We introduce a systematic approach for enhancing the absorbance of multilayer metamaterial absorbers (MMA) by combining deep-subwavelength spatially variable dielectric substrates with the increased Ohmic losses of MXene resonators. We choose MXenes to form the MMA resonators as they are ultrathin conductive materials that offer higher Ohmic losses than copper used in PCBs, alleviate the need for the post-treatment required by metal inks, and are considerably thinner than conductive filaments. Previous multilayer MMAs in the literature typically involve structured metal layers with a uniform dielectric profile or pyramidal-shaped substrates. The simplicity of the dielectric structure limits the design freedom and operational bandwidth of MMAs. In this work, we explore an alternative route to achieving increased design flexibility and enhanced absorption, by tailoring the dielectric substrates and consequently the underlying physics on a deep subwavelength scale. Advances in stereolithography (SLA) three-dimensional (3D) printing, allow the synthesis of suitable spatially variable 3D-printable dielectric structures. We inversely design the multilayer MMA by topology optimization, with the MMA substrate cells assuming dielectric constant values in the continuous range between air and the 3D printer’s resin. We develop a simple postprocessing methodology, BINACONN3D, that transforms the optimized nonmanufacturable MMA into a manufacturable one, while preserving performance. The BINACONN3D uses manufacturable configurations of a prescribed local air and resin composition to realize each designed dielectric material and accommodates detailed connectivity constraints across consecutive layers, to allow multilayer fabrication and assembly. Our work demonstrates the advantages of combining inversely designed spatially variable dielectric structures with the increased Ohmic losses of MXene resonators. We fabricate and experimentally characterize the synthesized MMA, with measurements in good agreement with the simulations. Our approach paves the way for improving the performance of existing metamaterial devices by leveraging high-resolution spatially variable dielectric structures.

In pursuit of superconducting quantum computing, fluxonium qubits have recently garnered attention for their large anharmonicity and high coherence at the sweet spot. Towards the large-scale integration of fluxonium qubits, a major obstacle is the need for precise external magnetic flux bias: to achieve high performance at its sweet spot, each qubit requires a flux-bias line. However, such lines inductively coupled to the qubits bring in additional wiring overhead, crosstalk, heating, and decoherence, necessitating measures for mitigating the problems. In this work, we propose a flux-trapping fluxonium qubit, which, by leveraging fluxoid quantization, enables optimal phase biasing without using external magnetic flux control at the operating temperature. We introduce the design and working principle, and demonstrate the phase biasing achieved through fluxoid quantization.

In spin-orbit-coupled systems, the charge and spin transport are generally coupled to each other, namely, a charge current will induce a spin current and vice versa. In the presence of time-reversal symmetry $\mathcal{T}$, the cross-coupling transport coefficients describing how one process affects the other are constrained by the famous Onsager reciprocal relations. In this paper, we generalize the Onsager reciprocal relations of charge and spin transport to systems that break the time-reversal symmetry but preserve a combined symmetry of $\mathcal{T}$ and some other symmetry operation $\mathcal{O}$. We show that the symmetry or antisymmetry of the cross-coupling transport coefficients remains in place provided that the operator $\mathcal{O}$ meets certain conditions. Among many candidate systems where our generalized Onsager relations apply, we focus on a conceptually simple and experimentally realized model in cold atomic systems for explicit demonstration and use these relations to predict highly nontrivial transport phenomena that can be readily verified experimentally.

We present a scheme for generating stable and tunable entanglement between two localized Bloch domain walls in nanomagnetic strips kept inside a chiral optical cavity. The entanglement is mediated by the effective optomechanical interaction between the cavity photons and the two macroscopic, collective modes of the pinned domain walls. By control of the pinning potential and optical driving frequency, the robust, steady-state entanglement between the two macroscopic domain walls can survive beyond the typical millikelvin temperature range.

Harmonic generation in underdense spatially homogeneous plasma is generally expected to be inefficient: in an unmagnetized uniform plasma the fundamental and its harmonics cannot be phase matched, resulting in third-harmonic generation efficiencies of no more than ${10}^{-5}$. Here, we describe how a strong uniform magnetic field allows phase-matched harmonic generation in constant-density plasma. We derive phase-matching relations for type-I and type-II second-, third-, and fourth-harmonic generation, and confirm these relations with particle-in-cell simulations. These simulations show that for weakly relativistic femtosecond pulses the efficiencies of second-, third-, and fourth-harmonic generation can reach at least 70%, 14%, and 2%, respectively. Additionally, if driven by a two-color beam, third-harmonic generation is found to be over 70% efficient and fourth-harmonic generation is found to be over 30% efficient.

We introduce an alternative method for fabricating all-aluminum Josephson junctions with highly transmitted conduction channels. Such properties are typically associated with structures requiring intricate fabrication processes, such as atomic contacts or hybrid junctions based on semiconducting nanowires and two-dimensional materials. In contrast, our approach relies solely on standard nanofabrication techniques. The resulting devices exhibit a key signature of high-transmission junctions—multiple Andreev reflections—in their current-voltage characteristics. Furthermore, we propose a straightforward superconducting circuit design based on these junctions, enabling the implementation of a parity-protected qubit.

Hybrid mechanical-superconducting systems for quantum information processing have attracted significant attention due to their potential applications. In such systems, the weak coupling regime, dominated by dissipation, has been extensively studied. The strong coupling regime, where coherent energy exchange exceeds losses, has also been widely explored. However, the transition-coupling regime, which lies between the above two and exhibits rich, unique physics, remains underexplored. In this study, we fabricate a tunable coupling device to investigate the coupling of a superconducting transmon qubit to a seven-mode surface acoustic-wave resonator (SAWR), with a particular focus on the transition-coupling regime. Through a series of phonon oscillation experiments and studies in the dispersive regime, we systematically characterize the performance of the SAWR. We then explore the complex dynamics of energy exchange between the qubit and the mechanical modes, highlighting the interplay between dissipation and coherence. Finally, we propose a protocol for qubit readout and fast reset with a multimode mechanical cavity using one mode for readout and another mode for reset. We have demonstrated in simulation that the qubit achieves both fast reset and high coherence performance when the qubit is coupled to the reset mode in the transition-coupling regime.

Memristors are emerging components in neuromorphic computing due to their ability to retain memory through resistive switching. In this work, we report the fabrication and characterization of low-cost memristive devices based on self-assembled structures of carbon quantum dots (CQDs). These structures were produced via evaporation-induced self-assembly of CQDs dispersed in water, deposited on silicon substrates at controlled low temperatures. Morphological analysis revealed that drying temperature plays a critical role in the resulting spatial configurations, with temperatures around $5{}^{\circ }\mathrm{C}$ yielding elongated, millimeter-scale wirelike structures that suppress the typical coffee-ring effect. Electrical characterization of these structures showed pronounced hysteresis in the current-voltage curve, indicative of memristive behavior. Further analysis confirmed space-charge-limited conduction as the dominant transport mechanism, and transient current response supported the participation of oxygen-containing functional groups in charge trapping and release. These findings demonstrate that self-assembled structures of CQDs can act as effective memristors, offering a scalable and biocompatible platform for future applications in neuromorphic systems and flexible memory technologies.

Spins in semiconductor quantum dots hold great promise as building blocks of quantum processors. Trapping them in $\mathrm{Si}$MOS transistorlike devices eases future industrial-scale fabrication. Among the potentially scalable readout solutions, gate-based dispersive radio-frequency reflectometry only requires the already existing transistor gates to read a quantum dot state, which alleviates the need for additional elements. In this effort toward scalability, traveling-wave superconducting parametric amplifiers significantly enhance the readout signal-to-noise ratio (SNR) by reducing the noise below that of typical cryogenic low-noise amplifiers, while offering a broad amplification band, essential to multiplex the readout of multiple resonators. In this work, we demonstrate a 3-GHz gate-based reflectometry readout of electron charge states trapped in quantum dots formed in $\mathrm{Si}$MOS multigate devices, with SNR enhanced due to a Josephson traveling-wave parametric amplifier (JTWPA). The broad tunable 2-GHz amplification bandwidth combined with more than 10-dB ON-OFF SNR improvement of the JTWPA enables frequency and time-division-multiplexed readout of interdot transitions, and noise performance consistent with JTWPA characteristics at higher frequencies. In addition, owing to a design without superconducting loops and with a metallic ground plane, the JTWPA is flux insensitive and shows stable performance up to a magnetic field of 1.1 T at the quantum dot device, compatible with standard $\mathrm{Si}$MOS spin-qubit experiments.

This work investigates amplitude-dependent nonlinear corrections to the dissipative conductivity in superconductors, using the Keldysh-Usadel theory of nonequilibrium superconductivity, which captures the nonequilibrium dynamics of both quasiparticles and the pair potential. Our rigorous formulation naturally incorporates both the direct nonlinear action of the photon field and indirect contributions mediated by nonequilibrium variations in the pair potential, namely, the Eliashberg effect and the Higgs mode. The third-harmonic current, often regarded as a hallmark of the Higgs mode in disordered superconductors, arises from both the direct photon action and the Higgs mode. Our numerical results are in excellent agreement with previous studies. In contrast, the first-harmonic current, and consequently the dissipative conductivity, receives contributions from all three mechanisms: the direct photon action, the Higgs mode, and the Eliashberg effect. It is shown that the nonlinear correction to dissipative conductivity in dirty-limit superconductors can serve as a fingerprint of the Higgs mode, appearing as a resonance peak at a frequency near the superconducting gap $\mathrm{\Delta }$. In addition, our results provide microscopic insight into amplitude-dependent dissipation at frequencies well below $\mathrm{\Delta }$, which is particularly relevant for applied superconducting devices. In particular, the long-standing issue concerning the frequency dependence of the amplitude-dependent quality factor is explained as originating from the direct nonlinear action of the photon field, rather than from contributions by the Higgs mode and the Eliashberg effect. Our practical and explicit expression for the nonlinear conductivity formula makes our results accessible to a broad range of researchers.

The $3\omega$ method is widely used to measure the thermal conductivity and the specific heat of wires and thin films. These measurements are typically performed under high vacuum conditions, which justify the use of heat-transfer models that exclude thermal losses to a surrounding fluid. Here, we study the effect of thermal conduction from a joule-heated wire to a surrounding gas on pressure-dependent $3\omega$ measurements, and show how a one-dimensional (1D) heat-transfer model may be used to reliably determine the wire’s thermal properties. We derive a full analytical solution of the 1D heat transfer equation with finite heat-transfer coefficient $h$ and validate it experimentally using a 16-$\text{μ}\mathrm{m}$ diameter platinum wire in air across pressures from ${10}^{-5}$ to ${10}^3$ mbar. We introduce a model for heat transfer between the wire and the surrounding gas based on kinetic gas theory that accurately describes the data across continuum to free-molecular gas regimes, with $h$ varying from near-zero in high vacuum to approximately $700{\mathrm{W}/(\mathrm{m}}^2\mathrm{K})$ at atmospheric pressure. We show that use of a validated $h(p)$ model allows extracting both thermal conductivity $\kappa$ and volumetric heat capacity $\rho c_p$, whereas volumetric heat capacity can be extracted even without invoking a specific $h(p)$ model. Our approach facilitates the characterization of fine wires with moderate to low thermal conductivities and may enable accurate thermal measurements of suspended wires with diameters on the nanometer scale.

Nuclear spins associated with the nitrogen-vacancy (NV) center are useful resources for quantum information processing and quantum sensing, especially as quantum memories. They are also an emerging platform for constructing inertial sensors. The native nitrogen spin of the NV center can serve as a gyroscope using Ramsey interferometry protocols. The sensitivities of these nuclear-spin-based NV gyroscopes are limited by the phase coherence time of the nuclear spin, which is in turn limited by the longitudinal coherence time $(T_1)$ of the NV center’s electron spin. There is an active research effort to decouple the nuclear spin from the electron spin and other sources of decoherence to extend the phase coherence time past the NV center electron $T_1$. However, this presents an associated challenge—how to read out the nuclear spin ensemble if the electronic spins have relaxed into a thermal state. We introduce an optical repump pulse to repolarize electron spins from an artificial thermal state and investigate the effect on the readout of nuclear spins in this regime. We find that for ensemble-based sensors our readout protocol has around a sixfold improvement in sensitivity around the excited-state level anticrossing (ESLAC) at 500 G compared to low fields (200 G), despite the presence of deleterious spin flip-flop dynamics in the excited state. Our results highlight how ESLAC dynamics can benefit inertial sensing and other sensing applications involving nuclear quantum memories.

This study presents a simple theoretical model describing narrow envelope surface acoustic waves (phonons) and spin waves (magnons) in an ultrathin ferromagnetic film. Based on the general principles of weak wave turbulence, the model considers interactions between beams of an ideal phonon gas and a weakly nonideal magnon gas, which represent magnetoacoustic oscillations in the system. Equations for the wave envelopes of phonons and magnons, along with their harmonics, are derived, incorporating nonlinear effects from three- and four-particle interactions. In the general nonresonant case, linear stationary envelope simulations are sufficient. These clarify the experimentally observed angular dependence of the transmitted acoustic signal with respect to the orientation of the magnetic field. The study highlights increased energy losses associated with enhanced magnetoacoustic coupling. Given the broad interdisciplinary interest in weak turbulence phenomena within condensed-matter physics and nonlinear wave dynamics, our model offers significant predictive capabilities and greatly simplifies calculations of quasiparticle beam interactions.

We report broadband, multimode microwave absorption in obliquely sputtered Permalloy films where the in-plane anisotropy is tuned by deposition geometry. As the sputtering angle approaches normal incidence, the films evolve from uniform in-plane magnetization to well-ordered stripe domains (SDs), accompanied by a transition from single-peak ferromagnetic resonance to up to seven resolvable modes with bandwidths up to 5.0 GHz and average spectral granularity less than 1.0 GHz (configuration dependent). Angle- and field-resolved measurements under orthogonal ($h_{\mathrm{rf}}$ ⊥ H) and parallel ($h_{\mathrm{rf}}$ ∥ H) geometries reveal mode families associated with domain precession and domain-wall dynamics, including geometry-driven conversions between acoustic-like and optical-like branches. Micromagnetic simulations reproduce the domain evolution, the emergence and suppression of modes with field, and the configuration selectivity, establishing in-plane anisotropy as a deterministic control parameter that sets the SD texture and its high-frequency response. The results provide a lithography-free, wafer-compatible route to tunable, multifrequency, broadband magnetic functionality for microwave, sensing, and spintronic applications.

Superconducting qubits in today’s quantum processing units are typically fabricated with angle-evaporated aluminum–aluminum-oxide–aluminum Josephson junctions. However, there is a need for higher yield and tighter parameter control when scaling up the number of qubits and junctions into tens of thousands and beyond. Fabrication methods based on subtractive patterning of superconductor-insulator-superconductor trilayers, used for more classical large-scale Josephson junction circuits, could provide the solution but they in turn often suffer from lossy dielectrics incompatible with high qubit coherence. In this work, we utilize native aluminum oxide as a sidewall passivation layer for junctions based on aluminum–aluminum-oxide–niobium trilayers, and use such junctions in qubits. We design the fabrication process such that the few-nanometer-thin native oxide is not exposed to oxide removal steps that could increase its defect density or hinder its ability to prevent shorting between the leads of the junction. With these junctions, we design and fabricate transmonlike qubits and measure time-averaged coherence times up to $30\text{μ}\mathrm{s}$ at a qubit frequency of 5 GHz, corresponding to a qubit quality factor of one million. Our process uses subtractive patterning and optical lithography on wafer scale, enabling high throughput in patterning. This approach provides a scalable path toward fabrication of superconducting qubits on industry-standard platforms.

Oscillatory recurrent networks, such as the harmonic oscillator recurrent network (HORN) model, offer advantages in parameter efficiency, learning speed, and robustness relative to traditional nonoscillating architectures. Yet, while many implementations of physical neural networks exploiting attractor dynamics have been studied, so far implementations of oscillatory models in analog-electronic hardware that utilize the networks’ transient dynamics are lacking. This study explores the feasibility of implementing HORNs in analog-electronic hardware while maintaining the computational performance of the digital counterpart. Using a digital-twin approach, we trained a four-node HORN in silico for sMNIST (sequential Modified National Institute of Standards and Technology) classification and transferred the trained parameters to an analog-electronic implementation. A set of custom error metrics indicated that the analog system is able to successfully replicate the dynamics of the digital model in most test cases. However, despite the overall well-matching dynamics, when using the readout layer of the digital model on the data generated by the analog system, we observed only 28.39% agreement with the predictions of the digital model. An analysis shows that this mismatch is due to a precision difference between the analog hardware and the floating-point representation exploited by the digital model to perform classification tasks. When the analog system was utilized as a reservoir with a retrained linear readout, its classification performance could be recovered to that of the digital twin, indicating preserved information content within the analog dynamics. This proof of concept establishes that analog-electronic circuits can effectively implement oscillatory neural networks for computation, providing a demonstration of energy-efficient analog systems that exploit brain-inspired transient dynamics for computation.

Acoustic metalenses that enable wide-incident-angle and high-efficiency focusing are in high demand for diverse applications, from underwater imaging to biomedical diagnostics. In this work, we introduce a design paradigm for an acoustic metalenses based on a quadratic phase profile, which can incorporate a synergistic combination of a central metasurface and a peripheral metagrating. By our integrating grating diffraction theory with phase engineering and applying an intelligent optimization algorithm, our design achieves high-efficiency, ultrawide-angle focusing of underwater sound across a continuous angular range from 0° to ±85°, with an average efficiency of 31.72%. Thanks to its wavelength-scale thickness and distinct design principle, this metalens provides a compact platform suitable for integration into advanced acoustic systems with complex functional requirements.

We study parametric oscillations of two capacitively coupled Kerr parametric oscillators (KPOs) with frequency-chirped two- and one-photon drives. The two-KPO system adiabatically evolves from the initial vacuum state to an oscillation state corresponding to a solution state in quantum-annealing applications. Frequency chirping dynamically changes the detuning between resonance and oscillation frequencies during parametric modulation and reduces unwanted population transfer to excited states caused by pure dephasing and photon loss. We observe that frequency chirping increases the success probability to obtain the solution state and that simulations taking into account pure dephasing reproduce experiments with and without frequency chirping. This study demonstrates the effectiveness and applicability of frequency chirping to a KPO-based quantum annealer.