In briefQuantized scar multiplets and dissipative cat states in an open quantum baker map
SummaryThe paper studies an open quantum baker map with a position window of width w centered at q_c. Classical pruning divides the (q_c, w) plane into diamond-shaped regions where the leading resonances form root-of-unity multiplets. At w = 1/2, one periodic orbit survives for almost every q_c, and the multiplets have modulus 2^{-1/2} with phase equal to the orbit action.
In briefElectrostatic Bounds on Quantum Walk Search
SummaryThe paper proves that a quantum walker cannot search a two-dimensional lattice in Grover's O(√N) time, settling a question raised by Aaronson and Ambainis in 2003. Modelling the marked vertex as a point charge, the authors derive a lower bound of Ω(√(N log N)) local steps, even with unlimited memory and free queries. This shows that Tulsi's algorithm is asymptotically optimal.
WhyUses an electrostatic analogy to prove a tight lower bound for 2D quantum search, resolving a long-open question; full verification remains pending.
In briefHow cell temperature affects a warm atomic vapor quantum memory's entanglement distribution rates
SummaryLong-distance quantum communication requires quantum repeater nodes with robust, scalable quantum memories. This paper studies a warm atomic vapor memory operating under electromagnetically induced transparency (EIT), measuring and simulating its optical depth-based performance. The authors convert the optical depth and efficiency results into expected entanglement distribution rates. They assess whether such memories are feasible for optical quantum repeater nodes.
Kenny Gregory, Khaled Mnaymneh, Connor Kupchak et al.
In briefFast Plasma Parameter Inference for Fusion Control Using Quantum Ising Machines
SummaryThis paper proposes a Bayesian inversion framework that uses a Coherent Ising Machine, a quantum computing architecture based on coupled optical oscillators, to estimate plasma parameters in tokamaks. The method maps the negative log-posterior onto a spin Hamiltonian and was validated on plasma current profile inversion for the EAST tokamak, with a single-run solution time of about 1 ms. Because current qubit counts are limited, the authors use a block-wise iterative scheme, so full real-time execution is not yet achieved.
In briefFibre-integrated heralded single-photon source using Zn-indiffused PPLN waveguides at telecom wavelengths
SummaryThis paper reports a fully fibre-integrated source of broadband polarisation-entangled photon pairs for telecom wavelengths. It uses a commercial Zn-indiffused MgO:PPLN ridge waveguide inside a Sagnac interferometer and covers the full degenerate SPDC spectrum, with a measured bandwidth of about 67 nm. Strong non-classical correlations are reported, including a two-photon interference visibility of 96.9 ± 0.2%, a Φ+ Bell state fidelity of 78.1%, and a CHSH parameter of S = 2.501 ± 0.005. The authors also examine how higher source brightness affects Bell-state performance, noting limits of accidental-corrected metrics at high flux.
Peter Iveson, Paolo L. Mennea, Goronwy Tawy et al.
In briefCayley access models for computing matrix functions on quantum computers, and their reachable class and cost
SummaryThe paper studies computing f(A)b on a quantum computer for Hermitian A, proposing a Cayley transform with parameters σ and γ as an alternative to the standard quantum access model. It lets accuracy be concentrated where f is difficult, reducing the required polynomial degree by about three to four times when difficulty is localized in the spectrum. Realizing the encoding from a block encoding requires solving a shifted linear system, which offsets part of the query advantage, though low-depth circuits can be built directly for structured matrices.
In briefConQUESTA: Topology-aware pruning of quantum neural networks after training
SummaryThis paper presents ConQUESTA, a post-training pruning framework for quantum neural networks that aims to keep task accuracy while reducing two-qubit gates, SWAPs, and depth on sparse hardware. It combines task saliency with compiler cost, screens candidate entanglers, and searches complete pruning masks under an explicit accuracy constraint, transpiling each mask across multiple coupling topologies. At 55% pruning, the authors report mean resource reductions of 61.6% on Breast Cancer, 72.0% on Digits01, and 82.2% on Iris.
In briefQuantum circuits for variable-coefficient Vlasov dynamics via Schrödingerisation
SummaryThis paper develops explicit quantum circuits for simulating Vlasov dynamics driven by a prescribed external field, without classical field updates. In a 1D1V setting, velocity-dependent streaming is compiled from the encoded velocity register, and a nonlinear cubic field is evaluated with reversible fixed-point arithmetic. As a proof of concept, the authors simulate a coupled 3D3V anharmonic Penning system on a six-dimensional phase space, reporting agreement with classical calculations and analysing resource costs.
Fong Yew Leong, Dax Enshan Koh, Wei-Bin Ewe et al.
In briefQuantum sensitivity of multi-component cat states, explained
SummaryThis paper extends earlier work on squeezed two-component Schrödinger cat states to a single-mode family with any number N of coherent components and general relative phases. It derives a closed overlap kernel for displacement, phase rotation, and squeezing, and compares equal-phase states for N=2 to 9 using quantum Fisher information at a common mean photon number. The authors note that a lower ideal local Cramér–Rao bound does not imply unlimited attainable precision, since prior phase information, sample size, loss, and measurement choice still matter.
In briefResonance crossings and diabolical points for DC electric field quantum sensors
SummaryThis paper studies quantum resonances in double-well heterostructures under a DC electric field. Experiments since the 1990s have shown that specific field strengths produce pronounced wave packet oscillations. The authors perform a quantitative analysis of resonances near a crossing point. This lays the theoretical groundwork for a quantum sensor that can quickly check whether a DC field lies within a narrow target range.
In briefDesigning Robust Quantum Gates: Existence Criteria and Numerical Constructions
SummaryThe paper studies whether quantum gates can be made resilient to errors, not just realized. It establishes existence criteria for robust gates in d-level systems, showing a universal family of robust gates exists if and only if the driven Hamiltonians share no common symmetry. When the criteria hold, explicit protocols are numerically constructed that reduce average gate infidelity by roughly two to seven orders of magnitude under Hamiltonian perturbations and environment-induced noise.
WhyEstablishes existence criteria for robust quantum gates and numerically constructs protocols cutting infidelity by two to seven orders of magnitude, a significant advance with broad platform impact.
In briefPaper showing Bell scenarios encode classical non-causality
SummaryThe paper unifies Bell and contextuality scenarios in a hypergraph framework and shows that measurements of composite Bell scenarios correspond exactly to process functions, which are deterministic classical communication protocols that may be non-causal. The authors characterize these process functions using only normalization and no-signaling, and give a graphical criterion identifying when a process function is non-causal.
Andreas Leitherer, Kyrylo Simonov, Ravi Kunjwal et al.
In briefTemperature-dependent Casimir force between layered plates via the argument principle
SummaryThe paper uses the complex-analysis argument principle to derive a temperature-dependent formula for the Casimir-Lifshitz dispersion force between two arbitrary plane-layered structures. The separation is either a vacuum gap of size d or a layer of size d made of an arbitrary dispersive, dissipative dielectric. The formula is the temperature-dependent Lifshitz formula plus a temperature-dependent contour integral.
In briefSpinControl: Control Software for Testing Spin-Qubit Devices and Measurement Methods
SummaryThis paper presents the software design of SpinControl, control software for spin-qubit quantum computers. It aims for customizability, modularity and extensibility, and robustness, achieved through separating data from behaviour, splitting functions into components, and using CI pipelines with input validation. The software supports different measurement types and lets users build standardized experiments and run calibrations in custom, conditional order. It makes heavy use of open-source packages developed by Delft University of Technology.
Harold B. Meerwaldt, Dani\"el P. van der Velde, Pieter T. Eendebak et al.
In briefLearned angles for quantum approximate optimization
SummaryThe paper addresses the Quantum Approximate Optimization Algorithm (QAOA), whose performance depends on variational angles that normally require costly per-instance optimization. The authors train models that map a problem instance directly to high-quality QAOA angles in a single forward pass. They report speedups of several orders of magnitude with near-identical quality, generalization to unseen graph topologies, and hardware experiments showing indistinguishable results from solver-derived angles.
WhyReplaces per-instance QAOA angle optimization with a learned model, validated on quantum hardware, offering a useful practical advance for the subfield.
Johannes Jakubik, Isabelle Wittmann, Zaheed Gaffoor et al.
In briefUnconditional quantum learning advantage for Boolean functions with large errors
SummaryThis paper proves an unconditional super-polynomial separation between quantum and classical PAC learning of Boolean functions under the uniform distribution in the large error regime. A polynomial-time quantum learner reaches agreement 1/2+λ(n), while no polynomial-time classical learner, even with membership queries, achieves the same. The authors develop a near-optimal quantum learner that generalizes Fourier sampling from parity to quadratic hypotheses and uses interference to favor positively correlated hypotheses. They note that a similar separation in the small error regime would imply NP is not contained in BPP.
WhyProves an unconditional super-polynomial quantum-classical PAC separation via a new quantum learner generalizing Fourier sampling, with rigorous analysis; notable for learning theory.
In briefExact Pauli-algebra construction for a singlet state from oscillator vacuum
SummaryThe paper builds a pair of anticommuting Weyl displacement operators for a harmonic oscillator and uses bounded functional calculus to obtain exact dichotomic Pauli-algebra representatives. Two independent oscillators give commuting Pauli algebras for Alice and Bob, and the singlet-sector projector is applied to the two-oscillator vacuum. The projected vacuum is shown to have nonzero norm, exact singlet correlations, and reach the Tsirelson value 2√2 for the usual Bell-CHSH settings. The authors note that the construction generally realizes a singlet sector with multiplicity rather than a unique vector, and compare it with the earlier pseudospin approach to continuous-variable Bell tests.
In briefExperimental exponential-SWAP gate between trapped-ion motional modes
SummaryThis paper experimentally implements an exponential-SWAP (eSWAP) gate between two bosonic motional modes of trapped ions. The gate creates a coherent superposition of identity and SWAP operations with continuously tunable amplitudes. It uses spin-independent and spin-dependent beam splitter interactions. Measurements of selected slices of the joint characteristic function for different input states test the gate and show continuous control over the identity-SWAP superposition.
In briefControlled PROPs: Diagrammatic Reasoning Theory for Quantum Circuits
SummaryThe paper introduces a general diagrammatic framework that treats control as a constructor, extending standard PROPs to controlled PROPs to axiomatize control functors. The authors show that this framework gives a simple and complete axiomatization for quantum circuits. The axioms involve at most three qubits, whereas standard PROPs need axioms involving arbitrarily many qubits for completeness.
WhyIntroduces controlled PROPs and proves a complete axiomatization for quantum circuits using at most three qubits, improving on standard PROPs.
In briefQuantum solver for linear systems using sampled Krylov states with provable sampling bounds
SummaryThe paper proposes a sample-based quantum linear solver that measures Krylov states generated by the matrix A and classically diagonalizes a projected cost Hamiltonian to approximate the solution of Ax=b. It derives lower bounds on sampling probabilities and gives support-discovery guarantees for nonnegative-time and signed-time sampling. The authors also analyze how finite-length qDRIFT compilation and circuit reuse affect sampling and bound the infidelity of the reconstructed solution.
WhyReplaces cost-Hamiltonian simulation with Krylov-state sampling and derives shot complexity nearly matching a worst-case lower bound.
In briefLiouvillian non-invertible symmetry: a paper extending non-invertible dualities to open quantum systems
SummaryThe paper proposes a Liouville-space duality framework that extends Hilbert-space non-invertible dualities to open quantum systems. It applies the framework to a periodic transverse-field Ising chain with two collective Lindblad channels exchanged by Kramers-Wannier duality. The authors study the spectral structure at self-duality, including a momentum-resolved selection rule on Liouvillian Jordan blocks.
In briefMultiscale Quantum-Classical Simulation of Protein Autoproteolysis in a Million-Atom Membrane
SummaryThis paper presents a hybrid workflow combining molecular dynamics, density functional theory, and correlated wavefunction methods, integrating CPUs, GPUs, and quantum processors. It studies autoproteolysis, a maturation reaction in the adhesion GPCR ADGRG1, which had not previously been examined with correlated electronic-structure methods. The simulation covers a system of over one million atoms, using a 54-qubit IQM quantum processor and up to 1,200 NVIDIA H100 GPUs. The results illustrate how quantum computers can act as accelerators within scalable scientific workflows.
In briefFrom quantum emitters to technological platforms: a perspective on semiconductor quantum dots
SummaryPhotonic quantum technologies rely on controlled photon states, and quantum dots have emerged as excellent sources of single and entangled photons. This Perspective briefly reviews how quantum dots developed as photon sources, from early-2000s quantum emitters to today's advanced photonic devices. It highlights the interplay between fundamental research and industry and discusses photonic quantum technologies expected to emerge in the near future.
Klaus D. J\"ons, Dorian A. Gangloff, Doris E. Reiter
In briefNonergodicity from Hilbert-subspace cloning: a partial breakdown of ergodicity in quantum many-body systems.
SummaryThe paper studies a class of nonintegrable quantum many-body systems built from single Pauli strings. These systems have many noncommuting local conserved quantities and partially break ergodicity because of exponentially degenerate energy spectra. The authors propose a mechanism called Hilbert-subspace cloning, where the same chaotic Hamiltonian acts on exponentially many disconnected Hilbert subspaces. Dynamics within each clone thermalizes, but quantum coherence between clones persists and can be detected by local observables. As a result, long-time local observables are described by a coherence-preserving partial Gibbs ensemble.
In briefNon-equilibrium dynamical quantum phase transitions in the extended Agassi model
SummaryThis paper studies dynamical quantum phase transitions in the extended Agassi model after sudden quenches of three pairing-type interaction strengths. Using exact diagonalization, the authors analyze the Loschmidt echo and return-rate function, finding cusp-like non-analyticities that appear as system size grows. The authors report that distinct scaling behaviours across parameter channels show dynamical criticality is not determined solely by the equilibrium order of the transition.
Ritesh Kumar Palai, Rajiv Kumar, Venktesh Singh et al.
In briefCoupled time crystals in open Dicke systems can form simple logic gates
SummaryThe paper studies two coupled discrete time crystals in a dissipative Dicke dimer. Simulations show that coupling reduces oscillation amplitude, and strong coupling drives the system to a normal phase, with relaxation time diverging near a critical coupling, suggesting a continuous transition. The authors also examine quantum fluctuations and noise, and propose a scheme using three coupled time crystals to perform NAND and NOR operations.
Emmanuel D.G. U, Roy D. Jara Jr., and Jayson G. Cosme
In briefQuantum Tsallis Entropy Estimation: Near-Optimal Bounds and Better High-Precision Algorithms
SummaryThis paper presents quantum algorithms for estimating the q-Tsallis entropy (0<q<1) of a probability distribution, given purified quantum query access to it. For 0<q≤1/2, the algorithm's query complexity is Õ((n/ε)^{1/(2q)}), which is optimal up to polylogarithmic factors. For 1/2<q<1, a two-stage simultaneous probability estimation procedure is introduced, improving on prior work by Chen et al. (ICALP 2026) when ε=O(n^{1-2q}).
In briefError-correcting encodings and node design for distributed fault-tolerant fanout
SummaryThis paper studies how the choice of quantum error-correcting code used to encode logical qubits affects a distributed transversal fanout operation and the design of quantum network nodes. The authors compare encodings by physical qubit count, logical qubit count, code distance, and available fault-tolerant operations. Their experiments suggest that higher-distance encodings, though needing more ebits, can lower the logical error rate of distributed operations. They also find that upgrading an encoding before distributed operations and including a qubit cache in the node architecture can be useful.
In briefQuantum-assisted unambiguous discrimination of pure states, with robustness bounds
SummaryThis paper proposes a hybrid quantum-classical method for unambiguously distinguishing pure quantum states, combining a noisy intermediate-scale quantum semidefinite program solver with a reciprocal-state representation. Using the discriminated states as the ansatz reduces the optimization to N scalar variables, which lowers the number of variables and positive-semidefinite constraints. The authors derive robustness bounds against Gram matrix estimation errors and test the approach through simulations and experiments on IBM quantum hardware.
In briefQuantum approximate stochastic combinatorial optimisation: a variational quantum-walk method for two-stage decision problems under uncertainty
SummaryThe paper studies two-stage stochastic combinatorial optimisation, where discrete decisions are made before uncertainty is resolved and can then be adapted at a cost. It introduces QASCO, a variational quantum-walk ansatz that builds scenario-dependent recourse into its dynamics to search first-stage decisions without explicitly computing expected minimum recourse costs. The method is demonstrated on MaxCut with stochastic edge weights using exact state-vector simulation.
Edric Matwiejew, Paulo E. Santos, Jingbo B. Wang et al.
In briefImaging spin-wave direction by chirality using a quantum spin sensor
SummarySpin waves encode their travel direction in the handedness of their circularly polarized stray field, which ordinary scalar magnetometers cannot detect. The authors use a nitrogen-vacancy centre in diamond as a polarization analyser, using its two excited-state transitions to image Damon-Eshbach waves travelling in both directions in a yttrium iron garnet film. Reflection from an etched boundary reverses handedness, so incident and reflected waves are imaged separately in one spectrum. Reading both channels gives the spin-wave direction at a single point without a phase reference.
In briefLinking the POVM framework to the no-signaling hypothesis
SummaryMany quantum foundations arguments use the Born rule or the POVM framework to show that non-relativistic quantum mechanics cannot send superluminal signals. This paper formalizes the stronger no-signaling hypothesis, which forbids signaling at any speed between isolated systems, and asks what extra assumptions make it imply that all outcome probabilities are POVMs. It finds that, given the standard representation and two textbook claims about marginal probabilities, the hypothesis is equivalent to the universality of the POVM framework. The paper also shows that most of the probability-generating part of non-relativistic quantum mechanics can be derived from it.
In briefA full workflow from fabricating to testing silicon nitride quantum devices
SummaryThis paper presents an end-to-end process for silicon nitride quantum devices, covering in-house stoichiometric fabrication and characterization of optical losses and material properties. The authors use the measured refractive indices to simulate microring resonators. They demonstrate the application of these devices in generating optical solitons.
Connor Kupchak, Abubaker Tareki, Tara Moradi et al.
In briefQuantum Entanglement in Schwarzschild-de Sitter Spacetime: Multipartite Entanglement and Nonlocality Under Horizon Effects
SummaryThe paper studies genuine multipartite entanglement and genuine tripartite nonlocality in a noisy generalized GHZ state within Schwarzschild-de Sitter spacetime. It uses the genuine multipartite concurrence and an optimized Svetlichny parameter to measure these correlations. The authors report that the black hole and cosmological horizons distribute entanglement differently between accessible and inaccessible states, while Svetlichny violation appears only in the accessible state. Initial white noise suppresses both correlations, with nonlocality surviving over a narrower parameter range.
In briefThe Classical Limit of Quantum Computation: History-Resolved Causal Stochastic Machines and Classicalization Cost
SummaryThe paper asks what distinguishes quantum from classical computation when a classical model may keep every branch history and arbitrary causal memory. It introduces history-resolved causal stochastic machines (HCSMs) and proves their history laws coincide exactly with the fixed-basis, prefix-preserving diagonal sector of ideal quantum processes, while coherent quantum processes extend strictly beyond it. Using reversibility and a phase ledger, it argues that exact positive stochastic simulation supporting universal quantum continuations must retain predictive information not visible in probabilities.
In briefProgrammable Preparation of Topological Entangled States (a method to generate entangled quantum states on silicon photonic topological superlattices by tailoring the nonlinear pump)
SummaryThe paper proposes programmable generation of topological entangled states by inverse-engineering the nonlinear optical pump profile of an integrated photonic lattice. Experiments on silicon photonic topological superlattices show deterministic control over the dimensionality and modal structure of the entangled state while preserving its topological character. Site-resolved two-photon correlation measurements are reproducible across nominally identical fabricated devices, indicating robustness to nanofabrication disorder.
M. Javad Zakeri, Alaric Pan, Darren D Hudson et al.
In briefEffective Metric and Dispersive Dynamics of Phase Perturbations in Bohmian Quantum Mechanics
SummaryThe authors linearize the hydrodynamic equations from the Madelung transformation in Bohmian dynamics to derive an effective metric for phase perturbations around a background state. The previously obtained metric is shown to be a special case of a more general structure that retains the full functional variation of the quantum potential and can include external classical potentials. The additional terms introduce dispersive corrections that act as sources in the effective Klein-Gordon equation. The paper also identifies conditions under which these terms become negligible, recovering homogeneous propagation and the effective geometry for a free-particle Gaussian wave packet.
In briefArea theorems that extend EXIT-style conservation laws to quantum error correction
SummaryThis paper extends the classical EXIT and GEXIT area theorems to quantum error correction. For stabilizer codes, the authors define a coset-entropy formulation and show that the area under the quantum GEXIT function equals the number of encoded qubits per channel use. For CSS codes on the quantum erasure channel and under independent bit- and phase-flip noise, the problem reduces to two binary coset-decoding problems.
Avijit Mandal, Mert G\"{o}kduman, Henry D. Pfister
In briefNeural network hybrid for solving Lindblad master equations
SummaryThe paper proposes a variational method for solving Lindblad master equations, which describe open quantum systems, by minimizing a residual cost function. It combines a classical neural network with a parameterized quantum circuit, and represents the density matrix via purification so that positivity, Hermiticity and unit trace hold by construction. The authors bound the covering number of this compositional model and compare it with purely quantum neural networks. Numerical experiments check the method's accuracy and the predicted gradient concentration.
Rafael Florencio D\'iaz, Julio Guerrero Garc\'ia, Elvira Romera Guti\'errez
In briefCircuit synthesis for variational quantum algorithms: depth set by algebra and geometry
SummaryThis paper studies three questions for Hamiltonian Variational Ansätze: which states are exactly reachable from an initial state, how much native control depth suffices for local and global synthesis, and whether a bounded circuit extension can reveal a direction of decreasing cost. It uses dynamical Lie algebras of the circuits and the geometry of the initial state's orbit under the dynamical Lie group. The authors give local and global synthesis bounds with applications to Pauli-generated systems and constrained maximum independent set QAOA circuits, and state conditions for exact finite-depth ground state preparation.
WhyUnifies reachability and synthesis depth for variational circuits via Lie algebra and orbit geometry, giving rigorous finite-depth ground state results; theoretical advance with little numerical valid
In briefMinimum-energy problem for plasma dynamics, reformulated quantum-mechanically
SummaryThe paper addresses finding minimum-energy states of plasma, a key question for plasma physics and fusion theory. Building on Hong Qin's classical Hamiltonian approach, which faces topological difficulties, the authors introduce a quantum-mechanical formulation based on the Wigner transform and the symplectic geometry of Gaussian states.
In briefUniversal threshold laws for dipolar evaporation of molecular Fermi gases
SummaryThis paper studies evaporative cooling of shielded single-component ultracold dipolar molecular Fermi gases in the Wigner threshold regime. It finds that Fermi suppression of rethermalizing collisions follows universal laws set by the gas's effective dimensionality, scaling quadratically with temperature in 3D and linearly in 2D. The authors also report ab initio close-coupling calculations that agree well with experiments on KRb molecular Fermi degenerate gases.
In briefTrapping nanofabricated silicon dioxide discs in an optical lattice for sensing
SummaryThis paper describes fabricating 10-micrometer-diameter, 400-nanometer-thick silicon dioxide discs and loading them into a vacuum optical standing-wave trap. The authors combine interferometric and imaging methods to measure the center-of-mass motional spectra of the discs. The approach supports efficient loading and trapping of only a few particles with customizable geometries compatible with wafer-scale nanofabrication. Disc-like trapped particles are identified as promising for high-frequency gravitational-wave detectors or sensitive accelerometers.
Shelby Klomp, Shafaq Gulzar Elahi, Scott Grudichak et al.
In briefA two-dimensional classical spin model that is stable against temperature and Hamiltonian perturbations
SummaryThis paper examines the two-dimensional classical spin model constructed in arXiv:2605.10943. It shows that the model has many metastable states at non-zero temperature that remain stable under arbitrary Hamiltonian perturbations. The authors describe this as the first example of such a result. The proof uses a recursive application of the cluster expansion.
WhyProves a 2D classical spin model has metastable states stable to arbitrary perturbations at nonzero temperature, via recursive cluster expansion; first such example.
Shankar Balasubramanian, Margarita Davydova, Ting-Chun Lin et al.
In briefDriven Rydberg chain: resonant pair creation and melting of flat bands
SummaryThis paper studies a chain of Rydberg atoms driven by a two-tone periodic signal, which in the strong blockade limit reduces to the PXP model with exact Floquet flat bands. The authors use a time-dependent Schrieffer-Wolff transformation to determine when PXP dynamics remains valid once blockade-violating processes are included. Using Floquet perturbation theory, they identify two mechanisms by which finite-blockade flat bands melt, and their analytical results match exact diagonalization on a finite chain. They propose measuring nearest-neighbor pair correlations on Rydberg quantum simulators as an experimental test.
In briefEntropy production and thermalization in heavy-quark Langevin dynamics
SummaryThe paper treats heavy quarks as Brownian probes of the quark-gluon plasma and derives an entropy balance for their momentum distribution, separating entropy produced by collisions from driving due to an evolving medium. For a Bjorken temperature protocol it gives closed-form total entropy production in strong- and weak-coupling limits. Numerical solutions of a relativistic Fokker-Planck equation for charm and bottom quarks confirm the same structure.
In briefMulti-time states in general probabilistic theories: an axiomatic framework
SummaryThe paper develops an axiomatic framework for multi-time states within a class of operational probabilistic theories that includes quantum mechanics. It rests on three assumptions (compositionality, reconstructibility, and spatio-temporal marginal consistency) and accommodates both Markovian and non-Markovian dynamics. The authors fully characterize the unique multi-time state in boxworld and establish a correspondence with the process-matrix framework in non-Markovian quantum dynamics.
WhyAxiomatic framework for multi-time states in OPTs covers non-Markovian dynamics and links to process matrices; strong theory, but no experimental validation and impact mostly foundational.
Kaumudibikash Goswami, Archana Barvar, Manabendra Nath Bera
In briefProbing quantum phase transitions beyond Landau theory on a quantum processor
SummaryThis paper studies a Landau-forbidden transition from a ferromagnetic to a valence-bond-solid phase in a frustrated one-dimensional spin chain, using superconducting quantum processors. The authors combine matrix-product-state-assisted circuit preparation with hardware measurements to observe suppressed long-range ferromagnetic correlations and redistributed competing-order fluctuations. They also examine nonequilibrium dynamics starting from dimerized states.
In briefRandom superpositions of simple quantum states become "magical"
SummaryThe paper studies non-stabilizerness, or "magic," of quantum states, quantified by the stabilizer Rényi entropy (SRE), which indicates how hard a state is to simulate classically. The authors show that random superpositions of classically simulable states saturate the SRE to a symmetry-restricted Haar-random maximum. As the number of superposed components grows, the SRE scales logarithmically before plateauing at this maximum. The result is verified numerically for random stabilizer states and random Gaussian states.
Joshuah T. Heath, Andrew Urilyon, Damien Quinn et al.
In briefUsing large language models to discover state-of-the-art quantum circuits
SummaryThe paper proposes an evolutionary framework in which large language models propose quantum circuit designs and an independent evaluator verifies and scores them. It is applied to tasks including numerical computation, chemistry, optimization, quantum simulation, and number theory. In seven of the eight tasks, the discovered circuits significantly reduce both Toffoli and qubit counts compared with the state of the art. In the eighth, the search finds a new reversible architecture for prime-field modular inversion.
WhyAn LLM-plus-evaluator evolutionary search cuts Toffoli and qubit counts on seven of eight tasks and yields a new reversible modular-inversion architecture.
In briefStability of quantum error-correcting code states under local noise
SummaryThis paper studies how the normalized code-projector state of quantum LDPC codes holds up under local Pauli noise. The authors prove that, in two noise regimes, the conditional mutual information across a buffer region decays exponentially with the buffer's width, independent of system size. Under a space-uniformity assumption, they also show robustness of Levin-Wen topological entropy and, at weak noise, a quasi-local recovery channel result.
WhyProves exponential CMI decay for qLDPC code-projector states under local Pauli noise, giving a rigorous stability criterion with notable theoretical advances.
In briefMagic in noisy random quantum circuits via trajectory unravelings
SummaryThis paper studies non-stabilizerness (magic), measured by the stabilizer Rényi entropy, in quantum-trajectory unravelings of Haar-random and T-doped random Clifford circuits under local dephasing noise. It shows that a state-independent choice of Kraus operators, notably a two-outcome weak measurement, can substantially reduce the trajectory-averaged magic while keeping its linear scaling with system size. However, many trajectories retain Haar-random magic, and these high-magic trajectories dominate the cost of stabilizer-based classical simulation.
Sara Santos, Alessio Paviglianiti, Vincenzo Savona
In briefMagna: a cheap classical simulator for magic state factories
SummaryThis paper introduces magna, a classical simulator for magic state factories such as distillation, cultivation, and code switching, which are hard to simulate because they contain many non-Clifford gates. The tool expresses acceptance rate and accepted-state fidelity as tensor networks and reduces them globally using a correspondence with transversal gates on quantum codes. The authors report simulating Bravyi–Haah distillation with up to 100 outputs and achieving state-of-the-art sampling times for distance-5 magic state cultivation.
WhyNovel tensor-network global reduction simulates magic state factories efficiently, validated on 100-output distillation and cultivation benchmarks, impacting fault-tolerant quantum design.
In briefClassical Capacity of Single-Mode Bosonic Gaussian Channels
SummaryThis paper studies the maximum rate at which classical information can be reliably sent through single-mode bosonic Gaussian channels, such as loss and noise models for fibre and free-space optical links, under a mean input energy constraint. The authors prove that independently prepared Gaussian states with Gaussian-distributed random displacements achieve capacity at every input energy. They also bound how the probability of correct decoding decays exponentially above capacity, and give a rescaling formula relating capacity and error when only mean photon number is constrained.
WhyProves Gaussian encodings achieve the energy-constrained classical capacity of single-mode bosonic Gaussian channels, resolving additivity, with exact rate-error trade-off results.
Gerardo Adesso, Ludovico Lami, Vittorio Giovannetti
In briefAdding Temperature to Electron Correlation: Hybrid Functionals for Static and Dynamic Effects
SummaryThe paper extends the adiabatic connection approach of density functional theory to include a temperature dimension, producing thermally enhanced hybrid functionals. Static correlation is captured through fractional occupations from an effective correlation temperature in thermal Hartree-Fock, while dynamic correlation uses established density functional approximations. The framework unifies i-DMFT and TAO-DFT as special cases, and the authors test several such hybrids on cases where i-DMFT previously failed, along with different schemes for choosing the temperature on a biphenyl-derived benchmark set.
In briefSynDebug: A Framework for Finding Logic Bugs in Fault-Tolerant Quantum Programs
SummaryThis paper presents SynDebug, described as the first systems-level debugging framework for fault-tolerant quantum computing (FTQC) programs. It adds lightweight assertion-based debugging primitives that operate inside encoded FTQC execution flows. The authors evaluate it on several quantum error correction code families and workloads, including state preparation, entanglement validation, and Shor-style programs. They report an average 1.8% circuit depth overhead (0% in most cases) with no measurable increase in logical error rate.
In briefTransient heat conduction on quantum hardware: a variational solver's temperature-field accuracy and shot-count limits
SummaryThe paper tests a variational quantum linear solver (VQLS) on IBM quantum hardware, solving one backward-Euler step of one-dimensional heat conduction. A confirmatory comparison of N=4 and N=8 temperatures shows larger field error on hardware for N=8. An exploratory N=16 case and a shot-count follow-up show that increasing shots reduces variability but does not recover the mean cold-side temperature field.
In briefConstrained dissipation and quantum many-body scars: how dissipation affects long-lived quantum states in the PXP model.
SummaryThe paper studies how quantum many-body scars in the PXP model behave under Markovian dissipation. When local jump operators respect the Hamiltonian's symmetries, a tower of states resembling standard quantum scars appears in the Liouvillian spectrum. Whether scars dominate long-time dynamics depends on the real parts of the eigenvalues, which are set by the ratio of two relaxation rates. Replacing the full projection operator with a partial one breaks the symmetries and destroys these dissipative scars.
In briefProgrammable all-to-all entangling gates for neutral atoms coupled to a shared cavity
SummaryThis paper proposes a high-fidelity Mølmer-Sørensen-like entangling gate for neutral atoms coupled to a photonic cavity. The shared cavity coupling enables programmable all-to-all connectivity without moving atoms. Using experimentally realistic parameters, the authors report gate fidelities above 0.99, with higher fidelities possible through optimal control of pump amplitudes.
In briefEfficient quantum simulation of unitary gates using atomic ensembles
SummaryThe paper presents a method for efficiently simulating unitary time evolution of general spin Hamiltonians using ensembles of identical qubits, such as permutation-symmetric atomic ensembles. It applies Cartan decomposition to the Hamiltonian's Lie algebra to build symmetry-adapted generators, yielding compact circuits made of experimentally accessible collective spin operations. The authors report that the Cartan protocol outperforms Suzuki-Trotter formulas, with an error that stays independent of atom number while Trotter error grows with system size.
In briefBipartite Observables Classification III: Simplicity, Mixtures, and Quantum Error Correction
SummaryThis is the third paper in a series bringing model theory to quantum information. It translates the dividing lines of Shelah's classification theory into properties of bipartite observables, meaning expectation values obtained when two independently prepared quantum systems are idealized one after the other. The paper focuses on simple unstable theories and notes that the Pauli group, with anticommutation as its relation, has such a theory, like the random graph. It also states that in stabilizer codes, forking recognizes logical errors and the Kim–Pillay independence theorem glues syndromes.
In briefEnergy analysis of fault-tolerant spin-qubit quantum computing
SummaryThis paper estimates the power and energy needs of a spin-qubit quantum computer based on the Loss-DiVincenzo design, using the Quantum Fourier Transform compared with the classical Fast Fourier Transform. Cryogenic cooling is the main energy cost before error correction, while instrumentation and decoding dominate at larger scale. The authors report that optimizing the control-signal demultiplexing ratio can cut energy cost by about two orders of magnitude, and estimate roughly 100 kW for a system with about one million physical qubits.
Jo\~ao Santos, Jayshankar Nath, Marco Pezzutto et al.
In briefUpper bounds on GHZ graph dimension via connectivity
SummaryThis paper studies graph models of GHZ (multipartite entangled) quantum states, where the dimension of the produced GHZ state is linked to graph colourings. The authors prove that every simple connected GHZ graph with at least four vertices has dimension bounded by a function of its vertex connectivity. They also give new bounds in terms of edge connectivity and maximum degree.
In briefGyrators for superconducting circuit design: a method for modeling circuits with gyrators and nonlinear elements
SummaryThis paper presents a flux-charge symmetric Hamiltonian formalism for superconducting circuits built from gyrators, inductors, capacitors, and arbitrary nonlinear elements. It introduces a circuit duality for nonlinear non-reciprocal circuits and point transformations that insert, remove, or move reciprocal elements across gyrators while preserving the Hamiltonian spectrum. The authors extend Tellegen's result to nonlinear elements such as Josephson junctions and quantum phase slips, and give conditions under which non-reciprocal circuits can be transformed into dynamically equivalent reciprocal ones.
Ciro Salcedo, Sasha Cocquyt, Andrew A. Houck et al.
In briefAssigning a “temperature” to electron correlation for mean-field-cost calculations
SummaryThe paper presents a systematic framework that models the correlation energy as a function of a measure depending only on the one-particle reduced density matrix, placing it within reduced density matrix functional theory at mean-field cost. The variable conjugate to this measure is interpreted as a “correlation temperature,” linking correlation measures, functional theory, and effective temperatures. The authors illustrate the key concepts analytically for the Hubbard dimer and numerically for small molecular systems.
In briefPatchwork: automated lattice surgery compiler and space-time partitioning for real-time decoding
SummaryThe paper presents patchwork, a compiler that automates lattice surgery for arbitrary multi-qubit Pauli measurements on a fixed narrow-corridor surface-code layout. It uses geometric rules for stabilizer placement and scheduling, including logical Y measurements with twist defects, and reports preserving the full effective code distance for all tested distances. A wavefront algorithm partitions merged patches into space-time commit, buffer, and cleanup regions to enable parallel decoding. Simulations of three sequential multi-qubit Pauli measurements on ten logical qubits show staged decoding has total failure probabilities close to monolithic decoding.
Christopher Chamberland, Muyuan Li, Scott Thornton et al.
In briefPractical limits of entanglement generated by gravity between massive objects
SummaryThis paper examines whether two massive objects in spatial superposition can become entangled through gravity. It models finite-width Gaussian wave packets, spatially correlated dephasing, and residual electrostatic interaction, and tests whether the resulting state remains useful, using Bell violation and teleportation fidelity. The authors find that useful parameter windows shrink as wave packets broaden or dephasing strengthens, and that electrostatic interaction can cancel the gravitational nonlocal phase.
Atta ur Rahman, Muhammad Noman, Ying-Jian Zhu et al.
In briefBubble-sort exchange networks: symmetry rules and language-model distillation on spin chains
SummaryThe paper proposes a variational bubble-sort exchange network for chains of exchange-coupled quantum dots, with one parameter per pulse. It derives a selection rule for the two-spin singlet-triplet encoding and shows it is also sufficient. In noise-free simulation, next-token distributions from GPT-2 are distilled into the network and compared with matrix-product-state Born machines.
In briefGeneralized m-body mean-field projections for classical simulation of d-dimensional Heisenberg-picture dynamics
SummaryThis paper proposes a state-adapted Pauli-weight propagation method based on generalized m-body mean-field projections, which compress many-body observables into low-body representations. It combines this with adaptive Krylov-like restricted Heisenberg dynamics as an alternative to standard Hilbert–Schmidt Pauli-weight truncation. The authors derive accuracy bounds for low-body approximations and show state-dependent accuracy gains as well as regimes of reduced accuracy. For a three-dimensional system of 80 interacting spins, the method agrees closely with tensor-network simulations and yields sparser Pauli representations.
WhyProposes state-adapted generalized m-body mean-field projections with derived bounds, validated by numerical benchmarks and tensor-network agreement, offering practical impact for three-dimensional ma
Federico Tom\'as B. P\'erez, Gabriela W\'ojtowicz, Matthias Kost et al.
In briefEnergy channels in finite many-body quantum charging (a study of how a many-body system charges a quantum battery)
SummaryThis paper uses the Lipkin-Meshkov-Glick model to study how a finite many-body system can act as a charger for a single-qubit quantum battery. It measures battery ergotropy, the extractable useful work, while tracking energy flows within the combined system. The authors find that internal charger interactions reshape the spectrum, which can increase accessible charging energy but can also divert energy into many-body and battery-charger interaction channels. They conclude that battery ergotropy alone is insufficient, and the energetic origin of the work must be assessed too.
Dara Murphy, George Mihailescu, Anne Matthies et al.
In briefEstimating time delays without knowing losses, using two-photon bunching detection
SummaryThis paper studies using two-photon correlated quantum states for high-precision time estimation. Photon pairs are sent into a Hong-Ou-Mandel polarization interferometer to create N00N entangled states with N=2, and two- and four-detector schemes are compared by their precision and Fisher information. The four-detector scheme, which measures both coincidence and photon-bunching terms, reaches the quantum Fisher information limit without characterizing system losses. Accounting for correlations between repetitions caused by systematic errors, it still outperforms the two-detector scheme.
Juli\'an Defant, Agustina G. Magnoni, Miguel A. Larotonda et al.
