterized family of measurements. The certification is extended to products of Majorana observables, giving a robust self-test of the spin representation of the continuous pin group.
Alexander Kulpe, Giulio Malavolta, Simon Schmidt et al.
In briefFinite-bath projected ensembles in dual-unitary circuits: how small baths give near-random quantum states
SummaryThis paper studies emergent randomness in projected ensembles produced by dual-unitary circuits, where measuring part of the system leaves an ensemble of states on the rest. It proves, under three inverse-polynomial assumptions, that a bath of polynomial size suffices to form approximate k-designs. The authors also give a transport-based picture of this randomness and link it to quantum walks.
