Physical quantum systems are commonly composed of more than two levels and offer the capacity to encode information in higher-dimensional spaces beyond the qubit, starting with the three-level qutrit. Here, we encode neutral-atom qutrits in an ensemble of ultracold ${}^{87}\mathrm{Rb}$ and demonstrate arbitrary single-qutrit SU(3) gates. We generate a full set of gates using only two resonant microwave tones, including synthesizing a gate that effects a direct coupling between the two disconnected levels in the three-level $\mathrm{\Lambda }$-scheme. Using two different gate sets, we implement and characterize the Walsh-Hadamard Fourier transform, and find similar final-state fidelity and purity from both approaches. This work establishes the ultracold neutral-atom qutrit as a promising platform for qutrit-based quantum information processing, extensions to $d$-dimensional qudits, and explorations in multilevel quantum state manipulations with nontrivial geometric phases.

Compensated ferrimagnets (FIMs) made of rare-earth transition-metal compounds have stimulated increasing interest for enabling fast spin dynamics. Taking $\mathrm{Fe}$-$\mathrm{Tb}$ compounds as an example, substantial efforts have been made on the study of compensated magnetism and its potential spintronic applications. Current-induced spin-orbit torque (SOT) switching and its evolution with compensated ferrimagnetism in these compounds, however, remain to be systematically explored, which motivates the present study. By combining magnetometry and anomalous Hall effect measurements, a compositional magnetization compensation point ($x_c$ = 0.25) is determined for ${\mathrm{Fe}}_{1-x}{\mathrm{Tb}}_x$ films of a fixed thickness of 6.5 nm. The antiferromagnetic coupling between $\mathrm{Fe}$ and $\mathrm{Tb}$ sublattices is directly revealed by conducting element-specific x-ray magnetic circular dichroism measurements. The evolution of SOT switching as a function of $\mathrm{Tb}$ concentration (x) in $\mathrm{Pt}/{\mathrm{Fe}}_{1-x}{\mathrm{Tb}}_x/\mathrm{Ta}$ multilayers is subsequently investigated. An enhanced SOT efficiency (approximately 3 times) is obtained at $x_c$ = 0.25. By conducting an endurance test, reliable SOT switching is revealed for over ${10}^4$ cycles. Our work suggests that compensated FIMs of composition ${\mathrm{Fe}}_{1-x}{\mathrm{Tb}}_x$ could be implemented for realizing efficient and stable spin-orbitronic performances.

The nonlinear coupling between on-chip confined optical modes and free-space continuum modes is investigated. The radiation of second-harmonic wave due to the pump fields in integrated lithium niobate microcavities is experimentally observed. The mechanism of nonlinear optical radiation (NOR) is further verified by demonstrating the reversal process of NOR, i.e., the difference frequency generation between a free-space input and an on-chip pump field. The revealed mechanism of NOR is universal for all dielectric photonic integrated devices, which indicates unavoidable extra energy leakage channels of optical micro- and nanostructures, and also enables an alternative approach for spatial engineering of optical fields and light sources. For example, benefited from the phase-matching-free nature of NOR, an integrated atomic gas sensor for the absorption spectroscopy of Rb atoms is built.

Photons experience mirror asymmetry of macroscopic chiral media, as in circular dichroism and polarization rotation, since left- and right-handed circular polarizations differently couple with matter handedness. Conversely, free relativistic electrons with vanishing orbital angular momentum have no handedness so the question arises whether they can sense chirality of geometrically symmetric macroscopic samples. In this paper, we show that matter chirality breaks mirror symmetry of the scattered electrons’ quantum decoherence, even when the incident electron wave function and the sample shape have a common reflection symmetry plane. This is physically possible since the wave-function transverse smearing triggers electron sensitivity to the spatial asymmetry of the electromagnetic interaction with the sample, as results from our nonperturbative analysis of the scattered electron reduced density matrix, in the framework of macroscopic quantum electrodynamics. Furthermore, we prove that mirror asymmetry also shows up in the distribution of the electron lateral momentum, orthogonal to the geometric symmetry plane, whose nonvanishing mean value reveals that the electron experiences a lateral mechanical interaction entirely produced by matter chirality.

A half-mirror that divides a spin-polarized electron into two parallel copropagating spin-resolved quantum Hall edge channels one half each is presented in this study. The partition process is coherent, as confirmed by observing the Aharonov-Bohm oscillation at high visibility of up to 85% in a Mach-Zehnder interferometer, which comprises two such half-mirrors. The coherence length of the interferometer exceeds $200\text{μ}\mathrm{m}$, which reflects the robust nature of the copropagating channels against the decoherence caused by the coupling to the environment. In addition, the device characteristics are highly stable, making the device promising in the application of quantum information processing. The beam-splitting process is theoretically modeled, and the numerical simulation successfully reproduces the experimental observation. The partition of the electron accompanied by the spin rotation is explained by the angular momentum transfer from the orbital to the spin via spin-orbit interactions.

Wavefronts modulated by a discrete-phase-sampling lens, such as a spatial light modulator or a digital micromirror device, can be brought into focus after propagating through a random medium. Such techniques are a cornerstone for wave manipulations in multiple scattering environments. In this work, we examine prevailing focusing protocols, including matched filtering and inverse filtering, from the perspective of focus quality, which is defined as the contrast between the energy delivered to the focal peak and the total transmitted energy. Our results show that conventional protocols have limitations in achieving the best focus quality. Based on these analyses, we present an improved wavefront-shaping protocol that directly prioritizes focus quality. The influence of phase sampling resolutions is also analyzed in conjunction with these focusing protocols. Our results can merit the future design and implementation of intelligent lenses, which may potentially benefit various disciplines such as energy delivery, imaging, and communication.

The unique material property of silicon carbide ($\mathrm{Si}\mathrm{C}$) and the recent demonstration of low-loss $\mathrm{Si}\mathrm{C}$-on-insulator integrated photonics platform have attracted considerable research interests for chip-scale photonic and quantum applications. Despite the impressive progresses made in $\mathrm{Si}\mathrm{C}$ photonics, some of its beneficial photonic properties are yet to be fully explored. Here, we carry out a thorough investigation of the Kerr nonlinearity among $4H$-$\mathrm{Si}\mathrm{C}$ wafers from several major wafer manufacturers, and reveal that their Kerr nonlinear refractive index can be significantly different. By eliminating various measurement uncertainties in the four-wave mixing experiment, the best Kerr nonlinear refractive index of $4H$-$\mathrm{Si}\mathrm{C}$ wafers is estimated to be approximately 4 times, instead of the prior estimate of 2 to 3 times, of that of stoichiometric silicon nitride in the telecommunication band. In addition, experimental evidence is developed that the Kerr nonlinearity in $4H$-$\mathrm{Si}\mathrm{C}$ wafers can be stronger along the $c$ axis than that in the orthogonal direction. Our examination of the Kerr nonlinear refractive index also compels a useful correction to the existing model in high-index-contrast waveguides; otherwise, considerable errors can be introduced.

Ideal full Poincaré (FP) beams contain all possible polarization states on the surface of the Poincaré sphere and are readily created by linear optical techniques and, more recently, by nonlinear optical processes. An inherent limitation in the latter is the inability to achieve all polarization states, coined coverage, due to modal size, polarization, and modal weighting changes during the nonlinear conversion of the constituent modes. Here, we demonstrate a simple technique to control the coverage of FP beams, using second-harmonic generation as an example, from fully scalar (no coverage) to fully vectorial (full coverage). Our method for determining the coverage confirms the vectorial characteristics of the generated beams and reveals a balancing act between mode order, modal nonlinear efficiency, and initial relative modal weights, all in close agreement with that theoretically predicted. Our findings will hopefully be of value to the communities interested in nonlinear structured light, particularly for vectorial nonlinear modal creators and detectors and control of quantum hybrid entangled states.

Structural and electrical properties of a- and a + c-type threading dislocations in metal-organic vapor-phase epitaxy-grown $\mathrm{Si}$-doped $\mathrm{Ga}\mathrm{N}$ (0001) are determined by combining multiple scanning probe microscopy approaches. The analysis examines the space-charge region (SCR) formed around dislocation cores and clarifies the role it plays in influencing the local recombination, the surface-potential characteristic, and even the conductivity. Direct evidence of the SCR is obtained from a differential capacitance (dC/dV) measurement at dislocation sites on the (0001) surface. Experimental dC/dV (V) measurement results supported by technology computer-aided design calculations of capacitance, accounting for the theoretical deep levels related to different atom-core structures of the identified dislocations, reveal quantitative differences in their respective trap densities. This study is extended to p-n $\mathrm{Ga}\mathrm{N}$ vertical diodes to analyze the doping distribution across active layers. Through a correlated cross-section investigation combining electron-channeling contrast-imaging microscopy, the underlying dislocations within the depth limited by the screening of their SCRs are found to severely impact the homogeneity of the cross-section dC/dV contrast in the low-doped n-type drift layer of the diodes. This raises serious concerns regarding any quantification efforts by differential capacitance measurements in $\mathrm{Ga}\mathrm{N}$ on $\mathrm{Si}$, where the dislocation density is in the order of ${10}^9{\mathrm{cm}}^{-2}$.

A solid-state material with ultralow magnetic susceptibility $\chi$ is the key material candidate in aeronautical devices and special targeted drugs. In this work, we design a series of two-component alloy samples ${\mathrm{Au}}_{1-x}{\mathrm{Pt}}_x$, and study their magnetic structures and susceptibilities by using the first-principles calculations within a spin-polarized relativistic Korringa-Kohn-Rostoker coherent potential approximation. Our theoretical results demonstrate that by controlling the ratio parameter $x$, ultralow magnetic susceptibilities ($\chi <{10}^{-6}{\mathrm{cm}}^3/\mathrm{mol}$) occur in $\mathrm{Au}\mathrm{Pt}$ alloys around the sample ${\mathrm{Au}}_{0.75}{\mathrm{Pt}}_{0.25}$. Following the theoretical calculations, several realistic $\mathrm{Au}\mathrm{Pt}$ alloy samples with ultralow magnetic susceptibilities are fabricated successfully in experiments, and the experimental measurements on magnetic susceptibilities are well consistent with our theoretical predications. This work not only provides us changes to study physical properties of the materials with ultralow magnetic susceptibility, but also constructs unique materials towards special device applications in TianQin project and others.

Precise manipulation of the direction and redirection of vibrational wave energy is a key demand in wave physics and engineering. We consider the paradigm of a finite framelike structure and the requirement to channel energy away from critical regions, leaving them vibration free, and redirect energy along edges toward energy concentrators for damping or energy harvesting. We design an exemplar frame metamaterial, combining two distinct areas of wave physics. First, we consider topological edge states, taking an unconventional tetrachiral lattice. We control these highly localized protected edge states leveraging a hierarchy of scales through the addition of microresonators that impose tunable symmetry breaking and reconfigurable mass. This allows us to achieve precise positional control in the macroscale frame lattice, thereby opening up opportunities for robust signal transport and vibration control. Experiments, theory, and simulation are all utilized to provide a comprehensive analysis and interpretation of the physics.

Atom-based radio-frequency (rf) electromagnetic field sensing using atomic Rydberg states is a promising technique that has recently attracted significant interest. Its unique advantages, such as extraordinary bandwidth, self-calibration, and all-dielectric sensors, are a tangible improvement over antenna-based methods in applications such as test and measurement and development of broad-bandwidth receivers. Here, we demonstrate how an optical-frequency comb can be used to acquire data in the Autler-Townes regime of Rydberg-atom-based electrometry in a massively parallel fashion, eliminating the need for laser scanning. Two-photon electromagnetically induced transparency readout and preparation of cesium is used for the demonstration. A flat quasicontinuous optical comb is generated with the probe laser at 852 nm using an electro-optic modulator and arbitrary waveform generator. A single-frequency coupling laser at 509 nm is tuned to the Rydberg launch state. An enhanced transmission signal is obtained using self-heterodyne spectroscopy, where the comb signal is beat against a local oscillator derived from the single-frequency probe laser on a fast photodiode. The transmission of each probe-laser comb tooth is observed. We resolve electromagnetically induced transparency peaks with line widths below 5 MHz, with and without laser locking. Radio-frequency electromagnetic fields as low as $66\text{μ}{\mathrm{Vcm}}^{-1}$ are detected, with sensitivities of $2.3\text{μ}{\mathrm{Vcm}}^{-1}{\mathrm{Hz}}^{-1/2}$. The method offers a significant advantage for reading out electromagnetically induced transparency and Autler-Townes splitting, as neither laser needs to be scanned and slow frequency drifts can be tolerated in some applications. The method enables the detection of the amplitude of a pulsed rf electromagnetic field when the incoming pulse Autler-Townes splits the electromagnetically induced transparency peak.

In recent years, true random number generators (TRNGs) based on magnetic tunnel junctions (MTJs) have become increasingly attractive. This is because MTJ-based TRNGs offer some advantages over traditional CMOS-based TRNGs, such as smaller area and simpler structure. However, there has been no work thus far that has quantified the quality of the raw output of a MTJ-based TRNG and performed suitable randomness extraction to produce provably secure random bits, unlike the case for CMOS-based TRNGs. In the work presented here, we implement a MTJ-based TRNG and characterize the entropy of the raw output. Using this information, we perform postprocessing to extract a set of random bits that are provably secure.

The singlet states of the negatively charged nitrogen-vacancy centers in diamond play a key role in its optical spin control and readout. In this work, the hitherto unknown ionization energy of the singlet is measured experimentally and found to be in the range 1.91–2.25 eV. This is obtained by analyzing photoluminescence measurements incorporating spin control and nitrogen-vacancy charge state differentiation, along with simulations based on the nitrogen-vacancy’s master equation. This work establishes a protocol for a more accurate estimate of this ionization energy, which can possibly lead to improved readout methods.

Two-dimensional (2D) materials are attracting an increasing interest in the domain of energy conversion due to their thermoelectric and thermal properties foreseeing increased efficiency. Actual application as thermoelectric materials relies on the ability to fully explore their physical properties once included in real devices, which is a complex task due to the difficulty in managing thermal transport at the nanoscale. Furthermore, 2D materials are extremely sensitive to the environment and device-fabrication contaminants, that can alter their properties with respect to their isolated form. We demonstrate here a complete thermoelectric characterization of devices based on thin flakes ($5$–$6\mathrm{nm}$) of tungsten diselenide (${\mathrm{WSe}}_2$) and multilayer graphene (MLGN) deposited on hexagonal boron nitride ($h$-BN), by coupling electric and thermoelectric measurements with modulated thermoreflectance (MTR). Flake-by-flake MTR scans allow the separate extraction of the anisotropic thermal conductivities of each device’s layer. We find out values for the in-plane $k_{\parallel }$ and out-of-plane $k_{\perp }$ thermal conductivities of $k_{\mathrm{WS}{\mathrm{e}}_2\parallel }\sim 24{\text{W m}}^{-1}{\mathrm{K}}^{-1}$, $k_{\mathrm{WS}{\mathrm{e}}_2\perp }\sim 0.13{\text{W m}}^{-1}{\mathrm{K}}^{-1}$, $k_{\mathrm{MLGN}\parallel }\sim 1050{\text{W m}}^{-1}{\mathrm{K}}^{-1}$, $k_{\mathrm{MLGN}\perp }\sim 1{\text{W m}}^{-1}{\mathrm{K}}^{-1}$, $k_{h\text{-BN}\parallel }\sim 250-284{\text{W m}}^{-1}{\mathrm{K}}^{-1}$, and $k_{h\text{-BN}\perp }\sim 1.9-5.5{\text{W m}}^{-1}{\mathrm{K}}^{-1}$, which are generally in agreement with the literature. Our work unveils the possibility to perform selective nondestructive measurements of the thermal conductivity of thin flakes of 2D materials embedded in a device configuration, encouraging the use of MTR coupled to electric and thermoelectric characterization to evaluate the overall device thermoelectric performances.

Unlike optical imaging methods, where the Fourier representation of the object is created by wave diffraction, magnetic resonance imaging (MRI) scans the Fourier domain by spatially modulating the nuclear magnetization with magnetic field gradients. Therefore, the resolution of MRI is limited by signal strength rather than the wavelength of the diffracted wave. However, in several important applications, such as the imaging of water diffusion or blood oxygenation in the human brain, MRI must collect all the Fourier data during a single evolution of the signal to avoid artifacts caused by random fluctuations of its phase. The Fourier domain coverage of the “single-shot” MRI strategy is limited by the lifetime of the signal and results in a resolution limit analogous to the diffraction limit in optical microscopy. Consequently, recently developed optical superresolution methods may appear helpful. This work employs the recently developed method of phaseless encoding, which implements the idea of linear structured illumination microscopy (SIM) to enable multishot data acquisition and triple the MRI resolution regardless of the presence of spin phase fluctuations, and develops it further to enhance the resolution in two dimensions and to push its gain above a factor of 3 using “illumination patterns” with multiple harmonics, a concept borrowed from saturated SIM (SSIM) methodology. Results obtained with enhanced phaseless encoding on a 3-Tesla clinical scanner in phantoms and human brain are presented. This method will be beneficial when conventional multishot MRI is impeded by signal instability due to motion or other factors.

LDOS is a fundamental spectral property that plays a central role in various physical phenomena, such as wave-matter interactions and spontaneous emissions. The role of LDOS in acoustics was uncovered only in recent years and the measurement of acoustic LDOS has not yet been achieved. Here, we report on the direct measurement of the LDOS in acoustic systems. The acoustic LDOS is quantified here through the measurement of the volume flow rate and the acoustic pressure with a local excitation-probe configuration. Based on this method, we detect the LDOS in the one-dimensional acoustic Su-Schrieffer-Heeger model and observe the fractional topological charge of the system. Our work unveils the role of the LDOS in acoustic phenomena and paves the way toward characterizing and tailoring the LDOS in acoustic systems, which holds promise for applications in acoustic emission control, energy localization, and wave-matter interaction.

In most systems, thermal diffusion is intrinsically slow with respect to mechanical relaxation. We devise here a generic approach to accelerate the relaxation of the temperature field of a one-dimensional object, in order to beat the mechanical time scales. This approach is applied to a micrometer-sized silicon cantilever, locally heated by a laser beam. A tailored driving protocol for the laser power is derived to quickly reach the thermal stationary state. The model is implemented experimentally yielding a significant acceleration of the thermal relaxation, up to a factor 30. An excellent agreement with the theoretical predictions is reported. This strategy allows a thermal steady state to be reached significantly faster than the natural mechanical relaxation.

Quantum protocols based on adiabatic evolution are remarkably robust against imperfections of control pulses and system uncertainties. While adiabatic protocols have been successfully implemented for quantum operations such as quantum state transfer and single-qubit gates, their use for geometric two-qubit gates remains a challenge. In this paper, we propose a general scheme to realize robust geometric two-qubit gates in multilevel qubit systems where the interaction between the qubits is mediated by an auxiliary system (such as a bus or coupler). While our scheme utilizes stimulated Raman adiabatic passage (STIRAP), it is substantially simpler than STIRAP-based gates that have been proposed for atomic platforms, requiring fewer control tones and ancillary states, as well as utilizing only a generic dispersive interaction. We also show how our gate can be accelerated using a shortcuts-to-adiabaticity approach, allowing one to achieve a gate that is both fast and relatively robust. We present a comprehensive theoretical analysis of the performance of our two-qubit gate in parametrically modulated superconducting circuits comprising two fluxonium qubits coupled to an auxiliary system.