Domain-wall nanoelectronics has attracted extensive attention since the discovery of conductive domain walls, where domain-wall $p$-$n$ junctions are indispensable for device applications. Here, we report on the fabrication of a domain-wall $p$-$n$ junction based on $n$-type and $p$-type conductive domain walls in an $x$-cut lithium niobate thin film on an insulator using a lateral-electric-field poling technique. The electron and hole mobilities in the $n$-type and $p$-type domain walls are measured to be 337 and $93{\mathrm{cm}}^2{\mathrm{V}}^{-1}{\mathrm{s}}^{-1}$, respectively, more than 400 times higher than those in the parent bulk crystal. The successful fabrication of a domain-wall $p$-$n$ junction with large electron and hole mobilities in the domain walls makes lithium niobate on an insulator a promising platform for domain-wall nanoelectronics and optoelectronics.

Hybrid magnonic systems host a variety of characteristic phenomena such as the magnetically induced transparency (MIT) and Purcell effect, which are considered useful for future coherent quantum-information processing. In this work, we experimentally demonstrate a tunable MIT effect in the ${\mathrm{Y}}_3{\mathrm{Fe}}_5{\mathrm{O}}_{12}(\mathrm{YIG})/\mathrm{Permalloy}(\mathrm{Py})$ magnon-magnon coupled system via changing the magnetic field orientations. By probing the magneto-optic effects of Py and YIG thin films, we identify clear features of MIT spectra induced by the mode hybridization between the uniform mode of Py and the perpendicular standing spin-wave modes of YIG. By changing the external magnetic field orientations, we observe a tunable coupling strength between the YIG’s spin-wave modes and the Py’s uniform mode, upon the application of an out-of-plane magnetic field. This observation is theoretically interpreted by a geometrical consideration of the Py and YIG magnetization under the oblique magnetic field even at a constant interfacial exchange coupling. Our findings show high promise for investigating tunable coherent phenomena with hybrid magnonic platforms.

Most microwave readout architectures in quantum computing or sensing rely on a semiconductor amplifier at 4 K, typically a high-electron mobility transistor (HEMT). Despite its remarkable noise performance, a conventional HEMT dissipates several milliwatts of power, posing a practical challenge to scale up the number of qubits or sensors addressed in these architectures. As an alternative, we present an amplification chain consisting of a kinetic inductance traveling-wave parametric amplifier (KITWPA) placed at 4 K, followed by a HEMT placed at 70 K, and demonstrate a chain-added noise $T_{\mathrm{\Sigma }}=6.3\pm 0.5$ K between 3.5 and 5.5 GHz. While, in principle, any parametric amplifier can be quantum limited even at 4 K, in practice we find the performance of the KITWPA to be limited by the temperature of its inputs and by an excess of noise $T_{\mathrm{ex}}=1.9$ K. The dissipation of the rf pump of the KITWPA constitutes the main power load at 4 K and is about 1% that of a HEMT. These combined noise and power dissipation values pave the way for the use of the KITWPA as a replacement for semiconductor amplifiers.

We construct an analytical formulation for nonlinear photoelectron emission in a dc-biased metallic nanovacuum gap triggered by a laser field, by exactly solving the one-dimensional time-dependent Schrödinger equation. We theoretically investigate the photoelectron energy spectra and emission current from left- and right-side surfaces of the asymmetric nanojunction with various dc biases, laser fields, and gap distances. The underlying photoemission mechanisms transitioning form multiphoton over-barrier emission to photon-assisted field tunneling, and the spatiotemporal dynamics of electron transport inside the gap are analyzed in detail. Our calculation shows applying a dc field could greatly reduce the interference oscillation in the transmission current in the nanogap, due to the shift of dominant emission away from the multiphoton over-barrier regime. Our results demonstrate that, besides the dc bias, varying the gap spacing could strongly influence the rectification on the photoelectron emission in a dc-biased metal-vacuum-metal gap. Our study provides useful guideline to the design of ultrafast nanogap-based signal rectification devices, such as photoelectron emitters and photodetectors, by choosing an optimal combination of dc bias, gap spacing, and material properties.

Sound propagating inside a room is multiply scattered by the boundaries and other obstacles, forming a complex reverberating sound field (RSF). Such RSFs are not only spatially disordered but also temporally scrambled. Although the spatial control of steady-state RSFs at single frequencies is successfully achieved by extending the idea of wavefront shaping to acoustics, time-coherent polychromatic control of RSFs has remained out of reach. Here, we report spatiotemporal acoustic wavefield shaping by adaptively reshaping acoustic impulse responses at arbitrary positions and different instants in a reverberating room using spatial sound modulators—a reconfigurable and programmable membrane-type acoustic metasurface capable of encoding desirable phase factors over a finite bandwidth. We further analyze the mechanism and performance of spatiotemporal wavefield shaping with a simple numerical model derived from multiple scattering in the time domain. Our results expand the capabilities of RSF control to the temporal domain and demonstrate the possibilities for transient engineering of polychromatic sound in acoustic communication, imaging, and holography.

Thermal convection is one of the three basic mechanisms of heat transfer, which profoundly influences the natural environment, social production, and our daily life. However, the high complexity of the governing equation, which describes the coupling of heat and mass transfer, makes it difficult to manipulate thermal convection at will in both theory and experiment. Here, we consider the heat transfer in Hele-Shaw cells, a widely used model of Stokes flow between two parallel plates with a small gap, and apply the scattering-cancellation technology to construct convective thermal materials with bilayer structures and homogeneous isotropic materials. By tailoring thermal conductivities and viscosities, we demonstrate cloaking devices that can hide obstacles from heat and fluid motion simultaneously, and verify their robustness under various thermal-convection environments by numerical simulations. Our results show that about 80% of the temperature and pressure disturbances in the background caused by obstacles can be eliminated by the cloak. The developed approach can be extended to control other convection-diffusion systems or even other multiphysics processes, and the results pave a promising path for designing various metadevices such as concentrators or sensors.

In a typical quantum annealing protocol, the system starts with a transverse field Hamiltonian that is gradually turned off and replaced by a longitudinal Ising Hamiltonian. The ground state of the Ising Hamiltonian encodes the solution to the computational problem of interest, and the state overlap with this ground state gives the success probability of the annealing protocol. The form of the annealing schedule can have a significant impact on the ground-state overlap at the end of the anneal, so precise control over these annealing schedules can be a powerful tool for increasing success probabilities of annealing protocols. Here we show how superconducting circuits, in particular capacitively shunted flux qubits, can be used to construct quantum annealing systems by providing tools for mapping circuit flux biases to Pauli coefficients. We use this mapping to find customized annealing schedules: appropriate circuit control biases that yield a desired annealing schedule, while accounting for the physical limitations of the circuitry. We then provide examples and proposals that utilize this capability to improve quantum annealing performance.

Quantum sensors based on spin defect ensembles have seen rapid development in recent years, with a wide array of target applications. Historically, these sensors have used optical methods to prepare or read out quantum states. However, these methods are limited to optically polarizable spin defects, and the spin ensemble size is typically limited by the available optical power or acceptable optical heat load. We demonstrate a solid-state sensor employing a nonoptical state preparation technique, which harnesses thermal population imbalances induced by the defects’ zero-field splitting. Readout is performed using the recently demonstrated microwave cavity readout technique, resulting in a sensor architecture that is entirely nonoptical and broadly applicable to all solid-state paramagnetic defects with a zero-field splitting. The implementation in this work uses ${\mathrm{Cr}}^{3+}$ defects in a sapphire (${\mathrm{Al}}_2{\mathrm{O}}_3$) crystal and a simple microwave architecture where the host crystal also serves as the high quality-factor resonator. This approach yields a near-unity filling factor and high single-spin-photon coupling, producing a broadband magnetometer with a minimum sensitivity of $9.7\mathrm{pT}/\sqrt{\mathrm{Hz}}$ near 5 kHz.

Wideband absorption is a popular topic in microwave engineering to protect sensitive devices against broadband sources. However, the Bode-Fano criterion defines the trade-off between bandwidth and efficiency for all passive linear time-invariant systems. In this paper, we propose a broadband absorber beyond the Bode-Fano limit by creating an energy trap using time-modulated switches or diodes. This work starts with an ideal-circuit model to prove the concept, followed by two electromagnetic realizations—a frequency-selective-surface approach for general bandwidth broadening and a low-profile printed-circuit-board design. The prototype of the latter is built and measured, demonstrating a Bode-Fano integral larger than 1. This approach paves the way to many practical ultrawideband-absorber designs.

We demonstrate the two-color cooling and trapping of alkaline-earth atoms in a grating magneto-optical trap (GMOT). The trap is formed by a single incident laser beam together with four secondary beams that are generated via diffraction from a nanostructured wafer. A grating structure for a GMOT operating with strontium atoms is optimized and fabricated. We trap ${10}^6{}^{88}\mathrm{Sr}$ atoms on the ${}^1{S}_0{\to }^1{P}_1$ transition at $461\mathrm{nm}$ and transfer 25% of these atoms to the second cooling stage on the narrower ${}^1{S}_0{\to }^3{P}_1$ intercombination transition at $689\mathrm{nm}$, preparing a sample of $2.5\times {10}^5$ atoms at $5\mu \mathrm{K}$. These results demonstrate the applicability of the GMOT technology in conjunction with two widely differing wavelengths and enable the continued miniaturization of alkaline-earth-based quantum technologies like optical atomic clocks.

Ferroelectric tunnel junctions (FTJs) are very promising candidates for nonvolatile memory devices and a large tunneling electroresistance (TER) ratio is essential for their high performance. This work intends to achieve large TER ratio by interfacial doping in FTJs by taking ${\mathrm{Pt}/\mathrm{Ba}\mathrm{Ti}\mathrm{O}}_3/\mathrm{Pt}$ tunnel junctions as an example. By introducing Na (or $\mathrm{Li}$) substitutions for $\mathrm{Ti}$ atoms at the right interface, the resultant strong Coulomb repulsion from the negatively charged ${\mathrm{Na}\mathrm{O}}_2$ interface pushes the electrons to higher energy in an increasing manner from left to right in the whole ${\mathrm{Ba}\mathrm{Ti}\mathrm{O}}_3$ barrier, which leads to rapidly increasing potential energy profile and partial metallization close to the right interface in the left polarization state. However, in the right polarization state, since the right ferroelectric polarization produces a decreasing potential energy profile from left to right, although the ${\mathrm{Na}\mathrm{O}}_2$ interface also pushes the electrons to much higher energy and the slope of the potential energy profile changes from negative to positive, the final slope of the potential energy profile is much less steeper and the Fermi level is always inside the band gap, leading to a completely insulating state. The substantially different distributions of the electrostatic potential energy profile in the two polarization states lead to great differences in the transport properties. Based on density-functional-theory calculations, a TER ratio up to ${10}^5$% is achieved. The results indicate that a negatively charged interface based on interfacial substitution is a promising method for obtaining a large TER ratio in FTJs, and thus will have implications for the further understanding and design of high-performance FTJs.

We introduce photonic kernel machines, a scheme for ultrafast spectral analysis of noisy radio-frequency signals from single-shot optical intensity measurements. The approach combines the versatility of machine learning and the speed of photonic hardware to reach unprecedented throughput rates. We theoretically describe some of the key underlying principles, and then numerically illustrate the performance achieved in a photonic lattice-based implementation. We apply the technique both to picosecond pulsed radio-frequency signals, on energy-spectral-density estimation and a shape-classification task, and to continuous signals, on a frequency-tracking task. The optical computing scheme presented is resilient to noise while requiring minimal control on the photonic-lattice parameters, making it readily implementable in realistic state-of-the-art photonic platforms.

Topological pumping allows higher-dimensional topological phenomena to be explored in low-dimensional systems using synthetic dimension with time modulation. Extensive studies have been devoted to the one-dimensional pumping lattice with singly modulated parameters, which was shown to exhibit the mechanical-wave analog of the quantum Hall effect. Here, we study the topological pumping in the lattice chain with doubly modulated parameters, and report the theoretical finding of two additional topological phases with the large-gap Chern number, which has not been well disclosed previously in singly modulated mechanical systems. The edge state protected by the large-gap Chern number exhibits the faster edge-to-edge energy transportation under the slow temporal variation of modulating parameters. The adiabatic approximation of doubly modulated pumping is also analyzed, and it would not be violated in the process of the fast-pumping evolution of edge states. The finding is expected to be used for fast and robust energy transportation of mechanical waves.

In this work, we report on the bias-tunable and highly sensitive irradiance-dependent focus-induced photoresponse (FIP) in amorphous silicon p-i-n diodes for enhanced three-dimensional imaging applications. We identify a nonlinear current breakdown at irradiance down to at least $0.6\mu \mathrm{W}/\mathrm{m}{\mathrm{m}}^2$ due to defect-induced electrical field screening, surpassing state-of-the-art device sensitivities by at least a factor of 16 in the visible range. We further demonstrate the tunability of FIP by systematic device and field engineering to enable both precise and long-range high-resolution distance measurements in just one device architecture. We evaluate distance measurements up to at least 15 m and achieve a depth resolution of 2.1 mm at 3.3 m. The reproducible low-temperature (300 °C or lower) plasma-enhanced chemical vapor-deposition technology enables systematic tailoring of the FIP for three-dimensional imaging applications and allows for back-end sensor integration on top of silicon or flexible electronics with fill factors up to 100%.

Coherent gate errors are a concern in many proposed quantum-computing architectures. Here, we show that certain coherent errors can be reduced by a local optimization that chooses between two forms of the same Hermitian and unitary quantum gate. We refer to this method as hidden inverses, and it relies on constructing the same gate from either one sequence of physical operations or the inverted sequence of inverted operations. We use parity-controlled $Z$ rotations as our model circuit and numerically show the utility of hidden inverses as a function of circuit width $n$. We experimentally demonstrate the effectiveness for $n=2$ and $n=4$ qubits in a trapped-ion quantum computer. We numerically compare the method to other gate-level compilations for reducing coherent errors.

The rapidly developing quantum technologies and thermodynamics have put forward a requirement to precisely control and measure the temperature of microscopic matter at the quantum level. Many quantum thermometry schemes have been proposed. However, precisely measuring low temperature is still challenging because the obtained sensing errors generally tend to diverge with decreasing temperature. Using a continuous-variable system as a thermometer, we propose non-Markovian quantum thermometry to measure the temperature of a quantum reservoir. A mechanism to make the sensing error $\delta T$ scale with the temperature $T$ as the Landau bound $\delta T\simeq T$ in the full-temperature regime is discovered. Our analysis reveals that it is the quantum criticality of the total thermometer-reservoir system that causes this enhanced sensitivity. Efficiently avoiding the error-divergence problem, our result gives an efficient way to precisely measure the low temperature of quantum systems.

Ultrafast vortex motion has recently become a subject of extensive investigations, triggered by the fundamental question regarding the ultimate speed limits for magnetic flux quanta and enhancements of single-photon detectors. In this regard, the current-biased quench of a dynamic flux-flow regime—flux-flow instability (FFI)—has turned into a widely used method for the extraction of information about the relaxation of quasiparticles (unpaired electrons) in a superconductor. However, the large relaxation times ${\tau }_{ϵ}$ deduced from FFI for many superconductors are often inconsistent with the fast relaxation processes implied by their single-photon counting capability. Here, we investigate FFI in $15$-nm-thick $182$-$\mu \mathrm{m}$-wide MoSi strips with rough and smooth edges produced by laser etching and milling by a focused ion beam. For the strip with smooth edges we deduce, from current-voltage ($I$-$V$) curve measurements, a factor of 3 larger critical currents $I_c$, a factor of 20 higher maximal vortex velocities of 20 km/s, and a factor of 20 shorter ${\tau }_{ϵ}$. We argue that for the deduction of the intrinsic ${\tau }_{ϵ}$ of the material from the $I$-$V$ curves, utmost care should be taken regarding the edge and sample quality and such a deduction is justified only if the field dependence of $I_c$ points to the dominating edge pinning of vortices.

Deterministic sources of high-fidelity entangled qubit pairs encoded in the dual-rail photonic basis, i.e., presence of a single photon in one of two orthogonal modes, are a key enabling technology of many applications of quantum information processing, including high-rate, high-fidelity quantum communications over long distances. The most popular and mature sources of such photonic entanglement, e.g., those that leverage spontaneous parametric down-conversion (SPDC) or spontaneous four-wave mixing, generate an entangled (so-called continuous-variable) quantum state that contains contributions from high-order photon terms that lie outside the span of the dual-rail basis, which is detrimental to most applications. One often uses low pump power to mitigate the effects of those high-order terms. However, that reduces the pair generation rate, and the source becomes inherently probabilistic. We investigate a cascaded source that performs a linear-optical entanglement swap between two SPDC sources, to generate a heralded photonic entangled state that has a higher fidelity (to the ideal Bell state) compared to a free-running SPDC source. Furthermore, with the Bell swap providing a heralding trigger, we show how to build a multiplexed source, which despite reasonable switching losses and detector loss and noise, yields a fidelity versus success probability trade-off of a high-efficiency source of high-fidelity dual-rail photonic entanglement. We find, however, that there is a threshold of $1.5$ dB of loss per switch, beyond which multiplexing hurts the fidelity versus success probability trade-off.

Acoustic waves and strain pulses created by a piezoelectric or optical transducer represent an attractive tool for the generation of spin dynamics in magnetoelastic materials and heterostructures. The advantage of acoustic excitation consists in much lower power consumption compared with the classical excitation by a microwave magnetic field. The magnetization precession driven by elastic waves can be further used for spin pumping into normal metals and semiconductors. Here we describe theoretically the magnetization dynamics and spin flow induced by plane acoustic waves traversing trilayer structures involving two ferromagnetic ($F$) films separated by a layer of normal metal ($N$). The problem is solved by advanced micromagnetoelastic simulations, which allow for the two-way coupling between spins and strains in the $F$ films and their long-range dynamic interaction resulting from the spin flow across the $N$ spacer. To derive the expression for such an interaction, we solve the spin-diffusion equation in $N$ with the account of spin pumping created by dynamically strained $F$ films and spin backflow through the interfaces. Performing numerical simulations for the ${\mathrm{Fe}}_{81}{\mathrm{Ga}}_{19}{/\mathrm{Au}/\mathrm{Fe}}_{81}{\mathrm{Ga}}_{19}$ trilayers excited by longitudinal and transverse elastic waves, we quantify the inhomogeneous magnetization precession in the galfenol films and determine the spatial distributions of the oscillating spin current and spin accumulation in the Au spacers of different thickness. These distributions are further used to calculate the mean spin current and total spin accumulation in the spacer. It is found that both ac and dc parts of these quantities exhibit strong variations with the spacer thickness. Remarkably, the nonzero components of the total spin accumulation and mean spin current mostly have pronounced maxima at $\mathrm{Au}$ thicknesses amounting to about 0.25 and 0.75 of the wavelength ${\lambda }_N$ of the elastic wave in $\mathrm{Au}$, which is explained by an analytical model of strain distribution in the trilayer. Our theoretical results, which shed light on the acoustically excited generation of spin imbalance in magnetoelastic spin-valve structures, could be useful for the development of energy-efficient spin injectors into normal conductors with weak spin-flip scattering.

The mutual interaction between a chiral ferromagnetic disk with confined skyrmionic structures and a superconducting disk is studied. The interaction is accounted for by solving simultaneously the Brown and London equations. We find that for a superconductor under an applied uniform field, the stray field of the shielding currents can trigger switching between different skyrmionic states in the ferromagnet that is not possible without the superconductor. We discuss the effect of the different parameters on the results and some possible applications such as multivalued logic, storage, and skyrmionic metamaterials.