August 4, 2026

Detecting high-dimensional entanglement with simple measurements

The standard benchmark for high-dimensional entanglement is the number of dimensions in which entanglement must be present in order to generate the state. This is called the Schmidt number and its detection is usually based on implementing an appropriate set of local basis measurements. However, as quantum technology brings increasingly large physical dimensions within reach...

Finite-Syndrome Compression of Quantum Fisher Information

Readable error records can protect quantum sensing because they prevent physically distinct noise trajectories from being irreversibly mixed. A finite detector or ancilla, however, can retain only finitely many syndrome values, and a general criterion for deciding which records may be merged without losing metrological information is absent. We formulate the problem for a fi...

Learnable yet not simulable: a quantum resource theory of learning models

Quantum resource theory has sharpened our understanding of the intrinsic complexity of quantum systems, particularly their classical simulability. However, it remains unclear which quantum resource governs the classical learnability of quantum circuits, especially beyond the regime of efficient classical simulation. Here we close this knowledge gap by studying the expectatio...

Phase-Drift Limits and Adaptive Quadrature Readout in Programmable Photonic Processors

Phase fluctuations between optical inputs limit programmable photonic processors because their output powers depend on coherent interference. We study the phase-drift penalty that arises when sine and cosine quadratures are measured sequentially rather than simultaneously. The analysis is motivated by measurements from an eight-mode programmable photonic processor, including...

Quantum computer-based simulation of Stark many-body localization in a 1D Fermi-Hubbard model

Many-body localization (MBL) is a dynamical phenomenon that describes the non-ergodicity of isolated quantum many-body systems. In contrast to thermalization, this phenomenon leads to a long-lived memory of initial states of local systems and slow growth of entanglement. In this work, we study Stark MBL in a 12-qubit correlated fermionic system described by the one-dimension...

A Standard Quantum Mechanical Treatment to Rationalize the Delayed-Choice Quantum Eraser

Ever since the proposal of delayed choice quantum erasure and subsequent realization in the experiment by Kim et al., the interpretation and implications of delayed-choice experiments have remained a subject of intense foundational debate. This paper resolves the apparent paradox attached to the experiment using standard quantum mechanics. Using an extended Mach-Zehnder inte...

Adaptive Spectroscopy of Fast Two-Level-System Dynamics in Superconducting Qubits

Parasitic two-level-system (TLS) defects are a major source of energy relaxation and temporal instability in superconducting quantum processors. Our sub-second adaptive spectroscopy reveals telegraphic switching of TLSs with a characteristic timescale of a few seconds and spectral diffusion with diffusivity D ≈0.9 MHz^2/s. These timescales are abou...

Zero-G: A Pre-Decoder-Aware Decoder for Quantum Error Correction

Fault-tolerant quantum computing requires classical decoders that keep pace with the underlying hardware, translating syndrome measurements into corrections fast enough to avoid an exponential backlog. To meet this real-time constraint, pre-decoders have emerged as part of a hierarchical decoding approach to resolve simple, local errors before passing a sparser residual synd...

Squeezing-Fueled Quantum Otto Engine via Measurement-Induced Cooling: The Two-Qubit Quantum Rabi Model

We investigate a quantum Otto engine (QOE) constructed from the two-qubit quantum Rabi model, operating within a cavity quantum electrodynamics (QED) architecture. The engine operates with two qubits as the working substance and a single non-Markovian hot thermal bath, modeled via the hierarchical equations of motion (HEOM) formalism. In place of a conventional cold thermal...

Quantum resetting with memory

We introduce a quantum stochastic resetting protocol with uniform memory, in which each resetting event returns the system to a state visited at a time chosen uniformly from its entire history. The resulting dynamics is nonunitary, non-Markovian and a direct quantum generalization of the classical preferential relocation model. Working in the energy eigenbasis, we derive the...

Efficient re-sampling in quasi-probability decompositions

Near-term quantum devices are limited by noise and hardware constraints, motivating algorithmic approaches that trade circuit complexity for increased sampling overhead. Quasi-probability decompositions (QPDs), for example, allow replacing non-local operations by multiple circuits with local operations, but the associated sampling overhead generally scales exponentially and...

Reinforcement-Learned Electric-Field Sensing with Asymmetrically Blockaded Rydberg Arrays

We present a reinforcement learning-optimized Rydberg electrometer based on the asymmetric blockade effect and achieve high-sensitivity electric field sensing in Rydberg arrays. Microwave dressing induces asymmetric blockade to suppress interactions between target atoms, while keeping the coupling between the central control atom and target atoms field-tunable near Förster r...

Validation and calibration of quantum hardware through the many-body quantum Mpemba effect

We introduce a validation process that harnesses engineered many-body relaxation to control and calibrate quantum hardware. On two independently developed neutral-atom processors, we realize the many-body quantum Mpemba effect in an open system for the first time. Initial-state engineering creates fast and slow relaxation pathways: the fast pathway opens access to unreachabl...

Interspecies clock comparison below 5 ×10^(-18) uncertainty with a transportable clock

We report a measurement of the optical frequency ratio between the ^2S_(1/2)(F=0)--^2F_(7/2)(F=3) electric-octupole (E3) transition of ^(171)Yb^+ and the ^1S_0--^3P_0 transition of ^(87)Sr, ν_(Yb^+)/ν_Sr = 1.495 991 618 544 900 588 1(65). Reaching a fractional uncertainty of 4.3 ×10^(-...)

JIJ Raises US$5.2 Million in Funding Led by Global Brain

D-Wave and Nasdaq Verafin Announce Agreement for Quantum Computing Application Development

Nearly tight lower bounds for estimating quantum functionals: Uhlmann fidelity, trace distance, and von Neumann entropy

In this paper, we present a unified framework for proving lower bounds for estimating functionals of quantum states. We therefore resolve several open problems by establishing lower bounds that match known upper bounds: we show that it requires Ω(N^2) samples to estimate the Uhlmann fidelity, trace distance, and von Neumann entropy. Moreover, they immediately imp...

An Argmax Principle for Sum-of-Squares Relaxations on the Sphere

We develop an argmax principle for analyzing sum-of-squares relaxations of optimization problems over the unit sphere. Given a feasible pseudo-expectation, we form a polynomial of high-order pseudo-moments, such as Φ_k(u)=E⟨x,u⟩^(2k). Our guiding principle is that its maximizers are rounding candidates: their local and global optimality con...

Optimal Quantum de Finetti Theorems via Argmax Rounding

We prove optimal finite quantum de Finetti upper bounds. Given a bosonic state ρ_N∈D(Sym^N(C^d)), there is a probability measure ν on the unit sphere such that ‖ ρ_N^((2))-∫|u⟩⟨u|^(⊗2) dν(u) ‖_1 ≤(√(d-1))/(N-1). By purification, the bosonic theorem also gives the optimal O(d/N) upper bound for a...

Entanglement of flower states

The mysterious nature of entanglement, one of the most prominent exquisitely quantum phenomena, is reflected in its intricate operational structure, with a hierarchy of classes of free operations that enable its manipulation at different levels of effectiveness. Here we use the class of 'flower states', parametrised by their (even) local dimension $2k$, to shine light on som...

Thermalization of open quantum systems with pseudomodes

Pseudomode approaches allow for an exact and unapproximated description of a quantum system interacting arbitrarily strongly with a bath. In general, a system coupled to pseudomodes will not thermalize to the system's Gibbs state: This is to be expected when the system-bath coupling is non-perturbative, but conflicts with common thermodynamic intuition when the system-bath c...

Comparison of Lindblad and circuit approaches for quantum heat transport

We compare two popular models applicable to analyzing heat transport by thermal microwave photons in quantum circuits. The first model is derived from a weak-coupling Lindblad master equation, with transition rates determined by Fermi's golden rule induced by thermal dissipation sources. The second approach employs a circuit model, where thermal Johnson-Nyquist noise generat...

High-dimensional quantum process tomography with undetected photons

The goal of quantum process tomography is to fully characterize an operation performed on a quantum state. By considering high-dimensional quantum states (qudit), we show that it is possible to fully reconstruct an arbitrary operation without performing any measurement on the transformed qudit. Our method is interferometric and conceptually different from existing techniques...

Optimized Tensor-Network Renormalization for Quantum Dynamics: Resolving the Spectral Function of K_2Co(SeO_3)_2

Tensor-network methods have opened a powerful route for the study of dynamical spectral functions in two-dimensional quantum systems. However, existing approaches within the framework of infinite projected entangled-pair states construct the required renormalization tensors solely from the ground-state environment and can suffer from severe numerical instability. We identify...

Nanohertz Pendulum toward Macroscopic Entanglement under Structural Damping

Pendulums are attractive for macroscopic quantum control because gravity dilution reduces mechanical loss, while the 1/f force-noise spectrum associated with structural damping allows nearly lossless trapping to suppress the thermal noise sampled at an upward-shifted resonance. The same 1/f spectrum, however, produces a low-frequency tail that penalizes entanglement. Wit...

Spread complexity as a probe in generalized and long-range Aubry-Andre-Harper models

We investigate the spread complexity of quantum quenches in generalized and long-range Aubry-Andre-Harper (AAH) models, encompassing regimes with and without mobility edges. In particular, in the generalized AAH models supporting energy-dependent mobility edges, we demonstrate that the long-time averaged spread complexity exhibits nonanalytic behavior when the post-quench qu...

Caustics and Superenergy in the Quantum Bouncer

We investigate the quantum interference and energetic phenomena associated with classical caustics in the quantum bouncing ball problem, we refer to as quantum caustics. By considering an initial Gaussian wavepacket, we show that caustics associated with the underlying classical trajectory families are exhibited. We connect the associated phase singularity chains in the vici...

Measurement and control of the interaction frequency shift in bosonic optical lattice clocks

We report precise measurements of inter-level interactions in a bosonic optical lattice clock based on ^(88)Sr atoms. We observe a nonlinear density dependence of the clock shift, even without reaching quantum degeneracy. In a 2D lattice, the Rabi line shape exhibits an interaction sideband consistent with a collective spin model, while in a 1D lattice the shift is modifie...

Entanglement Generation Beyond Quantum Theory: From Product States to Popescu-Rohrlich Boxes

Entanglement generation is a fundamental dynamical capability in quantum information science and underpins many quantum advantages. While quantum theory enables it through unitary dynamics, boxworld, a generalized probabilistic theory admitting Popescu--Rohrlich boxes with supraquantum correlations, has no reversible transformation capable of generating entanglement. We show...

Revealing and reducing growth-induced interfacial disorder in preferentially aligned nitrogen-vacancy centers in diamond

Nitrogen-vacancy (NV) centers in chemical-vapor-deposition (CVD) diamond can form preferentially oriented ensembles with high sensing performance and low densities of lattice defects. Thin films of this material are a cornerstone of various imaging modalities. However, nitrogen injection needed to produce such films can transiently drive growth out of equilibrium, generating...

Effects of realistic pulse shapes in two-dimensional spectroscopy

Two-dimensional (2D) spectroscopy is a powerful pump-pump-probe technique for revealing couplings between quantum states and disentangling the different contributions to the optical response of a system. We present an efficient method for 2D spectroscopy simulations in the Markovian limit for the environment, capable of handling arbitrary pulse shapes and reproducing time-or...

Unconditionally successful quantum Time-Marching algorithm via LCU for nonlinear Burgers equation

Most recently proposed quantum algorithms for solving linear and nonlinear partial differential equations rely on non-unitary operations. These operations are typically implemented probabilistically, requiring postselection and thus increasing the computational cost. We show that quantum lattice gas algorithms enable unconditionally successful quantum simulation of nonlinear...

Better accuracy with fewer qubits: Single-particle basis set optimization for quantum chemistry on quantum computers

In spite of recent advances, quantum computers are expected to be sufficiently noisy in the coming few years to the extent of limiting quantum chemical calculations to relatively small number of orbitals. However, even with reasonable quality single particle basis sets, small active spaces with limited orbitals can result in a significant fraction of correlation energy being...

Field-Free Transverse Aharonov--Bohm Phase Gate for an Orbital l-Qubit

Free-space Aharonov--Bohm (AB) Bessel modes are known to carry a flux-dependent azimuthal Schrödinger probability current and kinetic orbital angular momentum. We extend this response to the spin-resolved conserved Dirac current of a core-excluded finite-wall annular guide and show that confinement converts its surviving orbital component into a transverse Aharonov--Bohm (TA...

Characterizing the nitrogen-vacancy center singlet transition and its phonon sideband for absorption-based room-temperature magnetometry

Magnetometry with nitrogen-vacancy (NV) centers in diamond has shown great promise in recent years. In particular, absorption-based magnetometry techniques, employing a cavity to enhance the absorption length, can improve the contrast and sensitivity compared to conventional techniques based on reading out the NV^- triplet fluorescence. The absorption techniques rely on ma...

Quantum Vortices in a Boundary Layer: New Results and Perspectives

Here, we investigate the motion of a thin circular quantum vortex filament near the infinite planar surface. The fluid surrounding this surface moves with a non-zero velocity bfv, which is parallel to the surface. We study the specific features of this quantum system and show that they are quite suitable for the boundary layer theory. The developed model allows us to ca...

Scaled Caldeira-Leggett Dynamics: Deterministic Trajectories and the Classical Limit

The dynamics of an open quantum system in the high-temperature regime of the Caldeira-Leggett model using a Bohmian language is investigated. By expressing the density matrix in polar form, generalized continuity and Hamilton-Jacobi equations are obtained. Thermal effects appear explicitly in the former, while they influence the latter only indirectly through an effective po...

Adaptive Reconstruction of Bosonic Quantum States

Bosonic quantum systems provide a hardware-efficient platform for quantum information processing but remain challenging to characterise due to their large Hilbert space and the high measurement cost of state tomography. Existing approaches estimate the fidelity with respect to a single target state, making them unsuitable for applications in which physically equivalent state...

Towards Tensor-Network SAT-Solvers for Quantum-Classical Workflows

Integrated HPC/QC systems aim to combine classical high-performance computing with quantum processors, but cannot be reduced to mechanisms for dispatching quantum kernels. An integrated architecture must support aspects such as observability, which cannot be implemented using QPUs alone, as well as fallback execution and cost-aware decisions on whether to replace quantum tas...

Convergence monitoring of quantum Gibbs samplers

Recent progress in fully quantum Markov chain Monte Carlo methods enables efficient Gibbs-state sampling on quantum computers [Chen et al., Nature 646, 561 (2025)]. Although rigorous worst-case bounds on mixing times remain largely inaccessible for classically intractable systems, experience from classical Monte Carlo suggests that convergence of relevant observables may nev...

Coarse-Graining and the Classification of Long-Range Correlations in Quantum Field Theory

A conservation-law-guided classification framework is developed for the execution of coarse-graining operations in quantum field theory. Coarse-graining produces a selection at the level of Feynman diagrams. Diagrams with nonzero momentum transfer are suppressed by oscillatory factors, zero-momentum-transfer ladder diagrams can accumulate through geometric series resummation...

Optimality of Gaussian Entanglement of Formation

We prove that the entanglement of formation of every two-mode Gaussian state coincides with its Gaussian restriction, solving a longstanding open problem in continuous variable quantum information theory. The key result is a sharp affine relation between entanglement and a generalized Einstein-Podolsky-Rosen observable, valid for arbitrary pure two-mode states, including non...

Symmetry-Projected Compatible Multiparameter Quantum Sensing

We establish a general symmetry-projection framework for multiparameter quantum sensing. Decomposing encoding generators into subspace-preserving and subspace-changing components relative to a symmetry sector identically eliminates all cross-sector elements of the quantum Fisher information matrix (QFIM) and the mean symmetric logarithmic derivative (SLD) commutator matrix....

The Sample Complexity of Fidelity Estimation to a Known Rank-r Reference State Is Θ(r^2/ε^2)

We settle the sample complexity of estimating the root Uhlmann fidelity F(ρ,σ)=tr√(√(σ)ρ√(σ)) between an unknown state ρ and a known rank-r reference state σ. Writing S(r,ε) for the sample complexity at additive error ε, we resolve the open problem posed by Wang by closing, up to logarithmic factors, the gap between the...

Quantum Simulation of Nuclear Shell Model Using GCM-Based Methods on NISQ Devices

Based on the Generator Coordinate Method (GCM), we use a Quantum GCM (QuGCM) within a hybrid quantum-classical framework to simulate low-lying eigenstates of nuclear systems on quantum devices. The generator basis states are constructed from Hartree-Fock (HF) reference states, excited via symmetry-adapted unitary coupled-cluster (UCC) operators. These states are prepared as...

Noise-robust discrimination of incoherent point sources with spatial-mode demultiplexing

We theoretically predict and experimentally demonstrate that a reduced spatial-mode demultiplexing (SPADE) measurement using only the two lowest-order Hermite-Gaussian modes exhibits remarkable robustness against background noise in discriminating between a single source and two incoherent point sources. We establish a theoretical framework incorporating uniform background n...

Ring Optimized M-APSK Modulation for Discrete Modulated CV-QKD

This paper proposes a multi ring M-APSK constellation optimization method for discrete-modulated continuous variable quantum key distribution. Unlike conventional APSK structures with fixed ring spacing and predefined ring probabilities, the proposed method optimizes the ring radius ratio and ring probability to improve the finite-size secret key rate. A method based on the...

Fate of moiré flat bands for a weakly repulsive Bose-Einstein condensate in one-dimensional PT-symmetric bichromatic optical lattices

One-dimensional (1D) superlattices provide one simplified platform for exploring moiré physics from a low-dimensional perspective, with the ratio of lattice constants playing a role analogous to the twist angle in two-dimensional bilayers. Here, we propose a 1D PT-symmetric bichromatic optical lattice for a weakly repulsive Bose-Einstein condensate and investigat...

Near-optimal quantum metrology with few-qubit measurements

Quantum metrology, which addresses parameter estimation in quantum systems, has broad applications across science and technology. Conventional metrology protocols for multi-qubit states in the multi-parameter regime typically require highly complex quantum measurements, leading to substantial quantum-resource costs. In this work, we introduce a family of metrology protocols...

PsiQuantum Invests $250,000 in South Chicago STEM and Quantum Education Programs

Researchers Develops Carbon Quantum Dots From Organic Waste for Pest Repellent Research

SEALSQ Highlights Role of Crypto-Agility in Preparing for Future Cryptographic Threats

China Forms Quantum Standards Committee to Coordinate Industry Development

Western Quantum Export Controls Are Evolving Into an Industrial Strategy, IISS Analysis Says

NSF Awards UC San Diego $18 Million Grant for Materials Science Research Center

Qubitrium Supports NATO Training Programme on Dual-Use Quantum Technologies