In briefA bound showing free positive maps cannot beat the reduction criterion
SummaryThe paper studies positive maps built from free probability, extending work by Collins, Hayden, and Nechita on entanglement detection. It proves that positive free maps tied to compactly supported freely infinitely divisible distributions are no stronger than the reduction criterion in every ancillary dimension. Consequently, these maps cannot detect positive partial transpose entanglement.
In briefBoundary-condition independence of infinite-chain ground states in the S=1 J-D antiferromagnetic chain
SummaryThis paper studies infinite-chain ground states of the S=1 J-D antiferromagnetic chain for sufficiently small |D|, comparing periodic chains with an even number of sites and open chains with an odd number of sites under the same magnetic field at both ends. The authors prove that both settings have infinite-chain limits along the full sequence and that the two limits coincide. The common limit is a symmetric, locally unique gapped ground state whose local expectation values depend continuously on D.
In briefTwo-qubit binegativity can rise under one-sided amplitude damping
SummaryThe paper examines the conjecture that the binegativity of two-qubit states is an entanglement monotone. The authors give a full-rank counterexample in which amplitude damping applied to only one qubit increases the state's binegativity, with the increase calculable exactly. They also construct a family of counterexamples that vary continuously with a parameter.
In briefExperimental observation of measurement-induced localization in a solid-state nuclear spin system
SummaryResearchers observed measurement-induced localization in an interacting carbon-13 nuclear spin system in diamond. Unlike earlier circuit-model experiments, the system evolves under a physical many-body Hamiltonian with measurements applied at intervals. Spin autocorrelation times increase substantially as measurement frequency rises, and numerical simulations support the conclusion that measurement can drive the many-body system into a localized regime.
WhyExperimentally observes measurement-induced localization in a solid-state spin system, supported by numerical simulations, though the evidence scope is limited.
In briefA minimal ancilla design for boosted type-I photonic fusion
SummaryFusion gates can create large entangled photonic states for linear-optical quantum computing, but without extra photonic resources their success probability is limited to 1/2. This paper proposes a boosted type-I fusion gate that uses only two independent ancillary single photons and no entangled ancillary input. It reaches a direct success probability of 5/8, matching a previous four-single-photon scheme while using half as many ancillary photons. The circuit is mostly passive, with one active element that applies a phase shift or swaps two modes based on intermediate photodetection results.
In briefResonant multiphoton conversion via a shared vibration in cavity QED
SummaryThe paper shows that a vibration shared by two emitter groups can create multiphoton resonance and constructive interference among conversion pathways. For opposite displacements with integer magnitude ratio r≥2, the displacements cancel, linking the displacement ratio to the conversion order. Independent vibrations can be tuned to resonance yet cancel conversion, showing energy resonance alone is insufficient. Relative displacement direction is presented as a means to control conversion and its noise response.
In briefEstimating covariance matrices for Stokes-like measurements under deformed phase space
SummaryThis paper studies how phase-space noncommutativity appears in an anisotropic oscillator and proposes an optomechanical protocol to test it using Stokes-like measurements of an optical field. A Darboux transformation maps the deformed dynamics to an equivalent Hamiltonian in canonical variables, from which the covariance matrix is derived. An interferometric scheme with a reference beam and photodetectors then yields the modified normal-mode frequencies, allowing estimation of the parameters θ and η.
In briefFeasibility of Distributed Fault-Tolerant Quantum Computing: Linking Quantum Processors to Run Algorithms
SummaryThis paper analyzes the resources needed for distributed fault-tolerant quantum computing, where superconducting processors are connected by microwave or optical links. Under forward-looking microwave-link assumptions of a 1 MHz Bell-pair generation rate and 90% fidelity, one communication channel per node can substantially reduce the physical qubits needed per node, but execution time rises about tenfold. Reducing that time overhead requires considerably more communication resources, such as higher Bell-pair fidelity and extensive multiplexing.
Takumi Kobayashi, Hodaka Kurokawa, Yasunari Suzuki et al.
In briefTwo exact quantum queries depend on at most six variables
SummaryThis paper gives a direct analytic proof that any total Boolean function computable exactly with at most two quantum queries depends on at most six input variables, and this bound is sharp. Earlier work relied on a numerical classification of Boolean functions on at most four variables, whereas this is, to the authors' knowledge, the first unconditional proof. The key technical step is a support-and-branch decomposition that handles interference, since query-path vectors need not be orthogonal.
In briefResource-optimal two-tier screening for characterizing quantum systems
SummaryQuantum processors need frequent benchmarking to track hardware drift, but standard methods such as randomized benchmarking consume substantial resources. The paper proposes a two-tier strategy in which a lightweight probe runs regularly and triggers full characterization only when a statistically significant change is detected, with the probe designed to maximize detection sensitivity under resource constraints. The framework is applied to gate-quality verification and compiler benchmarking, and experiments on Rigetti Ankaa-3, IQM Garnet, and IQM Emerald match the theoretical predictions for optimal circuit sizes.
In briefHidden Fisher Information in Many-Body Quantum Sensors: Readout Complexity Bottleneck
SummaryThe paper introduces a moment Fisher hierarchy that measures how much quantum Fisher information low-degree collective spin moments can access, and defines a readout-complexity scale k90. In a nonlinear collective-spin sensor for systems up to N=100, first moments access only about 10^-2 of the available information, and the required degree grows to roughly 28. This identifies a finite-size readout-complexity bottleneck in many-body quantum metrology.
Atta ur Rahman, Muhammad Noman, Samira Elghaayda et al.
In briefHelstrom geometry with spectral calibration that changes over time: a study of how a finite quantum-spectral model's distance measure responds when its link strengths vary
SummaryThis paper extends earlier work on a finite scalar-qubit-scalar spectral triple whose Connes distance matches the Bloch-ball trace metric up to a factor of 2/Λ. The authors analyse how the link strengths vary over time, separating the distinguishability and calibration contributions to the spectral rate. A depolarizing example shows spectral growth even while the trace distance contracts monotonically.
In briefGlobal V-Representability in TDDFT Beyond Singular Times: A Hubbard Dimer Study
SummaryThis paper studies whether the time-dependent density of an interacting two-particle Hubbard dimer can be reproduced by a non-interacting Kohn-Sham system, even beyond singular times where standard inversion formulas fail. The authors analyze both the conventional time-dependent variational formulation and a recently proposed geometric formulation of TDDFT. They prove global-in-time V-representability for both, show that singular times lead to non-uniqueness of the effective potential, and classify the resulting solution set.
In briefBenchmarking and environment-aware compilation of matrix product states for preparing strongly correlated molecular initial states
SummaryThis paper benchmarks existing methods for compiling classically optimized matrix product states into quantum circuits, comparing their accuracy, CNOT gate cost, classical runtime, and parallel scalability on hydrogen chains and iron-sulfur clusters. The authors also introduce a divide-and-conquer, environment-aware compilation algorithm (DCE). The results identify different methods as suited to different system sizes and accuracy targets. For the FeMo-cofactor, DCE combined with an MPS in entanglement-minimized orbitals is reported as a resource-efficient route to initial-state preparation.
In briefBanach-Cesàro positive operator-valued measure: a mathematical construction of covariant measures on the real line via averaging, with an integration theory and Fourier transform for them.
SummaryThe paper constructs bounded, finitely additive, covariant positive operator-valued measures on the real line by applying generalised Banach-Cesàro asymptotic averaging to locally finite covariant POVMs. Unlike the strictly shift-invariant case, the averaged operator values may fail to commute while the total mass is normalised. The authors develop an integration theory for complex-valued functions and define an operator-valued Fourier transform on the resulting integration spaces, analysing the algebraic constraints covariance places on exponential multipliers.
In briefEfficient block encodings for simulating molecular vibrations on quantum computers
SummaryThis paper develops more efficient ways to block-encode the vibrational Hamiltonian of molecules, a step needed for quantum simulation of molecular vibrations. The authors build linear-combination-of-unitaries representations using Pauli decomposition and tensor hypercontraction, and extend the BLISS technique to lower the LCU 1-norm. For the molecules studied, they report that BLISS-THC cuts the Toffoli cost of phase estimation by more than two orders of magnitude compared with existing approaches.
Shashank G. Mehendale, Ignacio Loaiza, Shreyas Malpathak et al.
In briefBell-CHSH observables induced by probes in the Fewster-Verch framework
SummaryThis paper gives an explicit operator-level construction, within the Fewster-Verch measurement framework, of observables that test the Bell-CHSH inequality in relativistic quantum field theory. Using local couplings to Majorana probes, it obtains dichotomic Bell observables for a free Majorana field in 1+1 dimensions. Under explicit attainability hypotheses, these induced observables reach the Tsirelson bound in a state prepared from the vacuum. The construction also extends to coupled scalar fields.
In briefTask-Directed Spectral Design for Local Quantum Tomography: Choosing Probe Directions
SummaryThis paper studies local pure-state quantum tomography when a parametric model, a credible center, and a differentiable downstream task are known before measurement. It uses generalized eigendirections defined by the pullback Fubini–Study metric and the task metric to build a fixed library of geodesic fidelity probes, and proves optimality results under stated conditions. In six-qubit numerical experiments, the proposed design yields lower mean task error than the best post hoc adaptive methods while using far fewer settings and no feedback.
