In briefPhase-conjugate twin-wave coherent reception over 100 km of fiber using injection locking
SummaryThis paper experimentally demonstrates a coherent receiver that recovers 200-MBaud signals with modulation formats up to 256-QAM after 100 km of optical fiber. Optical injection locking regenerates the local oscillator from a reference sent through the link, and pilot-assisted optical feedback stabilizes the signal-to-local-oscillator phase so that phase-conjugated twin waves combine at one balanced photodetector. The reported signal-to-noise ratio exceeds the ideal single-mode homodyne standard quantum limit benchmark and conventional heterodyne results by about 3 dB and 6 dB, respectively.
WhyThe authors report injection-locked phase-conjugated twin-wave reception over 100 km, with measured SNR above the single-mode SQL benchmark.
In briefTensor contraction using ZX calculus and graph-based rewriting
SummaryThe paper studies tensor contraction, the evaluation of tensor networks, which is widely used in computer science, physics, and applied mathematics. Finding an optimal bond-by-bond contraction order is NP-hard, so the author proposes first applying graph-theoretic rewrite preprocessing to obtain an equivalent network whose line graph has lower treewidth. The rewriting focuses on ZX calculus, a diagrammatic language for quantum circuits. Numerical simulations are presented to demonstrate the method's effectiveness.
In briefLong-term bond yields computed as quantum ground-state energies using a single-setting VQE on two NISQ devices
SummaryThe paper shows that the long-term yield of a short-rate model equals the ground-state energy of a Schrödinger operator derived from the Feynman-Kac bond-pricing equation, enabling computation by a variational quantum eigensolver (VQE). It covers the Vasicek, CIR and Black-Karasinski models, calibrated monthly to the U.S. Treasury curve from 1985 to 2026. On the ibm_cleveland and IonQ Forte Enterprise devices, the single-setting energy estimator yields errors about ten times smaller than a Pauli-measurement VQE on the same circuits.
Doyeol "David" Ahn (Department of Electrical, Computer Engineering, University of Seoul et al.
In briefRecovering quantum information from black-hole radiation beyond the mean emission yield
SummaryThe paper asks how much information an outside observer can recover from radiation escaping a black hole. At a fixed mean radiation yield, it establishes a sharp recovery limit for single-excitation channels and realizes the qubit limit with an autonomous quantum-memory emitter. Unequal transmissions balance retained coherence against information in failed collection events.
WhyThe authors establish a recovery frontier at fixed mean radiation yield for single-excitation channels and realize its qubit limit with a quantum-memory emitter.
In briefQuantum lower bounds for finding and testing k-to-one collisions in strings
SummaryThe paper studies quantum query complexity for Promised k-to-one Finding on an exactly k-to-one string over a fixed alphabet. It gives tight lower bounds for both adaptive algorithms and one-round non-adaptive algorithms, the latter matching classical birthday sampling even with entangled queries. It also proves a non-adaptive lower bound for k-to-one Testing, resolving an open question from Koiran, Landes, Portier, and Yao.
WhyThe authors report tight adaptive and one-round non-adaptive quantum query lower bounds for promised k-to-one finding on exactly k-to-one inputs, with the one-round bound matching classical birthday s
In briefObservable-algebra framework for quantum coherence in anyonic systems
SummaryThe paper models physical restrictions on operations as subalgebras of accessible observables and splits quantum coherence into three nonnegative contributions. Applied to anyonic systems, it separates the effects of local-charge superselection from those of non-Abelian fusion rules. For pure anyonic states with vacuum total charge, the optimized total and correlated coherence are shown to equal the total and conventional relative-entropy entanglement, respectively.
In briefQuantum-enhanced estimation of two phases in spin-1 condensates
SummaryThis paper studies quantum-enhanced two-phase estimation in a spin-1 Bose-Einstein condensate, where spin-exchange collisions create a spin-nematic squeezed state. The state's quantum Fisher information matrix for the two phases has rank one, so the phases cannot be resolved independently. The authors show that a parameter-independent passive three-mode transformation removes this rank deficiency and enables joint estimation. Analytical results in the undepleted-pump regime are confirmed by exact diagonalization calculations.
In briefReducing parameter sloppiness via intermediate controls in sequential spin interferometry
SummaryThis paper studies sequential multiparameter quantum sensing in which two phases encoded through the same generator are locally indistinguishable. Using a collective-spin interferometer, the authors show that parameter-independent intermediate controls, including a transverse collective rotation and intermediate one-axis twisting (OAT), separate the effective generators. For fixed particle number and matched twisting resource, both marginal precision bounds are lower than those of a separated-OAT strategy. For intermediate OAT, optimizing an upper bound on the Holevo cost yields asymptotic N^-2 scaling.
In briefSuppressing decoherence in quantum dense coding
SummaryQuantum dense coding uses entanglement to send information beyond the limits of classical communication and is a key part of many quantum technologies. The paper studies non-Markovian decoherence dynamics in two types of dense coding protocols, one using discrete-variable and one using continuous-variable systems. It shows that a bound state forming in the energy spectrum of the whole system, including each subsystem and its local channel environment, restores the quantum advantage of dense coding despite decoherence.
In briefBounds and Sufficient Conditions in Quantum Zeno Effect: Limits on state lifetime under repeated measurements and conditions for observing the inverse Zeno effect.
SummaryThis paper studies how repeated measurements on a quantum system change its state lifetime as the interval between measurements varies, either shortening it (Zeno effect) or lengthening it (inverse Zeno effect). It derives upper and lower bounds on the optimized state lifetime, expressed through characteristic time scales in the survival probability P(T), and analyzes bounds on optimal measurement periods or rates along with sufficient conditions for the inverse Zeno effect. The analysis is extended to non-monotonic survival functions and illustrated numerically with optically trapped ultra-cold atoms.
In briefAccess to measurement records and stability of error correction in continuous strategic codes
SummaryThis paper studies which parts of the measurement record a controller can use during recovery in continuous quantum error correction. It formulates continuous strategic codes using open continuous process tensors contracted with causal instruments and conditional recovery. For monitored stabilizer codes, it gives a criterion for merging records without loss and compares the costs of terminal labels and persistent memory. It also derives fidelity bounds and stability guarantees under model mismatch.
In briefFrom ghost SICs to SIC-POVMs: a Galois reduction of Zauner's conjecture
SummaryThe paper studies the existence of symmetric informationally complete POVMs (SIC-POVMs) in quantum information. The authors compute the isolated points of the complexified SIC variety for dimensions 4, 5 and 6, finding that exactly half are SICs. They show that passing from ghost SICs to genuine SICs is purely arithmetic and give a criterion based on a place law over a real quadratic field. Zauner's conjecture remains unproven in this work.
WhyThe authors reduce ghost-to-SIC passage to arithmetic via a Galois place law, reporting computations for d=4,5,6 and proofs for several dimensions, with the Stark part unproved.
In briefNear-optimal learning of quantum many-body Hamiltonians from Gibbs and metastable thermal states
SummaryThis paper studies learning a finite-range quantum Hamiltonian on an n-qubit lattice from copies of its Gibbs states at known inverse temperature β, or from its thermal metastable states. The proposed algorithm reduces the exponential dependence on β from e^{poly(β)} to e^{O(β)}, nearly optimal in the exponent. It builds on a stationarity-test framework and a temperature-independent frequency filter.
WhyThe authors improve the temperature exponent in Hamiltonian learning sample complexity from poly(β) to linear in β, proving a Fisher-information coercivity bound.
In briefSuperradiance from moiré exciton-biexciton condensates: entangled photon pairs versus supercurrent-driven emission
SummaryThis study examines the collective light emission of condensates formed by hybrid moiré excitons in twisted MoTe2 bilayers. Individual ground-state excitons have very long radiative lifetimes, and their emission becomes strong only once condensates form. The biexciton (molecular-type) condensate decays through superradiance that emits path-entangled biphotons, while the exciton (atomic-type) condensate is dark at rest and becomes superradiant when it carries a supercurrent.
In briefA paper on maximum purity, absolute separability, and spectral volumes of absolutely PPT quantum states
SummaryThis paper studies absolutely positive partial transpose (APPT) states and absolutely separable states in m⊗n quantum systems. Under specified dimension conditions, it determines their exact maximum purity and the unique maximizing ordered spectrum. These results disprove both cases of a maximum purity conjecture proposed by Ahiable, Kothakonda, and Winter. The paper also computes the purity maximum for completely absolutely separable states and the asymptotic order of the relative volumes of these sets under the uniform spectral measure.
WhyThe authors determine exact maximum purity and unique maximizing spectra for APPT and absolutely separable states, disproving a conjecture with explicit boundary spectra in quantum entanglement theory
In briefBoson sampling is weak against photon loss
SummaryThis paper asks whether boson sampling experiments remain computationally hard when photons are lost. It shows that even a small, fixed, nonzero uniform loss rate lets a classical computer sample the output distribution efficiently on average. The method exploits the fact that loss suppresses many-photon correlations, so low correlation orders suffice for approximation. The authors conclude that a large photon count alone does not guarantee computational hardness.
WhyThe authors prove that any fixed nonzero uniform photon loss allows average-case efficient classical sampling of boson sampling, with polynomial-time samplers for Fock and Gaussian variants.
In briefOptiPESS: a GPU-accelerated framework that adaptively allocates resources for quantum-chemistry PES scans
SummaryThis paper addresses batched VQE and QAOA potential energy surface scans, where many Hamiltonians differ only in coefficients. It proposes OptiPESS, a GPU-accelerated runtime that uses a Locality-Occupancy-Variance metric to measure Hamiltonian similarity and schedule iteration and shot budgets adaptively. Implemented on CUDA-Q, the authors report reductions of up to 78.3% in evaluations and 74.8% in wall-time while maintaining baseline accuracy.
In briefDiagnostic layer that checks whether quantum error-correction decoders preserve logical information
SummaryThe paper proposes a decoder-independent diagnostic layer for abelian Pauli stabilizer codes, aimed at fault-tolerant quantum computing. A nilpotent supercharge defined by an ancilla fermionic register has its degree-zero harmonic sector equal to the code space, and it is used to test whether a decoder's correction preserves every encoded input. The method also classifies residual errors modulo stabilizers into check violations, harmless stabilizer residuals, and syndrome-silent nontrivial logical actions.
In briefA bottom-up method linking scales to rebuild ground and excited states of extended molecular systems
SummaryThe paper proposes a hierarchical scale-bridging scheme, called encapsulation, for building first-principles electronic structure models of disordered extended molecular aggregates. Coarser-level variables parameterize finer-level operators through a recursive, graph-covariant structure. Applied to excitons, DFT and TDDFT results for monomers and dimers are combined via a many-body expansion to build aggregate-level operators, with a numerical demonstration on crystalline quaterthiophene.
In briefTheoretical estimation of nonlinear response functions and ultrafast spectroscopy of nitrogen-vacancy color centers
SummaryThis paper extends the displaced harmonic oscillator model used to describe the ultrafast optical response of nitrogen-vacancy centers by including state-dependent oscillator modes with different frequencies. The authors show that the nonlinear response function gains a correction term that can be evaluated with operator algebra techniques. This change affects two-dimensional correlation spectroscopy, which resolves ultrafast correlated electron-vibrational dynamics.
In briefFloquet Engineering of Quantum Relaxation: Using Periodic Control to Shape Decoherence
SummaryThis paper proposes a general Floquet formalism that maps periodic control onto relaxation and dephasing channels, decomposing environmental fluctuations into Floquet components that sample the noise spectrum at distinct frequencies. The authors experimentally test the approach on a single nitrogen-vacancy center in diamond under multi-pulse control. By tuning drive and detuning, they reach operating points where the dominant decoherence channel vanishes, strongly suppressing Floquet dephasing, with coherence gains following the predicted Floquet coupling coefficients.
In briefHidden selection rules and amplitude ceilings in quantum Fourier models
SummaryThis paper studies quantum models with Pauli data encodings, which compute trigonometric polynomials whose expressivity depends on the Fourier coefficients a circuit can reach. It identifies two structural rules that can be checked before training: an antiunitary time-reversal rule and a unitary reflection rule, which remove certain frequencies. For gate-level circuits, deciding whether such a rule exists reduces to a linear system over GF(2) solvable in polynomial time, and the time-reversal rule holds in 17.6% of 6,120 standard template configurations. The paper also derives a tight ceiling of 2^(-m) on the top coefficient for single-upload encodings and a depth-independent bound for re-uploading, which were not violated on a non-linearity benchmark and predicted trained performance on real data, with experiments on a 65-qubit IBM chain.
In briefMaximum purity of absolutely separable and PPT quantum states in qutrit-qudit systems
SummaryThis paper studies bipartite quantum states in qutrit-qudit systems C^3⊗C^n with n≥3. It determines the maximum purity of absolutely separable states and absolutely PPT states, showing both classes share the same maximum. The authors also bound the minimum partial-transpose eigenvalue reachable by global unitary transformations in terms of purity and characterize the states attaining this bound. These results confirm the inscribed-polytope purity conjecture for all qutrit-qudit systems.
WhyThe authors show that absolutely separable and absolutely PPT qutrit-qudit states in C³⊗Cⁿ (n≥3) share the same maximum purity, confirming the inscribed-polytope conjecture of Ahiable, Kothakonda and
In briefExponentially Suppressed Bit-Flip Errors in Dissipative Cat Qubits
SummaryThis paper studies a dissipative cat qubit subject to single-photon loss, described by the infinite-dimensional Lindblad generator L_ε=D[a²−α²]+εD[a]. For sufficiently large α and sufficiently small ε, it identifies a two-dimensional spectral subspace near zero. The authors establish an upper bound on the slow decay rate that decreases exponentially with α², uniformly in ε, proving exponential suppression of bit-flip errors.
WhyThe authors prove an exponentially small upper bound on the bit-flip decay rate in a dissipative cat qubit, uniform in the loss rate, a result relevant to quantum error correction.
In briefFast model-based calibration method for a nitrogen-vacancy quantum processor
SummaryThis paper presents a simulation-assisted calibration workflow for nitrogen-vacancy (NV) center quantum processing units. It combines a digital twin, optimal control pulses, and Fisher-information-guided experiment design into an iterative parameter estimation feedback loop. The authors report the same calibration precision as standard techniques with up to a 4x reduction in measurement time.
Tobias F. Sjolander, Marco Rossignolo, Lorena C. Bianchet et al.
In briefChaos and ergodic-like dynamics in repeated nonlinear quantum protocols
SummaryThis paper studies iterated nonlinear quantum protocols that realize nonlinear dynamics through measurement and postselection. The authors examine a protocol family whose nonlinearity order is set by the number of qubits used in each step. By analyzing the resulting rational maps with numerical diagnostics, they find parameter regions showing ergodic-like dynamics for orders 3, 4, and 5, and characterize the chaotic behavior using the distribution of Lyapunov exponents.
In briefFractal Structures in Iterated Quantum Protocols Under Noise
SummaryThe paper studies iterated quantum protocols where qubits are entangled with CNOT gates, most are postselected, and a parametrized unitary acts on the remaining qubit. The authors compute the box-counting dimension of pure-state Julia sets and examine how preparation noise, depolarizing errors, and coherent ZZ errors affect these dimensions. They also propose a diagnostic test combining conditional fidelity and acceptance statistics, demonstrated on IQM Emerald and Rigetti Cepheus-1-108Q hardware.
In briefTelecom-band InAsP quantum dots self-assembled by controlling the cooling path
SummaryThis paper reports a new epitaxial method for growing InAsP quantum dots on InP(001) substrates. High-temperature arsenic exposure forms a shallow near-surface InAsP layer through As-P exchange, and the cooling path plus continued arsenic supply determine whether three-dimensional islands form. Capped emitters span 1.2 to 1.6 micrometers, with single-photon emission observed up to 100 K, and an exchange dose calibration is provided for targeting the median emission wavelength.
Yiteng Zhang, Doaa Abdelbarey, Markus Etzkorn et al.
In briefDensity functionals for the Pauli-Fierz Hamiltonian
SummaryThis paper builds a density-functional theory for the Pauli-Fierz Hamiltonian of nonrelativistic quantum electrodynamics, following Lieb's convex-analytic approach. It uses the electron density and a combined current density as basic variables and proves representability results for these density-current pairs. The authors also analyze the mixed-state and pure-state functionals, the zero-coupling limit, and the long-wavelength dipole limit.
WhyThe authors extend Lieb's convex-analytic density-functional framework to the Pauli-Fierz Hamiltonian, proving representability, attainment of the infimum, zero-coupling recovery of Vignale-Rasolt, an
Mih\'aly A. Csirik, Andre Laestadius, Markus Penz et al.
In briefHow the pump scheme changes photon statistics in few-emitter lasers
SummaryThe paper tests whether replacing the full excitation cycle of a laser gain medium with a single two-level pump jump is a valid approximation in few-emitter laser models. It compares the two approaches at fixed cavity and laser-transition parameters, with the two-level pump rate fitted to the same mean photon number, using an exact solution of the cavity-emitter master equation. At matched photon number, the multilevel pump cycle drives the output counting Fano factor for two and three emitters well below one, while the fitted two-level model gets these statistics wrong.
In briefQubit links across a metamaterial, with less stray entanglement
SummaryThis paper proposes encoding superconducting qubits as dual-rail or spin-locked transmons coupled all-to-all through a metamaterial waveguide. The encoding suppresses spurious entanglement from shared-mode architectures. A simulation of two dual-rail transmons gives a gate infidelity of 1.4×10⁻³ over 152 ns, dominated by photon loss. The paper also bounds the array size under photon loss and mode crowding.
WhyThe authors propose encoded transmons in a metamaterial waveguide for all-to-all coupling; simulations of two dual-rail qubits report 1.4e-3 gate infidelity at 152 ns.
Or Golan, Alexey V. Gorshkov, Andreas Butler et al.
In briefBenchmark of quantum statevector simulators for scientific computing
SummaryThis paper benchmarks three open-source quantum simulators, Cirq (qsim), CUDA-Q, and Qiskit (Aer), on a single Azure virtual machine. The test simulates the 2D quantum acoustic wave equation for 7 to 29 qubits, measuring CPU and GPU runtime, multi-core scalability, and GPU-over-CPU speedup. The rankings differ across categories, and no single framework dominates in all configurations. The authors conclude that backend choice should depend on hardware and problem size.
In briefEstimating Quantum Divergences Using p-Power Means
SummaryThis paper studies the estimation of the quantum divergence Φ_p(ρ‖σ) defined with p-power means, a quantity previously investigated by Lam and Le (2021). For any constant p in (0,1), the authors present quantum algorithms that are efficient in both sample and query complexity. They further show that estimating Φ_p(ρ‖σ) is BQP-complete in the low-rank case.
In briefPhase-tunable Liouvillian topology with dual winding and skin effects
SummaryThis paper studies Liouvillian skin effects in open quantum systems and shows that directional edge localization can arise even when population exchange between sites is exactly balanced. A single tunable phase parameter α determines the direction of localization. By independently twisting the left and right indices of the density matrix, the authors reveal two winding structures linked by an antiunitary mirror symmetry.
In briefWeighted constrained shadow tomography for more accurate reduced density matrices
SummaryThis paper improves constrained shadow tomography (CST), a method for estimating reduced density matrices in quantum simulations of many-fermion systems. The authors orthogonalize the measurement constraints and weight each independent measurement direction by how strongly the quantum computer samples it, incorporating these weights into a semidefinite program via a Schur-complement least-squares objective. The approach is demonstrated on hydrogen chains using a quantum simulator and on azobenzene using a quantum processor, where the reconstructed 2-RDM accuracy improves without increasing the measurement budget.
In briefLimits on estimating several quantum parameters at once, for general and adaptive sensing strategies
SummaryThe paper develops a conic-programming framework for estimating several parameters of a quantum process under different classes of sensing strategies. For N uses of an identical channel, it proves an exact 1/N scaling for an RLD-based positive-cone lower bound, even with indefinite causal order. For fixed-order adaptive strategies, each process-side conic bound matches the state-estimation bound optimized over sensor combs. A noisy three-parameter field-sensing model illustrates the framework.
WhyThe authors propose a conic-programming framework for multiparameter quantum process estimation, prove an exact 1/N RLD positive-cone bound including indefinite causal order, and show equality with se
