It has recently been shown that terahertz sensors can effectively detect the spin resonances of Dirac fermions in graphene. The associated photovoltaic measurement technique allows for the investigation of the intrinsic spin-orbit coupling in graphene, as well as its topological properties, from microwave to terahertz frequencies. In this work, using graphene/${\mathrm{Mo}\mathrm{S}}_2$-based field-effect transistors, we observed a magnetic-resonance photovoltage signal in the gigahertz range that is independent on the gate bias. The dispersion of the associated spin-flip transitions remains intriguingly unaffected by the ${\mathrm{Mo}\mathrm{S}}_2$ layer. In parallel, the spin-related signal consistently appears as a drop in photovoltage, regardless of the signal’s polarity or origin, whether due to plasma-wave rectification or thermoelectric effects. This behavior is interpreted as a decrease in the system’s spin polarization due to spin-dependent recombination or scattering of photocarriers. Understanding the various photovoltaic signals in highly sensitive gigahertz and terahertz sensors paves the way for exploring spin-dependent mechanisms in two-dimensional quantum materials, influenced by proximity effects such as spin-orbit coupling, topology, and magnetism.

Spin-orbit torques (SOTs) generated in SOT-material/ferromagnet structures are classified as dampinglike (DL) and fieldlike (FL) torques for current-driven magnetization switching. It is well-known that both DL- and FL-SOTs originate from the SOT material and DL-SOT dominates the current-driven switching process while FL-SOT has a limited contribution, resulting in an incubation time (several nanoseconds) during collinear magnetization switching with the spin polarization because of the DL attributes. Here, we report that an FL-SOT originates from the ferromagnet, which is different from the origin of DL-SOT, and demonstrate that it dominates the collinear magnetization switching. We show that the FL-SOT and resultant collinear switching can be modulated, by one order of magnitude and a sign reversal, by controlling the ferromagnet. Because of no incubation time and higher charge-to-spin efficiencies in the FL switching, we also show that the switching time can be as low as 200 ps, with an order of magnitude lower critical switching current density compared with DL switching. These results indicate that FL switching may provide a practical solution for magnetic memory in speed-priority cache applications.

Ultrasound imaging is widely used in both engineering and medicine due to its advantages of deep penetration and no ionizing radiation. Focusing techniques can improve image resolution, but conventional methods often suffer from chromatic aberration. This blurring effect arises from the inherent dispersion of focusing lenses and significantly reduces image quality. We present an approach to ultrasound imaging that overcomes this challenge, which utilizes a stretchable and flexible metalens to experimentally achieve dynamic reconfigurable achromatic imaging. By carefully stretching and releasing the metalens, we can focus ultrasound of different frequencies at the same depth. This method features remarkable focusing resolutions of 0.6λ in the radial direction and 2.3λ in the axial direction. Notably, the high-resolution focusing is maintained throughout the entire modulation process, where a 13% deformation of the metalens enables effective compensation for chromatic aberration of ultrasound from 0.81 to 1 MHz. Furthermore, we demonstrate the dynamic achromatic imaging of microstructures, showcasing its ability to capture high-resolution ultrasound images. This flexible reconfigurable metalens for dynamic ultrasound achromatic imaging holds great promise for various applications, including ultrasound sensing, nondestructive testing, and improved medical diagnosis.

Hard-x-ray self-seeded (HXRSS) free-electron lasers (FELs) can provide nearly fully coherent radiation pulses in the hard-x-ray domain with extremely high spectral density, which opens up new possibilities for a wide range of scientific applications such as resonant inelastic x-ray scattering, nuclear resonance scattering, and x-ray Raman spectroscopy. Spectral bandwidth and signal-to-noise ratio (SNR) are two important parameters for seeded FELs. Our theoretical and experimental studies demonstrate that the bandwidth and SNR of HXRSS FELs are closely tied to the electron beam energy profile and current profile, respectively. Nearly Fourier-transform-limited bandwidth can be realized by flattening the energy profile. For beams with asymmetric current profiles, a higher SNR can be obtained by tuning the current peak towards the head. With proper manipulation of the longitudinal phase space of the beam, decreased bandwidth and improved SNR may further enable more demanding applications requiring higher spectral resolution.

We demonstrate a blackbody-radiation thermometer based on optically excited rubidium atoms in a vapor cell. The temperature measurement is fast, with statistical uncertainty as low as 0.1% in one second. We resolve temperature with a precision of 0.04% in the range 308–344 K when averaging for several seconds. Additionally, we describe an extension to this measurement scheme where the device operates as a self-calibrated, or primary, thermometer. We make progress toward realizing a primary thermometer by demonstrating a temperature-dependent self-consistent calibration scheme, with temperature accuracy of the order of 1% limited by the uncertainty in atomic transition dipole matrix elements.

Quantum computing has garnered attention for its potential to solve complex computational problems considerably more rapidly than classical computing. Despite notable advancements in the field, achieving meaningful scalability and noise control in quantum hardware remains challenging. Incoherent errors caused by decoherence restrict the total computation time, often making it very short. While hardware advancements continue to progress, quantum software specialists seek to minimize quantum circuit latency to mitigate dissipation; however, at the pulse level, fast quantum gates often lead to leakage, leaving minimal room for further optimization. Recent advancements have demonstrated the effectiveness of quantum control techniques in generating quantum gates that are robust to coherent error sources. Nevertheless, these techniques come with a trade-off—extended gate durations. In this paper, we introduce an alternative approach to pulse scheduling that enables the use of both fast and robust quantum gates within the same quantum circuit. The time-optimization framework models the quantum circuit as a dependency graph, implements the fastest quantum gates on the critical path, and uses idle periods outside the critical path to optimally implement longer, more robust gates from the gate set, without increasing latency. Experiments conducted on IBMQ Brisbane show that this approach improves the absolute success probability of quantum circuit execution by more than 25%, with performance gains scaling as the number of qubits increases.

Compared to traditional bulk metal-oxide-based resistive devices, atomristor devices based on two-dimensional layered metal oxides offer higher precision in adjusting electrical properties and better characteristics for miniaturization. Among metal oxides, ${\mathrm{Hf}\mathrm{O}}_2$ is particularly important in the electronics industry due to its high dielectric constant and large band gap. Recently, a monolayer of 1T-${\mathrm{Hf}\mathrm{O}}_2$, a tetragonal-phase variant of ${\mathrm{Hf}\mathrm{O}}_2$ with a honeycomb-like atomic arrangement, has been discovered. By combining the electrical and structural advantages of 1T-${\mathrm{Hf}\mathrm{O}}_2$, in this study, we investigate the resistance-switching mechanisms of monolayer 1T-${\mathrm{Hf}\mathrm{O}}_2$ atomristors using a metal-insulator-metal configuration with various metal electrodes. Our findings demonstrate that the electron injection efficiency in the 1T-${\mathrm{Hf}\mathrm{O}}_2$ atomristor is closely related to the tunneling barrier and Schottky barrier between the electrode and the dielectric layer. The resistance-switching behavior observed in the $\mathrm{Au}$/${\mathrm{Hf}\mathrm{O}}_2$/$\mathrm{Au}$ device can be attributed to the adsorption of $\mathrm{Au}$ atoms onto oxygen-vacancy defects and their dissociation, which triggers changes in the interfacial barriers. Our calculations show that the ratio of high resistance to low resistance is nearly 2 orders of magnitude. Furthermore, we find that the performance of the 1T-${\mathrm{Hf}\mathrm{O}}_2$ atomristor can be enhanced by introducing $\mathrm{Al}$ and $\mathrm{Ta}$ electrodes, which result in high on-off ratios, ranging from ${10}^6$ to ${10}^{10}$. These findings provide a more detailed understanding of the resistive switching properties of 1T-${\mathrm{Hf}\mathrm{O}}_2$ atomristors.

In this paper, a method for elastic Willis metamaterials that can retrieve effective parameters even when there is mode coupling is proposed. While recent progress has enlarged the research scope of acoustic and elastic metamaterials to Willis metamaterials, in which stresses and velocities have unique couplings, research on elastic Willis metamaterials has been relatively rare due to its complicated physics. Elastic metamaterials, especially, have more parameters due to the existence of the shear wave mode and the mode coupling between longitudinal and shear wave modes. If elastic Willis metamaterials have mode coupling, the governing equations become too complicated to be analyzed with the existing parameter retrieval method. Here, we propose a method that avoids the complicated equations and effectively retrieves the parameters. Our procedure is based on a transfer matrix decomposition involving eigenvalues and eigenvectors. As a validation, both a comparison to an ideal mass-spring system and the application to continuum elastic Willis metamaterials are performed. With the proposed method, we believe that new research areas based on elastic Willis metamaterials could be possible.

Quantum entanglement detection and characterization are crucial for various quantum information processes. Most existing methods for entanglement detection rely heavily on a complete description of the quantum state, which requires numerous measurements and complex setups. This makes these theoretically sound approaches costly and impractical, as the system size increases. In this work, we propose a multiview neural-network model to generate representations suitable for entanglement structure detection. The number of required quantum measurements shows a significant reduction compared to conventional quantum state tomography approaches as the qubit number increases. This remarkable reduction in resource costs makes it possible to detect specific entanglement structures in large-scale systems. Numerical simulations show that our method achieves over 95% detection accuracy for up to 19 qubit systems. By enabling a universal, flexible, and resource-efficient analysis of entanglement structures, our approach enhances the capability of utilizing quantum states across a wide range of applications.

We present a fault-tolerant universal quantum computing architecture based on a code concatenation of biased-noise qubits and the parity architecture. The parity architecture can be understood as a low-density parity-check code tailored specifically to obtain any desired logical connectivity from nearest-neighbor physical interactions. The code layout can be dynamically adjusted to algorithmic requirements on the fly. This allows for implementations with any desired code distance with a universal set of fault-tolerant gates. In addition to the previously explored toolsets for concatenated cat codes, our approach features parallelizable interactions between arbitrary sets of qubits by directly addressing the parity qubits in the code. The proposed scheme supports codes with lower physical qubit overhead than the repetition code at the same code distances, while requiring only weight-3 and weight-4 stabilizers and nearest-neighbor connectivity on a two-dimensional square lattice.

Herein, we propose a type of dual-layered piezoelectric acoustic metamaterial (D-PAM) integrating mechanical and electrical components for sound scattering manipulation. The D-PAM is a double-sided structure that comprises two identical piezoelectric acoustic metamaterials (PAMs) fixed at the outer boundaries and a sealed air cavity sandwiched in the middle. In the D-PAM, each layer of the piezoelectric acoustic metamaterial consists of a membrane-type oscillator and a piezoelectric patch connected to a shunt circuit. Since the acoustic impedance of each layer of the piezoelectric acoustic metamaterial can be adjusted by independently regulating the corresponding shunt circuit, the D-PAM is capable of precisely controlling sound reflection, sound transmission, and sound absorption. An analytical scattering model of the D-PAM is developed to reveal the adjustable range and the coupling relationship between the reflection and transmission coefficients. In addition, the influence of piezoelectric shunt circuits on sound scattering is analyzed by combining the scattering model and the electroacoustic model. Finally, experimental validation performed in an acoustic impedance tube confirms the effectiveness of the proposed D-PAM in customizable manipulation of the full sound scattering characteristics. Our work may enable promising applications in noise control, mechanical computation, and acoustic imaging.

Seismic noise in both translational and angular degrees of freedom poses significant challenges to high-precision measurements. To mitigate low-frequency seismic noise coupling, active vibration-isolation platforms have been developed, in which a combination of low-noise and single- or multiple-degree-of-freedom seismometers play a critical role. This paper presents the design and performance evaluation of a four-degree-of-freedom (4D) seismometer based on a single flexure inverted pendulum within a 15-cm cube. This seismometer employs a differential capacitive sensing scheme to measure the motion of a test mass, similar to that used in the Laser Interferometer Space Antenna gravitational-wave detector. Two sensing modes are employed: the 2D and 4D modes. In the 2D mode, translational motions are measured, with an optimal translational noise floor of $2\times {10}^{-10}{\mathrm{m}/\mathrm{s}}^2/\sqrt{\mathrm{Hz}}$ around $1\mathrm{Hz}$. In the 4D mode, a single seismometer can measure both translational and angular motion, whereas two spatially separated $xyz$ seismometers would typically be employed; however, the angular sensitivity is limited by the compactness of the seismometer and the intrinsic stiffness of the flexure, which is left for future optimization.

The generation of electro-optic (EO) combs has recently attracted broad interest in photonics due to their great original characteristics of reconfigurability, high comb power, and recent breakthroughs in bandwidth and conversion efficiency. This work explores the connection between EO-comb generation and the synthetic frequency dimension, presenting a theoretical framework that leverages the underlying dynamics in the synthetic frequency lattice to predict and potentially control comb spectra. Specifically, we study non-Hermitian mechanisms with physical factors such as group velocity dispersion and modulation detuning, as well as concepts involving effective gauge flux and Su-Schrieffer-Heeger lattice in the synthetic frequency dimension; and we explore their influence on the dynamics and spectral characteristics of EO combs. Using the concept of non-Hermitian dynamics in a synthetic frequency lattice, we provide physical insights into key phenomena, such as bandwidth limitations and anomalous non-Hermitian skin effect, that arise in comb generation. Our work offers a complementary perspective that may inspire comb generation applications.

The accurate first-principles description of strongly correlated materials is an important and challenging problem in condensed matter physics. Ab initio downfolding has emerged as a way of deriving compressed many-body Hamiltonians that maintain the essential physics of strongly correlated materials. The solution of these material-specific models is still exponentially difficult to generate on classical computers, but quantum algorithms allow for a significant speed-up in obtaining the ground states of these compressed Hamiltonians. Here, we demonstrate that using quantum algorithms to obtain the properties of downfolded Hamiltonians can indeed yield high-fidelity solutions. By combining ab initio downfolding and variational quantum eigensolvers, we correctly predict the antiferromagnetic state of one-dimensional cuprate ${\mathrm{Ca}}_2{\mathrm{Cu}\mathrm{O}}_3$, the excitonic ground state of monolayer ${\mathrm{W}\mathrm{Te}}_2$, and the charge-ordered state of correlated metal ${\mathrm{Sr}\mathrm{VO}}_3$. Numerical simulations using a classical tensor network implementation of variational quantum eigensolvers allow us to simulate large models with up to 54 qubits and encompassing up to four bands in the correlated subspace, which is indicative of the complexity that our framework can address. Through these methods we demonstrate the potential of classical preoptimization and downfolding techniques for enabling efficient materials simulation using quantum algorithms.

A method for measuring the electrical connectivity between parts of a rectangular superconductor has been developed for weak links making an arbitrary angle with the long side of a sample. The method is based on magneto-optical observation of characteristic lines where the critical current makes discontinuous deviations in the flow direction to adapt to the nonuniform condition created by the presence of the weak link. Assuming the Bean critical state model in the full penetration regime for a sample submitted to a perpendicular magnetic field, the complete flow pattern of screening currents is reconstructed, from which the transparency of the weak link, i.e., the ratio between its critical current and that of the pristine sample, $\tau =J_i/J_c$, is then related to the angle $\theta$ formed by two characteristic discontinuity lines, which, in turn, are intimately associated with the presence of the weak link. The streamline distribution is compared with magneto-optical observations of the flux penetration in $\mathrm{Nb}$ superconducting films, where a weak link was created using focused ion-beam milling. The present work generalizes previous analyses in which the weak link was perpendicular to the long sides of the rectangular sample. Equations and measurements demonstrate that the relationship between the transparency and the angle $\theta$ is not affected by the tilting of the weak link. Noticeably, in order to attain optimum connectivity, the weak link critical current can be less than that of the pristine sample, namely, ${\tau }_{max}=\sin \mathrm{\Phi }$, where $\mathrm{\Phi }$ is the tilt angle of the weak link. This expression generalizes the previous result of ${\tau }_{max}=1$ for $\mathrm{\Phi }={90}^{\circ }$.

Exploration of innovative approaches to achieving energy-efficient and compact device architectures is crucial for the semiconductor industry. One promising direction involves leveraging a combination of Gaussianlike transfer characteristics for superior energy scaling and ultrascaled two-dimensional (2D) field-effect transistors for reduced device footprints. Here, we demonstrate energy-efficient Gaussian transfer characteristics in a fabrication-friendly split-gate field-effect transistor using a single ultrascaled 2D channel material. We present the theoretical foundations of this architecture, showing how carefully controlled gate lengths can generate Gaussian features. Using multiscale quantum simulations, we show that tunneling transport is the fundamental operating mechanism for this phenomenon. This mechanism, supported by channels with large effective masses, allows the device to scale down to a channel length of 5 nm. We demonstrate the tunability of the amplitude, mean, and standard deviation of the Gaussian curve, which is crucial for applications in neuromorphic computing and artificial intelligence. Furthermore, we show that the separation of current levels corresponding to different offset biases enables the implementation of highly energy-efficient and gates using a single transistor. Our study opens promising pathways for developing energy- and area-efficient devices for future logic, neuromorphic, and artificial-intelligence-based applications.

Rubidium two-photon frequency standards are emerging as powerful contenders for compact, durable devices with exceptional stability. To date, the field has focused on single-color excitation; here, we demonstrate the key advantages of a two-color excitation of a two-photon optical frequency standard based on the $5S_{1/2}\to 5D_{5/2}$ transition of rubidium-87 using driving fields at 780 and 776 nm. Using the $5P_{3/2}$ intermediate state to resonantly enhance the transition, we show that frequency stabilities comparable to rubidium single-color two-photon frequency standards can be attained, notably with approximately tenfold lower optical power and tenfold lower rubidium vapor density. Optimization of the detuning from the $5P_{3/2}$ intermediate state and of the optical powers of the driving lasers has a dramatic effect on the frequency stability, achieving the best short-term stability of any two-photon rubidium frequency standard to date: $6\times {10}^{-14}$ at $\tau =1$ s. We demonstrate that this level of performance is compatible with a compact geometry by fully self-referencing the frequency standard using an integrated fiber frequency comb to simultaneously stabilize the 780-nm laser’s detuning from the $5P_{3/2}$ intermediate state, producing a frequency-stable microwave output. A comprehensive noise characterization underpins our observations of this two-color frequency standard, explaining the measured stability and showing that this frequency standard is initially shot-noise limited before becoming limited by light shifts in the long term. This work represents a major advance toward a low size, weight, and power frequency standard based on two-color excitation.