Quantum Journals

That author's affiliation: Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Científicas, Madrid, Spain Institution (first & last author): University of Grenoble Alpes, CEA, Grenoble INP, IRIG-Pheliqs, Grenoble, France

Coupling semiconductor qubit devices to microwave resonators provides a way to transfer quantum information over long distances. A flopping-mode qubit that combines strong coupling to photons with good coherence properties has now been demonstrated.

Higher-order interactions in quantum harmonic oscillator systems can result in useful effects, but they are hard to engineer. An experiment on a single trapped ion now demonstrates how spin can mediate higher-order nonlinear bosonic interactions.

Software testing is a critical component of the classical software development lifecycle, and this principle is expected to hold true for quantum software as it evolves toward large-scale production and adherence to industry standards. Developing and testing quantum software presents unique challenges due to the non-deterministic nature of quantum information, the high dimensionality of the underlying Hilbert space, complex hardware noise, and the inherent non-local properties of quantum systems. In this work, we propose a unifying theoretical framework based on probabilistic assertions, which encompasses several testing approaches—such as quantum tomography and statistical tests—for developing practical unit tests for quantum subroutines. The framework is built upon the semantic equivalence between quantum subroutines and parameterized quantum channels, as established in this work. To address the computational complexity associated with unit testing in quantum systems, we propose incorporating context-awareness into the testing process. The trade-offs between accuracy, state space coverage, and efficiency associated with the proposed theoretical framework for quantum unit testing have been demonstrated through its application to a simple three-qubit quantum subroutine that prepares a Greenberger–Horne–Zeilinger state, as well as to subroutines within a program implementing Shor’s algorithm.

That author's affiliation: Centre de Nanosciences et de Nanotechnologies First author institution: C2N, Marcoussis Last author institution: Centre de Nanosciences et de Nanotechnologies

Multi-dimensional frequency-bin entanglement-based quantum key distribution network

That author's affiliation: University of Vienna First author institution: University of Vienna Last author institution: Austrian Academy of Sciences

We probe the motion of a 6-$\text{μ}\mathrm{g}$ magnetically levitated superconducting microsphere using optical interferometry at $3\phantom{\rule{0.1em}{0ex}}\mathrm{K}$, achieving a resolution of the order of $1\phantom{\rule{0.1em}{0ex}}\mathrm{nm}/\sqrt{\mathrm{Hz}}$, and use the measured signa…

That author's affiliation: University of California, Santa Barbara First author institution: Institute of Physics, Academia Sinica Last author institution: Research Center for Applied Science, Academia Sinica

Scaffold-assisted window junctions for superconducting qubit fabrication

That author's affiliation: Istituto Nazionale di Fisica Nucleare, Sezione di Firenze Institution (first & last author): Istituto Nazionale di Fisica Nucleare, Sezione di Firenze

Bell state measurements, which project bipartite states onto the maximally entangled Bell basis, are central to a wide range of quantum information processing tasks, including quantum teleportation, entanglement swapping, and fusion-gate quantum computation. In photonic platforms, where information is encoded in optical degrees of freedom, the realization of efficient Bell state measurements is particularly challenging, especially when constrained to linear optical elements. In this review, we provide a comprehensive examination of existing proposals for the implementation of Bell state measurements, highlighting their fundamental limitations and the strategies developed to overcome them. Moreover, we survey recent advances and discuss open challenges, with a particular focus on Bell state measurements for high-dimensional systems, an area of growing interest due to its relevance for quantum repeaters and scalable quantum networks.

Quantum random-access memory (QRAM) is a critical primitive for quantum algorithms that require data lookup in superposition, but its lack of fault tolerance poses a major obstacle to practical deployment. Error filtration (EF) has been proposed as a hardware-efficient alternative to error correctio…

That author's affiliation: Columbia University Institution (first & last author): Columbia University

We develop an analytic framework to extract circuit parameters and loss tangent from superconducting transmission-line resonators terminated by reactive loads, extending analysis beyond the perturbative regime. The formulation yields closed-form relations between resonant frequency, participation ra…

The fluxonium qubit has emerged as a promising candidate for superconducting quantum computing due to its long coherence times and high-fidelity gates. Nonetheless, further scaling up and improving performance remain critical challenges for establishing fluxoniums as a viable alternative to transmon…

Magnetic flux trapping is a significant hurdle limiting the reliability and scalability of superconducting electronics, yet tools for imaging flux vortices remain slow or insensitive. We present a cryogenic widefield N-<i>V</i> diamond magnetic microscope capable of rapid, micrometer-scale imaging of flux …

That author's affiliation: IQM Quantum Computers, Ludwig-Maximilians-Universität München First author institution: IQM (Germany) Last author institution: University of Würzburg

Near-term fermionic simulation with subspace noise tailored quantum error mitigation

That author's affiliation: Los Alamos National Laboratory Institution (first & last author): Los Alamos National Laboratory

This letter shows how incoherent dynamics can lead to metrological advantages in quantum sensing. The results rely on the fact that incoherent dynamics lead to an additive contribution to the quantum Fisher information about time. Such an additive contribution can reduce the error of optimal estimation protocols, as implied by the quantum Cramér–Rao bound. I characterize regimes in which the estimation of a time interval or a frequency is enhanced by decoherence, thereby identifying cases in which incoherent dynamics serve as a metrological resource. The decoherence processes that yield enhanced precision of quantum sensors can be engineered by randomized Hamiltonian dynamics. I illustrate the results with protocols that display improved sensing of time intervals or global fields by qubit and photonic sensors. Enhanced precision of time intervals is achieved with Hamiltonians that include randomized global parameters. Enhanced precision in field estimation is obtained by randomized sensing times.

That author's affiliation: ICREA & Universitat Autònoma Barcelona First author institution: Università degli Studi di Palermo Last author institution: ICREA & Universitat Autònoma Barcelona

Entanglement percolation aims at generating maximal entanglement between any two nodes of a quantum network (QN) by utilizing strategies based solely on local operations and classical communication between the nodes. As it happens in classical percolation theory, the topology of the network is crucial, but also the entanglement shared between the nodes of the network. In a network of identically partially entangled states, the network topology determines the minimum entanglement needed for percolation. In this work, we generalize the protocol to scenarios where the initial entanglement shared between any two nodes of the network is not the same but has some randomness. In such cases, we find that for classical entanglement percolation, only the average initial entanglement is relevant. In contrast, the quantum entanglement percolation protocol (within the q-swap framework) degrades under these more realistic conditions as the width of the distribution increases, suggesting that random classical entanglement percolation may become the optimal LOCC strategy in sufficiently heterogeneous QNs.

That author's affiliation: Rutgers, The State University of New Jersey Institution (first & last author): Johns Hopkins University

The link between the strange metal with its linear-in-temperature resistivity and superconductivity is ambiguous. Now, a channel in the normal state whose scattering rate is linear in temperature is shown to drive superconductivity in FeTe1−xSex.

Surface-code hardware Hamiltonian

Distributed quantum inner product estimation with structured random circuits

Two-qubit gates using on-demand single-photons from ordered shape and size controlled large-volume superradiant quantum dots

That author's affiliation: Technion – Israel Institute of Technology First author institution: Technion – Israel Institute of Technology Last author institution: University of Konstanz

Entanglement between particles offers insights into quantum behaviour, but methods for studying it in free-electron systems are lacking. Now a two-electron quantum walk is used to probe decoherence of free electrons inside an electron microscope.

In addition to strongly protected topological phases that rely on exact symmetries, theory predicts that disorder can stabilize weakly protected phases in mixed quantum states, and an example of the latter is now observed in a Rydberg atom array.

Collective purification of interacting quantum networks beyond symmetry constraints

Quantum reservoir computing induced by controllable damping

Time-series forecasting with multiphoton quantum states and integrated photonics

Beyond boson sampling: higher spin sampling as a practical path to quantum supremacy

Frozen sound

Publisher Correction: Fiber-coupled broadband quantum memory for polarization-encoded photonic qubits

Lower-bounding entanglement in a general Bell scenario

Quantum simulation of equilibrium many-body systems requires the ability to sample from the thermal distribution of quantum states. An algorithm has now been proven to be an appropriate quantum analogue to classical Monte Carlo methods.

Exploiting the differences between quantum and classical physics typically requires nonlinear devices. Quantum nonlinear effects have now been demonstrated in a nanomechanical resonator due to strong coupling with an intrinsic two-level defect.

Controlling the dynamics of magnons at terahertz frequencies is important for fast and efficient information processing devices. Now optical excitation is shown to enable ultrafast manipulation of magnon spectra in an insulating antiferromagnet.

The practical value of non-Gaussian states for quantum computation, metrology, and networking is currently limited by the intrinsically low success rates of conventional generation methods like photon addition and subtraction. We introduce a scalable protocol that overcomes this bottleneck using postselected von Neumann measurements beyond the weak-coupling regime. Applied to standard Gaussian inputs, our method efficiently generates a suite of critical resources—including large-amplitude Schrödinger cat states, Gottesman–Kitaev–Preskill-like states, and two-mode entangled states—with considerably higher success probabilities. Quantitative analysis of Wigner negativity and entanglement confirms their high quality. This work establishes postselected von Neumann measurement as a general and scalable principle for quantum resource generation, moving beyond a fundamental limitation in quantum state engineering.

Entanglement between an electronic spin sensor and a nuclear ancillary spin in experiment allows for concurrent estimation of amplitude, frequency, and phase from a single measurement sequence.

We prove that the time required for sustained information scrambling in any Hamiltonian quantum system is universally at least logarithmic in the entanglement entropy of scrambled states. This addresses two foundational problems in nonequilibrium quantum dynamics. (1) It sets the earliest possible t…

Operator growth at finite temperature in quantum chaotic systems relies on coherent spreading in the Krylov basis.

Thermodynamics in quantum circuits aims to find improved functionalities of thermal machines, highlight fundamental phenomena peculiar to quantum nature in thermodynamics, and point out limitations in quantum information processing due to the coupling of the system to its environment. An important a…

A quantum-many-body-inspired tensor-network algorithm can compute local topological invariants for systems with hundreds of millions of sites by avoiding an explicit storage of Hamiltonian matrices.

Fusion-based implementation of qLDPC codes with quantum emitters

We propose a scalable and noise-resilient protocol for the detection of the entanglement transition in a projective version of the transverse-field Ising model. Entanglement transitions are experimentally difficult to observe due to the inherent randomness of projective measurements and noise in lar…

A persistent normal-state third-harmonic generation (THG) signal extending up to ten times T<math display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><msub><mrow></mrow><mi>c</mi></msub></math> and a multipeak THG spectrum in the superconducting state reveal an unexpected interplay between disorder, electronic correlations, and superconducting inhomogeneity.

Virtual purification complements quantum error correction in quantum metrology