October 19, 2026

Demonstration of Logical Error Suppression in a Surface Code Memory on a Cloud-Accessible IBM Superconducting ProcessorTier 3

Quantum error correction can suppress logical errors exponentially with code distance when physical noise is below threshold. Realizing this on hardware requires tight coordination among quantum gates, mid-circuit measurements, and qubit coherence. Device variation, noise asymmetry, and correlations across space and time complicate the translation of these capabilities into...

Previously: 2026-10-13, 2026-10-11, 2026-09-17

Encodings and Node Architecture: Lessons from the Fault-Tolerant Distributed Transversal FanoutTier 3

An encoding choice specifies the quantum error-correcting code used to encode logical qubits at a given node. Different encoding choices may differ in the number of physical qubits, the number of encoded logical qubits, the code distance, and the available fault-tolerant operations. We study different encodings for a distributed transversal fanout operation and look at its i...

Experimental Demonstration of a Balanced Travelling Wave Parametric AmplifierTier 3

Superconducting travelling-wave parametric amplifiers (TWPAs) provide broadband gain, low added noise, and high dynamic range, making them attractive for applications requiring wide instantaneous bandwidth. This is crucial for amplifying multiplexed narrow band signals spread over a wide frequency range, such as qubit resonator arrays, or amplifying inherently wide band sign...

Exponential-SWAP gate between bosonic motional modes of trapped ionsTier 3

The exponential-SWAP (eSWAP) gate generates a coherent superposition of identity and SWAP operations, with continuously tunable amplitudes. We experimentally implement this gate between two bosonic motional modes of trapped ions using spin-independent and spin-dependent beam splitter interactions. Measurements of selected slices of the joint characteristic function for disti...

From quantum emitters to technological platforms: a perspective on semiconductor quantum dotsTier 3

Photonic quantum technologies are based on controlled photon states. To generate these, quantum dots have emerged as excellent sources of single and entangled photons. In this Perspective, we briefly review the chronological development of quantum dots as photon sources, from their beginnings as quantum emitters in the early 2000s to the advanced photonic devices being devel...

Leveraging verifiable structure in quantum circuits to find more efficient compilations with agentic AITier 3

We discuss an effective paradigm of utilizing AI agents to better compile quantum circuits when one can constrain bottleneck subroutines to have some form of classically verifiable structure. For example, when critical subroutines are composed exclusively of reversible classical logic, phasing operations, and measurement based uncomputation, one can efficiently simulate exec...

Transport and thermalization under noncommuting localized constraintsTier 3

We investigate the effects of spatially localized conserved quantities on transport and thermalization in quantum and classical many-body systems. We consider several related models: the integrable quantum Volterra model, its nonintegrable classical limit, and two cellular automata derived from the latter. Although localized constraints are often associated with lattice gaug...

Solving Large-Scale Parameter Inference in Controllable Nuclear Fusion via Coherent Ising Machines and Block Coordinate DescentTier 3

Bayesian inference enables self-consistent plasma parameter inversion in tokamak integrated data analysis by fusing multi-source diagnostics. However, under nonlinear Gaussian likelihoods, finding the maximum a posteriori (MAP) estimate typically relies on sampling methods whose high computational overhead precludes real-time plasma control. To address this bottleneck, we pr...

SpinControl: Control Software for Prototyping and Benchmarking of Spin-Qubit Devices and Measurement ProtocolsTier 3

Quantum computers require software to control the states of the qubits. As the actions on qubits grow in complexity with circuit execution, calibration, and benchmarking, the complexity of the control software grows in tandem. Spin-qubit quantum computers are at a stage where experimentalists need low-level access for tuning and calibration, and quantum algorithm researchers...

Task-aligned spectral inductive biases in parameterized quantum circuitsTier 3

Parameterized quantum circuits are widely investigated in quantum machine learning, yet how their architecture can provide task-aligned inductive biases remains poorly understood. We study data reuploading quantum circuits with two distinct inputs: a signal that varies between samples and a fixed, task-defined spectral query that specifies how the signal should be probed. We...

Anyonic Neural Network WavefunctionsTier 3

The macroscopic behavior of a non-interacting gas of Abelian anyons has remained unsettled for many decades. Prior numerical methods employing exact diagonalization in the continuum and on the plane have been limited to small system sizes, at most N = 4 anyons. Using the rapidly developing technology of neural network wavefunctions, we develop variational ansatze appropria...

Expressivity of IQP Feature-Map Quantum Kernels via Reproducing Kernel Hilbert SpacesTier 3

Quantum kernels are among the most promising methods in quantum machine learning, providing a natural way to embed data into high-dimensional Hilbert spaces via quantum circuits and capturing non-linear relationships in data. Their learning behaviour is governed by the function class they represent, which is formally characterized by the structure of the associated Reproduci...

Cayley access models for matrix functions: reachable class and costTier 3

We study how to compute f(A)b on a quantum computer, where A is Hermitian. When f is nonsmooth or has localized difficulty in the spectrum, classical numerical linear algebra approximates it with rational functions rather than polynomials. We propose the Cayley transform, parameterized by σ∈R and γ> 0, as an alternative to the standard quantum access mo...

ConQUESTA: Topology-Aware Post-Training Structural Pruning of Quantum Neural NetworksTier 3

Deploying quantum neural networks (QNNs) on sparse hardware requires preserving task accuracy while reducing compiler-induced two-qubit gates, SWAPs, and depth. We present ConQUESTA (\underline{C}onstrained \underline{Qu}antum \underline{E}ntangler \underline{S}election with \underline{T}opology \underline{A}wareness), a post training pruning framework that combines task sal...

Sample-Based Quantum Linear Solver and Bounds on Krylov-State SamplingTier 3

To solve linear systems Ax=b, we propose a sample-based quantum linear solver combining quantum Krylov-state sampling with classical variational diagonalization. Rather than simulating the cost Hamiltonian H_b(A)=A^†(I-|b⟩⟨b|)A, we measure quantum Krylov states e^(-iAT)|b⟩ generated by the original Hermitian operator A in the computational ba...

Quantum approximate stochastic combinatorial optimisationTier 3

Two-stage stochastic combinatorial optimisation concerns discrete decisions made before all relevant information is known. An initial decision is made; once uncertainty is resolved, it can be adapted to the realised scenario, at a cost. The aim is to find the initial decision that minimises the upfront cost plus the expected cost of optimal adaptation. The first-stage decisi...

Holographic two-point functions across a PT symmetry-breaking transitionTier 3

In parity-time (PT)-symmetric non-Hermitian systems, an exceptional point, where eigenvalues and eigenvectors coalesce, typically separates a real spectrum from complex-conjugate eigenvalues. In logarithmic conformal field theories (LCFTs), such an exceptional point appears in the spectrum of scaling dimensions. Holographic models of LCFTs, such as the dipole model, are buil...

Chirality-resolved imaging of spin waves with a quantum spinTier 3

Spin waves carry their propagation direction in the handedness of their circularly polarized stray field, a property inaccessible to scalar magnetometers. In the Damon-Eshbach surface wave of an in-plane magnetized film, the dipolar field above the film rotates with a handedness fixed by the direction of travel. The nitrogen-vacancy (NV) centre in diamond is an intrinsic pol...

A Fibre-Integrated SPDC Heralded Single-Photon Source Using Zn-Indiffused PPLN Ridge Waveguides at Telecom WavelengthsTier 3

We demonstrate a fully fibre-integrated source of broadband polarisation-entangled photon pairs at telecom wavelengths based on a commercially available Zn-indiffused MgO:PPLN ridge waveguide incorporated within a Sagnac interferometer. Operating across the full degenerate SPDC spectrum using pump-suppression filtering only, the source exhibits a measured bandwidth of approx...

Quantum-Assisted Unambiguous Discrimination of Pure States with Robustness BoundsTier 3

We propose a hybrid quantum-classical framework for the unambiguous discrimination of pure states by combining the noisy intermediate-scale quantum semidefinite program solver (NSS) with the reciprocal-state representation. In NSS, a given semidefinite program (SDP) is represented within a subspace spanned by chosen ansatz states, with the required quantities estimated using...

Quality-of-Transmission Estimation in Quantum Networks: Compute, Simulate, or Learn?Tier 3

Future quantum networks will rely on control-plane decisions such as routing, scheduling, entanglement provisioning, purification, and memory allocation. Each decision depends on a timely and reliable estimate of the quality of the entanglement that a candidate path can deliver, with end-to-end fidelity as a central metric. Inspired by the optical-networking experience with...

UKRI Backs UK Quantum Businesses With Share of £50 MillionTier 2

Insider Brief A share of £50 million is going to British businesses developing quantum technologies for uses that include keeping railways running, shortening eye scan waits and maintaining military connectivity, UKRI said. The money forms part of a new government package. According to UKRI, the package is delivered through its Quantum Technologies Priority Programme, as ...

Scaling of entanglement with distance between subsystems: detection of phase transitions in the t'-π-flux modelTier 3

The system-size scaling of bipartite entanglement can be used to detect phase transitions. We develop a related approach for strongly correlated electron models where large density matrices or large system size scaling are inaccessible. To this end, we demonstrate that phase transitions of various kinds are signaled by a sharp signature in the first- or second-order logarith...

Recursive Operator Localization and Spectral Gap Descent via the Geometry of Local Spectral ExpansionTier 3

We introduce Recursive Operator Localization (ROL), a framework for constructing hierarchies of local energy problems linked by linear maps between Hilbert spaces. To address spectral-gap problems, including those arising in quantum systems, we study a realization of ROL by nested subspaces indexed by a weighted simplicial complex. Using spectral gaps of auxiliary classical...

Impact of Irrep Truncations on Quantum Simulations of QCDTier 3

Quantum simulations of lattice gauge theories with continuous gauge groups require a choice of basis (how states of the gauge theory map to the qubit computational basis) and truncation scheme (which of the infinitely many gauge theory basis states should be omitted in the map to the finite dimensional qubit Hilbert space.) The most common choices are adapted to an electric...

Delta-sigma noise shaping for low-resolution quantization in Gaussian-modulated continuous-variable quantum key distributionTier 3

Low-resolution digital-to-analog conversion can simplify continuous-variable quantum key distribution (CVQKD) transmitters, but coarse quantization increases excess noise and can generate data-correlated spectral replicas. We demonstrate digital delta--sigma modulation (DSM) for low-resolution waveform generation in Gaussian-modulated CVQKD. In a 500-MBaud CVQKD system over...

Partially isophase electro-magnetic configurationsTier 3

Separation of variables in Schrödinger equation allows an infinite-dimensional family of physically distinct field configurations that are dynamically indistinguishable in one selected sector, labeled by a conserved quantum number, while differing in all others. We call such a symmetry a partial isophase symmetry. Two main examples are considered: axially symmetric magnetic...

Certifying information flow in multi-agent behavioursTier 3

We study which input-output behaviours of several agents can be produced by a declared communication schedule, that is, a fixed sequence of senders, recipients, message alphabets, and output times, together with shared randomness. Since a schedule admits only finitely many deterministic protocols, membership is a linear program, and an infeasible target is excluded by a sepa...

Improving the estimation of spin-bath parameters via initial correlations and a two-qubit probeTier 3

We study how a second qubit can improve the estimation of spin-environment parameters when only one of the two qubits is measured. Both qubits are coupled to a common spin bath through the exactly solvable central-spin model, in which populations and coherences both evolve. Because the bath operator coupled to the qubits commutes with the bath Hamiltonian, the environment in...

Action-Quantized Scar Multiplets and Dissipative Cat States from Fractal Period-Locking in the Open Quantum Baker MapTier 3

We open the quantum baker map with a position window of width w and center q_c. Classical pruning tiles the (q_c,w) plane into diamonds where the T leading resonances form root-of-unity multiplets. At w=1/2 one periodic orbit survives for almost every q_c, and the multiplets are quantized without free parameters: their modulus 2^(-1/2) saturates the pressure bo...

Electrostatic Limits on Quantum Spatial SearchTier 3

We prove that a quantum walker cannot search a two-dimensional lattice in Grover's O(√N) time, resolving the long-standing open question posed by Aaronson and Ambainis in 2003. A walker that hops between neighbouring sites of an L×L lattice, N=L^2, needs Ω(√(Nlog N)) local steps at least to find a marked vertex, even with unlimited memory and free que...

Temperature dependence of a warm ensemble based memory on quantum communication ratesTier 3

The success of long-distance quantum communication will hinge on quantum repeater nodes equipped with robust and scalable quantum memories. Such memories must possess specific operating characteristics to make these nodes practical. An attractive option for these memory devices is an atomic warm vapor system operating under the conditions of electromagnetically induced trans...

Quantum Circuits for Variable-Coefficient Vlasov Dynamics via SchrödingerisationTier 3

High-dimensional Vlasov equations present promising use cases for quantum simulation, but their transport coefficients must be implemented coherently in order to preserve a compact quantum representation. We develop explicit Schrödingerised circuits for prescribed external field Vlasov dynamics without classical field updates. In 1D1V, velocity-dependent streaming is compile...

Quantum Sensitivity of N-Component Cat StatesTier 3

We extend our previous study of squeezed two-component Schrödinger cat states to a phase-referenced single-mode family with an arbitrary number N of coherent components and general relative phases. Within the established circular-state construction, we derive a closed complex overlap kernel for the ordered action of displacement, phase rotation, and squeezing, retaining ex...

Resonance crossings and diabolical points for DC electric field quantum sensorsTier 3

Since the 1990s, experiments on double-well heterostructures have highlighted a key phenomenon: applying an external DC electric field induces pronounced wave packet oscillations at specific field strengths. \ To gain a deeper insight into this effect, a comprehensive quantitative analysis of the properties of quantum resonances near a crossing point is required. \ This appr...

Bell scenarios encode classical non-causalityTier 3

Bell and contextuality scenarios are unified within the Acín-Fritz-Leverrier-Sainz hypergraph formalism, in which measurements are hyperedges. Multipartite measurements are obtained from product rules that combine independent contextuality scenarios into a single hypergraph. Several such rules exist: they are structurally distinct, yet yield the same classical, quantum, and...

Temperature dependence of the Casimir force between plane-layered structures: an approach based on the principle of argumentTier 3

Based on the complex analysis theorem the principle of argument, a temperature-dependent formula for the Casimir-Lifshitz dispersion force of the interaction of two arbitrary plane-layered structures separated by either a vacuum gap of size d or a layer of size d consisting of an arbitrary dissipative dielectric with dispersion is derived. The formula consists of the tempera...

Anticommuting Displacement Operators, Exact Pauli Algebras,and the Singlet State from the Oscillator VacuumTier 3

We give an explicit construction of a pair of anticommuting Weyl displacement operators for a harmonic oscillator and use bounded functional calculus to obtain exact dichotomic representatives of the Pauli algebra. Two independent oscillators provide commuting Pauli algebras for Alice and Bob. The standard singlet-sector projector, written entirely in terms of these bounded...

Controlled PROP: Theory and Applications to Quantum CircuitsTier 3

Control is a fundamental concept in quantum and reversible computational models. It enables the conditional application of a transformation to a system, depending on the state of another system. We introduce a general framework for diagrammatic reasoning featuring control as a constructor. To this end, we provide an elementary axiomatization of control functors, extending th...

Liouvillian Non-Invertible SymmetryTier 3

Non-invertible symmetries extend conventional symmetries beyond group-like transformations and play an important role in quantum field theory and many-body physics. However, a general framework of non-invertible symmetries in open quantum systems is still lacking. Here, we formulate a general Liouville-space duality framework that extends Hilbert-space non-invertible dualiti...

Multiscale Quantum-Classical Simulation of Protein Autoproteolysis in a Million-Atom Membrane EnvironmentTier 3

Predicting chemical reactions in biomolecules is challenging because reactive centers are embedded within complex environments that strongly influence their energetics and mechanisms. Here, we present a hybrid quantum-classical workflow that combines molecular dynamics, density functional theory, and correlated wavefunction methods, tightly integrating CPUs, GPUs, and quantu...

Previously: 2026-10-15, 2026-10-15, 2026-09-16

Nonergodicity from Hilbert-Subspace CloningTier 3

We identify a class of nonintegrable quantum many-body systems composed of single Pauli strings that possess an extensive number of noncommuting local conserved quantities and exhibit partial ergodicity breaking due to exponentially degenerate energy spectra. We show that such systems exhibit a novel mechanism, Hilbert-subspace cloning, where the identical chaotic Hamiltonia...

Nonequilibrium Dynamical Quantum Phase Transitions in the Extended Agassi ModelTier 3

We investigate dynamical quantum phase transitions (DQPTs) in the extended Agassi model following sudden quenches of same level pairing (Σ), monopole-monopole (χ) and cross level pairing (Λ) strengths. Using exact diagonalization, we characterize the non-equilibrium dynamics through the Loschmidt echo and intensive return-rate function. Quenches across equilibrium phas...

Concrete Functions in Private Simultaneous Quantum Messages: Quantum Advantages and Structural LimitationsTier 3

Private simultaneous quantum messages (PSQM) provide a minimal model of noninteractive secure multiparty quantum computation, yet their communication complexity for concrete functions remains poorly understood. We show that familiar total functions already exhibit both genuine quantum advantages and strong structural limitations. For three-party equality on n-bit inputs, w...

Discrete time crystals and classical logic gates in coupled open Dicke modelsTier 3

We investigate the dynamics of coupled discrete time crystals (DTCs) in the coupled Dicke model or Dicke dimer (DD) with dissipation. By numerically simulating the mean-field dynamics of the system, we show that coupling two DTCs decreases their oscillation amplitude following a transient relaxation period. For sufficiently strong coupling, the coupled DTCs become unstable,...

Quantum Tsallis Entropy Estimation: Near-Optimal Bounds and High-Precision ImprovementsTier 3

Estimating statistical properties of probability distributions is a fundamental problem in statistics and theoretical computer science. We develop quantum algorithms for estimating the q-Tsallis entropy H_q^(Tsa)(P) =(Σ_(i=1)^n p_i^q-1)/(1-q) when $0

On the relationship between the POVM framework and the no-signaling hypothesisTier 3

The quantum foundations literature contains dozens of "no-signaling" arguments that rely on the Born rule or, more generally, the positive operator-valued measure (POVM) framework to show that the resources of non-relativistic quantum mechanics (NRQM) cannot be used to send superluminal signals. What these arguments typically establish, however, is not a prohibition on super...

Development of a fabrication-to-benchtop process for SiN-based quantum devicesTier 3

Silicon nitride has emerged as a key material for the advancement of future quantum communication and computational devices. However, challenges persist in establishing a comprehensive development process, spanning from fabrication to optical characterization, essential for advancing these devices to their next stage of potential. Maintaining control over the entire process,...

Quantumness of Entanglement in Schwarzschild de Sitter SpacetimeTier 3

We investigate genuine multipartite entanglement and genuine tripartite nonlocality of a noisy generalized GHZ state in Schwarzschild-de Sitter spacetime. The genuine multipartite concurrence and optimized Svetlichny parameter are employed to characterize these two quantum correlations. It is shown that the black hole and cosmological event horizons redistribute genuine mult...

Unconditional Quantum PAC Learning Advantage in the Large Error RegimeTier 3

We establish an unconditional super-polynomial separation between quantum and classical PAC learning of Boolean functions under the uniform distribution in the large error regime. For every advantage λ(n) = n^(-ω(1)), we construct a concept class that a polynomial-time quantum learner learns to agreement 1/2+λ(n) with success probability at least 1-1/n^k. The learner u...