In briefDephasing-Induced Melting of Crystalline Spectral Form Factors: how energy dephasing in open quantum systems weakens long-range spectral order and how that order can be controlled
SummaryThe paper studies how energy dephasing in open quantum systems affects long-range spectral order. In spectral form factors, nearly crystalline spectra show sharp Bragg peaks at integer multiples of the Heisenberg time. The authors find that these peaks decay algebraically with revival order and dephasing strength over an extensive intermediate regime. Despite an extreme decoherence rate, the peaks persist up to the lifetime of nearest-neighbor coherences.
In briefA chiral waveguide model for error-correctable quantum computation
SummaryThe paper builds a first-principles framework linking microscopic waveguide scattering to quantum error correction and algorithm performance. For polarization-encoded photons interacting with two-level atoms in a chiral waveguide, it derives an effective polarization quantum channel by tracing out frequency and uses it as the noise model for a rotated planar code, observing threshold behavior. The effective noise is strongly biased toward X errors, and incorporating the resulting logical errors into quantum phase estimation shows that a Hadamard-basis implementation improves algorithmic performance.
In briefSimulability frontiers of photonic quantum computing: the device size at which exact classical sampling becomes too slow
SummaryThe paper proposes the time a classical computer needs to draw one exact sample from a photonic device's output distribution as a common unit for comparing when such devices outgrow classical simulation. It defines the simulability frontier as the device size at which the fastest exact sampler yields one sample per second on a fixed machine. Using photonic-engines, an open-source GPU library, the authors measure frontiers on one NVIDIA H100 GPU: 38.3 single photons, 31.0 entangled photons from one emitter, and 41.5 squeezed photonic inputs.
WhyThe authors propose exact per-sample sampling time as a common unit and report frontier values for several light sources.
Jean Senellart, Benjamin Stott, Stephen Wein et al.
In briefClosed-form hidden symmetry operators for the asymmetric quantum Rabi model and its two-photon and two-mode variants
SummaryThe paper studies the asymmetric quantum Rabi model, a two-level system coupled to a boson mode, which shows level crossings when the bias is an integer multiple N of the mode frequency. These crossings are due to a hidden symmetry operator J, and the authors derive its closed form for every N. The operator is expressed as the parity of the symmetric model multiplied by a continuant built from N first-order operators. The same structure extends to the asymmetric two-photon and two-mode models, and the authors relate the formula to known recursion relations for J's coefficients.
In briefBoosting valley splitting in Si/SiGe Wiggle Well quantum dots with integrated stressor-gate designs
SummaryThis paper proposes patterned stressed thin films to generate shear strain in the quantum well of Si/SiGe quantum dot devices, aiming for controllable valley splitting. Finite-element simulations indicate that compressively stressed TiN films can produce shear strains above 0.1% at the quantum well, enough for valley splittings of hundreds of µeV in strain-assisted Wiggle Wells. The strain extends across multiple quantum dots and persists in realistic gate geometries, offering a fabrication-compatible route to scaling deterministic valley splitting to quantum dot arrays.
In briefGARI++: A General-Purpose Decoder for Quantum Error Correction
SummaryThe paper presents GARI++, a two-stage decoding pipeline for quantum error correction. It reaches accuracy competitive with state-of-the-art methods on surface, bivariate bicycle and color codes without using ensembles. The second stage runs only when the first stage fails to converge, and it can be configured for the chosen code.
Arshpreet Singh Maan, Francisco Garcia-Herrero, Daniel Bascones et al.
In briefA short proof of a conjecture on quantum query complexity and deterministic algorithms
SummaryThis paper gives a short proof of the Aaronson-Ambainis conjecture, which relates the quantum query complexity of partial Boolean functions to the number of queries deterministic algorithms need. The proof uses the completion framework and yields a more general bound based on the classical adversary measure. The authors also derive a stronger variant, the bounded-polynomial influence conjecture, in an appendix.
WhyThe authors give a short proof of the Aaronson-Ambainis conjecture via completion, bounding in terms of classical adversary measure and deriving the bounded-polynomial influence conjecture.
Thomas Huffstutler, David Miloschewsky, Supartha Podder
In briefSimulating quantum channels on digital quantum computers
SummaryThis paper reviews the theory of quantum channels and proposes a method to simulate them on digital quantum computers, using the Choi-Kraus operator-sum representation and Stinespring dilation. It covers three applications: preparing mixed states, implementing POVM measurements, and simulating Markovian quantum dynamics. For the latter, the authors introduce a residual operator that builds a first-order quantum channel from the Liouvillian, allowing an Euler-like simulation without Trotterization. The simulations were run with IBM Qiskit's AerSimulator, and the code is available on GitHub.
In briefUniversal semiclassical drift velocity of magnetic edge channels
SummaryMagnetic edge channels form at the edge of a two-dimensional electron gas in a magnetic field and travel unidirectionally along it, protected by topology. Using semiclassical quantization of electron skipping orbits, the paper shows that when many edge channels cross the Fermi level, their drift velocity equals half the electron Fermi velocity. This result holds for hard edges with isotropic dispersion and was checked numerically for massive electrons and massless electrons in graphene. Smooth electrostatically defined edges do not show this universality.
In briefSelf-energy construction for chain representations of open quantum systems
SummaryThe paper treats the self-energy as the environment's response to the system and examines how it transforms under shifts of the system–environment cut. For a semi-infinite chain with asymptotically uniform parameters, this transformation has a fixed point that defines the asymptotic boundary self-energy, whose spectral density is the Wigner semicircle. A pseudo-hyperbolic self-energy distance, invariant under cut shifts, is introduced and used to measure the error of finite damped-oscillator closures independently of the cut, offering a more accurate fitting scheme than time-domain correlation fitting.
In briefA unified neutral-atom architecture that can build any two-qubit gate
SummaryThis paper proposes a unified architecture for two-qubit gates on neutral-atom quantum processors, covering the complete gate set. It relies on a single resource, an XXZ interaction with tunable anisotropy, combined only with single-qubit operations. The authors realize this tunable XXZ interaction using Rydberg atoms and pair it with optimally controlled global microwave pulses to implement the B, QFT, iSWAP, and √iSWAP gates, along with a continuous gate family interpolating from CZ to iSWAP via the B gate.
In briefAn efficient classical algorithm for estimating OTOCs in chaotic quantum circuits
SummaryThe paper presents a polynomial-time classical algorithm for estimating four-point and eight-point out-of-time-ordered correlators in typical one-dimensional random quantum circuits. It exploits dephasing caused by quantum chaos to suppress subleading terms in a rapidly converging series. At larger circuit depths, the authors report higher signal-to-noise ratio than recent 2D experiments by Google.
WhyThe authors propose a polynomial-time classical algorithm for OTOCs in 1D random circuits, exploiting chaos-induced dephasing; numerical results are compared with Google's 2D experiments.
In briefSuccinct Lyapunov and LQR Value Problems Shown BQP-Complete
SummaryThe paper studies two basic computational problems in linear systems: evaluating infinite-horizon output energy for autonomous systems, characterized by Lyapunov equations, and computing optimal value functions for controlled systems, characterized by algebraic Riccati equations. System matrices are sparse and encoded succinctly by Boolean circuits, with input length polynomial in the logarithm of the system dimension. The authors prove the succinct Lyapunov value problem (SLV) is BQP-hard and give a quantum algorithm for the more general succinct LQR value problem (SLQRV), so both are BQP-complete.
WhyThe authors report that succinct infinite-horizon Lyapunov and LQR value problems are BQP-complete, with a quantum algorithm and a hardness reduction.
In briefComparing Sequential and Parallel Ways to Share Quantum Advantage in Communication Tasks
SummaryThis paper studies two experimentally feasible ways of sharing a quantum system among several observers, parallel and sequential sharing, to extract encoded information. With two observers, any statistics from parallel sharing can be reproduced sequentially, but with more observers some parallel statistics cannot be. The authors show that quantum advantage cannot be shared in parallel for a class of tasks with two decoding measurements, and discuss 3-bit random access codes, where parallel sharing becomes possible in the parity-oblivious variant.
WhyThe authors show parallel and sequential sharing are equivalent for two observers but differ for more, with arbitrarily large gaps.
SummaryThe paper builds a recursive oracle O and a unary language L that lies in EQP^O but outside both IP^O and PH^O. This strengthens the BQP versus IP oracle separation of Bouland et al. to exact quantum computation. The separation uses a variant of Forrelation in which the normalized correlation is promised to be exactly +1/2 or -1/2. A uniform polynomial-time quantum algorithm distinguishes the two cases with certainty using only three oracle queries.
WhyThe authors extend the BQP versus IP oracle separation to exact quantum computation, using an Forrelation variant with exact correlations and a repair method; a three-query algorithm is reported.
In briefQuantum robustness of expectations under sandwiched Rényi divergence limits
SummaryThe paper asks how much the expectation of an observable can change when a quantum state is known only approximately. It takes the worst-case expectation over all states within a sandwiched Rényi divergence budget of a reference state, for every order in [1/2, ∞]. Convex duality reduces this to a one-dimensional optimization, and a classicalization theorem shows the quantum problem matches a classical one under a suitable probability measure. Classical Hoeffding, Bernstein and Markov–Krein bounds therefore carry over.
WhyThe authors reduce worst-case quantum expectations under sandwiched Rényi divergence to a classical problem, transferring classical concentration bounds and showing variance deflation from noncommutat
In briefSpin transport through chiral molecular bridges between quantum dots, with gate and holonomy analysis
SummaryThis paper examines whether chiral molecular bridges between silicon quantum dots can serve as two-qubit entangling resources via the chirality-induced spin-selectivity effect. Using Makhlin invariants and a gauge argument, the authors show that a single chiral bond is locally equivalent to isotropic exchange and so is not a new entangling class. Breaking this gauge symmetry reveals chiral utility, including synthetic gradients and non-Abelian holonomy-based geometric gates.
Amitoj S. Miglani (1), Rajdeep R. Dwivedi (2), Balsant S. Tiwari (3) et al.
In briefNo Exponential Quantum Advantage for Local-Decoder DQI
SummaryThis paper studies decoded quantum interferometry (DQI) on random D-regular k-sparse instances, which reduces optimization and Gibbs-measure sampling to decoding a linear code from a quantum state. Using statistical-physics phase transitions, the authors show that local decoders cannot recover the codeword with high probability above the tree reconstruction threshold, while belief propagation with quantum messages reaches that threshold. They also show the optimal decoder succeeds exactly below the condensation threshold, suggesting local-decoder DQI gives no exponential speedup for these tasks.
WhyThe authors link DQI decoding thresholds to tree reconstruction and condensation transitions, proving a local-decoder information obstruction and a tight bound for the optimal decoder.
Brandon Augustino, Shouvanik Chakrabarti, Enrico Fontana et al.
In briefQuantum algorithms that use polynomial space, built from classical branching methods
SummaryThe paper gives quantum algorithms for exponential-time problems on n vertices or elements, with bounded error and polynomial space, without quantum random access memory. It covers 4-colouring, k-colouring, dominating set variants, and a quantum form of monotone local search. It also gives approximation algorithms and states the time bounds for each problem.
In briefSingle-particle resonances and eigenstate thermalization in periodic free-fermion lattices
SummaryThis paper studies particle-number fluctuations in energy eigenstates of the nearest-neighbour free-fermion model on a periodic cubic lattice. It proves that the particle-number variance is bounded by order NL^{d-1} for every eigenstate, and gives a corresponding eigenstate-thermalization estimate. At positive density the bound decays as the inverse linear size. The bounds are shown to be optimal in every dimension.
Tristan Benoist, Vojkan Jak\v{s}i\'c, Claude-Alain Pillet et al.
In briefQuantum-assisted selection of determinants for better ground-state energies
SummaryThe paper proposes a modular hybrid quantum-classical method that improves selected configuration interaction at a fixed final determinant budget. Quantum measurements supply complementary determinants, which are accepted only if they outrank classical candidates under a common energy criterion. The approach targets multistep excitations that perturbative methods may miss in strongly correlated systems. On the Quantinuum Reimei trapped-ion computer, measured proposals for H12 at a stretched geometry lowered the variational energy compared with classical-only selection.
Kentaro Yamamoto, Ikko Hamamura, Juan W. Pedersen et al.
In briefHigher tensor network states in 2D: a fundamental theorem for open boundaries
SummaryThe paper builds two-dimensional tensor network states by categorifying matrix product states, with bond spaces given by 2-vector spaces tied to the 2-cells of the lattice. Tensor network representations are defined as module categories over a free monoidal category encoding the lattice geometry. The authors prove that two representations generating the same states under suitable open boundary conditions are equivalent as module categories. They also introduce 2-injectivity, a categorified analogue of injectivity for matrix product states.
In briefNeutronic Field-Effect Transistor: a device controlling neutron-wave output via interference and spin
SummaryThis paper demonstrates a neutronic field-effect transistor (NFET), analogous to the Datta-Das electron spin transistor and atomtronic devices. The device is based on a perfect-crystal Mach-Zehnder neutron interferometer. Phase shifts are applied to both the spin and path degrees of freedom to control its operation.
Dusan Sarenac, Charles W. Clark, Owen Lailey et al.
In briefApparent time advance of quantum clocks via postselection
SummaryThis paper examines how quantum postselection can make a quantum clock appear to run ahead, reversing the usual relativistic time-dilation result. Using an analytically solvable quantum clock model, the authors postselect the center-of-mass motion and obtain an effective time advance through anomalous weak values. The analysis is extended to a weak gravitational field and illustrated with a hydrogen-like atom.
In briefReducing the number of provers in distributed quantum verification
SummaryThis paper studies the distributed quantum Merlin-Arthur (dQMA) model, in which a network of quantum nodes verifies a global property using a quantum proof from an untrusted prover. It extends the setting where proofs are unentangled across nodes to k unentangled provers, denoted dQMAS(k). The authors examine how per-node proof size and communication cost change when the number of provers is reduced.
Alex Della Schiava, Atsuya Hasegawa, Fran\c{c}ois Le Gall et al.
In briefTransferring usable energy over long distances using spin chains with weaker end couplings
SummaryThis paper studies how the extractable energy (ergotropy) of a quantum battery can be moved across a distance. The authors use spin chains whose couplings are weakened at the two boundaries, which create localized edge states that enable high-fidelity transfer within a given time. Both nearest-neighbor and long-range interaction models are examined, and weakening boundary couplings is reported to increase the maximum transferred ergotropy for long chains.
In briefAll-to-all qubit coupling in a superconducting flux processor using adiabatic ZZ interactions
SummaryThis paper proposes a baseband-driven adiabatic ZZ gate that entangles any selected pair of flux qubits coupled through a common cavity, without requiring tunable couplers. The qubits stay biased at their flux sweet spot, while strong low-frequency drives applied through local flux lines tilt the quantization axes and generate a tunable longitudinal ZZ interaction. Numerical simulations report coherent gate errors below 10^-4 and robustness against frequency fluctuations.
In briefFinite projective classification of complex spinors using momentum maps
SummaryThe paper classifies projective orbits of complex spinors through the momentum map, covering irreducible spin modules in odd dimensions 1 to 11 and half-spin modules in even dimensions 2 to 14, the only cases with finitely many orbits. Representatives are built in the Clifford–Fock model as critical points of the squared momentum norm, and their momentum values distinguish the orbits. Completeness follows from Vinberg's theory of graded Lie algebras, yielding 1, 1, 1, 2, 3, 5 orbits in odd cases and 1, 1, 1, 2, 2, 4, 9 in even cases. In dimension fourteen, the closure order of the orbits is also determined.
In briefTopological states in fractals via a self-similar tensor network encoding
SummaryThis paper presents a tensor network method that exactly and compactly encodes Hamiltonians on self-similar fractal lattices, such as the Sierpiński gasket. The authors use this encoding to study a Chern insulator, the flux kagome model, confined to the fractal geometry and examine its topological states. The approach reaches much higher fractal generations than dense-matrix methods, resolving the density of states of a deep fractal with over 100 million sites.
Zebedeus F. Osseweijer, Jagoda Malag, Jose L. Lado et al.
In briefA paper on constructing quantum channels that preserve kappa-additivity and make outputs singular
SummaryThe authors build quantum channels by averaging unitary shift conjugations using kappa-additive probability measures on measurable abelian groups. The channels act on the duals of operator algebras generated by shifts and bounded measurable multiplication operators. They preserve kappa-additivity of quantum states and have a weak-* integral representation on this class. If the averaging measure vanishes on singletons, every output state is singular. An appendix proves the corresponding Fubini theorem for kappa-additive measures.
