Stimulated Raman adiabatic passage (STIRAP) is a powerful technique for robust state transfer capabilities in quantum systems. This method, however encounters challenges for its implementation as a gate in qubit-subspace due to its sensitivity to initial states. By incorporating single-photon detuning into the protocol, the sensitivity to the initial state can effectively be mitigated, enabling STIRAP to operate as a gate. In this study, we experimentally demonstrate the implementation of robust $\pi$ and $\pi /2$ rotations in a dual-rail qubit formed by two strongly coupled fixed-frequency transmon qubits. We achieve state preparation fidelity in excess of 0.98 using such rotations. Our analysis reveals these gates exhibit significant resilience to errors. Furthermore, our numerical calculations confirm that these gates can achieve fidelity levels in excess of 0.999. This work suggest a way for realizing quantum gates which are robust against minor drifts in pulse or system parameters.

Microwave cavity modes with long coherence times are used in many different quantum computing systems. During normal operation of such systems, these modes, called “memory modes,” often need to be set to different coherent photonic occupations. In this work we present a technique we call “Rabi-driven reset” in which the state of a memory mode is transferred into a decaying mode. This is done through a Rabi-driven qubit that is coupled to both modes via sideband driving tones. The outcome of the method is the initialization of the memory mode in any required coherent state. Simulations are presented to demonstrate the effectiveness of this technique, along with a comparison to an existing coupling method. Our simulations predict a decrease of an order of magnitude in initialization times compared with existing methods.

The recently emerging ${\mathrm{Mo}\mathrm{Si}}_2{\mathrm{N}}_4$ monolayer has attracted great attention due to its excellent electronic properties. Here, various ${\mathrm{Mo}\mathrm{Si}}_2{\mathrm{N}}_4$ derivatives and related heterojunctions are proposed, and their structural stability, electronic properties, and potential applications are studied systematically. Ten monolayer derivatives are obtained by the layer-by-layer etching simulations. Upon the assessment of energetic, thermodynamic, dynamic, and mechanical stability, we find that eight derivatives are stable, behaving as semiconductors, metals, and a bipolar magnetic semiconductor, respectively. Particularly, the five stable metallic derivatives are combined with semiconducting parent ${\mathrm{Mo}\mathrm{Si}}_2{\mathrm{N}}_4$ to construct two-dimensional metal-semiconductor van der Waals heterojunctions (vdWHs), in which two vdWHs are structurally stable, with extremely low intrinsic Schottky barrier height and Ohmic contact, respectively, favorably to electron injection in devices. Based on such stable vdWHs, we design various high-performance field effect transistors (HPFETs), and the combined effects of various factors such as gate dielectric material, underlap length, and doping concentration are considered. Interestingly, it is found that the subthreshold swing for four FETs is lower than the thermodynamic limit (60 mV/dec), breaking through “Boltzmann tyranny” restricting traditional semiconductor devices, and for most of the suggested FETs, their current on-off ratios reach ${10}^3$ order, satisfying the orders of magnitude requirement of the on-off ratio in the International Technology Roadmap for Semiconductors standard. This study not only predicts the stability and outstanding electronic properties of ${\mathrm{Mo}\mathrm{Si}}_2{\mathrm{N}}_4$ derivatives and related heterojunctions, but also indicates that those stable vdWHs are promising candidates for developing HPFETs with low-power consumption.

Magnetic cooling based on many-body effects has recently gained significant interest as a cost-efficient and user-friendly alternative to ${}^3\mathrm{He}$-based refrigeration techniques. Adiabatic demagnetization refrigeration (ADR) using frustrated magnetic materials is essential for modern cooling applications. This requires finding alternative materials with improved magnetic frustrations. This article examines the thermodynamic properties and ADR performance in ${\mathrm{Gd}\mathrm{Cr}\mathrm{Ti}\mathrm{O}}_5$, a material characterized by competing exchange interactions. Magnetization and specific heat measurements identified magnetic ordering at a Néel temperature of 1.05 K. Magnetization measurements under external fields showed a decrease in the ordering temperature with increasing field strength, establishing a phase boundary for the antiferromagnetic ordered phase. Entropy calculations from specific heat data revealed accumulation around a field value of 1.2 T. To confirm this, ADR tests were conducted at base temperatures of 1.8, 2.7, and 3.7 K using a home-built setup, achieving minimum temperatures of 0.4, 0.67, and 0.88 K, respectively. These minima appeared at field values at which enhanced entropy observed in specific heat data. Furthermore, ${\mathrm{Gd}\mathrm{Cr}\mathrm{Ti}\mathrm{O}}_5$ demonstrated a hold time exceeding an hour, suggesting it as a possible future intermediate stage of a continuous ADR system.

The voltage-controlled magnetic anisotropy-based writing process of magnetic random-access memory relies on the precessional dynamics of the free-layer magnetization resulting from a voltage pulse. The success of the switching strongly depends on the spatial orientation of the magnetization when the pulse is turned off. For this reason, precise control over the voltage pulse parameters is fundamental to enable reliable writing operation. This study finds experimentally an optimal region for voltage amplitudes slightly above the voltage threshold for switching where a high switching probability is observed for a maximum range of pulse widths. Moreover, we report that the switching efficiency depends not only on pulse width, but also on pulse amplitude. We observe a second voltage amplitude threshold that limits the switching probability. Our macrospin simulations corroborate this finding and attribute this to a variation in the magnetization precessional dynamics at higher voltage amplitudes.

Dynamic control of image display plays a crucial role in many infrared applications, particularly in infrared image steganography and thermal camouflage. In this paper, we experimentally demonstrate flexible and electrically tunable metasurfaces for infrared image steganography through dynamic polarization conversion in a broadband regime. Our metasurface consists of an array of gold nanobricks deposited on a thin film of vanadium dioxide (${\mathrm{VO}}_2$). The electrical tunability is achieved by actively controlling the phase transition of ${\mathrm{VO}}_2$. By modulating the applied current, the metasurface can be dynamically and reversibly tuned from a half-wave plate to a mirror across a broadband infrared regime. Furthermore, the flexibility of the metasurface enables operation even in bent states. We showcase the application of these flexible and electrically tunable metadevices for infrared image display. By encoding intensity images into the orientation of the nanobricks within the metasurface, we demonstrate the reversible hiding or displaying of infrared images through electrical tuning. This dynamic process effectively serves as infrared image steganography, offering tunable concealment capabilities for sensitive information. Our results reveal potential applications in conformal infrared target simulation, flexible anticounterfeit, and wearable thermal camouflage devices. Additionally, our strategy for dynamic tuning highlights promising pathways for future developments in reconfigurable device technology.

Strong bulk spin-orbit coupling and the presence of robust, spin-momentum-locked surface states make topological insulators uniquely advantageous as spin detectors for potential spin-orbitronics applications. In this work, the role of the surface states in the spin-detection functionality is explored by studying the temperature dependence of spin pumping in a ${\mathrm{Bi}\mathrm{Sb}\mathrm{Te}}_{1.5}{\mathrm{Se}}_{1.5}(\mathrm{BSTS})/{\mathrm{Co}}_{20}{\mathrm{Fe}}_{60}{\mathrm{B}}_{20}(\mathrm{Co}\mathrm{Fe}\mathrm{B})$ bilayer using ferromagnetic resonance spectroscopy. Across the studied temperature range, significantly broader linewidths are detected in the bilayer sample compared to a reference $\mathrm{Co}\mathrm{Fe}\mathrm{B}$ film, while the frequency dependence of linewidths show a linear behavior illustrating that the damping is predominantly Gilbert type. Significant temperature-dependent modification of the Gilbert damping and the resonance condition are observed and further demonstrated to closely correspond to the temperature-dependent transport characteristics. As the temperature decreases below the point where the surface-dominated conduction appears in the resistance vs temperature characteristics, both the damping modulation and the resonance condition show drastic changes, consistent with enhanced dynamical exchange-driven spin-pumping efficiency in the surface-dominated transport regime. Consequently, the room-temperature spin-pumping efficiency, quantified by spin-mixing conductance, is shown to be more than double at low temperatures.

Low-noise amplifiers are of great significance in the field of quantum technologies. We study a thermally driven parametric amplifier based on a superconductor-insulator-graphene-insulator-superconductor ($S$-$I$-$G$-$I$-$S$) junction coupled to a superconducting microwave cavity. The strong nonlinearity in the temperature dependence of our device leads to thermal self-modulation that produces impedance oscillations at frequencies around twice the angular cavity resonance frequency ${\omega }_{\mathrm{r}}$. In particular, reactance modulation of the effective capacitance yields a gain of 18.6 dB over a frequency span of 125 kHz with a minimum noise temperature of $T_{\mathrm{N}}=1.4\mathrm{K}$. Our theoretical modeling gives insight into the exact mixing processes, confirmation of the electron-phonon coupling parameter and possible improvements of the studied system.

Wurtzite $(\mathrm{Al},\mathrm{Sc})\mathrm{N}$ ferroelectrics are attractive for microelectronics applications due to their chemical and structural compatibility with wurtzite semiconductors, such as $\mathrm{Ga}\mathrm{N}$ and $(\mathrm{Al},\mathrm{Ga})\mathrm{N}$. However, the leakage current in epitaxial stacks reported to date should be reduced for reliable device operation. Here, we demonstrate low leakage current in epitaxial ${\mathrm{Al}}_{0.7}{\mathrm{Sc}}_{0.3}\mathrm{N}$ films on $\mathrm{Ga}\mathrm{N}$ with well-saturated ferroelectric hysteresis loops that are orders of magnitude lower (i.e., 0.07 A ${\mathrm{cm}}^{-2}$) than previously reported films (1–19 A ${\mathrm{cm}}^{-2}$) having similar or better structural characteristics. We also show that, for these high-quality epitaxial $(\mathrm{Al},\mathrm{Sc})\mathrm{N}$ films, structural quality (edge and screw dislocations), as measured by diffraction techniques, is not the dominant contributor to leakage. Instead, the small leakage in our films is limited by thermionic emission across the interfaces, which is distinct from the large leakage due to trap-mediated bulk transport in the previously reported $(\mathrm{Al},\mathrm{Sc})\mathrm{N}$ films. To support this conclusion, we show that ${\mathrm{Al}}_{0.7}{\mathrm{Sc}}_{0.3}\mathrm{N}$ on lattice-matched ${\mathrm{In}}_{0.18}{\mathrm{Ga}}_{0.82}\mathrm{N}$ buffers with improved structural characteristics but higher interface roughness exhibit increased leakage characteristics. This demonstration of low leakage current in heteroepitaxial $(\mathrm{Al},\mathrm{Sc})\mathrm{N}$ films and understanding of the importance of interface barrier and surface roughness can guide further efforts toward improving the reliability of wurtzite ferroelectric devices.

Ultrasonic testing methods exhibit great potential for nondestructive evaluation in various industrial materials including composite materials. However, the wave-propagation behavior in composite materials becomes complicated due to the combined effects of anisotropy and dispersion, which brings great challenges to defect detection in anisotropic media. In this work, the method for imaging defects in anisotropic materials is proposed by combining phase-shift migration (PSM) and coordinate transformation. As a demonstration, the Lamb wave propagation in highly anisotropic composite plates is analyzed, and described with a two-dimensional equivalent model, which is established by mathematically mapping the anisotropic wave propagation into an equivalent isotropic form. After obtaining the ultrasound field at the scanning positions corresponding to the transformed coordinates, the PSM is applied to image defects in such equivalent isotropic systems. The actual defect position is retrieved according to the geometric relationships. This work demonstrates the feasibility and application potential of the proposed method in the field of defect evaluation in anisotropic composite materials.

We theoretically study the antiferromagnetism-involved Andreev reflection (AR) in a graphene-based ferromagnet/superconductor/antiferromagnet hybrid structure, with the ferromagnetic exchange field rotated in the ferromagnet region. The local and nonlocal ARs are considerably characterized by the spin polarization of the antiferromagnet region. A switching effect of perfect spin-singlet nonlocal AR processes can be achieved by conversion from the parallel to the antiparallel configuration for the ferromagnetic and antiferromagnetic exchange fields. Particularly, under the noncollinear scenario, a quasiperfect oblique-spin nonlocal AR process can be realized. It could bring about novel spin quantum entanglement, which cannot be lost in the presence of only one stray field and has scarcely been explored thus far.

Full characterization of surface-acoustic-wave (SAW) devices requires imaging the spatial distribution of the acoustic field, which is not possible with standard all-electrical measurements where an interdigital transducer is used as a detector. Here we present a fiber-based scanning Michelson interferometer employing a strongly focused laser beam as a probe. Combined with a heterodyne circuit, this setup enables frequency- and spatially resolved measurements of the amplitude and phase of the SAW out-of-plane displacement. We demonstrate this by investigating a 1-GHz SAW cavity, revealing the presence of frequency-overlapping transverse modes, which are not resolved with an all-electrical measurement. The frequency overlap of these transverse modes leads to mode superpositions, which we analyze by quadrature decomposition of the complex acoustic field.

Acousto-optical modulation (AOM) is a powerful and widely used technique for rapidly controlling the frequency, phase, intensity, and direction of light. Based on Bragg diffraction, AOMs typically exhibit moderate diffraction efficiency, often less than 90% even for collimated inputs. In this work, we demonstrate that this efficiency can be significantly improved using a composite (CP) setup comprising a pair of 4-$F$-linked AOMs, enabling beam splitting with fully tunable splitting amplitude and phase. The efficiency enhancement arises from two effects, termed “momentum echo” and “high-order rephasing,” which can be simultaneously optimized by adjusting the relative distance between the two AOMs. This method is resource efficient, does not require ultra-collimation, and maintains control bandwidth. Experimentally, we achieve a diffraction efficiency exceeding 99% (excluding insertion loss) and a 35-dB single-mode suppression of the zeroth-order beam, demonstrating a full-contrast optical router with a switching time of less than 100 ns. Theoretically, we formulate the dynamics of CP AOM in terms of multimode quantum control and discuss extensions beyond the $N=2$ configuration presented in this work. The substantially enhanced performance of CP AOMs, coupled with reduced acoustic amplitude requirements, may significantly advance our ability to accurately control light at high speeds with low-loss acousto-optics.

A primary challenge in wireless power-transfer (WPT) systems is to achieve efficient and stable power transmission when load conditions change dynamically, which often requires the load-to-source communication to share the load-variation information for source control. Addressing this issue, we propose a third-order pseudo-Hermitian WPT system whose output characteristics exhibit a stable frequency and constant power. The frequency-selection mechanism and energy efficiency of the nonlinear WPT system based on pseudo-Hermitian under the coupling-mode theory approximation are analyzed. Theoretical analysis indicates that under certain coupling coefficients and load conditions, the proposed system can achieve frequency adaptation in a stable frequency mode without the need to change the circuit frequency. When the load changes dynamically, the stability of the power output is maintained using a proportional-integral (PI) control strategy that only collects the voltage and current at the transmitting end, eliminating the need for wireless communication circuits with feedback from the receiving side. Experimental results demonstrate that the proposed design scheme can achieve constant power transmission when load conditions change, maintaining stable and relatively high transmission efficiency. The proposed scheme exhibits benefits in practical applications since no communication is required.

When a nonreciprocal lattice strongly couples to a reciprocal lattice, it can imbue the reciprocal system with nonreciprocal properties through hybridization. We demonstrate that nonreciprocal hybridization generates nonreciprocity via two mechanisms: first, the formation of a nonreciprocal partial band gap; and second, nonreciprocal destructive interference between two wave modes propagating in the same direction. Critically, for structures with a limited number of unit cells, destructive interference can generate significantly stronger nonreciprocity and attenuation compared to the nonreciprocal band gap in the same system. We use this principle to realize linear and time-invariant elastic nonreciprocity by coupling an elastic waveguide to a nonreciprocal electrical lattice using the piezoelectric effect. By designing the electrical lattice to hybridize with the elastic waveguide, broadband nonreciprocal dissipation is observed in the overall system. We validate the theoretical predictions experimentally, observing a nonreciprocal antiresonance with 7.4 times (17.4 dB) contrast between left-to-right and right-to-left responses at steady state. This result opens alternative research directions by greatly simplifying the realization of nonreciprocal elastic dissipation, paving the way for elastic “circuits” that freely manipulate sound and vibration.

In terms of energy efficiency and computational speed, neuromorphic electronics based on nonvolatile memory devices are expected to be one of most promising hardware candidates for future artificial intelligence (AI). However, catastrophic forgetting, networks rapidly overwriting previously learned weights when learning new tasks, remains a pivotal obstacle in either digital or analog AI chips for unleashing the true power of brainlike computing. To address catastrophic forgetting in the context of online memory storage, a complex synapse model (the Benna-Fusi model) was proposed recently [M. K. Benna and S. Fusi, Nat. Neurosci. 19, 1697 (2016)], the synaptic weight and internal variables of which evolve following diffusion dynamics. In this work, by designing a proton transistor with a series of charge-diffusion-controlled storage components, we have experimentally realized the Benna-Fusi artificial complex synapse. Memory consolidation from coupled storage components is revealed by both numerical simulations and experimental observations. Different memory timescales for the complex synapse are engineered by the diffusion length of charge carriers and the capacity and number of coupled storage components. The advantages of the demonstrated complex synapse for both memory capacity and memory consolidation are revealed by neural network simulations of face-familiarity detection. Our experimental realization of the complex synapse suggests a promising approach to enhance memory capacity and to enable continual learning.