Wireless ultrasonic power transfer and data transmission through a metallic wall requires a direct contact of transducers with the wall owing to the significant impedance mismatch between the surrounding fluid and the wall. Here, a pillar-based acoustic metamaterial is proposed for wireless and contactless ultrasonic power transfer and data transmission through a metallic wall by leveraging the pillar’s vertical elongation mode. Experiments conducted in water demonstrate a 33-fold power transmission enhancement (from 2% to around 66%) at approximately 450 kHz through a 1-mm-thick metallic wall. Furthermore, our experiments show that a commercial light-emitting diode can be illuminated by harvesting the metamaterial-enhanced transmission of ultrasonic energy, which would not have been possible with the metallic wall alone even at an input voltage approximately 5 times greater. In addition, data transmission through the metallic wall is demonstrated by employing amplitude-shift keying modulation to transmit an image, showcasing the remarkable improvement in image quality enabled by the metamaterial. This study paves the way for a future generation of wireless and contactless ultrasonic power transfer and data-transmission applications.

With a numerical reconstruction algorithm proposed, the complete far-field wave-fronts of harmonics, which are emitted from relativistic plasma surfaces, have been retrieved from their complex spatial-temporal distributions. Combining theoretical analysis and three-dimensional simulations, the impact of the plasma density gradient, driving pulse quality, and polarization have been comprehensively investigated. Abundant information on the generation mechanism, optical properties, and aberration evolution of the generated harmonics, as well as the relativistic plasma surface structure are decoded from the reconstructed wave-front. Furthermore, proper defocusing incident lasers are proposed to achieve aberration-free attosecond sources at the extreme ultraviolet region with Gaussian-like intensity distribution. Providing powerful numerical tools and practical advice, current work is essential for analyzing wave-fronts, studying relativistic plasma properties and utilizing attosecond pulses in ultrafast metrology and control.

Hybridized magnonic-photonic systems are key components for future information-processing technologies such as storage, manipulation, or conversion of data in the quantum regime owing to its ability to achieve collective excitation of spin waves and excellent properties of low damping rate, high spin density, and highly tunable excitations. We propose to realize fast and controllable topological single- and multiexcitation quantum state transfers (QSTs) through a magnon-circuit-QED chain. Various time-dependent magnon-photon and photon-photon couplings are tailored via the Kerr nonlinearity of the magnons and superconducting quantum interference devices, which are implemented fast magnon-magnon excitation transfers by mapping the system to a Su-Schrieffer-Heeger model. We analytically derive the edge state of the system, qualitatively explain the mechanism of fast QST, and numerically show the robustness of QST against on-site potential defects, the fluctuation of couplings, and losses of the system. Furthermore, when larger on-site defects are added to different types of lattice sites in the two ends, alternative single-excitation controllable magnon-photon, photon-magnon, and photon-photon transfers are also accessible. Our work opens up prospects for realizing a fast and controllable quantum channel in magnon-circuit-QED system and for facilitating further applications of topological matter in robust quantum information processing in magnonics and photonics.

Programmable linear optical processors (LOPs) can have widespread applications in computing and information processing due to their capabilities of implementing reconfigurable on-chip linear transformations. A conventional LOP that uses a mesh of Mach-Zehnder interferometers (MZIs) requires $2N+3$ stages of phase shifters for $N\times N$ matrices. However, it is beneficial to reduce the number of phase-shifter stages to realize a more compact and lower-loss LOP, especially when long and lossy electro-optic phase shifters are used. In this work, we propose a structure for LOPs that can implement arbitrary matrices as long as they can be realized by previous MZI-based schemes. Through numerical analysis, we further show that the number of phase-shifter stages in the proposed structure can be reduced to $N+2$ and $N+3$ for a large number of random dense matrices and sparse matrices, respectively. This work contributes to the realization of compact, low-loss, and energy-efficient programmable LOPs.

We introduce a general framework called neural-network- (NN) encoded variational quantum algorithms (VQAs), or NNVQA for short, to address the challenges of implementing VQAs on noisy intermediate-scale quantum (NISQ) computers. Specifically, NNVQA feeds input (such as parameters of a Hamiltonian) from a given problem to a neural network and uses its outputs to parameterize an ansatz circuit for the standard VQA. Combining the strengths of NN and parameterized quantum circuits, NNVQA can accelerate the training process of VQAs and handle a broad family of related problems with varying input parameters with the pretrained NN. To concretely illustrate the merits of NNVQA, we present results on a NN variational quantum eigensolver (VQE) for solving the ground state of parameterized $XXZ$ spin models in one and two dimensions. Our results demonstrate that NNVQE is able to estimate the ground-state energies of parameterized Hamiltonians with high precision without fine tuning, and significantly reduce the overall training cost to estimate ground-state properties across the phases of the given Hamiltonian. We also employ an active learning strategy to further increase the training efficiency while maintaining prediction accuracy. These encouraging results demonstrate that NNVQAs offer an alternative hybrid quantum-classical paradigm to utilize NISQ resources for solving more realistic and challenging computational problems.

A quantum point contact (QPC)—a constriction in a semiconducting two-dimensional electron system with a quantized conductance—is a building block of novel spintronic and topological electronic circuits. QPCs can also be used as readout electronics, charge sensors, or switches in quantum nanocircuits. A short and impurity-free constriction with superconducting contacts is a Cooper-pair QPC analogue known as a superconducting quantum point contact (SQPC). The technological development of such quantum devices has been prolonged due to the challenges of maintaining their geometrical requirement and near-unity superconductor-semiconductor interface transparency. Here, we develop advanced nanofabrication, material and device engineering techniques and report on an innovative realization of nanoscale hybrid SQPC arrays with split gate technology in semiconducting 2D electron systems. We exploit the special gate tunability of the quantum wells, and demonstrate the first experimental observation of conductance quantization in hybrid InGaAs-Nb SQPCs. We observe reproducible quantized conductance at zero magnetic fields in multiple quantum nanodevices fabricated in a single chip and systematically investigate the quantum transport of SQPCs at low and high magnetic fields for their potential applications in quantum metrology, for extremely accurate voltage standards, and fault-tolerant quantum technologies.

Most modern high-data-rate optical communication systems require at each end a light source to transmit the data and a detector to receive the data. In order to realize a communication scheme where the transmitter unites with the receiver, we take advantage of a coupled injection-locked semiconduct. From the theoretical description of two mutually coupled diode lasers using a set of six nonlinear differential-delay equations we outline the stable compound cavity solutions of this system and investigate their dependencies in terms of locking bandwidth, coupling strength and coupling phase. From these modeling results we then design a remarkably simple communication system without any additional detectors that exploits compound laser states of different frequency detunings of the coupled laser system as information carriers with simultaneous upstream information of the first laser and downstream information of the second laser. The data recognition is accomplished by evaluating the compound state utilizing the change in the terminal voltage of both lasers (laser-as-detector principle) with respect to their solitary case (i.e., the terminal voltage of the uncoupled lasers), yielding the message via the agreed decoding scheme. The functionality of the principle had been demonstrated by a table-top experiment with good error-free transmission and potential to improve the transmission speed of this proof-of-principle demonstration. Our concept reduces the complexity compared to conventional transmission systems, thus providing the potential to significantly reduce the costs of the overall transmission setup an,d in particular, transferring the concept to other challenging wavelengths and other semiconductor lasers. Since the optical signal then no longer needs to be detected by an optical detection unit, the amount of optical components required for ordinary data transmission is reduced.

We present an experimental realization of a noise-free and high-bandwidth quantum memory scheme using a rubidium vapor that is confined within the hollow core of a photonic crystal fiber. We achieve the same internal efficiencies as similar free-space experiments (30%) for 4.5-ns-long optical pulses but with a 100-fold reduction in the control-field power required. Modeling indicates that this efficiency could be improved to 88% with higher control powers and the implementation of techniques such as light-induced atomic desorption to increase the optical depth. The compactness, robustness, and low drive power of this approach lends itself to direct integration into large-scale fiber-based quantum processors.

Magnetic resonance imaging (MRI) is a crucial tool for medical visualization. In many cases, performing a scanning procedure requires the use of additional equipment, which can be powered by wires as well as via wireless power transfer (WPT) or wireless energy harvesting. In this study, we propose a scheme for WPT that uses a higher-order mode of the birdcage coil of the MRI scanner for energy transmission. In contrast to the existing WPT solutions, our approach does not require additional transmitting coils. Compared to energy harvesting, the proposed method allows the supply of significantly more power. We perform numerical simulations demonstrating that one can use the fundamental mode of the birdcage coil to perform a scanning procedure while transmitting the energy to the receiver at a higher-order mode without any interference with the scanning signal or violation of safety constraints, as guaranteed by the mode structure of the birdcage. Also, we evaluate the specific absorption rate along with the energy-transfer efficiency and verify our numerical model by a direct comparison with an experimental setup featuring a birdcage coil of a 1.5-T MRI scanner.

Valley kink states and valley-polarized chiral edge states, whose topologically protected properties have great application potential in high-speed information processing and communication, have recently become important frontiers in topological photonics. However, valley photonic topological insulators mainly support single-type topological states through breaking lattice spatial symmetry. It remains difficult for different types of topological states to coexist in a specific photonic system. In this paper, we propose judiciously designed substrate-integrated topological photonic crystals (but without metal vias) with $C_3$ symmetry that can support valley kink states and valley-polarized chiral edge states in different waveguide channels. Via numerical simulations and measurements, we demonstrate the robust transmission of both valley kink states and valley-polarized chiral edge states through sharp corners and we show high-efficiency coupling between classical guided waves and topological waves. More importantly, we achieve smooth transitions between chiral and trivial edge states, trivial edge states and valley kink states, as well as valley kink states and valley-polarized chiral edge states by bridging different waveguide channels. Our proposed design is beneficial for interfacing with existing functional photonic waveguides or devices and opens up an alternative pathway for advanced planar integrated topological photonic systems with subwavelength thicknesses.

Exploring and controlling chiral spin textures has attracted enormous interest from the perspective of fundamental research and spintronic applications. Here, we report the emergence of spiral spin states, bulk spin-orbit torque (SOT), and the Dzyaloshinskii-Moriya interaction (DMI) induced with the combination of Bloch- and Néel-type in a single $\mathrm{Gd}\text{−}\mathrm{Fe}\text{−}\mathrm{Co}$ layer with a vertical composition gradient. Using polarized neutron reflectometry, the magnetization M is found to rotate with depth through the gradient, due to the nonzero out-of-plane DMI (${\mathbf{\text{D}}}_{\mathrm{OOP}}$). Meanwhile, the deterministic SOT magnetization switching in a single $\mathrm{Gd}\text{−}\mathrm{Fe}\text{−}\mathrm{Co}$ layer without a heavy metal, where the sign of the bulk SOT and in-plane DMI (${\mathbf{\text{D}}}_{\mathrm{IP}}$) is governed by the direction of the composition gradient. The presented results pave the way for flexibly engineering the spin currents and DMI in the ferrimagnetic materials, which have potential applications for future ferrimagnetic SOT devices.

Preserving qubit coherence and maintaining high-fidelity qubit control under complex noise environment is an enduring challenge for scalable quantum computing. Here we demonstrate an addressable fault-tolerant single spin qubit with an average control fidelity of 99.12% via randomized benchmarking on a silicon quantum dot device with an integrated micromagnet. Its dephasing time $T_2^{\ast }$ is $1.025\text{μ}\mathrm{s}$, and can be enlarged to $264\text{μ}\mathrm{s}$ by using the Hahn-echo technique, reflecting strong low-frequency noise in our system. To break through the noise limitation, we introduce geometric quantum computing to obtain high control fidelity by exploiting its noise-resilient feature. However, the control fidelities of the geometric quantum gates are lower than 99%. According to our simulation, the noise-resilient feature of geometric quantum gates is masked by the heating effect. With further optimization to alleviate the heating effect, geometric quantum computing can be a potential approach to reproducibly achieving high-fidelity qubit control in a complex noise environment.

Single-photon detection played an important role in the development of quantum optics. Its implementation in the microwave domain is challenging because the photon energy is five orders of magnitude smaller. In recent years, significant progress has been made in developing single microwave photon detectors (SMPDs) based on superconducting quantum bits or bolometers. In this paper we present a practical SMPD based on the irreversible transfer of an incoming photon to the excited state of a transmon qubit by a four-wave mixing process. This device achieves a detection efficiency $\eta =0.43$ and an operational dark count rate $\alpha =85{\mathrm{s}}^{-1}$, mainly due to the out-of-equilibrium microwave photons in the input line. The corresponding power sensitivity is $\mathcal{S}={10}^{-22}\mathrm{W}/\sqrt{\mathrm{Hz}}$, one order of magnitude lower than the state of the art. The detector operates continuously over hour time-scales with a duty cycle ${\eta }_D=0.84$, and offers frequency tunability of at least 50 MHz around 7 GHz.

In this paper, we study the stability of nuclear magnetic resonance gyroscope (NMRG), which employs Xe nuclear spins to measure inertial rotation rate. The Xe spin polarization is sensed by an in situ Rb magnetometer. The Rb magnetometer works in a parametric oscillation mode (henceforth referred to as the Rb parametric magnetometer, or Rb PM), in which the Larmor frequency of the Rb spins is modulated and the transverse components of Xe nuclear spin polarization are measured. As the measurement output of the Rb PM, the phase of the Xe nuclear spin precession is eventually converted to the Xe nuclear magnetic resonance (NMR) frequencies and the inertial rotation rate. Here we provide a comprehensive study of the NMR phase measured by the Rb PM, and analyze the influence of various control parameters, including the dc magnetic field, the frequency and phase of the modulation field, and the Rb resonance linewidth, on the stability of the NMR phase. Based on these analyses, we propose and implement a self-calibrating method to compensate the NMR phase drift during the Rb-PM measurement. With the self-calibrating Rb PM, we improve the bias instability of the NMRG from $1$ to $0.2\mathrm{deg}/\mathrm{hr}$ for datasets of 8 h, or to $0.02\mathrm{deg}/\mathrm{hr}$ for the best approximately $5000\mathrm{s}$ dataset.

We theoretically study the spin Hall effect in a simple tight-binding model of the stacked kagome Weyl semimetal ${\mathrm{Co}}_3{\mathrm{Sn}}_2{\mathrm{S}}_2$ with ferromagnetic ordering. We focus on the two types of spin Hall current: one flowing in the in-plane direction with respect to the kagome lattice (in-plane spin Hall current), and the other flowing in the stacking direction (out-of-plane spin Hall current). We show that the spin Hall conductivities for those spin currents drastically change depending on the direction of the magnetic moment. In particular, the out-of-plane spin Hall current may induce surface spin accumulations, which are useful for magnetization switching via spin-orbit torque.