In briefLinear-optical quantum computing using qubits within high-dimensional qudit resource states
SummaryThis paper proposes a linear-optical quantum computation scheme that begins with high-dimensional entangled qudits but computes on qubits defined in their subspaces. It raises the success probability of linear-optical fusion from 50% to 1-1/d for qudits of dimension d, without ancilla photons or quantum codes. The authors show that a 2D qubit cluster state can be built from 5-qudit 1D cluster states via pairwise fusion, and numerically report improved loss tolerance for a percolation-based scheme at constant photon number per resource state.
In briefOptimizing quantum error correction by attributing errors to circuit components
SummaryThis paper introduces an error attribution method that measures how much each circuit component affects the logical error rate in quantum error correction. The sensitivities are estimated from the same Monte Carlo samples used for the logical error rate. In simulations of rotated surface codes and lifted product codes, halving noise on about 5%-7% of sensitivity-selected components cut logical error rates by roughly 15%-25%, about twice the reduction from random selection.
In briefMultivariate quantum signal processing with optimal query complexity: a method for applying polynomial transformations of several variables in quantum circuits using the fewest possible data queries.
SummaryThe paper presents a quantum circuit that implements any multivariate trigonometric polynomial up to an explicit normalization. Each variable is queried exactly as many times as its degree, and the authors prove this query complexity is optimal. The construction is extended to commuting unitaries, and the paper also studies gradient variance and initialization for trainable-rotation quantum learning models.
WhyPresents a circuit realizing any multivariate trigonometric polynomial with proven optimal query complexity, a substantial improvement over per-monomial methods.
In briefQuantum utility routing for CV-QKD networks with trusted and untrusted relays
SummaryThis paper proposes Quantum Utility Routing (QUR), a routing framework for continuous-variable quantum key distribution networks that combines trusted links with untrusted measurement relays. It incorporates finite-size secret key rates directly into route search and compares a graph-optimized version and a machine-learning fixed-weight version against A* and Max-Min routing. At the default configuration, both QUR variants improve mean path key rate over A* while using substantially fewer network resources than Max-Min.
In briefDegree-based annealing offsets change which certified optima quantum annealers sample for minimum vertex cover
SummaryThis paper studies whether setting node-dependent anneal offsets according to vertex degree (DC-OSQA) changes the composition of optimal solutions sampled by a quantum annealer solving Minimum Vertex Cover. Compared with a zero-offset baseline on sparse Barabási-Albert graphs with N=70 to 150, the mean number of distinct certified candidates rose from 171.7 to 455.8. Hamming-distance families also increased from 22.5 to 80.0 on average. The results indicate that the observed certified optima shift within a fixed read budget.
In briefProof that quantum advice prevents size-preserving error amplification
SummaryThe paper shows that, unlike quantum Merlin-Arthur games, polynomial-time quantum computation with quantum advice does not admit error reduction without increasing the advice size. It presents decision problems where even a vanishing additive error reduction requires longer advice. The authors prove a stronger separation, establishing that BQP classes with different error bounds are strictly distinct.
WhyShows size-preserving amplification fails with quantum advice, giving a rigorous separation with explicit error gaps, a notable theoretical advance.
In briefDistance-independent universality of the Clifford+T gate set
SummaryThe paper studies the well-known theorem that the Clifford+T gate set is universal for quantum computing. The authors define projective distance measures using four axioms and prove the universality theorem for every distance measure satisfying them. They show the Hilbert-Schmidt distance qualifies and give a construction that turns other distances into projective ones. The proof is also formalized in Lean.
In briefLevel-3 quantum bootstrap is not tight for a 3D double well at an excited level
SummaryThe paper studies the coupled three-dimensional double-well Hamiltonian and constructs, at the first excited level and at the ground state, a linear functional on polynomials of degree at most 6. This functional satisfies all constraints of the standard level-3 eigenstate bootstrap and has a strictly positive definite moment matrix, yet assigns a negative value to a nonnegative polynomial, so no quantum state realizes it. The authors note that eigenstate constraints never reach the top-degree momentum moments, a fact holding at every level. All algebraic steps are exact rational certificates, with numerics done in rigorous ball arithmetic.
WhyConstructs a strictly positive level-3 bootstrap interior point realized by no quantum state, exposing a structural gap in eigenstate constraints. Evidence rests on exact rational certificates and rig
In briefQuantum algorithm that speeds up discrete simulation optimization at the best possible rate.
SummaryThis paper asks whether quantum computing can speed up the convergence of discrete simulation optimization under a fixed simulation budget. The authors derive a minimax lower bound on the expected optimality gap for any quantum algorithm, showing a quadratic improvement in dependence on the budget but a worse dependence on the number of decisions. They propose QUEST, the first fixed-budget quantum algorithm for this problem, and prove it reaches the optimal rate up to logarithmic factors. Numerical experiments show QUEST outperforms its classical counterpart.
In briefQuantum key distribution using entanglement-swapped photons from a quantum dot source
SummaryThis paper tests whether correlated photons distributed through entanglement swapping can support secret key distribution, a basic step in a quantum repeater. The authors use a deterministic photon source built from a strain-tuned GaAs quantum dot in a photonic cavity to run a source-independent QKD protocol between two nodes. They show that high-resolution temporal post-selection can enable secure key exchange, and note that rates may improve with further device and protocol optimization.
Michele B. Rota, Francesco Basso Basset, Alessandro Laneve et al.
In briefBeyond Pure Dephasing: Why Single-Molecule Quantum Error Correction Needs Multiple Spins
SummaryThis paper proposes multi-spin molecules as a possible architecture for fault-tolerant quantum computing. It introduces a correction protocol that handles both diagonal errors (dephasing) and off-diagonal errors (relaxation) using a hybrid encoding. The scheme first suppresses the leading pure dephasing error, then uses a multi-qubit code within a multi-spin molecule for the remaining off-diagonal errors. Numerical results indicate the approach may perform well even with a limited number of spins per logical unit.
Matteo Mezzadri, Silvia Macedonio, Luca Lepori et al.
In briefLearning Noise-Robust Stabilizer Structure via Bell Sampling
SummaryThe paper studies how to learn the stabilizer group of a noisy quantum state using Bell sampling. It shows that the ideal state's stabilizer group remains encoded in the noisy state as the set of Pauli operators under which the state is invariant. The authors give algorithms whose sample and runtime costs are polynomial for sufficiently weak global depolarizing noise, with classical processing costs growing as 2^t or 4^t in the stabilizer nullity t.
WhyNoise-robust stabilizer learning via Bell sampling with a finder-verifier scheme and multi-regime complexity bounds; strong theory, limited empirical validation, impact confined to quantum state learn
In briefFree-fermion black holes behave as polarised mirrors that reflect some information faster than others.
SummaryThe paper studies a random free-fermionic model of black hole dynamics to see whether the mirror behaviour known from Haar-random models persists. It finds that information release is governed by representation-theoretic structure, so low fermionic-degree information is retained while high-degree information is reflected quickly. Adding a fixed Clifford unitary restores reflective behaviour, and in the high-fidelity limit recovering a single-qubit message needs about 37% fewer emitted qubits than in the fully Haar-random case.
WhyExtends Hayden-Preskill mirror behaviour to random free fermion models via representation theory, with Clifford augmentation outperforming Haar-random case, supported by quantitative analysis.
In briefHamiltonian eigenvalue transformation using tridiagonal gadgets
SummaryThe paper shows how a single time-independent local Hamiltonian can act as a polynomial P(H) of a local Hamiltonian H on an explicitly described invariant subspace, to any prescribed accuracy. Short chains of ancilla qubits are attached to H, and a weighted sum of chains of different lengths reproduces a given polynomial term by term. The authors prove uniqueness, analyticity and length-uniform coefficient bounds, and apply the construction to filtering a marked eigenstate and to replacing the non-local driver in adiabatic optimisation.
Arthur Braida, Joseph Cunningham, J\'er\'emie Roland
In briefKernel-based method for efficiently and reliably measuring information processing capacity in dynamical systems
SummaryInformation processing capacity (IPC) is a general metric for a dynamical system's computational ability, widely used in quantum reservoir computing. Standard IPC calculation relies on linear regression over polynomials up to a chosen degree, and its cost grows combinatorially with degree and delay. The paper introduces Kernel-IPC (KIPC), which computes total IPC with kernel methods without enumerating basis functions, covering the full infinite basis. It also provides a null-hypothesis test for comparing the KIPC of two systems, validated on an echo state network and a disordered spin chain.
In briefPricing quantum portfolios of linked assets using graph theory
SummaryThis paper combines quantum finance with graph-theoretic methods and contextuality to study quantum assets that are non-commuting operators. It examines when holding such assets can offer advantages over classical assets. The authors build a "quantum market" from nonlocal games such as the CHSH game and show it can function as a market with well-defined financial structure. They give upper bounds on fair quantum asset prices using graph quantities such as the independence number and the Lovász theta number.
In briefPathway-resolved analysis of internal conversion using Gaussian boson sampling
SummaryThis paper maps the internal conversion (IC) rate constant k_IC onto the output of Gaussian Boson Sampling (GBS), including Duschinsky rotations and Herzberg–Teller contributions. The framework is validated with sampling simulations of dibenzoterrylene, reproducing reported k_IC values. The photon-number patterns encode the vibrational mode combinations, called non-radiative pathways, that drive IC. Duschinsky rotations raise the fraction of k_IC linked to correlated vibrational pathways from 46% to 86%.
Mikhail Roiz, Rashid Valiev, Jan-Lucas Eickmann et al.
In briefMulti-compilation for faster distributed quantum computing
SummaryDistributed quantum computing connects multiple quantum processors to scale beyond a single chip, but generating Bell pairs between them is slow and limits how quickly results are obtained. Existing compilers produce one implementation per circuit, so throughput is bottlenecked by the busiest link while others sit idle. The paper proposes running several logically equivalent compilations of the same circuit concurrently and pooling their samples to use idle Bell pairs, with simulations and hardware experiments reporting higher throughput and fidelity.
WhyPools samples from logically equivalent compilations to raise distributed quantum throughput, proving NP-hardness and validating gains in simulation and hardware.
In briefPulse-by-pulse phase control of squeezed light at 93 MHz using a bulk lithium-niobate modulator
SummaryThis paper demonstrates phase control of squeezed vacuum states applied pulse by pulse at a 93 MHz repetition rate, using a low-loss bulk lithium-niobate electro-optic modulator driven by a broadband RF amplifier. An interferometric calibration gave a maximum differential phase excursion of 1.93 rad. The method was tested on a 1035 nm squeezed field, and the resulting quadrature scan matched one obtained by piezoelectric control of the local oscillator phase.
Edoardo Suerra, Igor Vasiljevic, Sebastiano Corli et al.
In briefQuantum-inspired tensor-network methods for particle-in-cell plasma simulation codes
SummaryThis paper examines tensor-network methods as an alternative to conventional particle-in-cell codes for simulating plasmas, which involve costly high-dimensional nonlinear equations. The authors report recent progress and discuss how the approach may address bottlenecks of standard simulations. They extend the tensor-network formulation to insert electromagnetic fields at arbitrary spatial locations and demonstrate this by injecting a laser field to accelerate a plasma.
Ryan J. J. Connor, Andrew J. Daley, Callum W. Duncan et al.
In briefStimulated Parametric Down-Conversion: A Review of Seeded Photon Processes for Structured Light
SummaryThis review covers stimulated parametric down-conversion, a seeded version of the process underlying photonic quantum information, in which a coherent seed replaces the vacuum input. It unifies image and coherence transfer, phase conjugation, orbital angular momentum, and vector vortex beam processing under a single relation. The authors also discuss StimPDC as a measurement instrument, its quantum regime, and open problems with prospective applications.
M. F. Z. Arruda, M. G. Damaceno, G. H. dos Santos et al.
In briefControlling noiseless subsystems with two-body interactions lets qutrit teleportation beat the classical fidelity limit
SummaryThis paper studies a system of r fundamental and s dual qutrits whose collective noise leaves some degrees of freedom unaffected, so they can store quantum information. The authors show that adjacent exchanges within each type and one singlet-projector interaction between the types can generate any special unitary gate on these noiseless subsystems using a finite pulse sequence, and they give a numerically optimised 24-pulse example. Under correlated Weyl noise and stated assumptions, they identify noise ranges where encoded qutrit teleportation exceeds the classical fidelity bound of 1/2.
Otavio A. D. Molitor, Sergii Strelchuk, Micha\l{} Studzi\'nski
In briefCovertness as a limit on precise quantum target detection
SummaryThe paper studies quantum sensing that detects low-reflectivity targets in thermal noise while avoiding an adversary's discovery. The covertness requirement limits the usable probe energy, creating a trade-off with sensing performance. The authors link covert target discrimination with quantum parameter estimation and introduce a covertness-constrained quantum Fisher information to quantify the best achievable precision for target reflectivity. They conclude that covertness acts as a quantitative resource constraint on the metrological limits of quantum target sensing.
In briefEvolving compact hybrid quantum-classical networks for image classification
SummaryThe paper extends EXAQC, an evolutionary framework, to automatically discover parameterized quantum circuits that sit between classical feature-extraction and prediction layers for image classification. It reports 98.42% on MNIST, 90.62% on Fashion-MNIST, and 85.47% on CIFAR-10, with gate counts comparable to other quantum architecture-search methods. On CIFAR-10, an evolved hybrid model reaches 85.68% with over 25 times fewer parameters than a 10-layer CNN. Rotation-based encodings outperform amplitude encoding by 22 to 25 points on CIFAR-10.
In briefSolving the two-center Dirac equation with Gaussian basis functions
SummaryThe paper presents a method for solving the two-center Dirac equation using Gaussian-product basis functions designed for the axial symmetry of diatomic molecules. For the H2+ ground state at internuclear distance 2.0 a0, it reports relativistic energies with relative precision around 10^-18. The basis allows an analytic Fourier transform of the wave function, which is used to compute the zero-potential one-loop self-energy contribution in Feynman and Coulomb gauges as a proof of principle for future QED calculations.
In briefVerifying quantum error-correcting code parameters with short, provably sized certificates
SummaryQuantum error-correcting codes are described by physical qubit count, logical qubit count, and distance, and the distance is usually obtained from a solver. This paper shows that code parameters can be certified by short certificates whose correctness a proof assistant's kernel checks by computation, with certificate size itself proved as a theorem. The authors settle distances for two published code families and report results for eleven code families and thirty-nine parameter sets.
WhyIntroduces short certificates checkable by a proof assistant kernel, settling distances of two published code families across many parameter sets; impact mainly in formal verification of quantum codes
In briefLower bounds show Hamiltonian locality testing misses the Heisenberg limit
SummaryThis paper studies Hamiltonian property testing when only the time-evolution operator can be queried, not its inverse, with distances measured in normalized Frobenius norm. The authors show that testing whether a Hamiltonian is k-local or ε-far from all k-local Hamiltonians requires Ω(1/ε²) total evolution time, matching known upper bounds. They also show the same lower bound for testing whether an unknown Hamiltonian equals a target or is ε-far from it, and for amplitude estimation to precision ε. These results are obtained by adapting the continuous-time adversary method to forward Hamiltonian evolution.
WhyProves Ω(1/ε²) lower bounds matching known upper bounds, ruling out Heisenberg-limited scaling for natural Hamiltonian testing problems.
Francisco Escudero Guti\'errez, Junseo Lee, Sebastian Zur
In briefDissipation emerging from fluctuating quantum-network connectivity
SummaryThis paper studies how dissipation arises in a quantum network when its interaction topology fluctuates over time. Averaging the dynamics gives a Markovian master equation, where the mean network sets the coherent part and the covariance sets the dissipative structure. Two ensembles with identical spectra but different eigenvectors evolve differently despite equal purity. A physically realizable model yields an analytic dissipative gap, suggesting fluctuating connectivity can be used to engineer dissipation and protection.
In briefTopological phase transition in a symmetric blockade model: a numerical study
SummaryThis paper numerically studies a blockade Hamiltonian with a local Z2 symmetry. Topological order was rigorously proven only for weak Rabi driving, leaving the phase diagram at stronger driving unclear. The authors use large-scale infinite-size DMRG simulations on a cylinder to map the full phase diagram. They find a single continuous transition between a topologically ordered phase and a trivial paramagnetic phase.
Johannes M\"ogerle, Simon Fell, Tobias F. Maier et al.
In briefSelf-testing ideal quantum measurements: a way to verify whether a quantum measurement is ideal using only test results
SummaryThe paper studies ideal quantum measurements, which give the same outcome when repeated and do not disturb other jointly measurable quantities. The authors show that quantum mechanics allows any ideal measurement to be self-tested. Using only the output statistics of bipartite Bell tests, sometimes with a non-demolition measurement added, one can certify in a device-independent way whether the added measurement is ideal.
WhyShows any ideal measurement can be self-tested using only bipartite Bell test statistics, certifying idealness in a device-independent way; a notable theoretical advance.
In briefPerformance of photonic quantum solvers for financial-risk feature selection depends on problem structure
SummaryThis paper benchmarks classical branch-and-bound (Gurobi), photonic entropy computing (QCI Dirac-3), and simulated photonic boson sampling (Piquasso) on feature selection for credit card fraud and consumer default detection. It tests thirteen methods on two datasets. On the ULB dataset, Dirac-3 with MI-Spearman matches the all-features model using 13 of 30 features. On AmEx, performance rises with the feature budget and all paradigms approach F1 = 0.80 only near the full feature set.
In briefLayered nitrogen-vacancy diamond structures that self-organize with preferred orientation in diamond films.
SummaryResearchers fabricated two-inch wafer-scale single-crystal diamond films containing three-dimensional layers of negatively charged nitrogen-vacancy (NV⁻) centers. They alternated chemical vapor deposition with oxygen-plasma etching to form layered inverted pyramids with flat {111} sidewalls, then overgrew them with nitrogen-doped diamond. The resulting facets are NV⁻-rich with uniform N-V bond arrangement, which the authors suggest could support quantum devices such as data processors, memory cells, and magnetic sensors.
Vadim Lebedev, Alejandro Mart\'inez-M\'endez, Jes\'us Moreno-Meseguer et al.
In briefInfrared memory of a Majorana shutter: low-frequency behavior of a local time-dependent scattering defect
SummaryThe paper models a finite-width Majorana shutter as a local, time-dependent scattering defect and examines which infrared memory features are independent of its spatial profile. Overlaps of pre- and post-shutter Gaussian vacua show Anderson orthogonality, and lattice calculations of quasiparticle number match the predicted logarithmic growth. When an entanglement cut passes through the shutter, entropy agrees with the effective central charge description of a conformal defect at the percent level. The authors also state remaining limits, including finite-memory corrections to the continuum kernel and the controlled continuum limit of large-interval spatial entropy.
In briefReducing redundant measurements in quantum-selected CI by placing the Hartree-Fock determinant classically
SummaryThis paper studies quantum-selected configuration interaction (QSCI) and its adaptive extension ADAPT-QSCI for computing molecular ground-state energies. The authors place the Hartree-Fock configuration in the diagonalization subspace before measurement to reduce redundant samples, and derive a replacement operator-selection criterion. They report CNOT and shot counts for H4 and H6, noting that the advantage depends on the per-iteration shot budget.
Ayaka Fujimoto, Norifumi Matsumoto, Shota Kanasugi et al.
In briefCertifying high-dimensional entanglement in continuous-variable quantum systems
SummaryThe paper introduces fidelity bounds for detecting the Schmidt number, a measure of entanglement dimensionality, using measurements of the first and second statistical moments of continuous-variable quantum states. These measurements are more practical to perform than those needed for direct fidelity estimation. The authors provide analytical formulas for the bounds and test them on Gaussian and non-Gaussian families, including two-mode squeezed thermal states and photon-added displaced two-mode squeezed vacuum states. The bounds are compared with other certification methods based on the same measurements.
Ida Mishra, Simon Morelli, Kl\'ara Baksov\'a et al.
In briefCounting Symmetry Sectors in Mixed Quantum Spectra
SummarySpectral fluctuations of complex quantum systems are often modeled with random matrix spectra, but this agreement holds only for pure spectra, not composite ones that mix levels from different symmetry sectors. The paper proposes a Best Subset Technique that determines the number of symmetry sectors by comparing spectral fluctuations with an appropriate random matrix ensemble, without needing de-symmetrization. The method is tested on Gaussian, Wishart and Ginibre ensemble spectra, as well as on many-body quantum systems, in both Hermitian and non-Hermitian settings.
In briefComputing Chern Numbers on Discrete Grids via Bargmann Invariants
SummaryThe paper introduces a finite-state geometric framework based on third-order Bargmann invariants to evaluate Chern numbers and describe local quantum-state geometry. It uses gauge-invariant state overlaps to compute the Chern number directly on discretized parameter spaces, keeping local information through phase-derived and amplitude densities. The method is applied to the Qi–Wu–Zhang, Hofstadter (1/3 and 1/4 flux), SSH, and Rice–Mele models, including a rank-2 extension.
In briefOrbital-rotation shadows cut classical post-processing cost of quantum-classical AFQMC
SummaryThe paper addresses the classical post-processing bottleneck in quantum-classical auxiliary-field quantum Monte Carlo (QC-AFQMC) by using particle-number-preserving fermionic shadows implemented as orbital-rotation shadows. The authors derive efficient estimators for overlaps, force biases, and local energies, and prove the overlap estimator is unbiased with bounded variance. With a GPU implementation, they project that the full classical workflow for pentacene (22e, 22o active space, 356 total orbitals) could finish in slightly more than two days on 8 A100 GPUs.
Luning Zhao, Joshua Goings, Evgeny Epifanovsky et al.
In briefAnalytical control method for dispersive multi-qubit interactions in mediator-coupled quantum registers
SummaryThe paper introduces DIAL, an analytical method that uses off-resonant driving of a mediator to create multi-qubit Z interactions whose strengths depend linearly on drive intensities, avoiding iterative simulation of the full dynamics. Numerical tests on 100 register realizations for sizes n=2 to 5 target the highest-order interaction that produces a GHZ state. Reported typical gate fidelities are above 0.997, with average transient mediator excitation near 1%.
Bora Baran, Tommaso Calarco, James O'Sullivan et al.
In briefDirectly estimating g^(2)(0) from click counts of a multiplexed detector
SummaryThis paper proposes a method to directly estimate the second-order correlation function g^(2)(0) from click statistics of a multiplexed detector made of M binary on-off channels. It uses linear estimators of the first and second moments of the photon-number operator and remains accurate even at substantial mean photon numbers. Adding losses before the detector extends its range, and a nonclassicality criterion based on the estimate is derived.
In briefQuantum approach to sampling rare events with lower computational cost
SummaryThe paper proposes a method for sampling rare, high-consequence events using quantum stochastic models. It combines the memory advantages of quantum stochastic modelling with the speed-up from quantum amplitude amplification. The authors state this yields simultaneous reductions in spatial and temporal computational complexity compared with classical Monte Carlo approaches.
In briefTwo-qutrit Werner states always admit local hidden-variable models
SummaryThis paper studies Werner states of two three-level quantum systems (qutrits). For scenarios with two projective measurements per site and three outcomes per measurement, the authors show that the state admits a local hidden-variable model for all values of the parameter. The proof uses a simple sufficient condition for satisfying the Collins-Gisin-Linden-Massar-Popescu inequality for arbitrary observables, which Werner states always meet.
In briefInteractions shift the period of Kohn oscillations in a PT-symmetric trap
SummaryThis paper studies how a Bose-Einstein condensate's center of mass oscillates in a harmonic trap with a parity-time-symmetric gain-loss gradient. Without interactions the frequency is unchanged, but with interactions the gain and loss alter the atom number, which changes the cloud width and feeds back to shift the oscillation period. At small gain the period grows quadratically with gain strength, and at a critical gain the orbit resonates with highly excited trap states. A five-variable moment model reproduces the period and width nearly up to that critical gain.
In briefCorrelations of Einstein–Langevin sources in closed non-relativistic systems
SummaryThis paper studies the Einstein–Langevin noise kernel of stochastic semiclassical gravity by projecting it onto closed, particle-number-conserving non-relativistic sources. It separates the source covariance from a reduced matter channel and finds that the connected one-particle covariance depends on the state, differing from the universal potential-noise law of the Diósi–Penrose model. The authors relate the source spectrum to dephasing of a probe and compare coherent and incoherent many-body preparations. They identify the assumptions needed to link source fluctuations to matter-decoherence models.
In briefQuaternionic resource theory: every pure state can be replicated for exact quantum simulation
SummaryThe paper introduces aquaternionicity, a resource theory for even-dimensional qudits (d≥4) based on a quaternionic structure given by an antiunitary Θ with Θ²=−I. It shows that every pure state is alchemical, meaning it can be exactly replicated by free operations, and gives an upper bound on the dimension of admissible pure-mixing sets that aquaternionicity attains. Under standard dephasing and dissipative noise, the framework substantially outperforms imaginarity and parity asymmetry.
In briefQuantum algorithms scaling with the square root of sparsity for simulation and linear solving
SummaryThe paper presents quantum algorithms for Hamiltonian simulation, linear differential equations, and linear systems whose query complexity scales with the square root of sparsity. It gives query bounds for sparse Hermitian matrices in terms of evolution time and precision, along with a joint lower bound that nearly matches the time, sparsity, and precision dependence. Results are also given for dissipative differential equations and linear systems, together with gate-efficient implementations.
WhyImproves sparsity dependence to square-root order with matching joint lower bounds, a notable theoretical advance broadly relevant to quantum simulation and linear solvers.
Dominic W. Berry, Abhishek Rawat, Sophia Simon et al.
In briefPredicting noise in a trapped-ion simulation of a lattice gauge theory
SummaryThis paper studies how noise affects a trapped-ion quantum simulation of a lattice gauge theory, aiming to predict its effects before the device is run. Using only the reported noise rates, the authors derive a decay formula and an upper bound for each measured quantity. They find that heating violates the local conservation law at a rate that grows as the vibrational mode warms, and that switching on the electric field makes the frozen state leak, for which they give an exact formula and a guaranteed bound.
In briefSimulating materials on quantum computers using quasiparticle Bethe-Salpeter methods
SummaryThis paper presents a quantum simulation method for multi-exciton states of materials, based on the Bethe-Salpeter equation (BSE) and designed for fault-tolerant quantum computers. The authors build a block encoding of the multi-exciton BSE Hamiltonian and reduce its cost using integral factorization and crystal symmetries. For semiconductor models of about O(10^3) atoms, they report Toffoli counts 10^6 to 10^7 times lower than full Hamiltonian simulation, with a qubit-optimized version needing only a few hundred logical qubits.
In briefTransferring spectral gaps to make quantum Gibbs sampling converge at all temperatures
SummaryThe paper studies how to prepare quantum Gibbs states through dissipative dynamics, where convergence depends on the spectral gap of the dynamics' generator. The authors prove that a spectral gap estimate at infinite temperature gives a lower bound on the gap of the CKG quantum Gibbs sampler at every finite positive inverse temperature, for arbitrary finite-dimensional Hamiltonians. For Hodge Laplacians of simplicial complexes, they construct coupling operators whose infinite-temperature gap matches that of a classical simplicial down-up walk.
Caesnan M. G. Leditto, Kuo-Chin Chen, Min-Hsiu Hsieh
In briefHeat-equilibrium approach in a qubit model with memory effects
SummaryThis paper studies how memory affects the thermalization of a qubit in a repeated-interaction model. A memory qubit interacts repeatedly with the system, and both undergo collisions with fresh thermal ancillas. The authors derive exact closed evolution equations for their populations and mutual coherence. The system converges to the target thermal state, but the approach is non-monotonic and shows a Mpemba-like reversal.
In briefError-corrected quantum memories preserve proper time
SummaryThe paper asks how quantum error correction affects relativistic proper time. It shows that two error-corrected memories on distinct worldlines, each controlled by local references, have local correction histories that factor exactly into their proper-time difference. Error correction does not erase time dilation; it appears as a relational phase rotation, which at certain code-admitted phases acts as a deterministic logical gate, such as an S-type Clifford gate at π/2.
In briefDesign automation for a Gray-code quantum read-only memory
SummaryThe paper proposes GQROM, a programmable quantum read-only memory that uses Gray code encoding to load classical data into quantum circuits. Because consecutive addresses differ by only one bit, it reduces initialization overhead and gate-induced errors. The complete design, including a systematic EDA flow, was implemented and validated on the Qiskit platform.
In briefSMP: A general hyperedge-based framework for circuit-level quantum error correction
SummaryThis paper introduces Syndrome Motif Projection (SMP), a framework that extracts hyperedge fault information from measured syndromes with linear-complexity preprocessing while keeping the matching decoder backend. It can serve as a lightweight front end for existing fast matching decoders. The authors test SMP on surface code, color code, and logical gate circuits. They report improvements on Google's Willow surface code data, up to 77.8% lower logical failure probability for color codes with Chromobius, and a 35.5% reduction for a six-CNOT circuit relative to logical observable matching.
In briefMemory effects of the surrounding environment in how radical pairs sense magnetic fields
SummaryThis paper studies a radical-pair model of animal magnetoreception, where light creates spin-linked molecules whose reaction yields depend on orientation. The authors model both the surrounding spin bath and boson bath, focusing on how the spin bath retains memory of past states. They apply the hierarchical equations of motion (HEOM/DEOM) method and compare it with a Markovian Lindblad master equation. The results indicate that this non-Markovian memory effect is a key factor in radical-pair magnetoreception.
In briefRandom quantum LDPC codes that approach the Gilbert-Varshamov bound
SummaryThe paper shows that for any rate and error parameter, there is an infinite family of p-ary quantum LDPC codes whose normalized distance approaches the quantum Gilbert-Varshamov bound. A random code from the constructed ensemble is close to this bound with high probability. The ensemble matches random stabilizer codes on the erasure channel and for memoryless Pauli channels, including the depolarizing channel. The construction combines known asymptotically good QLDPC codes with expander-based distance amplification, while quantitatively controlling code degeneracy.
WhyConcatenating degeneracy-controlled QLDPC codes with random inner codes approaches the quantum GV bound and matches random stabilizer codes on erasure and depolarizing channels.
Tushant Mittal, Shashank Srivastava, Madhur Tulsiani et al.
In briefA simpler, provably optimal way to detect quantum states without computing likelihoods.
SummaryThe paper shows that adaptive Bayesian state detection in fluorescence experiments reduces to comparing elapsed time against two arithmetic time sequences. This method, called sequential deadline detection, needs no real-time probability calculations and is proven optimal in mean detection time. Closed-form expressions for detection times and error rates are derived and validated by Monte Carlo simulation and Ba⁺ fluorescence detection.
In briefGaussian Fisher Information Is Superadditive: Joint Measurement of Two Independent Modes Can Beat Separate Measurement
SummaryThe paper asks whether measuring two independent modes jointly with Gaussian measurements, such as linear optics and homodyne detection, can beat measuring them separately. It proposes Bell homodyne, a balanced beam splitter followed by two homodyne detectors, which outperforms the best separate readout when the modes differ in quadrature width and in how that width depends on the parameter. The authors prove the gain is below 17.157% for width-carried parameters and report a peak gain of 12.699% at frequency ratio 3.318 for thermal modes at one temperature.
WhyProves superadditivity of Gaussian Fisher information with tight bounds and a peak gain for thermal modes, a notable theoretical advance.
In briefQuantum codes with proven distance and low-weight measurements
SummaryThe paper studies a family of quantum subsystem codes on rectangular coordinate grids of any dimension with even side lengths of at least four. The directly measured operators act along coordinate lines. For each code, the authors derive the number of protected logical qubits and prove its dressed distance without numerical search. Under a limit of 10,000 data qubits, they determine the tradeoff between encoding rate and measurement weight at distances 16, 32, and 64.
In briefEntangled graph colouring with over three colours is shown undecidable
SummaryThis paper studies constraint satisfaction problems in which variables are assigned operators, to analyse the decision complexity of the entangled value of nonlocal games. The authors generalise polymorphism-based reductions from classical CSPs to gap-preserving reductions between entangled CSPs. Using this approach, they prove that entangled graph colouring with more than three colours is undecidable. Earlier hardness reductions based on commutativity gadgets had not resolved this problem.
WhyGeneralises polymorphism reductions to gap-preserving entangled CSP reductions, proving undecidability of entangled graph colouring beyond three colours, a previously resistant problem.
In briefQuantum transport in 1D disordered stealthy hyperuniform Kronig-Penney-like models
SummaryThis paper studies one-dimensional quantum transport through identical point scatterers whose positions have stealthy hyperuniform (SHU) disorder. The authors present what they describe as the first perturbation theory for this setting. They show that lower-order terms cancel exactly due to the Fourier-space stealthy condition, and that the lowest non-vanishing fourth-order term in the Lyapunov exponent is further suppressed by the real-space hyperuniform constraint.
In briefAdding a single photon to multimode quantum light in lithium niobate crystals at telecom wavelengths
SummaryThis paper presents a theoretical analysis and numerical simulations of single-photon addition (SPA) and mode-selective single-photon addition (MSSPA) to multimode quantum fields at telecom wavelengths. The study covers congruent lithium niobate, 5% MgO-doped lithium niobate, and various concentrations of ZnO-doped lithium niobate crystals. It also examines spectro-temporal mode-selective SPA over temperatures from 0°C to 15°C and identifies phase-matching parameters for non-Gaussian state engineering, mainly at 1550 nm.
In briefRobust optimization of repulsive Casimir forces in a biased-semiconductor cavity
SummaryThis paper studies how to achieve nonequilibrium Casimir–Lifshitz repulsion in a planar stack of conductors, vacuum, and biased GaAs, framing the design as a robust constrained optimization under fabrication and drive uncertainty. In the optically thick-slab limit, the authors prove that a symmetric optimizer exists. At 300 K with gap uncertainty of ±10 nm and drive uncertainty of ±0.005, the optimized design gives a worst-case outward pressure of 2.257 mPa, and a finite-slab scattering calculation agrees closely with the reduced model.
In briefEntanglement dynamics under dynamical decoupling and initial qubit-environment correlations
SummaryThis paper studies the exact entanglement dynamics of two qubits coupled to a shared bosonic environment through pure dephasing. It compares the case where qubits and environment were correlated before the qubit state was prepared with the uncorrelated case. Initial correlations are shown to make entanglement sudden death occur earlier, with the gap growing quadratically with coupling strength in the weak-to-moderate coupling regime. A symmetric sequence of periodic π pulses on both qubits is shown to extend entanglement lifetime by close to a factor of seven over the pulse numbers studied.
In briefUsing a chiral cavity's vacuum to control quantum Hall electron systems
SummaryThis paper studies how a chiral cavity interacts with a two-dimensional electron gas and the cavity vacuum. Co-rotating helicities show vacuum Rabi splitting with a bare vacuum ground state, while counter-rotating helicities show vacuum-mediated energy shifts and a two-mode squeezed ground state. The authors also predict handedness-dependent corrections to Hall resistivity and asymmetric Shubnikov–de Haas oscillations at finite polariton broadening, which are absent in achiral cavities.
Kiran M. Kulkarni, Andrey Baydin, Motoaki Bamba et al.
In briefQuantum error-correcting codes for qudits built from Singer difference sets and quadrics in PG(d,q)
SummaryThe paper proposes Q(q,d), a family of q-ary non-CSS qudit stabilizer codes built from Singer difference sets and non-degenerate quadrics in PG(d,q). It presents several structural theorems and a closed-form formula for the logical dimension. In Monte-Carlo simulations over 1.5 × 10^6 trials, Q(5,2) is reported to achieve about a 70-fold per-logical-qudit improvement over the Steane code at depolarising rate 10^-3, with no silent logical errors.
In briefFrom static Lindblad stabilizability to robust physical control sequences
SummaryThis paper studies how dissipative dynamics can stabilize a quantum state at a target, even when the available finite control operations are imperfect. The authors derive checkable conditions that bound convergence, errors during operations, and physical cost, covering pulses, idle intervals, and background dynamics. They also present a finite-library search that yields a control sequence for a specified four-level cascade model, with an explicit preparation-time bound.
In briefDense encoding halves QROM cost again for fault-tolerant quantum algorithms
SummaryThis paper addresses the non-Clifford cost of quantum read-only memory (QROM) in fault-tolerant algorithms, where limited qubits make table loading the dominant expense. The authors introduce a dense encoding that stores two bits per dirty qubit by using both Z and X bases. Alone it reduces the leading Toffoli count to N/λ, and combined with sequential bit packets it reaches (1/2)(1+1/b)N/λ.
In briefHeisenberg-limited spin squeezing in multi-level spins, protected by local interactions
SummaryThis paper proposes a general way to create entanglement useful for metrology, called generalized spin squeezing, in multi-level (qudit) spin systems with power-law interactions. It extends spin-nematic squeezing from spinor BECs to spatially extended lattices. Without all-to-all connectivity, dynamics leak into non-collective modes and lose Heisenberg scaling. Adding local su(D) exchange interactions opens an energy gap that protects the symmetric collective manifold, achieving ξ²∝1/N scaling in one to three dimensions.
Sakshi Bahamnia, Sagar Chaudhary, Arman Duha et al.
In briefHow much quantum behavior bottomonium keeps in quark-gluon plasma.
SummaryThe paper simulates bottomonium's evolution in quark-gluon plasma using an open quantum system approach, with a Lindblad equation derived from potential nonrelativistic QCD. It computes the negativity of the Wigner transform of the density matrix as a measure of nonclassicality and a test of classical Langevin-type approximations. The medium suppresses negativity, which plateaus near the 1S state value, with excited-state overlaps arising from nearly canceling phase-space contributions. The authors attribute the residual quantum structure to conditional purification, concluding that classicalization is partial and observable-dependent.
In briefCounterdiabatic circuits without a Hamiltonian: a gauge-potential method for unitary dynamics
SummaryThis paper develops a theory of the adiabatic gauge potential (AGP) for parameter-dependent unitary operators, which does not require a Hamiltonian. It gives exact and regularized AGP forms obtained from a Hermitian, banded linear system, with cost comparable to the Lanczos method, avoiding diagonalization and matrix logarithms. The authors show fast convergence of a truncated Krylov approximation for the kicked top and an integrable brickwork circuit built from unitary Ř matrices.
Ankit Wenju Shrestha, Budhaditya Bhattacharjee, and Adolfo del Campo
In briefHomological Thresholds in Randomly Monitored Quantum Error-Correcting Codes: a study of how quantum error-correcting codes withstand random measurements, sorting their thresholds into two types.
SummaryThe paper studies how stabilizer quantum error-correcting codes hold up under one round of independently sampled single-qubit Pauli measurements. It classifies their threshold behavior into geometric and homological percolation transitions, with the toric code and color code as principal examples. The authors analyze logical-support criteria and estimate critical exponents from simulations of systems with over one million qubits. The framework extends to non-CSS, subsystem, higher-dimensional, and Floquet codes, and the robustness of the gross code is discussed.
In briefEntanglement needs fluctuations: a lower bound linking capacity and entropy at conformal interfaces
SummaryThe paper conjectures that the universal logarithmic coefficient of capacity of entanglement is bounded below by the corresponding entropy coefficient at conformal interfaces. The bound is proven for free boson and fermion CFTs and holographic models with interface branes, using defect perturbation theory. Numerical results for interacting tricritical Ising and Ising CFT interfaces also support it.
In briefSemiclassical entanglement wedge in double-scaled SYK, explained
SummaryThis paper studies how partially entangled thermal states in double-scaled SYK are structured when matter insertions carry flavor degrees of freedom in a mixed state. In the semiclassical and heavy-probe limits, a replica calculation yields a Faulkner-Lewkowycz-Maldacena-type formula splitting boundary entropy into a flavor-independent area term and a bulk matter entropy. Moving operator insertion points produces sharp transitions in boundary entropy, interpreted as matter excitations crossing the wedge boundary.
WhyDerives an FLM-type entanglement wedge formula in double-scaled SYK with sharp transitions, supported by probabilistic and 6j-symbol proofs; impact limited to this model's subfield.
In briefSingle-Particle Spectral Estimation: Recovering Quasiparticle Energies Hidden Behind a Global Unitary
SummaryThe paper studies learning the single-particle energy weights of a Hamiltonian whose non-interacting modes are concealed by an unknown global unitary, without reconstructing that unitary. The authors show the problem is DQC1-hard despite its non-interacting structure. They introduce SPICES, which combines a Hadamard test with a new classical postprocessing step to recover the spectral distribution in Wasserstein distance under certain assumptions.
Adrian Chapman, Charles Derby, Steven T. Flammia et al.
In briefLearning SYK Hamiltonians: recovering a dense quantum Hamiltonian from samples of its Gibbs state
SummaryThis paper studies how to learn the dense Sachdev–Ye–Kitaev (SYK) Hamiltonian from copies of its Gibbs state. Existing Hamiltonian learning methods rely on locality or bounded interaction degree, which SYK lacks. The authors prove that at any constant temperature, with high probability over the random couplings, the full Hamiltonian can be learned to inverse-polynomial accuracy with polynomially many samples. For sufficiently small constant inverse temperature, they also construct a quasipolynomial-time learning algorithm.
Anurag Anshu, Srinivasan Arunachalam, Sitan Chen et al.
In briefFrom Permutation Symmetry to Communication Bounds and Additivity
SummaryThe paper studies how correlations across multiple uses of a quantum channel can affect quantum communication rates. It shows that for any finite-dimensional memoryless channel, full permutation invariance limits this advantage, so the optimized coherent information per use converges to the single-use maximum and attains it at a finite block length. The paper also proves a strong converse for pure-source entanglement generation with permutation-invariant inputs and gives related results on additivity and output entropy.
WhyUses full permutation invariance to bound correlation advantages, giving finite-block optimality, a strong converse, and unified proofs of known additivity results.
In briefExponential lower bounds on fermionic and bosonic Gaussian rank for non-Gaussian quantum states
SummaryThis paper studies the Gaussian rank, which measures the complexity of classically simulating quantum systems by decomposing states into free states. It proves that for any pure non-Gaussian state on finitely many modes, the approximate border Gaussian rank of its tensor powers grows at least exponentially at any fixed norm error below one. Explicit exponential bounds are given for the four-mode fermionic GHZ state and the bosonic single-photon state.
WhyProves exponential growth of approximate border Gaussian rank for tensor powers of non-Gaussian states, with rigorous bounds limiting decomposition-based classical simulation.
In briefPolynomial-time classical and quantum simulation of quantum impurity models
SummaryThis paper studies the computational complexity of simulating quantum impurity models, which consist of a small set of interacting fermions coupled to a large noninteracting bath. The authors give classical algorithms that estimate ground-state energy and thermal partition functions in polynomial time, so static properties can be computed efficiently without quantum hardware. They also find that dynamical properties, such as nonequilibrium Green's functions, are hard for classical computers but efficiently simulable on a quantum computer.
WhyImproves ground-state energy estimation from quasipolynomial to polynomial time and gives first rigorous thermal polynomial-time guarantees for impurity models.
In briefBeyond Light Cones: Complexity of Preparing States for Quantum Spin Glasses
SummaryThis paper introduces a method for studying how hard it is to prepare states of dense quantum p-spin Hamiltonians, going beyond limits based only on circuit light cones. It uses an effective profile complexity derived from Pauli profiles. The authors show that near-ground-state energy requires Ω(n²/log n) one- and two-qubit gates, and they give depth-width, entanglement and matrix product state lower bounds.
WhyCombines a quantum de Finetti theorem with Gaussian process entropy bounds to go beyond lightcone limits, yielding Omega(n^2/log n) gate lower bounds and magic-hierarchy obstructions.
In briefLearning many-body quantum Hamiltonians using only one measurable qubit
SummaryThis paper shows that a single measurable qubit is enough to learn all O(N) independent parameters of a bounded-degree two-body Hamiltonian on N qubits. The protocol uses robust SWAP gates built by quantum signal processing to coherently transfer states from distant parameters to the measurable qubit. It achieves Heisenberg-limited precision and extends to arbitrary bounded-degree interaction graphs.
WhyShows one measurable qubit with QSP-synthesized SWAPs learns all O(N) Hamiltonian parameters at Heisenberg limit, with near-optimal scaling bounds.
In briefThe Robustness of QAC0: How Well Quantum Constant-Depth Circuits Tolerate Errors and Gate Changes
SummaryThis paper studies how robust the quantum circuit class QAC0 is to error tolerance and to changes in its gate set. The authors remove the error in the parallel W-test using exact amplitude amplification, showing that QAC0 can exactly simulate TC0 with polynomially many input copies. They also show that for each fixed prime p, exact QAC0 can compute total Boolean functions outside AC0[p]. Finally, QAC0 remains powerful when restricted to generalized Toffoli, S, and Hadamard gates, since any QAC0 circuit can be approximated efficiently by such a circuit.
WhyEliminates parallel W-test error via exact amplitude amplification, showing exact QAC0 simulates TC0 and computes functions beyond AC0[p].
In briefPolynomial-time estimation of output probabilities for shallow quantum circuits
SummaryThe paper presents a deterministic classical algorithm that estimates the probability of a given output string from a constant-depth quantum circuit to within a specified additive error. The stated running time is polynomial in the number of qubits and the inverse of the error. The authors report that this improves on prior best algorithms for the same task.
WhyImproves constant-depth circuit output probability estimation from quasi-polynomial to polynomial time, a significant theoretical advance with rigorous algorithmic analysis.
Matthew Coudron, Michael J. Gullans, Jon Nelson et al.
In briefProvable quantum advantage in approximate optimization via decoded quantum interferometry
SummaryThis paper studies decoded quantum interferometry (DQI), a quantum method for approximate optimization. In an oracle setting using a task called folded optimal polynomial intersection, the authors prove DQI's approximation ratio strictly exceeds that of any polynomial-time classical algorithm. For code rate 0.3, DQI achieves expected scores of about 0.85, while exceeding the classical threshold of 0.65 requires super-polynomially many classical membership queries.
WhyExtends classical lower-bound methods to approximation, giving a strict oracle separation with DQI; novel but limited to random-oracle settings.
Maximilian J. Kramer, Elies Gil-Fuster, Benjamin D. M. Jones et al.
In briefTurning any CSS quantum LDPC code into a single-shot error-correcting code
SummaryThe paper proves that any single-shot quantum error-correcting code is self-correcting. It then shows that any [[n,k]] CSS quantum LDPC code can be transformed into an [[nm,k]] CSS code with single-shot error correction and a local decoder running in O(log m) parallel time. Below a constant threshold, the logical failure probability over T rounds is bounded by O(Tn)exp[-Ω(m^α)]. If the input code has a single-shot decoder, the output code enhances error suppression to Ω(m^α n^β).
WhyTransforms any CSS QLDPC code into one with single-shot correction and local decoding, giving a threshold and exponential error suppression; a strong theoretical advance mainly within quantum error co
In briefRandom Quantum Circuits Beyond Moment Matching: Accuracy Guarantees for Output Probability Distributions
SummaryThis paper studies how accurately approximate unitary designs, which reproduce the moments of Haar-random unitaries, capture the full distribution of individual output probabilities. The authors prove that the Kolmogorov distance to the Porter-Thomas distribution is bounded by a term of order sqrt(2^n/(k(k+2^n))) plus epsilon, and show this bound is optimal up to constants. They also show that local invariance under unitary translations yields an exponential improvement in k, with guarantees in total variation distance as well.
WhyExtends moment matching to full output-probability distributions with an optimal Kolmogorov bound and an exponential improvement under local invariance, rigorously proven.
In briefA generalized quantum Stein lemma on von Neumann algebras
SummaryThis paper proves a generalized quantum Stein lemma for independent and identically distributed normal states on arbitrary von Neumann algebras, against convex, tensor-stable families of alternatives. Assuming an alternative state with finite relative entropy to the null state exists, the worst-case type-II error exponent is achieved by the regularized relative entropy at every type-I error tolerance, with a strong converse. The proof combines an integral representation of relative entropy via hockey-stick divergences, a modular testing bound, and a convex minimax argument.
WhyExtends quantum Stein's lemma to arbitrary von Neumann algebras and convex families, with a strong converse via hockey-stick integral representation; a substantial theoretical advance.
In briefConstructing optimal quantum transducers using symmetry groups
SummaryThis paper studies transducers, a quantum computing framework that describes an algorithm as a unitary mapping an input state to a target state while leaving a catalyst vector unchanged. The authors show that using the symmetry group of state-conversion problems, an optimal catalyst can be chosen covariant under a group representation, and the transducer can be chosen block diagonal in the isotypic decomposition of the Hilbert space. Using these methods, they derive optimal transducers with optimal constants for unstructured search, amplitude amplification, and amplitude estimation.
WhyUses symmetry groups and representation theory to systematically construct optimal transducers with optimal constants for search, amplitude amplification, and estimation.
Beno\^it Dubus, Julien Ladeuze, J\'er\'emie Roland
In briefQuantum impurity models: easy at equilibrium, universal in motion
SummaryThis paper studies the computational complexity of quantum impurity models, which consist of a small interacting subsystem coupled to a large bath of free fermions. It shows that ground energy and thermal equilibrium properties can be efficiently approximated by classical algorithms. It also shows that time evolution under a fixed, constant-size impurity Hamiltonian is BQP-complete.
WhyProves polynomial classical approximations for ground and thermal properties, improving prior quasi-polynomial runtime, plus a BQP-completeness result for dynamics.
Srinivasan Arunachalam, Sergey Bravyi, Anirban Chowdhury et al.
In briefSpiking neural networks for streaming qubit readout
SummaryThis paper introduces spiking neural network discriminators for reading out superconducting qubit states. The networks process the measurement window in successive time chunks and update classification scores as data arrive. They outperform matched-filter discrimination and approach the accuracy of a full-trace artificial neural network. Using quantisation-aware training and hls4ml synthesis, each FPGA inference update is reported to finish before the next readout chunk arrives.
In briefLocal random quantum circuits reach Porter-Thomas distribution at polynomial depth
SummaryThis paper studies the output distribution of local random quantum circuits built from nearest-neighbor Haar random gates. It shows that brickwork circuits of depth O(n^{2m+1} log n) produce a fixed-bitstring output distribution within total variation distance O(1/n^m) of the Porter-Thomas distribution. The proof relies on moment bounds from approximate designs, analytic estimates for characteristic functions, and a local anticoncentration property.
WhyRigorously proves polynomial-depth local random circuits converge inverse-polynomially to Porter-Thomas, resolving a long-open question with broad relevance to random circuit sampling.
In briefUnitary Schur sampling of qudits using random SWAP tests to locate antisymmetric subsystems
SummaryThis paper shows that unitary Schur sampling, which extracts permutation-invariant information from many qudits, can be carried out using only pairwise SWAP tests. The protocol repeatedly finds and extracts the largest antisymmetric subsystem and achieves a stated error bound in diamond distance. The authors also apply the method to quantum purity amplification, showing that keeping one designated output qudit and discarding the rest yields the optimal purified state.
Shrigyan Brahmachari, David Jakab, Henry D. Pfister et al.
In briefAn exponential gap between entanglement-assisted and unassisted one-way quantum communication
SummaryThe paper addresses whether entanglement can reduce quantum communication cost for some tasks, a question open for total Boolean functions. It shows an exponential separation in the one-way setting. The authors exhibit a family of total Boolean functions that need only O(log n) classical bits with prior entanglement but Omega(n^(1/3)) qubits without it.
WhyGives the first exponential separation for a total Boolean function in one-way quantum communication, via a rigorous theoretical construction based on subgroup membership.
Ryan Anselm, Srijita Kundu, Olivier Lalonde et al.
In briefNo-go theorem: order-two Clifford realization of electric-magnetic duality in toric codes
SummaryThe paper asks whether electromagnetic duality in the toric code can be realized microscopically as an order-two Clifford operation. For the Z2 toric code, it proves that no locality-preserving Clifford realization of electric-magnetic exchange can have order two. For the ZN toric code, an order-two realization exists when N is odd but is impossible when N is even. The results show that the group law of an emergent duality need not faithfully lift to its microscopic Clifford realization.
In briefQuantum state preparation for weighted d-DNNF circuits
SummaryThe paper studies quantum state preparation, which asks for an efficient quantum circuit that generates a state from its description. The authors show that for states described by weighted d-DNNF (deterministic, decomposable pseudo-Boolean circuits), such a circuit can be obtained in linear time, up to complex arithmetic.
In briefA one-way quantum private retrieval protocol using only one server and NISQ devices
SummaryThis paper proposes a one-way quantum symmetric private information retrieval (SPIR) protocol that uses a single database server. The user obtains only one chosen bit without revealing the index, and the server learns nothing about the user's choice, with security against an unrestricted eavesdropper. The scheme assumes both parties have noisy intermediate-scale quantum (NISQ) devices with no long-term quantum memory. The authors prove secrecy, database privacy and user privacy, and give a numerical example in which blocks of about a thousand qubits suffice for a 10^4-bit database at database privacy 10^-6.
In briefStationarity as a one-mode constraint on quantum correlation
SummaryThe paper argues that a stationary scalar correlation energy admits an exact one-mode terminal representation even when the microscopic correlated response is strongly multimode. The authors test predictive realizations built from specified stationary information carriers in two-electron systems, He-like ions and harmonium, which share Coulomb repulsion but differ in confinement. Results show small correlation-energy errors for the Coulomb sequence, a validity limit at H⁻, and agreement with reference values for harmonic confinement at larger frequencies.
In briefEstimating a Specific Output Probability in 1D Chaotic Quantum Circuits
SummaryThis paper studies how to approximately compute a specified output probability of a one-dimensional chaotic brick-wall quantum circuit. It uses the Sweeping RTM algorithm, a tensor-network contraction based on reduced transition matrices, to jointly compress the left and right temporal boundary states. Numerical evidence indicates that the bond dimension needed for stable estimates at fixed relative precision grows subexponentially over the accessible time window.
Matilde Grassi, Stefano Carignano, Luca Tagliacozzo et al.
In briefThin-capping-layer epitaxial quantum dots for near-field quantum photonics
SummaryThis paper reports the growth and optical characterisation of InAs/GaAs quantum dots with GaAs capping layers of 10 nm, 20 nm and a standard 95 nm. The thin-capped dots show emission linewidths up to 5 times narrower than previously reported, with unchanged excitonic lifetimes. The results suggest high optical quality can be kept when emitters sit close to the surface, enabling studies of near-field light-matter interaction.
Yuting Guo, Jonathan Bar-David, Pasquale Cilibrizzi et al.
In briefA map of when the transverse field Ising model's partition function can be efficiently approximated
SummaryThis paper studies the transverse field Ising model and sets a computational boundary for approximating its partition function and Pauli string observables of the Gibbs state. When the spectral width of the interaction matrix times tanh(βη)/η is at most 1, the authors give a randomized classical algorithm that approximates the partition function to relative error in polynomial time. When this quantity exceeds 1, they prove that approximation within an exp(o(n)) multiplicative factor is NP-hard.
WhyGives a polynomial-time approximation regime for the transverse field Ising partition function and proves NP-hardness beyond the threshold, a sharp theoretical boundary.
In briefUniversal limit and phase transition in many-body fermionic non-Gaussianity
SummaryThis paper studies fermionic non-Gaussianity, a resource for universal quantum computation that interactions can generate in many-body systems. Using magic Rényi entropy (MRE) as the measure, the authors derive a universal upper bound and Haar mean, showing that typical Haar-random states reach a maximal density of ln(4/3) per Majorana in the large-system limit. Evolving Gaussian states under the Sachdev-Ye-Kitaev Hamiltonian, they identify a first-order transition with a kink in MRE density and spontaneous breaking of permutation symmetry, which is not visible in the thermal free energy.
WhyDerives a universal bound and Haar mean for fermionic non-Gaussianity and finds a first-order transition with permutation symmetry breaking in SYK dynamics, a notable advance supported by analytic and
