In briefUnequal quantum resource costs in distinguishing multipartite states
SummaryThe paper studies how much quantum resource is needed for local operations and classical communication (LOCC) to distinguish orthogonal multipartite quantum states. It shows that different pairs of orthogonal multipartite maximally entangled states require unequal amounts of resources. The authors also analyze larger sets of locally distinguishable and indistinguishable states, finding a nontrivial hierarchy in entanglement consumption.
In briefMeasuring fermionic non-Gaussianity in the SYK model with replica twist entropy
SummaryThe paper proposes replica twist entropy, defined via a replica rotation operator with tunable angle α, as a probe of non-Gaussianity in pure fermionic states. The authors develop a general framework for this quantity in solvable Sachdev-Ye-Kitaev models in the large-N limit. Applied to the thermofield double state, it reveals a dynamical phase diagram in the (α, t) plane, including spontaneous Z2 symmetry breaking at α=π/4 and universal cusps in the long-time regime.
In briefTrade-off between Wigner negativity and decoherence time in cubic Gaussian quantum states
SummaryThe paper studies cubic Gaussian states, made by applying a cubic gate to a Gaussian state, as sources of Wigner negativity. It shows that a larger negativity N forces a shorter decoherence time τ, bounded above by N⁻². Optimal states reaching this bound need squeezing that grows as ln N and cubicity that scales as N⁻¹, yet their decoherence time still falls as negativity grows and their preparation is highly sensitive to thermal noise.
Matthieu Arnhem, Valerio Crescimanna, Giuseppe Patera et al.
In briefCan we make sense of negative kinetic energy? A study of whether 'ghost' states with negative energy can remain stable.
SummaryThe paper studies simplified quantum mechanical models in which normal and negative-energy ghost subsystems are coupled. Because their full spectra are unbounded from below, no true ground state exists, so the authors examine a 'would-be ground state', a zero-energy eigenstate of the decoupled system. They find that across a broad range of couplings this state does not decay and stays dynamically stable over long times.
In briefMoment methods for uniform average mixing on strongly regular graphs
SummaryThis paper studies continuous-time quantum walks on connected, non-complete strongly regular graphs observed at a random time drawn from a chosen probability law. It constructs bounded, compactly supported time densities and gives a finite Toeplitz criterion for integral spectra. The authors determine which strongly regular graphs admit uniform average mixing and correct an earlier classification of instantaneous uniform mixing.
In briefCausal confusion in quantum systems: telling direct cause from common cause apart
SummaryThe paper compares two measurement setups: a direct-cause scenario, where one quantum state is measured twice in series with a quantum channel in between, and a common-cause scenario, where a shared bipartite state is measured in parallel. It identifies input states for which Pauli observable joint expectation values match in both setups, a situation called causal confusion. The authors prove that, for arbitrary finite-dimensional systems, a channel exhibits causal confusion for some input state if and only if it is a positive-partial-transpose (PPT) channel. For qubit channels, the channels admitting such an input state are exactly the entanglement-breaking channels.
Krisztina Tolotti, Riley Blank-Matthews, Arthur J. Parzygnat
In briefCotunneling-driven redistribution of nonpassivity in a photosynthetic junction
SummaryThis paper models the Photosystem II reaction center as a nonequilibrium molecular junction and studies how cotunneling affects passive-state ordering. The authors quantify passive-state changes using ergotropy and energetic capacitance, and find that these smooth thermodynamic quantities can hide microscopic state rearrangements. Cotunneling redistributes extractable nonequilibrium energy among the quinone acceptor, the donor-pheophytin radical pair, and excitonic states. At high Coulomb interaction, cotunneling produces no passive-state reordering.
Manjet Rajak, Trishna Kalita, Debasish Sharma et al.
In briefDissipation-selected photon-phonon pair and photon-bundle emission in a tripartite Mollow system
SummaryThis paper studies a tripartite Mollow system in which a strongly driven two-level emitter couples simultaneously to cavity photons and motional phonons. It finds that the symmetry of bosonic dissipation channels selects and switches the emitted quantum resource. Symmetric dissipation produces strongly correlated photon-phonon pairs and multipair bundles, while asymmetric dissipation decouples the two degrees of freedom and yields high-purity single-photon and two-photon bundles.
In briefA study of the expressive power and capacity of quantum data reuploading models
SummaryThis paper analyzes the frequency spectrum of data reuploading in quantum neural networks, giving an exact characterization of the accessible frequencies. It shows that the spectrum's directions stabilize after one reupload while the spectrum itself keeps growing with the number of reuploads. The authors derive a capacity bound based on spectrum size and compare the models with parameter-matched classical networks on approximation and classification tasks.
In briefSufficient quantum provenance: which execution details to keep and how precisely
SummaryThe paper asks which details of a quantum execution must be retained, and at what precision, so that executions sharing a provenance record agree within a declared Hellinger tolerance. Under a specified channel model, the authors certify recording precision without simulating outputs. For depth-one four-qubit QAOA, a 13-bit comparison record suffices at tolerance 0.05, and six-qubit hardware measurements certify minimum label counts.
George Kourousias, Sergio Carrato, Roberto Pugliese et al.
In briefBeyond Spectroscopic Strong Coupling: Operational Benchmarks for Quantum Transfer
SummaryThe paper argues that normal-mode splitting shows coherent cavity-magnon hybridization but does not guarantee finite-time quantum-state transfer. The authors model the system as a thermal-loss channel and derive conditions for single-rail qubit fidelity, Bell-pair entanglement retention, and squeezed-vacuum preservation. They find that a conventional linewidth-based strong-coupling criterion does not ensure quantum-transfer performance, while entanglement or squeezing can survive below that reference when added noise is low enough.
In briefKerr-filtered hybrid quantum states via double-squeezed tripartite interactions
SummaryThis paper studies how double squeezing and cavity Kerr nonlinearity together enable controllable engineering of hybrid quantum states in a tripartite spin-photon-phonon system. Double squeezing exponentially enhances the spin-mediated photon-phonon pair-generation channel, while the Kerr interaction selectively reshapes the photonic component. The authors report a fourfold phase-space manifold associated with spontaneous parity breaking and propose a strategy that combines interaction amplification with mode-selective nonlinear filtering.
In briefDirectional quantum light from path complementarity in hybridized cavity polaritons
SummaryThis paper proposes a microscopic path-complementarity mechanism in hybridized cavity polaritons that yields both asymmetric photon statistics and single-photon path entanglement. In a Zeeman-split ring-cavity QED system, cavity backscattering hybridizes counterpropagating modes while the Zeeman splitting creates spectrally asymmetric excitation channels. Under weak driving, one input direction shows antibunching and the opposite direction shows bunching, with path concurrence nearly preserved over a broad parameter regime.
In briefExtensively degenerate superradiant phase in a giant-atom quantum Rabi ring
SummaryThis paper studies a quantum Rabi ring of N sites in which each giant atom couples to two cavities two sites apart. As the atomic-to-cavity frequency ratio goes to infinity, the authors show there are 2^N degenerate superradiant configurations that survive quadratic quantum fluctuations. At finite frequency ratios, second-order processes select ferro- or antiferro-superradiant configurations, and four-site calculations support the predicted coefficients.
In briefCoherent consensus method for estimating and classifying quantum phases
SummaryInspired by quantum metrology, the paper proposes a coherent consensus method that helps independent quantum classifiers work together near decision boundaries. It prepares a GHZ state on n qubits, encodes each classifier's output as a phase, and gathers all phases onto one qubit. The authors report that sampling error falls by a factor of √n compared with majority voting, and they demonstrate the method on a trapped-ion quantum computer using imperfect phase gates.
Roberto Ruiz, Alessandro Luongo, Sergi Ramos-Calderer et al.
In briefSpacetime quasicrystals and computational complexity in the road toward quantum gravity: a theory paper on semiclassical gravity and Lorentzian quasicrystal structures
SummaryPart I assumes a classical gravitational field coupled to quantum fields through the semiclassical Einstein field equations, and argues that the weak-field dynamics of a massive non-relativistic qubit could in principle solve an NP-complete problem in polynomial time. The authors attribute this power to the nonlinear qubit dynamics and treat the resulting conflict with the Physical Extended Church–Turing Thesis as evidence for quantum gravity. Part II generalizes quasicrystals such as Penrose tilings to Minkowski spacetime, constructs the first Lorentzian quasicrystals, and explores possible links to fundamental physics, causal set theory, and hyperuniformity.
In briefRedundant Past Records: Unifying Quantum Darwinism and Decoherent Histories
SummaryThis paper addresses two frameworks for records in isolated quantum systems, decoherent histories and quantum Darwinism, which are rarely connected. The authors propose a unified "past redundancy" framework and link redundancy to history decoherence and the probability sum rule via the Bhattacharyya coefficient (or fidelity). Various examples suggest that past redundancy is more widespread than the fine-tuned models required by quantum Darwinism.
In briefQuantum optimization of the Color-of-Money problem on IBM hardware: a proof-of-concept
SummaryThis paper addresses the Color-of-Money problem, which concerns how firms allocate funds across accounts, currencies and periods under constraints. The authors reformulate it as a QUBO and solve a small instance (3 assets, 3 obligations, 2 periods) on real IBM quantum hardware using a variational algorithm with Pauli Correlation Encoding and error mitigation. The quantum result matched the optimum found by the classical solver SCIP, but the noisy hardware did not outperform classical methods on this small case.
In briefMixed quantum states for improved Rabin oblivious transfer
SummaryThis paper studies the use of mixed quantum states in Rabin oblivious transfer, a cryptographic primitive for two-party computation. The authors present three mixed-state protocols built with two different methods, one extending an existing pure-state scheme and one using a probabilistic approach. They report that these protocols perform better than classical and pure-state quantum protocols across a range of parameters.
In briefStimulated emission from a three-level artificial atom in a waveguide
SummaryThis paper theoretically studies a three-level ladder quantum system interacting with a continuous electromagnetic field in a one-dimensional open waveguide, modeling stimulated emission as a single-photon exponential pulse scattering off an excited emitter. Using a real-space formalism, the authors derive an analytical expression for the system's wavefunction. They find that for a relative anharmonicity below 4% (|α_r| < 4%), typical of transmons, the third level largely suppresses stimulated emission. The three-level system can also produce photon bunching in the reflected field, which can be switched off by tuning the incident photon parameters.
O. A. Chuikin, Ya. S. Greenberg, V. V. Taravkova et al.
In briefAutomatically simplifying fault-tolerant quantum circuits by fault-equivalent rewriting
SummaryThis paper presents an automated search method that simplifies fault-tolerant circuits through rewrites that preserve fault equivalence. For Shor-style syndrome extraction with the [[7,1,3]] code, one measurement round drops from 30 to 18 ancilla preparations and from 54 to 42 CNOT gates. At a physical two-qubit error rate of 10^-3, the logical error rate is reduced by about 21%.
In briefA Minimal Bicomplex Extension of Quantum Mechanics' Complex Scalars with an Ideal-Valued Sector
SummaryThe paper asks whether the complex numbers used in quantum mechanics can sit inside a larger commutative, associative scalar algebra. It shows that adding a stable complex-like analytic sector that is a proper ideal forces zero divisors in finite dimension and requires at least four real dimensions. The bicomplex algebra realizes this minimum, and under an added compatibility assumption the four-dimensional realization is unique. Restricting the Born rule to the complex sector recovers its standard form, and whether the construction has physical significance remains open.
In briefEfficient Detection of Spectral Cluster States: Simultaneously Characterizing a 60-Node Continuous-Variable Cluster State
SummaryThe study demonstrates multimode optical parametric amplification (MOPA) as a method for detecting multimode entangled light, accessing many modes and their correlations across a broadband range. The authors characterized a broadband 60-node dual-rail continuous-variable cluster state, observing nearly uniform squeezing from -7.2 to -6.5 dB across spectral modes. By evaluating the van Loock-Furusawa criterion over all relevant bipartitions, they verified genuine multipartite entanglement throughout the 60-node state.
In briefSpurious zero-dispersion continua in full (2,q)-positivity from a solvable counting operator
SummaryThis paper examines whether a fixed level of the semidefinite constraint hierarchy in variational two-particle reduced-density-matrix methods can correctly recover a simple many-fermion spectrum. For an exactly solvable operator counting fermions in half the spin orbitals, the authors determine all values accepted by the dispersion test at every level of the full particle-hole hierarchy. Besides the integers, an entire interval of noninteger values is accepted unless the level grows linearly with particle number, and the exact threshold is given.
WhyGives an exact linear hierarchy-depth lower bound with explicit pseudo-RDMs for a solvable counting model; strong theory, narrow scope.
In briefDifferential structure of generators of KMS-symmetric quantum Markov semigroups
SummaryThis paper studies KMS-symmetric quantum Markov semigroups, which are fully determined by the quadratic forms they induce on the GNS Hilbert space, known as quantum Dirichlet forms. The authors give a complete description of bounded quantum Dirichlet forms in terms of derivations and an explicit characterization for type I factors. They also show that every unbounded quantum Dirichlet form can be represented through derivations.
In briefProbing topology with momentum-selective measurements on a superconducting processor
SummaryThe paper proposes a method that directly measures band topology by selecting specific momentum states with an auxiliary probe. It is demonstrated on a superconducting quantum processor with a highly connected architecture. The authors realize an extended SSH model, map its topological phase diagram, and extract quantized winding numbers.
In briefOptimal control that curbs leakage in superconducting qubits
SummarySuperconducting qubits use the lowest two levels of an anharmonic oscillator, but their low anharmonicity lets population leak into higher states. This paper adapts a sub-Riemannian geodesic-based optimal control method to two superconducting qubits with leakage levels, analyzing an Rx(π/2) single-qubit rotation and an iSWAP two-qubit operation. For the single-qubit gate, the optimal pulses improve average gate fidelity and reduce leakage compared with Gaussian and DRAG pulses, especially for short durations. For iSWAP, leakage stays roughly the same, but fidelity is considerably higher at the cost of a slightly longer evolution time.
Adonai Hil\'ario da Silva, Tanmoy Pandit, Francesco Cosco
In briefLinks between asymptotic quantum many-body scars in closed systems and diffusive Nambu-Goldstone modes in open systems
SummaryThis paper studies how rainbow quantum many-body scar states in closed systems relate to diffusive Nambu-Goldstone modes in open quantum systems. The authors establish a spectral correspondence between the parent Hamiltonian and the effective Lindbladian of strongly dissipative systems, and construct asymptotic rainbow scar states. For uniform transition rates, the two operators are proportional and share eigenmodes, so an exact quadratic parent-Hamiltonian branch maps directly to a diffusive Nambu-Goldstone mode.
In briefQuantum anomaly detection on real scarce data: a hybrid approach for photovoltaic plants
SummaryThis paper addresses anomaly detection on small, unbalanced datasets by proposing a novel two-step hybrid classical-quantum architecture for sequential data. The method is tested on automated anomaly detection in large-scale photovoltaic plants. The authors report that it can work with far fewer trainable parameters and smaller datasets, achieving good generalization and competitive prediction accuracy.
Emanuele Casciaro, Fabio Mascherpa, Alfonso Amendola et al.
In briefDivide-and-conquer quantum neural networks for modular hybrid computing systems
SummaryThis paper proposes a training method that splits quantum neural networks into smaller components and optimizes them separately, aiming to reduce the number of qubits and quantum gates needed. The approach is tested on real-world prediction tasks, including the status of electric vehicle charging stations and the global air quality index. The authors suggest a design principle for quantum machine learning across many applications, which can be tested on current quantum processors or modular quantum architectures.
Emanuele Casciaro, Fabio Mascherpa, Alfonso Amendola et al.
In briefSample-based quantum simulation of polyyne chain vibrational structure
SummaryThis paper applies a sample-based quantum diagonalization (SQD) framework to compute anharmonic vibrational energies and infrared spectra. The method combines quantum state preparation and sampling, configuration recovery, diagonalization in a subspace of basis configurations, and transition-dipole calculations. It is applied to the polyynes C2H2 and C4H2, with representations requiring up to 104 qubits.
Sarah Mostame, Tanvi P. Gujarati, Alberto Baiardi et al.
In briefGrover Search for a Threshold-Fraction Variant of the Travelling Salesman Problem
SummaryThis paper studies a robust variant of the Travelling Salesman Problem, formulated as a promise problem asking whether a given fraction of tours have length within a threshold. It shows that Grover's quantum search decides this using O(1/√p) oracle queries, independent of the number of cities. Each query is a polynomial-size quantum circuit, so runtime is polynomial in the number of cities for fixed p.
In briefQuantum Approximation Complexity: Whether quantum computing can improve worst-case approximation guarantees for classical optimization problems
SummaryThe paper defines bounded-error quantum versions of classical approximation complexity classes (APX, PTAS, FPTAS), requiring an algorithm to return feasible solutions meeting the approximation ratio with probability at least 2/3 on every input. Under the assumption NP is not contained in BQP, the authors establish a strict hierarchy for logarithmic, polynomial, and exponential approximation factors. They also give conditional quantum-classical separations based on factorization and discrete logarithm problems. A quantum-classical gap for common problems such as MaxCut or MaxSAT remains open.
WhyDefines bounded-error quantum approximation classes and gives conditional hierarchy and quantum-classical separations, a notable theoretical contribution.
In briefTime-bin behavior of photon pairs from a 2 GHz waveguide resonator
SummaryThe study generates degenerate photon pairs, called signal and idler, through parametric down-conversion in a waveguide resonator with about 2 GHz bandwidth in the telecom C-band. After selecting a single resonator mode, the researchers used standard photon counting to measure the sub-nanosecond pulse shapes, or time bins, of each photon. The time-bin durations differ significantly between signal and idler, which the authors attribute to their different optical losses. The work also simulates the temporal properties via the Fourier transform of the joint spectrum.
In briefVibrational sample-based quantum diagonalization on IBM QPUs with unitary-cluster-Jastrow ansätze
SummaryThis paper extends sample-based quantum diagonalization to anharmonic vibrational spectra and benchmarks vibrational ansätze on IBM quantum processors with up to 72 qubits. It compares five particle-conserving circuits warm-started from vibrational coupled-cluster amplitudes, using a self-consistent configuration-recovery loop to reconstruct correlated states from hardware samples. The method computes ground-state energies for H2O, CH2O and CH2ClF and one fundamental vibrational frequency per molecule.
Kunal Kumar, Erik L\"otstedt, Yuri Kobayashi et al.
In briefLearning Analytics on Novice Work in Quantum Circuit Simulator Tasks
SummaryThis paper presents a learning analytics framework for quantum circuit simulator tasks and applies its task-level analysis to anonymised logs from an introductory quantum computing course. The dataset includes 492 learners, 47,533 valid submissions, and 21 obligatory circuit exercises. The study identifies bottleneck tasks, broad solution spaces, and recurring wrong-answer patterns that final scores alone do not reveal. It also proposes a plain-text representation of observed answer spaces to make open-ended circuit submissions easier for instructors to interpret.
In briefThe Geometry of Lee-Yang Tensors: Spectral Gaps and Gibbs States in Quantum Many-Body Systems
SummaryThe paper gives a geometric description of Lee-Yang tensors, building on recent results of Bravyi, Gosset, Liu, and Wong. Using complex Perron-Frobenius theory, it generalizes a key lemma to bound the spectral ratio of non-normal operators with Lee-Yang radius above one. This yields a local-to-global principle for lower-bounding spectral gaps of Suzuki-Fisher Hamiltonians using only each local operator's Lee-Yang radius. The authors also show that Gibbs states of k-local Hamiltonians with k≥3 cannot have Lee-Yang radius at least one at all inverse temperatures.
In briefMatched-budget audit of quantum natural gradient with exact metric
SummaryThis paper examines how reporting conventions affect comparisons of variational quantum optimizers. It compares Adam, SPSA, and quantum natural gradient (QNG) by pricing each step in circuit evaluations under a common budget and computing the exact metric QNG uses. Counting only runs that reach the target hides SPSA's higher evaluation cost. The authors recommend charging every miss to the budget and reporting verdicts across several targets.
In briefChern insulator induced by non-Hermitian cooperation
SummaryConventional Chern insulators need magnetic or synthetic gauge fields to break time-reversal symmetry. This paper shows that a static lattice without any gauge field can become a Chern insulator through the combined action of on-site loss and non-reciprocal coupling. Neither effect works alone, but together they open a topological gap and produce robust chiral edge states with nonzero Chern number.
In briefDistance structure of insertion kernels and local port response in non-reciprocal SSH chains
SummaryThis paper studies non-reciprocal Su–Schrieffer–Heeger (SSH) chains with staggered gain and loss, linking the insertion kernel to coherent transmission intensity. It gives asymptotic results for strong and weak insertion regimes. Finite-chain calculations and driven dynamics are used to test these results.
In briefQuantum method for estimating thermal properties while conserving particle number
SummaryThe paper presents an end-to-end quantum simulation framework for estimating canonical thermal properties of particle-number-conserving Hamiltonians, combining mixed Dicke state preparation, particle-number-preserving Trotterized simulation, and generalized quantum signal processing. It further proposes a grand-canonical reconstruction scheme that reuses the same quantum measurement data through classical reweighting for arbitrary chemical potentials. The authors prove that there exist temperature regimes, independent of system size, where both schemes have lower asymptotic time complexity than classical Lanczos methods, up to polynomial factors. Numerical results for the two-dimensional Hubbard model in weak- and intermediate-coupling regimes are provided to validate the theory.
In briefAmplifying target quantum states in hybrid CV-DV processors when the selection is imperfect
SummaryThis paper introduces non-orthogonal amplitude amplification (NOAA) for hybrid continuous-variable and discrete-variable quantum processors, where the CV-assisted projector is not perfectly selective. The authors derive a bound on achievable target-state fidelity, set by the initial target amplitude and the selectivity of the reflection operator. Numerical simulations indicate that for small initial target amplitudes, the protocol achieves higher fidelity and efficiency than the repeat-until-success method.
In briefQuantum error-correcting codes that run CCZ gates transversally, built with projective geometry and SAT solvers
SummaryThe paper constructs CSS codes with three logical qubits whose logical CCZ gate is implemented by transversal physical T/T† gates, with Z-distance at least 3. The X-stabilizers are defined using projective geometry, and a SAT solver finds X-logical operators compatible with the transversal CCZ. Codes are built at thirteen block lengths from n=48 to n=496. The authors also prove that no such code of this class exists below n=39.
In briefCross-checking two open-source quantum network simulators on basic networking tasks
SummaryThis paper compares two open-source quantum network simulators, QuISP and SeQUeNCe, by running common scenarios such as entanglement generation, purification, and swapping. The authors find that the simulators differ by a constant factor in task completion time, which they attribute to their connection models. Under identical error parameters, however, the two agree on the fidelity of distributed resources. The work is presented as a first step toward more reliable and reproducible quantum network simulation.
Joaquin Chung (1, 2), Michal Hajdu\v{s}ek (3) et al.
In briefTesting Quantum Bayesian Inference Against Classical Learning
SummaryThis paper asks whether an agent's predictions can show that its reasoning uses a quantum rather than classical model. The authors show that with at most four measurement outcomes, quantum predictions always have a classical explanation, but a five-outcome measurement on a single qubit violates an explicit classical bound. The bound depends only on the agent's initial and updated predictions, so the difference can be verified without access to its internal description.
In briefA quantum-classical method that models manipulative chat cues to flag affinity and romance-investment scams
SummaryThe paper proposes a hybrid quantum-classical framework that detects affinity and romance-investment fraud by modelling cognitive biases in manipulative conversations. A parameterized quantum circuit encodes these biases, the temporal order of reframing, and narrative co-occurrence, and is trained jointly with a reinforcement-learning agent that decides turn by turn whether to flag the conversation. The model is evaluated on synthetic conversations, including hard negatives and legitimate but urgent or pushy sales dialogues.
In briefThe coupler Eve missed: no-signalling reports from interacting cavities
SummaryThe authors build a cavity-based counterexample showing that non-signalling statistics from two opaque devices cannot by themselves establish physical isolation. The devices interact via a shared coupling after their inputs arrive, yielding a CHSH score of S=13/4 for four repetitions, approaching 4 for large blocks, while the reported marginals remain exactly non-signalling. The high scores arise from interaction during the devices' response, not from any violation of quantum mechanics.
In briefInteraction-assisted spin coherence in trapped atoms: interactions restore Ramsey contrast lost to thermal detuning spread.
SummaryThis paper studies how mode-dependent detunings in a thermally occupied multimode trapped atomic ensemble can suppress Ramsey contrast even when the dynamics is coherent. The authors develop a Hamiltonian theory in which exchange interactions, treated at the mean-field level, reduce phase dispersion and restore collective contrast. The crossover depends on the ratio of the exchange scale to the thermal detuning spread, and weak irreversible pure dephasing limits but does not eliminate this recovery.
In briefGeometric heat pumping demonstrated on a superconducting quantum processor
SummaryThe study implements geometric heat pumping on a superconducting quantum processor, where a driven qubit repeatedly interacts with two thermal ancilla qubits emulating reservoirs. Energy measurements before and after each interaction record the heat exchanged with each reservoir. Reversing the driving contour isolates a pumping-related heat contribution. The results match exact collision-model simulations and approach the geometric limit of the corresponding Lindblad dynamics in the slow-driving regime.
Ger\'onimo J. Caselli, Luis O. Manuel, Liliana Arrachea et al.
In briefHeating and escape of atoms trapped in colored noise
SummaryThis paper studies how long particles in finite-depth, softening trapping potentials, such as trapped atoms or ions, take to escape when driven by power-law colored noise. Under weak-noise conditions, the authors derive mean escape times using stochastic averaging and compare them with Monte Carlo simulations of the full equations of motion. Applied to lifetime measurements in a microfabricated ion trap, they find that spectral color alone cannot explain the observed rapid escape, but quasi-static barrier tilting from a plausible stray field could.
Joseph M. Ryan, Katherine Jonas, Christopher Monroe
In briefTeleporting a programmable quantum gate with Charlie's help
SummaryAlice and Bob each hold a qubit and want to apply a two-qubit gate to them with Charlie's assistance. The gate depends on a parameter known to Charlie, received later as classical information, or encoded in a program state. The paper compares having Alice and Bob send their qubits to Charlie for entangling and using teleportation to entangle them with his state. It also examines the conditions under which the required local corrections, based on Charlie's measurement results, are possible.
In briefValley transitions during spin shuttling in Si/SiGe heterostructures
SummaryThis paper theoretically studies valley dynamics in a moving quantum dot in Si/SiGe heterostructures, modeling the two lowest valley states as a two-level system. Depending on shuttling velocity, the system falls into one of three regimes. In one regime, quantum information survives valley excitations, enabling coherent spin shuttling regardless of distance. The authors also propose partial Landau-Zener-based strategies to improve valley shuttling fidelity.
In briefEfficient variational polaron master equation for spin-boson dynamics with transformed initial states
SummaryThis paper presents an efficient variational polaron master equation for studying non-Markovian dynamics in a quantum spin-boson model and examines how initial states affect them. The method recasts the integro-differential equations as ordinary differential equations in an extended auxiliary Liouville space and provides a simplified way to compute general observables. The authors find that coherent superposition initial states produce stronger nonequilibrium effects than localized states, and they compare results with the weak-coupling master equation.
In briefComputable bounds on energy-limited quantum reading capacity
SummaryThis paper studies quantum reading, where classical messages are encoded in sequences of quantum channels and recovered by probing them. Under an average energy limit on probing, the authors derive a converse upper bound for finite families of channels that can be approximated with semidefinite programs. They also construct achievable lower bounds on rates. For jointly classical-quantum channels, non-adaptive protocols are shown to match the unconstrained reading capacity.
In briefMatter-wave bistability in a momentum-chirped condensate: a theory of interaction-driven bistable transmission in a matter-wave Fabry-Perot interferometer.
SummaryThis paper theoretically studies a matter-wave analogue of a Fabry-Perot interferometer, in which a Bose-Einstein condensate wavepacket passes through a cavity formed by two light-induced Gaussian barriers. The authors show that engineering a momentum chirp in the wavepacket can balance the interaction-induced cavity energy shift, enhancing resonant spectra and producing bistability via interaction-assisted tunneling. They also determine the optimal chirp and the contrast of near-discontinuous transmission spectra. The authors suggest the approach could enable matter-wave switching and high-precision velocity measurements.
Mikhail Mamaev, Nicholas Mantella, Noah P. Baker et al.
In briefHigh-fidelity quantum gates between two atomic species using two-photon laser driving
SummaryNeutral atom arrays are promising for quantum information processing, and high-fidelity entangling gates are usually performed by exciting atoms to Rydberg states via two-photon processes. This paper models how laser crosstalk affects inter-species Rydberg gates driven by two photons, and shows that appropriate gate design can suppress this crosstalk to arbitrarily small levels. For an 85Rb/87Rb system in the near-detuned case, the authors report gate fidelities above 99.8% with conservative experimental parameters.
In briefZero-mode operators at charge-conjugation defects in non-Abelian fractional quantum Hall-superconductor systems
SummaryThis paper studies zero modes bound to charge-conjugation defects in heterostructures combining fractional quantum Hall states with superconductors. The authors extend the construction of localized zero-mode operators to non-Abelian parent topological orders. They derive zero-mode algebras for Laughlin, generalized Moore-Read, and k=3 Read-Rezayi states. For the Read-Rezayi case, they report that operator tunneling and direct anyon transfer give different universal amplitude ratios.
In briefEnergy-constrained two-way capacity bounds for noisy Gaussian channels: a new upper limit on communication rates over noisy bosonic links under limited photon energy
SummaryThis paper derives a unified adaptive weak-converse bound for bosonic channels with thermal attenuation, noisy amplification, and additive Gaussian noise, under a mean photon-number constraint. The bound covers arbitrary adaptive protocols with quantum memories and limits several two-way capacities, including quantum, entanglement-distribution, private, and secret-key capacities. It is zero in the entanglement-breaking region and approaches the PLOB bound at infinite energy. At finite energy, it improves the evaluated Gaussian squashed-entanglement and PLOB bounds in relevant regimes, and comparison with hashing rates shows the remaining gap to achievability.
WhyDerives a unified finite-energy adaptive weak-converse bound for noisy Gaussian channels, improving prior evaluated upper bounds in relevant regimes.
In briefObserving a magic Mpemba effect in localized dynamics on a digital quantum computer
SummaryThis paper asks whether quantum magic (nonstabilizerness, a key resource for universal quantum computation) can show a Mpemba-like reversal, where a state with less initial magic reaches higher saturated magic and saturates sooner. The authors identify interaction-induced dephasing as the mechanism, supported by exact simulations of an ℓ-bit model and localized spin chains. They report observing these features on IBM superconducting quantum processors.
In briefSample and measurement complexity of self-consistent entanglement certification
SummaryThe paper studies the complexity of a self-consistent entanglement certification protocol based on generalized noncontextuality, which needs no prior device characterization. At fixed local dimension, it gives the optimal number of distinct local effects needed for a given trace-distance resolution. It also shows the number of target-state copies needed for certification with bounded error.
In briefNo-disturbance-without-uncertainty generates the quantum set in the simplest Bell scenario
SummaryThis paper characterizes the set of quantum nonlocal correlations using information-theoretic constraints. It shows that, when one party has two binary measurements and the other has any finite number of settings and outcomes, the convex hull of no-signalling behaviors satisfying a common-overlap no-disturbance-without-uncertainty condition equals the finite-dimensional quantum set. In the simplest binary input-output Bell scenario, this recovers the full eight-dimensional set of quantum behaviors, including local marginals.
WhyProves that a common-overlap no-disturbance condition exactly recovers the quantum set in the simplest Bell scenario, with an explicit quantum realization construction.
In briefEntanglement Manipulation and Magic Area Laws: How Entanglement and Non-Stabilizerness Scale in Quantum Many-Body States
SummaryThe paper observes that in local many-body quantum systems, entanglement typically follows an area law while non-stabilizerness (magic) usually follows a volume law. Under a recent classification, area-law states split into entanglement-dominated states, whose magic obeys an area law and whose entanglement can be manipulated efficiently, and magic-dominated states, whose subsystem magic grows faster than the area and which require inefficient algorithms. The authors also introduce the stabilizer regime, a restricted quantum phase that allows efficient entanglement manipulation and has area laws for both magic and entanglement.
In briefEfficient learning of structured fermionic states under general quadratic evolution
SummaryThe paper proves that copy-optimal learning of the full Gaussian orbit of paired magic states on n fermionic modes is possible. A nonadaptive learner needs Θ(n^6/ε^2) copies to return a Gaussian preparation within trace distance ε, and no learner in this measurement model can do better. The authors extend learning to pure states built from superpositions of bounded-particle-number occupation patterns, giving a batch-adaptive algorithm that uses Õ(n^7/f) copies to reach infidelity f.
WhyProves copy-optimal learning of fermionic Gaussian states under general quadratic evolution and extends it to superposition states with rigorous bounds, though applicability is narrow.
In briefQuantum algorithms for building multivariable polynomial transformations of matrices and quantum channels
SummaryThe paper develops a constructive synthesis theory for multivariable polynomial transformations of noncommuting matrices under joint block access. For a degree-D polynomial, it achieves (1+τ)-optimal normalization with O(D/√τ) queries, and exactly D queries under row-block access. The framework is extended to quantum channel transformations, enabling synthesis of noncommutative polynomial maps as completely positive operations and of causal Choi-specified channel transformations as fixed-order quantum combs.
WhyPresents a complete constructive synthesis theory for noncommuting multivariable polynomials extended to quantum channels; novelty is strong, evidence is mainly rigorous theory with query bounds.
In briefEntanglement Sudden Death: Eberly's Work on Local Dynamics' Limits
SummaryThis paper revisits entanglement sudden death (ESD), where entanglement vanishes abruptly at a finite time, extending from two-qubit systems to multipartite entanglement. For two independently damped qubits, concurrence vanishes at a finite time while populations and coherences remain nonzero. For generalized GHZ states under depolarization, global and independent local dynamics yield the same single-qubit evolution but different multipartite ESD times, and their ordering can reverse with the initial state.
SummaryThe paper proposes a simple visualization for pure two-qubit states, built from two Bloch balls for the marginal qubits and an entanglement component combining a rotoreflection and a contraction. The author proves the parametrization is a global diffeomorphism onto the state space, with no gaps or degeneracies. The picture is then used to visualize conditional states, entanglement degrees of freedom, and single-qubit rotations.
In briefFault-tolerant resource estimate for Hubbard ground-state preparation via Lindblad simulation
SummaryThis paper estimates the quantum resources needed to prepare ground states of the fermionic Hubbard model using Lindblad dynamics simulation, following a single-ancilla approach. The authors derive rigorous error bounds with constant prefactors and compare them with empirical errors and practical convergence parameters from circuit-level simulations. They report that empirically chosen parameters can reduce resources by orders of magnitude, giving about 7.7×10^8 T gates per unit of time evolution for a 36-site model, with accurate filtering of energy transitions identified as the main cost.
In briefExact analytic results for the Shannon entropy of the critical Ising chain
SummaryThis paper studies the Shannon entropy of the critical transverse-field Ising chain in the computational basis, a quantity that carries universal subleading information. It represents the full Born distribution as the odd-degree boundary of independent long-range Bernoulli edges, which handles the singular Shannon case n=1 directly. For the periodic chain it isolates an analytic edge anomaly and gives linked-sector coefficients as finite-dimensional integrals, while for an interval it derives the edge term and reconstructs the known coefficient γ1=0.060020(3) from exact finite-size probabilities.
In briefAutomated layout tool for planar superconducting quantum chips, replacing manual design
SummaryLayout of superconducting quantum chips is still mostly manual and can take days or weeks. This paper introduces a formal geometric abstraction of device physics and a three-stage automated flow for partitioning, port assignment, and routing. The authors report that the flow produces manufacturing-ready layouts within seconds to minutes and is up to 25x faster than the state of the art on complex instances. The tool is released open-source as mqt-scpd.</summary>
Michael Feldmeier, Marcel Walter, Gerhard B. P. Huber et al.
In briefMeasurement cost of estimating normalized linear functionals from quantum solution states
SummaryQuantum numerical algorithms often store a positive solution in the amplitudes of a quantum state, while scientists need a normalized linear functional of that solution. The paper studies this output-interface problem and defines a target-dependent susceptibility χ_φ that determines how many copies of the solution state are needed. Near a fixed positive reference state, the optimal copy count is Θ(χ_0 ε⁻² log(1/β)), and two fixed single-copy measurements achieve the same rate.
In briefUniversal critical g factor for spin-1/2 Aharonov-Bohm bound states
SummaryThis paper addresses the long-debated question of whether the spin-1/2 Aharonov-Bohm Hamiltonian has bound states. The authors show that Hagen's solution corresponds to one particular member of the one-parameter family of self-adjoint extensions describing the singular Zeeman interaction. Matching the extension parameter to a finite-radius flux tube gives a critical g factor of g_c=2, independent of flux sector and regularization radius.
Vin\'icius Salem, Edilberto O. Silva, Fabiano M. Andrade
In briefOptimal lower bound on GHZ extraction from MABK Bell violations
SummaryThis paper determines the minimum GHZ extractability compatible with a given Mermin-Ardehali-Belinskii-Klyshko (MABK) Bell score for systems of more than two parties. Extractability is the largest squared overlap with a GHZ state achievable using separate local quantum channels. The exact minimum is an affine interpolation between one half and one, and the authors resolve the previously open case of six or more parties. They also give the exact minimum when every local system is a qubit.
WhyGives exact minimal GHZ extractability for arbitrary party numbers and local dimensions with a uniform analytic proof, a substantial theoretical advance with narrow applicability.
Avraham Kreindel, Aryeh Lev Zabokritskiy (Yohananov)
In briefExact catalysis cannot overcome Gaussian steering for remote Wigner negativity
SummaryThe paper studies whether copies, ancillas, or catalysts can let Bob's measurement make Alice's state Wigner negative at a distance when Alice is limited to Gaussian operations. It introduces steered negativity, a multiplicative monotone whose logarithm equals Gaussian steerability, which bounds the negativity Bob can herald. For strictly unsteerable Gaussian states, even a negative or steerable catalyst that is returned exactly cannot help create remote negativity.
WhyIntroduces a multiplicative monotone and rigorously proves copies, ancillas, and catalysts cannot overcome Gaussian steering for remote Wigner negativity; strong theory but narrow scope.
In briefQuantum algorithms for four density peak clustering problems
SummaryThis paper proposes a quantum Monte Carlo approach to density estimation, a key step in density peak clustering. Building on this, the authors develop quantum algorithms for the full clustering problem and three related tasks: decision clustering, cluster counting, and heavy cluster counting. Under assumptions on how dataset-dependent parameters scale, each problem achieves a polynomial quantum query speedup. Numerical experiments suggest these conditions hold in several practically relevant settings.
