We report the first capture and time-of-flight spectrometry of highly charged ions (HCIs) produced following annihilations of trapped antiprotons in a Penning-Malmberg trap. A multistep nested-trap technique was developed at the AEḡIS experiment at CERN to trap and identify the annihilation-linked ions using external scintillators. The successful capture and mass analysis of helium and argon ions confirm the viability of the approach. This proof-of-principle demonstration establishes the foundation for future high-resolution mass spectrometry of recoil-filtered nuclear annihilation fragments. This methodology could enable studies of antiprotonic atom formation and cascade dynamics, allow the in-trap synthesis of radioactive HCIs, and provide a particularly sensitive probe of the neutron-to-proton composition at the outer periphery of the nucleus.

Mathematical analysis of the spectral properties of the time-evolution operator in quantum walks is essential for understanding key dynamical behaviors such as localization and long-term evolution. The inhomogeneous three-state case, in particular, poses substantial analytical challenges due to its higher internal degrees of freedom and the absence of translational invariance. We develop a general framework for the spectral analysis of three-state quantum walks on the one-dimensional lattice with arbitrary time-evolution operators. Our approach is based on a transfer-matrix formulation that reduces the infinite-dimensional eigenvalue problem to a tractable system of two-dimensional recursions, enabling exact characterization of eigenstates. This framework applies broadly to space-inhomogeneous models, including those with finite defects and two-phase structures. We rigorously derive necessary and sufficient conditions for the existence of point spectrum, along with a complete description of the corresponding eigenvalues and eigenstates, which are known to underlie quantum localization phenomena. Furthermore, we give a complete spectral decomposition—discrete spectrum, flat-band eigenvalues (of infinite multiplicity), and absolutely continuous spectrum—with explicit characterization of each component. Using this method, we perform exact numerical analyses of the Fourier walk with spatial inhomogeneity, revealing the emergence of localization despite its delocalized nature in the homogeneous case. Our results provide mathematical tools and physical insights into the structure of quantum walks, offering a systematic path for identifying and characterizing localized quantum states in complex quantum systems.

We report the first observation of narrow-band 1.3 MeV $\gamma$ radiation from a crystalline diamond microundulator. A diamond superlattice was grown with a periodically varying boron doping profile. Four sinusoidally deformed (110) periods resulted with a period length of $5.0 \mu \mathrm{m}$ and an amplitude of 0.098 nm. A channeling experiment was performed with the 855 MeV electron beam of the Mainz Microtron MAMI accelerator facility. A clear peak was detected with a large sodium iodide scintillation detector close to the expected photon energy of 1.28 MeV. Key characteristics of the peak, including photon energy, width, and intensity, were reproduced fairly well by Monte Carlo simulation calculations. Based on the latter, optimized boron doping profiles were designed for a hypothetical 3 GeV electron beam, enabling preparation of a highly directional $\gamma$-ray beam with a photon energy of 14.5 MeV. The predicted spectral bandwidth is 13%, however, with a high-energy continuum tail. The on-target photon flux at a beam current of $100 \mu \mathrm{A}$ would be about ${10}^{12}{\mathrm{s}}^{-1}$.

Beams of light or matter that carry well-defined states of orbital angular momentum (OAM) are promising probes of topological and textured condensed matter systems such as magnetic skyrmions. Using spin-echo small-angle neutron scattering, a phase-sensitive technique that allows for a relatively low intensity beam, we demonstrate the production of vortex neutron beams from forked phase gratings of various topological charges. This type of interferometric verification of OAM we present here could be further extended to other platforms using probes that are similarly limited by the coherence and strength of the currently available sources.

So far, entanglement harvesting has been extensively studied in free-space setups. Here, we provide a detailed analytical and numerical analysis of entanglement harvesting in cavities. Specifically, we couple the quantized electromagnetic field to two identical Gaussian detectors located on the symmetry axis of a cylindrical cavity via Gaussian switching. Our numerical investigations reveal a strong dependence on the cavity length, while showing invariance under changes in the cavity radius in regimes of maximal entanglement. Moreover, we identify different scalings of the detector system parameters for entanglement inside and outside the light cone. Finally, we uncover a strong dependence of the harvested correlations on the cavity-induced parity of the electromagnetic field.

We investigate the nonequilibrium dynamics of the nearest-neighbour Ising model subjected to stochastic resetting, where the system is intermittently returned to an initial configuration with magnetization $m_0$, with the inter-reset times drawn from the power law distribution $\alpha {\tau }_0^{\alpha }/{\tau }^{\alpha +1}$. The heavy-tailed resets generate magnetization distributions that differ significantly from both equilibrium dynamics and the previously studied Ising model with exponentially distributed reset times. In two dimensions, for $T>T_C$, we find a quasiferro state for all $\alpha$, marked by a double-peaked distribution that diverges at $m=0$ and $m=m_0$; no steady state exists for $\alpha <1$, while a stationary state emerges for $\alpha >1$. For $T<T_C$, power law resetting produces two distinct regimes separated by a crossover exponent ${\alpha }^{*}=1-c$: a single-peaked ferromagnetic phase localized at $m_{\text{eq}}$ for $\alpha <{\alpha }^{*}$, and a dual-peaked ferromagnetic phase with divergences at $m_{\text{eq}}$ and $m_0$ for $\alpha >{\alpha }^{*}$. Analytic results in one and two dimensions, supported by simulations, yield a rich phase diagram in the $(T,\alpha )$ plane and reveal how heavy-tailed resetting generates nonequilibrium phases very different from those seen in the case of exponential resetting.

We address the challenge of certifying quantum behavior with single macroscopic massive particles, subject to decoherence and finite data. We propose a hypothesis-testing framework that distinguishes between classical and quantum mechanics based on position measurements. While interference pattern visibility in single-particle quantum superposition experiments has been commonly used as a sufficient criterion to falsify classical mechanics, we show that, from a hypothesis-testing perspective, it is neither necessary nor efficient. Focusing on recent proposals to prepare macroscopic superposition states of levitated nanoparticles, we show that the likelihood ratio test—which leverages differences across the entire probability distribution—provides an exponential reduction in measurements needed to reach a given confidence level. These results generalize to a broad class of quantum states, and offer a principled, efficient method to falsify classical mechanics in interference experiments, relaxing the experimental constraints faced by current efforts to test quantum mechanics at the macroscopic scale.

We introduce a family of multimode, rotationally symmetric bosonic codes inspired by the group-theoretic framework introduced by Denys and Leverrier [Phys. Rev. Lett. 133, 240603 (2024)]. Such a construction inverts the traditional paradigm of code design by identifying codes from the requirement that a group of chosen logical gates should be implemented by means of physically simple logical operations, such as linear optics. Leveraging previously unexplored degrees of freedom within this framework, our construction results in codes that display rotational symmetry across multiple modes, while enabling linear-optics implementation of the full Pauli group. These codes exhibit improved protection against dephasing noise, outperforming both single-mode analogues and earlier multimode constructions. Notably, they allow exact correction of correlated dephasing and support qudit encoding in arbitrary dimensions. We analytically construct and numerically benchmark two-mode binomial code instances, and demonstrate that, unlike single-mode rotationally symmetric bosonic codes, these exhibit no trade-off between protection against dephasing and photon loss.

Topological particlelike excitations such as skyrmions and hopfions offer rich opportunities for spintronic and photonic applications. While skyrmions have been extensively studied, the stabilization mechanisms and phase behavior of three-dimensional hopfions remain largely unexplored. Here, we investigate the formation, stability, and interactions of hopfions in thin chiral magnetic films with surface anchoring, using three-dimensional micromagnetic simulations within a material-independent framework applicable to both magnetic and liquid crystalline systems. We identify four distinct types of isolated hopfions, generated by rotating bimeron and fingerlike solitons around a central axis. The metastability regions of these precursor textures closely follow the boundaries of modulated finger phases, enabling their size to be continuously tuned through anisotropy-driven inflation and collapse. Remarkably, we demonstrate that hopfions near their inflation threshold possess energies comparable with the homogeneous state, allowing them to enclose regions of modulated phases or other solitons, forming higher-order, baglike domains. In contrast, periodic hopfion lattices remain intrinsically unstable under confinement, spontaneously relaxing into finger phases. These findings establish general principles for stabilizing, tuning, and assembling three-dimensional topological solitons in confined chiral systems, suggesting experimentally accessible routes for texture engineering in liquid crystals via electric-field control.

Accurate computation of multiple eigenvalues of quantum Hamiltonians is essential in quantum chemistry, materials science, and molecular spectroscopy. Estimating excited-state energies is challenging for classical algorithms due to exponential scaling with system size, posing an even harder problem than ground-state calculations. We present a quantum algorithm for estimating eigenvalues and singular values of parametrized matrix families, including solving generalized eigenvalue problems that frequently arise in quantum simulations. Our method uses quantum amplitude amplification and phase estimation to identify matrix eigenvalues by locating minima in the singular value spectrum. We demonstrate our algorithm by proposing a quantum computing formulation of the pseudospectral collocation method for the Schrödinger equation. We estimate fault-tolerant quantum resource requirements for the quantum collocation method, showing favorable scaling in the size of the problem $N$ [up to $\tilde{\mathcal{O}}\left(\sqrt{N}\right)$] compared to classical implementations with $\tilde{\mathcal{O}}\left(N\right)$, for certain well-behaved potentials. Additionally, unlike the standard collocation method, which results in a generalized eigenvalue problem requiring matrix inversion, our algorithm circumvents the associated numerical instability by scanning a parametrized matrix family and detecting eigenvalues through singular value minimization. This approach is particularly effective when multiple eigenvalues are needed or when the generalized eigenvalue problem involves a high condition number. In the fault-tolerant era, our method may thus be useful for simulating high-dimensional molecular systems with dense spectra involving highly excited states, such as those encountered in molecular photodynamics or quasicontinuum regimes in many-body and solid-state systems.

Maximum likelihood decoding (MLD) achieves optimal accuracy but is computationally infeasible for large-distance codes. Tensor-network-based MLD (TN-MLD) improves efficiency but has so far only been shown to work for small-distance surface codes. We introduce a hypergraph-based approximate MLD (HAMLD) that enables more efficient decoding of more general codes under circuit-level noise. Unlike TN-MLD, our HAMLD employs syndrome-guided hyperedge selection and probability-based truncation to reduce redundant computation. We benchmarked our approach on surface codes, color codes, and bivariate-bicycle (BB) codes under a circuit-level noise model. Numerical results demonstrate that HAMLD can decode BB codes with hundreds of qubits, which MLD and TN-MLD cannot handle. For a surface code with distance and repetition rounds both equal to 3, HAMLD achieves optimal decoding accuracy while being about $323\times$ faster than MLD and about $551\times$ faster than TN-MLD. HAMLD also achieves higher accuracy than common decoders—minimum-weight perfect matching, Chromobius, and $\mathrm{BP}+\mathrm{OSD}$—in the two smallest parameter settings we considered, reducing logical error rates by an average of 27.8% for surface codes, 58.5% for color codes, and 74.4% for BB codes through degeneracy-aware and precise hypergraph selection.

We investigate Josephson transport in a fully closed, two-dimensional superfluid circuit formed by a ring-shaped ${}^{87}\mathrm{Rb}$ Bose-Einstein condensate that contains two optical barriers acting as movable weak links. Translating these barriers at controlled speeds imposes a steady bias current, enabling direct mapping of the current-chemical-potential ($I\text{−}\mathrm{\Delta }\mu$) characteristics. For narrow junctions ($w\approx 1\mu \text{m}$), the circuit exhibits a pronounced dc branch that terminates at a critical current $I_c=9\left(1\right)\times {10}^3{\text{s}}^{-1}$; above this threshold, the system switches to an ac, resistive regime. Classical-field simulations that include the moving barriers quantitatively reproduce both the nonlinear $I\text{−}\mathrm{\Delta }\mu$ curve and the measured $I_c$, validating the underlying microscopic picture. Analysis of the ensuing phase dynamics shows that dissipation is mediated by the nucleation and traversal of vortex-antivortex pairs through the junctions, while the bulk condensate remains globally phase locked—direct evidence of the ring's topological constraint enforcing quantized circulation. These results establish a cold-atom analog of a superconducting quantum interference device in which Josephson dynamics can be resolved at the single-vortex level, providing a versatile platform for atomtronic circuit elements, nonreciprocal Josephson devices, and on-chip Sagnac interferometers for multiaxis rotation sensing.

Scalable quantum technologies demand long-range interactions between many distant quantum emitters (QEs). We introduce nonlocal metasurfaces supporting bound states in the continuum (BICs) as a promising platform to achieve this goal. We show that efficient QE interactions depend almost entirely on emitter-BIC coupling efficiencies ($\beta$ factors), which in our system can exceed 80% even without additional mode engineering. These values rival those of one-dimensional waveguides but are achieved here in a geometry that naturally accommodates large two-dimensional QE arrays. Using this platform, we explore entanglement generation between two remote QEs, finding that it develops faster than in free space, is significantly amplified, and persists over separations spanning several emission wavelengths. Optimal inter-QE interactions require large $\beta$ factors but only moderately small Purcell factors, both within experimentally achievable ranges. Our results establish nonlocal metasurfaces as a practical and scalable platform for leading-edge quantum nanophotonics.

Causal set theory is an approach to quantum gravity in which spacetime is fundamentally discrete while retaining local Lorentz invariance. The Benincasa-Dowker-Glaser action is the causal set equivalent to the Einstein-Hilbert action underpinning Einstein's general theory of relativity. We present a $\tilde{O}\left(n^2\right)$ running-time quantum algorithm to compute the Benincasa-Dowker-Glaser action in arbitrary spacetime dimensions for causal sets with $n$ elements, which is asymptotically optimal and offers a polynomial speedup compared to all known classical or quantum algorithms. To do this, we prepare a uniform superposition over an $O\left(n^2\right)$-size arbitrary subset of computational basis states encoding the classical description of a causal set of interest. We then construct depth $\tilde{O}\left(n\right)$-depth oracle circuits testing for different discrete volumes between pairs of causal set elements. Repeatedly performing a two-stage variant of quantum counting using these oracles yields the desired algorithm.

With intensive studies of quantum thermodynamics, quantum batteries (QBs) have been proposed to store and transfer energy via quantum effects. Despite many theoretical models, decoherence remains a severe challenge and practical platforms are still rare. Here, we propose a QB based on the coherent Ising machine, in which the signal field acts as the core energy-storage unit. To clarify the role of quantum coherence in resisting dissipation, we decompose the ergotropy, i.e., the maximum extractable work from the QB, into its coherent and incoherent components. We find that the coherent part decays at a rate roughly half that of the incoherent part, exhibiting much stronger robustness against decoherence. More importantly, the coherent ergotropy and the average charging power reach their respective maxima at essentially the same moment, which defines the optimal instant to switch off the pump field. Finally, by coupling the QB to a two-level system as the load, we demonstrate an efficient energy discharge process of the proposed QB. Our work establishes a realistic and immediately implementable QB architecture on a mature optical platform, laying a foundation for experimental exploration of quantum energy storage.

Quantum measurements under realistic conditions reveal only partial information about a system. Yet, by performing sequential measurements on the same system, additional information can be accessed. We investigate this problem in the context of semi-device-independent randomness certification using sequential maximum-confidence measurements. We develop a general framework and versatile numerical methods to bound the amount of certifiable randomness in such scenarios. We further introduce a technique to compute min-tradeoff functions via semidefinite programming duality, thus making the framework suitable for bounding the certifiable randomness against adaptive attacking strategies through entropy accumulation. Our results establish sufficient criteria showing that maximum-confidence measurements enable the distribution and certification of randomness across a sequential measurement chain in single-party systems.

We provide a quantum mechanical description of phonon amplification in a heterostructure consisting of a two-dimensional electron gas (2DEG) stacked on top of a piezoelectric material. An applied drift voltage effectively creates a population inversion in the momentum states of the 2DEG electrons, giving rise to spontaneous emission of phonons. Once an acoustic wave is launched, the pumped electrons release phonons via stimulated emission, returning to depleted ground states before being pumped back to the excited states. We show that whereas efficient amplification using a one-dimensional electron gas requires the acoustic wavelength to roughly equal the mean distance between electrons, a 2DEG enables efficient amplification for any wavelength greater than this distance. We derive the imaginary and real parts of the 2DEG’s first-order acoustic susceptibility as functions of electronic drift velocity in specific limits and derive the gain per unit length for the signal and the quantum noise, with the gain matching the classical result in the short-electronic-lifetime (low-mobility) regime. Moreover, we analyze the gain clamping due to pump depletion and calculate the maximum achievable intensity. Our results provide a framework for designing acoustic devices including a quantum phononic laser and phase-insensitive quantum phononic amplifiers.

We study light-mediated interactions between spatially separated molecules using real-time quantum-electrodynamical time-dependent density functional theory based on the Pauli-Fierz Hamiltonian. An ultrashort delta-kick excitation selectively perturbs a single molecule, while a second, distant molecule remains initially unexcited. In free space, the excitation stays localized and no response is observed in the second molecule. In contrast, when both molecules are coupled to the same cavity mode, the initial excitation induces coherent dynamics in the distant molecule through the shared quantized electromagnetic field.

The Remeika series superconductor, ${\left({\text{Ca}}_x{\text{Sr}}_{1-x}\right)}_3{\text{Rh}}_4{\text{Sn}}_{13}$, shows a rare nonmagnetic quantum critical point (QCP) associated with the continuous charge-density wave (CDW) and structural transition under the “dome” of superconductivity achieved by tuning composition and applying pressure. Here, we use a nonmagnetic pointlike disorder induced by 2.5 MeV electron irradiation to suppress the CDW and drive the system to and even beyond the QCP. This conclusion is based on a clear evolution of temperature-dependent resistivity, $\rho \left(T\right)$, from the Fermi liquid to the non-Fermi liquid regime with increasing amount of disorder. Starting on the CDW side, below the suggested QCP concentration of $x_c=0.9$, added disorder resulted in a progressively larger linear term and a reduced quadratic term in $\rho \left(T\right)$. Nearly perfect $T\text{−}\mathrm{linear}$ dependence is observed at the dose at which long-range CDW order is suppressed to $T=0$, consistent with the expectations. We refine the QCP location in this system and place it in the interval between $x=0.75$ and 0.85. Our results strongly support the concept that the disorder can tune the system to the quantum critical regime and even beyond. It follows from the argument by Imry and Ma that any ordered phase is unstable toward quenched disorder. Introduced in a controlled way, this disorder becomes a nonthermal tuning parameter likely applicable to a variety of different systems.