In briefSampling gauge field plaquettes exactly for lattice gauge theories via local constraint solves
SummaryThis paper proposes a multilevel normalizing-flow method that samples lattice gauge theory configurations directly in plaquette space while enforcing Bianchi constraints exactly. A coarse-to-fine factorization turns a globally coupled constraint problem into a sequence of local solves. The method is validated for U(1) in two and four dimensions and for SU(2) in two dimensions, where it outperforms link-space baselines, with the advantage growing toward weak coupling.
Ankur Singha, Jacob Finkenrath, Karl Jansen et al.
In briefA silicon-on-SiC chip platform for coupling to telecom-band vanadium defects
SummaryThe paper presents a silicon-on-SiC photonic platform in which silicon nanocavities evanescently couple to shallow vanadium dopants in commercial 4H-SiC, improving photon collection at the zero-phonon line. The authors report high-purity single-photon emission from isolated vanadium centers with a Purcell-enhanced lifetime of 109 ns. The full optical interface runs through a single lensed fiber, including a 905 nm repump laser. The work positions the platform as a scalable route to telecom-wavelength spin-photon interfaces.
Timothy Draher, Nolan Bitner, Vasileios Niaouris et al.
In briefSpeed-Fisher Information: A Unified Measure of Chaos and Irreversibility
SummaryThe paper proposes a unified way to study classical and quantum chaos by measuring how a system's stationary states respond to slow driving. This sensitivity to average protocol speed is called speed-Fisher information and is linked to irreversible entropy production. The authors show that chaos appears as divergence of this information with protocol time, controlled by low-frequency spectral weight of the perturbation. The approach applies to Hamiltonian quantum and classical systems and extends to non-Hamiltonian classical flows, illustrated with simple examples.
Nachiket Karve, Nathan Rose, David Campbell et al.
In briefOptimal Query Complexity for Preparing Ground States
SummaryThis paper determines the optimal number of queries needed to prepare a quantum system's ground state to trace-distance error ε, given a known energy threshold in the spectral gap. It presents two algorithms, one with expected query count O((α/Δ)(γ⁻¹+log(1/ε))) and another with worst-case count O((α/(γΔ))log(1/ε)). A lower bound matching the expected query count is also proven.
WhyGives matching upper and lower bounds on ground-state preparation query complexity, improving known spectral-filter methods with rigorous proofs.
In briefAn Optimal Quantum Linear Systems Algorithm: Tight Query Bounds for Solving Linear Equations on Quantum Computers
SummaryThe paper studies the quantum linear systems problem, where one has query access to a sparse matrix A with condition number κ and must produce a quantum state approximating the solution x of Ax = b. The authors show the query complexity is Θ(κ√d·log(1/ε)), improving previous upper and lower bounds. They also resolve an open question of Berry and Childs by showing any N×N unitary can be implemented with bounded error using O(√N) matrix-entry queries.
WhyProves a tight Θ(κ√d log(1/ε)) query bound for quantum linear systems and resolves an open problem of Berry and Childs, a significant theoretical advance.
Carlos Bravo-Prieto, Aram W. Harrow, Robin Kothari
In briefThe Power of Oracle Access: Optimal Complexity for the Abelian State Hidden Subgroup Problem
SummaryThis paper studies the state hidden subgroup problem, which asks for the symmetries of an unknown quantum state. For finite abelian groups, it gives a query-model algorithm using O(log(|G/H|)/√ε) forward and inverse queries together with a matching lower bound. In the sample model it shows Θ(log(|G/H|)/ε) copies are necessary and sufficient. The quadratic improvement in ε therefore comes from coherent access to the preparation circuit.
WhyMatching upper and lower bounds in query model plus sample-optimality proofs give strong evidence and meaningful advances for a subfield.
In briefOptimal performance of a chaotic Floquet quantum battery, explained as a quantum device that stores and releases energy.
SummaryThe paper studies a battery of N uniformly interacting qubits charged by periodic transverse kicks and disorder in the interaction direction. Disorder takes the dynamics out of the permutation-symmetric subspace, increasing stored energy; in the large-disorder limit, random matrix theory gives exact results and energy fluctuations become negligible. With dephasing noise in the storage phase, large disorder keeps ergotropy close to stored energy, with efficiency approaching unity.
In briefLearning sparse quantum states using only single-qubit measurements
SummaryThe paper studies learning sparse quantum states, whose density matrices have at most s nonzero entries in an unknown product basis. It shows such states, even with long-range entanglement, can be learned efficiently using only single-qubit measurements, without entangling gates. For constant sparsity, sample and classical computational complexity are polynomial. For sparsity growing polynomially with n, sample complexity remains polynomial.
WhyShows sparse entangled states can be learned with only single-qubit measurements, with polynomial sample and, for constant sparsity, classical complexity guarantees.
In briefEvaluating Machine Unlearning in Materials Science: Retraining Baselines and the Deletion Floor
SummaryThe paper notes that in materials machine learning, closely related retained data can keep property predictions accurate after a record is deleted, so post-deletion error is an ambiguous measure of unlearning. The authors define the deletion floor as the expected target loss under a specified retraining procedure for the deleted request, and provide theoretical bounds and empirical comparisons. They recommend reporting reference loss, prediction change, and retained utility together.
In briefElectrothermal behavior of superconducting nanowires in a commercial CMOS process
SummaryThis paper studies titanium nitride nanowires built in the polysilicon resistor layer of a 22 nm FD-SOI commercial CMOS process. The authors measure current-voltage characteristics and compare retrapping currents with thermal models of longitudinal conduction and interfacial phonon cooling. They find interfacial cooling dominates and report an effective cooling coefficient and film thermal conductivity.
Mohamed Gharib, Leonid Popryho, Salma Abdelzaher et al.
In briefLow-weight canonical logical bases built from pair-partition codes
SummaryThe paper builds complete canonical logical bases for qubit CSS codes by assigning quaternary coefficients to binary circulant permutation matrix pair-partition checks, then constructing, normalizing, and expanding logical representatives into binary matrices. It reports parameters, check ranks, and basis weights for seven binary codes. For example, the [[2048,512,24]] code has canonical logical representatives with binary weight 27 on both the X and Z sides.
In briefExponential lower bounds for low-degree strategies in quantum position-based cryptography
SummaryThis paper studies lower bounds on the resources needed for non-local quantum computation (NLQC), in which two distant players cooperatively implement a bipartite unitary. The authors consider a family of diagonal ±1 unitaries indexed by Boolean hypercube elements and show that, under a low-degree polynomial condition on the first round, implementing at least one of them requires resources growing exponentially. The result matters for the security of position-based quantum cryptography, and the proof relies on type constants of particular Banach spaces and random estimates of Boolean functions.
WhyProves exponential resource lower bounds for low-degree NLQC strategies via Banach space type constants, addressing a major open problem with rigorous proof and implications for position-based quantum
Isabel M. Moreno-Cuadrado, David Perez-Garcia, Carlos Palazuelos
In briefQC-Stark: A Multi-Task Benchmark Showing Uneven LLM Abilities on Quantum Computing Tasks
SummaryThe paper introduces QC-Stark, a benchmark that tests large language models on 11 quantum computing tasks, including circuit construction, debugging, compilation, error correction, and simulation. In 2,750 evaluations, overall model rankings were found to hide large differences between individual tasks. For 4 of the 11 tasks, the correlation between overall and per-task rankings was statistically insignificant.
In briefQuantum query complexity beyond worst-case inputs using smoothed analysis
SummaryThis paper brings smoothed analysis, a classical framework for explaining algorithm performance beyond worst-case inputs, into quantum query complexity. It shows a total function whose smoothed quantum query complexity is exponentially smaller than its classical query complexity. It also gives near-tight characterizations for symmetric Boolean functions and quantum speedups for string problems such as pattern matching and edit distance.
WhyFirst systematic study of quantum smoothed analysis, giving exponential query separations and unifying worst- and average-case results for symmetric Boolean functions.
In briefSublinear Pauli-measurement protocol for estimating quantum fidelity
SummaryThe paper presents a protocol for estimating the quantum fidelity, to precision ε, between a known target state and an unknown lab-prepared state. The protocol uses a sublinear number of Pauli basis measurements, o(d^0.9908/ε²). The source abstract states only this result and gives no further detail.
Jayadev Acharya, Abhilash Dharmavarapu, Yuhan Liu et al.
In briefAsymmetric Errors in Noisy Quantum Computer Experiments
SummaryThis paper extends earlier analyses of NISQ experiments, including Google's 2019 quantum supremacy experiment, with a focus on asymmetric readout errors. The authors use experimental data and simulations to examine how gate and readout errors affect the fractions of zeros and ones in the output samples. For 12 to 53 qubits, Google's experimental data show that these fractions reflect only the reported asymmetry in readout errors, with no sign of the increased zero fraction predicted for amplitude damping gate errors.
In briefWhere coherence comes from in quantum and classical induced-coherence interferometers, and how to control it
SummaryThis paper studies wave-particle duality in induced-coherence interferometers, a type of interference setup. Earlier work showed that Young's double-slit interference obeys a triality relation linking coherence, predictability, and entanglement. The authors show this triality persists in the quantum induced-coherence interferometer, while the classical version reduces to the well-known duality inequality. They also examine the origin and control of coherence and entanglement, finding that path indistinguishability plays a complementary role in both.
Balakrishnan Viswanathan, Ravi Kamal Pandey, Devendra Kumar Mishra et al.
In briefHow fast can a parent estimate its children's value? A quantum algorithm for stochastic games
SummaryThis paper presents a quantum algorithm for two-player stochastic games whose trees alternate adversarial and chance layers. It estimates the game's value using queries to leaf values and gives an upper bound on the query complexity. The authors show that quadratic speedups known for adversarial trees and single expectations both carry over when nested.
WhyNests quantum adversarial-tree speedup with quantum mean estimation, retaining quadratic speedups in both branching factor and accuracy.
Marien Raat, Merlin Incerti-Medici, James R. Wootton et al.
In briefElectron decoherence from cylindrical holes and circular apertures in metal films
SummaryThis paper studies how fast free electrons lose coherence when passing through two canonical geometries: a cylindrical hole in a realistic metal and a circular aperture in a thin perfectly conducting film. Using an electromagnetic Green-tensor approach with the fluctuation-dissipation theorem and full retardation, the authors derive decoherence probability and elastic phase. For the cylindrical hole, a universal expression linear in temperature emerges in the high-conductivity, high-temperature limit.
In briefCircuit design rules for placing gates and entanglement in quantum neural networks using Fourier analysis
SummaryThis paper gives an explicit rule for arranging local rotations and entangling layers in a parameterized quantum circuit so that a target Fourier coefficient of its output can contribute. It decomposes operator space into frequency-indexed two-dimensional invariant planes using the adjoint action of the encoding generator. The design is validated on a single encoding layer through a placement ablation, regression tasks from PDEBench and physics-informed Maxwell field modeling, and tests showing robustness to moderate simulated gate noise and damping.
In briefTrade-offs in high-dimensional time-bin entanglement for quantum key distribution
SummaryThis paper examines whether high-dimensional time-bin entanglement or simpler qubit encodings give better results in quantum key distribution. The authors study single Franson-based interferometers, using asymptotic key rate and shared entanglement as main metrics, and introduce a flexible noise model covering the relevant parameters. They find that high-dimensional encoding can still outperform qubit-based protocols in some regions when the pair arrival rate is limited, for example by loss or limited pump power.
Alexandra E. Bergmayr-Mann, Gl\'aucia Murta, Marcus Huber
In briefMaking HEOM simulations of strongly coupled open quantum systems more numerically stable
SummaryThe hierarchical equations of motion (HEOM) method simulates open quantum systems, but truncating its hierarchy for bosonic baths can cause numerical instability. The authors use an auxiliary Fock-space picture to identify unbalanced hierarchy-raising terms and apply a non-unitary similarity transformation that balances them, reducing their numerical impact. They demonstrate the approach on a spin-boson model with a Brownian oscillator spectral density and then a structured spectral density, reporting that it permits simulations at much stronger system-bath coupling.
Salvatore Gatto, Samuel L. Rudge, Bokang Hou et al.
In briefDiscrete scale invariance in Ising mesons: how kink motion in a magnet gives log-periodic energy levels
SummaryThe paper studies composite excitations in a transverse-field Ising chain with long-range bonds decaying as 1/r^4. The authors show that dressed domain walls experience an asymptotic inverse-square attraction whose strength is set by spontaneous magnetization. The curvature of the dressed two-kink threshold sets the kinetic scale, and together these determine the scale-anomaly exponent and the meson hierarchy. Full-spin exact diagonalization and a fourth-order weak-field Hamiltonian are reported to support the coupled energy-size scaling in a finite window.
In briefA classical algorithm that efficiently estimates coarse-grained Boson Sampling statistics.
SummaryThis paper studies a type of coarse-grained statistic for Boson Sampling, called linear statistics, which are linear functions of output photon occupation numbers. The authors present an efficient classical algorithm that approximates these statistics within additive error for input states such as Fock and squeezed states. The framework unifies prior results on simulating molecular vibronic spectra and classically approximating detector-binned distributions. The algorithm can also classically evaluate a proposed Boson Sampling-based one-way function, while other cryptographic proposals fall outside its scope.
In briefFixed-time Gaussian state transfer using only collective dissipation
SummaryThis paper proposes a fully static method for transferring Gaussian quantum states using only dissipation from collective coupling to a shared environment, with no coherent transport or time-dependent control. An analytic transfer time is derived. Amplitude-level asymmetries leave performance largely unaffected, while phase-level detuning disrupts transfer and produces revival behavior. In the fast-memory regime, the channel recovers the Markovian limit.
In briefA dilation theorem for continuous quantum stochastic processes
SummaryThis paper presents a dilation theorem for continuum quantum stochastic processes, linking stochastic dynamics on a system to deterministic Schrödinger evolution on a larger space. The authors show that any continuous process tensor can be approximated arbitrarily well by an explicit closed description in which system and environment are coupled by a bounded Hamiltonian. These regular representations form a dense, easily handled subspace, enabling a continuum version of Choi duality and a rigorous treatment of continuum controls.
Jon\'a\v{s} Fuksa, Clara Wassner, Jens Eisert et al.
In briefHeuristic lower bounds on real Grothendieck constants, finite and infinite
SummaryThis paper proposes candidate lower bounds on the real Grothendieck constants K_G(d) and their infinite-dimensional limit K_G using rotationally invariant cubic kernels. It identifies a threshold above which hemispherical binary strategies become unstable under cubic boundary deformations, and conjectures these strategies are globally optimal there. If true, this gives K_G ≥ 9π/16, improving the rigorous bound 6π/11. Large-scale optimization supports these predictions and suggests improved bounds for dimensions 4 to 24.
