Nucleation of vortex-antivortex pairs (VAPs) is believed to play a central role in the photon detection mechanism of superconducting detectors; however, their direct dynamic observation has remained challenging. Here, we report the direct observation of photon-induced VAP dynamics in a current-carrying superconductor as quantized voltage signals following photon absorption. The observed signals are interpreted as discrete phase-slip events, where each vortex traversal induces a $2\pi$ phase change of the superconducting order parameter, resulting in a quantized voltage pulse whose time integral is given by the magnetic flux quantum ${\mathrm{\Phi }}_0$. We analyze the resulting quantized signals as a function of bias current, base temperature, and input photon-number states and find that the number of VAPs generated per absorbed photon becomes effectively stabilized under specific conditions. Under these conditions, we demonstrate photon-number-resolving capability by directly counting phase-slip-induced voltage quanta. Our results reveal a detection mechanism governed by phase dynamics rather than conventional resistive transitions and represent the first demonstration of photon-number resolution based on VAP counting, enabling fast multi-photon-resolving superconducting detectors for quantum optics.

Atom interferometric inertial sensors offer exceptional sensitivity but are fundamentally constrained by the periodic phase response of matter-wave interference, which imposes an intrinsic half-fringe dynamic-range limit and prevents continuous inertial tracking. In multiaxis configurations, additional cross-coupling between acceleration and rotation further complicates closed-loop operation. Here we demonstrate dual-channel closed-loop operation of an atomic beam interferometer, realizing decoupled feedback control of acceleration- and rotation-induced phases and overcoming the half-fringe limitation. Using continuous, transversely cooled ${}^{87}\mathrm{Rb}$ atomic beams, the interferometric phases associated with rotation and acceleration are independently extracted, tracked across multiple fringes, and actively compensated through Raman frequency modulation. This closed-loop scheme enables unambiguous measurements up to $\pm 1°/\mathrm{s}$ (i.e., $\pm 0.017\mathrm{r}\mathrm{a}\mathrm{d}/\mathrm{s}$) in rotation and $\pm 0.17\mathrm{g}$ (i.e., $\pm 1.67\mathrm{m}/{\mathrm{s}}^2$) in acceleration while maintaining high fringe contrast, corresponding to nearly two orders-of-magnitude extension beyond the conventional half-fringe limit. The sensor achieves a long-term stability of $4\times {10}^{-4}°/\mathrm{h}$ for rotation and $4\mathrm{\mu }\mathrm{g}$ for acceleration at an averaging time of $1000\mathrm{s}$. By converting the intrinsically periodic interferometric response into stabilized phase-encoded inertial channels, this work demonstrates a dual-channel closed-loop operation of atomic beam interferometry and represents a step toward practical quantum inertial navigation under dynamic conditions.

Battery-free and wireless sensing presents a crucial challenge for large-scale and inaccessible infrastructure, where the difficulty of power supply severely limits continuous monitoring. Here, we develop a quartz-crystal-microbalance (QCM) technique that enables fully passive sensing at distances exceeding 50 m, far beyond the operating range of conventional battery-free sensors. This capability is enabled by a few-millimeter-sized MEMS-QCM sensor incorporating integrated antennas for efficient coupling between mechanical resonance and free-space electromagnetic waves. On the sensor side, an extended antenna of approximately 100 mm in length is connected to the MEMS-QCM to enhance wireless signal transmission. On the instrumentation side, Yagi–Uda antennas are employed for efficient signal reception and transmission. By exploiting controlled bending of an ultrathin quartz resonator, we achieve battery-free strain sensing at distances of over 50 m. We further introduce a new sensing mechanism for displacement measurement based on polarization relaxation on the electrodeless quartz surface, which also operates wirelessly and without an onboard power source. In addition, the platform is shown to be applicable to the wireless, battery-free hydrogen-gas sensing. These results establish a general framework for long-range, battery-free mechanical and chemical sensing, opening a path toward continuous, nondestructive monitoring of social and industrial infrastructure.

Controlling how waves slow, stop, and localize lies at the heart of modern condensed-matter and metamaterial physics. Flexoelectricity, the coupling of strain gradients and polarization that is universally present in all dielectrics, scales with structure size, thus offering a route to size-dependent electromechanics, especially in materials with nanoscale feature size. We show that a suitably designed flexoelectric medium permits a tunable landscape of band extrema where elastic and electric fields strictly co-localize, thus leading to localized vibrations, and zero-group-velocity and stationary-inflection modes that trap energy in place. The resulting defect-cavity modes exhibit dual amplification of open-circuit voltage and mass responsivity, both scaling inversely with the localization length that is determined by the curvature of the dispersion curve and frequency shift from the minimum. This framework unifies nonlocal lattice physics with continuum electromechanics, establishing a continuum route to engineer and electrically read out band-edge phenomena for ultrasensitive detection and reconfigurable energy harvesting.

Superconducting nanowire single-photon detectors (SNSPDs) have demonstrated timing jitter in the few-picosecond regime, yet their timing resolution deteriorates substantially under high-count-rate operation. Existing interpretations mainly attribute this degradation to deterministic waveform distortions, such as multiphoton responses and pulse pile-up; however, the experimentally observed jitter broadening at high count rates cannot be fully accounted for within this picture. Here, we show that stochastic baseline fluctuations arising from finite-memory readout dynamics constitute an intrinsic source of the count-rate-dependent timing jitter in SNSPD systems. For stochastically arriving photons, overlapping recovery responses accumulate in the readout chain and generate statistically fluctuating baselines, which are converted into timing uncertainty through threshold-based timing extraction. We develop a stochastic-process framework that quantitatively connects photon statistics, readout dynamics, and timing jitter. The framework predicts characteristic scaling behaviors, including a nonmonotonic dependence of baseline fluctuations under pulsed excitation with a maximum near half of the repetition frequency. These predictions are quantitatively verified through systematic variations of count rate, circuit time constant, and detector dynamical properties. Our results identify stochastic baseline dynamics as a fundamental mechanism limiting timing resolution in high-count-rate SNSPD operation and provide a general framework for optimizing finite-memory high-speed photon-counting systems.

High-performance numerical methods are essential not only for advancing quantum many-body physics but also for enabling integration with emerging quantum computing platforms. We present a scalable, general-purpose parallel algorithm for quantum simulations based on or-represented quantum algebra (ORQA). This framework applies to arbitrary spin systems and naturally integrates with quantum circuit simulation in the Heisenberg picture, making it particularly relevant to recent large-scale experiments on superconducting qubit processors [Y. Kim et al. Nature (London) 618, 500 (2023)]. As a benchmark, we simulate the kicked Ising model on a 127-qubit heavy-hexagon lattice, tracking the time evolution of local magnetization using up to $1\times {10}^{12}$ Pauli strings. Executed on the supercomputer Fugaku, our simulations exhibit strong scaling up to $2^{17}$ parallel processes with near-linear communication overhead. These results establish ORQA as a practical and high-performance tool for quantum many-body dynamics and highlight its potential for integration into hybrid quantum-classical computational frameworks, complementing recent advances in tensor network and surrogate simulation techniques.

Volatile resistive switching in correlated-electron systems, characterized by an abrupt resistance decrease under applied current, is crucial for developing next-generation electronics. Despite its technological significance, the underlying physics remains elusive. Inorganic thin films on substrates—the widely studied platform for resistive switching—usually exhibit broad temperature-induced metal-insulator transitions (MITs) and substantial heat dissipation. These factors complicate the nonlinear thermal effect induced by Joule heating, a key contributor to resistive switching, rendering it excessively complex and difficult to decipher. Here, we investigate a resistive-switched state in the bulk organic conductor $($$d7\text{−}\text{DMe}\text{−}\text{DCNQI}{)}_2\text{Cu}$, which undergoes an extremely sharp first-order MIT and exhibits weak heat dissipation, using resistance and ${}^1\mathrm{H}\text{−}\text{NMR}$ measurements. These extreme conditions make the Joule heating effect vivid, allowing us to observe peculiar phenomena, including temperature locking to the MIT and “inverse Ohm’s law”—an inverse proportionality between voltage and current. These findings provide fundamental insights into the nonlinear thermal effect in resistive switching, offering a pathway to efficient resistive switching technologies.

We report an experimental study of a Si/SiGe double quantum dot (DQD) directly coupled to a niobium superconducting coplanar stripline microwave resonator. This hybrid architecture enables high-bandwidth dispersive readout suitable for real-time feedback and error-correction protocols. Fast and sensitive readout is achieved primarily by optimizing the DQD gate lever arm, guided by MaSQE quantum dot simulations, which enhances the dispersive signal without requiring high-impedance resonators. We demonstrate a signal-to-noise ratio of unity with an integration time of 34.54 ns, corresponding to a system bandwidth of 14.48 MHz and a charge sensitivity of $1.86\times {10}^{-4}e/\sqrt{\mathrm{Hz}}$. Analysis of the voltage power spectral density (PSD) of the in-phase $(I)$ and quadrature $(Q)$ baseband signals characterizes the system’s readout noise, with the PSD’s dependence on integration time providing insight into distinct physical regimes.

Pyrite ${\mathrm{FeS}}_2$ is an approximately 1-eV-band-gap semiconductor composed of exceptionally earth-abundant, low-cost, and nontoxic elements, with applications in numerous electronic and energy technologies. Facile and scalable synthesis of ${\mathrm{FeS}}_2$ from natural resources is thus highly desirable but must generate high-purity, semiconductor-quality material to access the widest range of applications. Here, we demonstrate that various forms of commercial iron ore, most notably taconite-based ore, can be used to synthesize semiconductor-quality ${\mathrm{FeS}}_2$ via remarkably simple methods, despite very high initial impurity content. These ores can be reduced to Fe, sulfidized to ${\mathrm{FeS}}_2$, then used in vapor-phase crystal growth to synthesize surprisingly high-quality ${\mathrm{FeS}}_2$ with no additional purification. This is found to be possible due to two synergistic effects: very few elements efficiently dope ${\mathrm{FeS}}_2$, and the sulfidation and crystal growth steps introduce significant unexpected purification, which we track via detailed trace element analyses and rationalize via thermodynamic parameters. The result is pyrite single crystals with room-temperature Hall electron densities down to a remarkable ${10}^{16}{\mathrm{cm}}^{-3}$ with corresponding mobilities exceeding $100{\mathrm{cm}}^2{\mathrm{V}}^{-1}{\text{s}}^{-1}$, surprisingly close to crystals grown from high-purity reagents. We thus demonstrate facile synthesis of semiconductor-quality ${\mathrm{FeS}}_2$ from commercial iron ores, potentially unlocking a new renewable-energy revenue stream for an abundant natural resource.

Spin waves are promising information carriers for analog and wave-based computing, where functionality relies on compact and precisely engineered scattering landscapes. Focused-ion-beam (FIB) irradiation enables such control by locally tailoring the spin-wave dispersion in yttrium iron garnet. However, a nonmonotonic dependence of the spin-wave wavelength on increasing ion dose hinders predictive landscape design. Here, we present an experimentally validated framework that explains this nonmonotonic spin-wave steering by linking phenomenological strain-induced anisotropy to its magnetoelastic origin. Irradiation-induced lattice dislocations drive elastic and plastic deformation, which evolve into partial amorphization, each stage contributing distinctly to the dispersion behavior. We combine postirradiation wet-chemical etching and atomic force microscopy to quantify thickness changes and track the dispersion in etched regions using time-resolved magneto-optical Kerr effect microscopy. Fitting the data to the Kalinikos–Slavin formalism with an added effective magnetoelastic field isolates contributions from elastic and plastic deformation. Validation is achieved by mapping the deformation evolution onto a three-phase scenario based on SRIM simulations, reproducing the extracted field trends, and consistent strain-tensor and micromagnetic analyses. These results establish a physical basis for FIB-engineered graded-index spin-wave landscapes and magnetoelastically programmable magnonic devices.

Errors in superconducting qubits that are correlated in time and space can pose problems for quantum error correction codes. Radiation from cosmic and terrestrial sources can increase the quasiparticle (QP) density in a superconducting qubit device, resulting in an increased rate of QPs tunneling across proximal Josephson junctions (JJs) and causing correlated errors. Mechanical vibrations, such as those induced by the pulse tube (PT) in a dry dilution refrigerator, are also a known source of correlated errors. We measure two types of errors in the same device, linking the first to ionizing radiation and the second to PT operation. We present a method for distinguishing these two types of errors by their temporal, spatial, and frequency-domain features, enabling physically motivated error-mitigation strategies. We also present accelerometer data to study the correlation between PT-induced vibrations and the errors. We measure arrays of transmon qubits where the difference in superconducting gap across the JJ is less than the qubit energy, as well as those where the gap is greater than the qubit energy, which has been shown to mitigate radiation-induced errors. The rate of both types of errors is reduced in these latter devices, suggesting that gap engineering is also protective against PT-induced errors.

Spin-wave-based computing has emerged as a promising approach to overcome the fundamental limitations of complementary metal-oxide-semiconductor technologies. However, the increasing demand for device miniaturization down to a 100 nm scale presents significant challenges for long-distance spin-wave transport. Gallium-substituted yttrium iron garnet (Ga:YIG) offers a potential solution to these challenges due to its unique magnetic properties. The reduced saturation magnetization in Ga:YIG enables efficient excitation of exchange-dominated spin waves, which exhibit enhanced transport characteristics compared with dipolar-dominated modes in conventional materials. Here, we present the first comprehensive study combining experimental, analytical, and numerical investigations of spin-wave propagation in Ga:YIG waveguides down to 145 nm width and 73 nm thickness. Using microfocused Brillouin light scattering spectroscopy, TetraX simulations, and analytical dispersion calculations, we demonstrate that Ga:YIG waveguides support spin waves with significantly higher group velocities up to $600\mathrm{m}/\mathrm{s}$. This value remains constant for structures with different widths, leading to longer spin-wave propagation lengths in nanowaveguides compared with nonsubstituted YIG. These results reveal that gallium substitution provides access to faster and longer-lived spin waves, opening significant possibilities for implementing this material in nanoscale magnonic devices.

We employ the Boltzmann transport approach to derive the spontaneous Nernst coefficient for ferromagnetic metals, explicitly treating the transverse current density due to Berry curvature as a Fermi surface property. We find that the spontaneous Nernst coefficient is proportional to the inverse of the scattering time constant, implying that efficient spontaneous Nernst materials should exhibit relatively strong scattering, a stark contrast to ordinary Nernst materials. Furthermore, we establish a direct connection between the strength and sign of the spontaneous Nernst coefficient and the itinerant contribution to orbital angular momentum density arising from the Bloch bands. Finally, we construct a rigid two-band model to evaluate the thermoelectric coefficients by which we find a good agreement with the signs and orders of magnitude of the experimental coefficients of magnetic $3d$ transition metal ferromagnets. We finally propose some practical recipes for maximizing the spontaneous Nernst effect through electronic band structure tailoring.

Visualizing the free surface of superfluid helium offers a rare opportunity to explore wave dynamics in the limit of vanishing viscosity. Such measurements are nonetheless challenging due to helium’s low refractive index contrast, restricted optical access to the cryogenic setups required to maintain helium in its superfluid phase, and mechanical vibrations from the various cooling stages. Overcoming these limitations will enable quantitative studies of surface-wave dynamics with applications in fluid mechanics, quantum simulation, and quantum optomechanics. Here, we report an implementation of off-axis digital holography for full-field imaging of the free surface of superfluid ${}^4\mathrm{He}$. We perform noncontact measurements of nanometer- to micrometer-scale interface fluctuations in two cryogenic systems: a traditional helium bath cryostat and a cryogen-free refrigerator. We employ machine-learning-based analysis to isolate noise-driven normal modes and their spatial structure in both systems. This enables reconstruction of the dispersion relation for gravity-capillary waves in macroscopic samples and, for thick films, determination of the film thickness from the measured dispersion, providing a quantitative benchmark for our approach. These proof-of-concept experiments show that digital holography is a powerful and versatile tool for high-resolution, minimally invasive studies of superfluid surfaces, with strong potential for integration into diverse experimental platforms.

Eliminating residual $ZZ$ interactions in a two-qubit system is essential for reducing coherent errors during quantum operations. In a superconducting circuit platform, coupling two transmon qubits via a transmon coupler has been shown to effectively suppress residual $ZZ$ interactions. However, in such systems, perfect cancellation usually requires the qubit-qubit detuning to be smaller than the individual qubit anharmonicities, which exacerbates frequency crowding and microwave crosstalk. To address this limitation, we introduce transmon-fluxonium-transmon (TFT) architecture, wherein two transmon qubits are coupled via a fluxonium qubit. The coupling mediated by the fluxonium eliminates residual $ZZ$ interactions even for transmons detuned by more than their anharmonicities. We experimentally identified zero-$ZZ$ interaction points at qubit-qubit detunings of 409 and 616 MHz from two distinct TFT devices. We then implemented an adiabatic, coupler-flux-biased controlled-Z gate, achieving gate fidelities of 99.64(6)% and 99.68(8)% across the two devices.

Short-range correlations in electrolyte solutions lead to oscillatory profiles of water polarization and ionic concentration at electrode-electrolyte interfaces. The recently developed density-potential-polarization functional theory (DPPFT) provides a comprehensive framework to incorporate these short-range correlation effects. In the present work, the parameters describing short-range solvent-solvent and ion-solvent correlations in DPPFT are determined from the wave- number-dependent dielectric susceptibility spectrum of pure water and ion solvation energies, respectively. The experimental trends in the ionic-radius-dependent hydration energies of alkali metal cations and halide anions are reproduced by the solvation model. Within this model, the charge hydration asymmetry is phenomenologically rationalized by a stronger short-range repulsion between cations and water molecules than between anions and water molecules. Using these parameters, DPPFT is then applied to describe short-range correlation effects at the Ag(111)-NaF aqueous electrolyte interface. The water polarization profiles obtained from DPPFT calculations agree with ab initio molecular dynamics simulations. Furthermore, as the strength of short-range ion-solvent repulsion increases, the peaks of anionic and cationic layers shift from regions near centers of positive and negative polarization charges, respectively, toward those of opposite sign, thereby preserving solvation configurations similar to those in bulk solution. This work develops a procedure for parametrizing short-range correlation effects within the DPPFT framework, thereby enabling a more quantitative and computationally efficient description of atomic-scale phenomena at electrochemical interfaces.

A model including random alloy disorder is used to account for the outstanding optical properties of (In,Ga)N quantum wells. The model provides excellent agreement with experimental observations on various structures. This study clarifies the prevalent role played by disorder in optical features such as the luminescence lineshape, the Stokes shift, and the radiative rate. Finally, the relationship between disorder and the peculiar properties of long-wavelength (In,Ga)N emitters is investigated.

We present experimental and theoretical studies of the off-resonant and strongly nonlinear regime of Josephson transmission lines (JTLs) with galvanically coupled nonlinear elements. The transition from the weakly to the strongly nonlinear regime of a JTL induced by increasing the input power of the pump is probed by two-tone spectroscopy. Measurements of the phase of the transmission coefficient for a weak probe signal reveal a large increase and pronounced oscillations in the phase-length variation as a function of the microwave power of the pump. Experimental observations are explained on the basis of the developed theoretical approach suitable for the description of the nonlinear response of strongly driven JTLs. Using the derived nonlinear wave equation, we show that the behavior of the phase-length variation is associated with the oscillatory dependence of the Josephson inductances on the microwave power. It is demonstrated that the dissipation-induced propagation losses increase in the strongly nonlinear regime and also lead to smearing of the phase-length oscillations. The developed theoretical analysis is in good agreement with experimental observations.

In a recent Letter [H. Munoz-Bauza and D. Lidar, Phys. Rev. Lett. 134, 160601 (2025)], quantum annealing was reported to exhibit a scaling advantage in approximately solving quadratic unconstrained binary optimization (QUBO) problems. Here, we revisit these findings by employing the simulated bifurcation machine (SBM), a nonlinear dynamical system that exploits chaotic behavior rather than thermal fluctuations. Our approach originates from quantum dynamics and shares key operational features with quantum annealing: (i) nearly parallel evolution and (ii) a well-defined relation between the energy gap, run-time, and solution quality. We obtain comparable or superior scaling, closing the reported quantum-classical gap. We further show that the small instances studied previously are insufficient to infer asymptotic behavior. Extending the analysis to larger problems reveals robust classical performance, indicating that current quantum annealers are unlikely to exhibit a clear scaling advantage over SBM-like solvers on quantum-annealing-correction-type QUBO problems under the run-time accounting studied here. Finally, we identify sparse problem classes where future quantum devices could achieve a genuine scaling advantage once hardware overheads are mitigated.

Micron scale imaging of magnetic fields based on quantum sensors is a significant tool for understanding the evolution of magnetism through phase transitions and as a result of interactions inside of heterostructures. However, most imaging platforms, such as the nitrogen-vacancy (N-$V$) center in diamond, are restricted to applying magnetic fields along the quantization axis of the quantum sensor. This greatly restricts the utility of these systems for exploring materials that emit strong fields or exhibit variable response with respect to the applied field direction. Here we explore an alternative approach using weakly coupled spin pairs in hBN that exhibit a spin-1/2-like behavior and an isotropic response to the magnetic field. We demonstrate that the spin-pair system can operate in the presence of strong fields from a thin film magnet that were incompatible with N-$V$ diamond imaging even with applied fields along the quantization axis. Further, we demonstrate that using this platform allows for imaging with an arbitrary applied magnetic field direction, allowing us to probe the anisotropy and spin-reorientation transition in the ferrimagnet ${\text{TbMn}}_6{\text{Sn}}_6$. Finally, we propose an improved geometry for imaging small anisotropy contributions such as crystalline anisotropy. These results demonstrate how this or similar spin-1/2 systems might be used for imaging magnetic materials that are incompatible with other techniques despite the reduction in sensitivity compared with N-$V$ in diamond imaging.