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.

We study injection locking of two different spin wave (SW) modes (a field-localized linearlike interior mode and a self-localized SW bullet soliton) in a single nanoconstriction-based spin Hall nano-oscillator. Mode selection is achieved by varying the oblique magnetic field angle and magnitude. The two modes show dramatically different responses to injection locking, in terms of locking bandwidth and linewidth and output power in the locked state. Extracting the locking range graphically from the experimental data yields apparent thresholds for the required injected power, with the bullet mode showing a larger threshold than the linearlike mode. By instead fitting the full detuning behavior using a model including thermal noise, the apparent threshold vanishes, while the very different locking behavior of the two modes can instead be ascribed to the order of magnitude difference in their mode volumes.

We present a scheme to implement a universal set of quantum gates based on achievable interactions, and the gates can be protected against decoherence through a dynamical-decoupling approach without encoding. By properly designing system evolution, the desired system interactions commute with the elements forming dynamical decoupling pulses. Thus, the effect of decoherence can be eliminated by repeatedly applying the pulses, without noticeably affecting the system evolution governed by the desired system interactions given a small enough time interval between pulses. Moreover, due to the commutation between the elements forming the pulses and the desired system interactions, our scheme is resistant to different types of decoherence, and so not limited to specific decoherence. Our scheme also works well in the case that the desired system interactions cannot be achieved ideally due to imperfect control of system parameters, through the action of dynamical-decoupling pulses.

Robust and high-fidelity control of electron spins in solids is the cornerstone for facilitating applications of solid-state spins in quantum information processing and quantum sensing. However, precise control of spin systems is always challenging due to the presence of various noises originating from the thermal environment and control fields. Here, noise-resilient quantum gates, designed with robust optimal control (ROC) algorithms, are demonstrated experimentally with nitrogen-vacancy centers in diamond to realize tailored robustness against detunings and Rabi errors simultaneously. In the presence of both 10% off-resonance detuning and 10% deviation of a Rabi frequency, we achieve an average single-qubit gate fidelity of up to 99.89%. Our experiments also show that, ROC-based multipulse quantum sensing sequences can suppress spurious responses resulting from finite widths and imperfections of microwave pulses, which provides an efficient strategy for enhancing the performance of existing multipulse quantum sensing sequences.

We report the development of photon-number-resolving superconducting single-photon detector with micron-scale $\mathrm{Nb}\mathrm{N}$ strips. The detector is designed as serial meander-shaped strips with resistors connected in parallel to each strip. We investigate the performance of the detectors comprising of 5–14 strips with the widths in the range $0.3$–$1\text{μ}\mathrm{m}$ and covering an area as large as $70\times 70\text{μ}{\mathrm{m}}^2$ making it feasible for coupling to multimode fibers. We demonstrate resolution of up to six photons and analyze the sources of errors in photon-number resolution.

We build and characterize a dual-species all-optical magnetometer based on a Cs-K hybrid vapor cell with a paraffin coating. Using the amplitude-modulated Bell-Bloom scheme and Faraday-rotation measurement, we show that the spin polarization of Cs and K atoms can be generated and detected independently. The noise floor of the Cs channel is $35\mathrm{fT}/\sqrt{\mathrm{Hz}}$, whereas that of the K channel is $260\mathrm{fT}/\sqrt{\mathrm{Hz}}$, which is affected mainly by the magnetic resonance broadening in the presence of mutual spin-exchange collisions. With use of the proposed device, in situ magnetic field stabilization is realized by use of (i) the K channel to monitor and compensate for the magnetic field noise and (ii) the Cs channel to read out the magnetic field after active stabilization. The low-frequency magnetic field noise can be suppressed by a factor of more than $1000$ in the presence of magnetic field gradients. When applied to magnetic field stabilization, such in situ measurement is achieved more compactly and is more accurate than ex situ measurement that is realized with two spatially separated vapor cells. In addition, the proposed scheme could also be applied in a practical ground-surveying magnetometer based on dual working species.

Despite their proven effectiveness in localizing and steering subwavelength elastic waves, locally resonant elastic topological insulators (TIs) with surface-mounted or embedded resonators are often challenged because of their structural complexity and the difficulty in realizing multiple topological band gaps. Here we present a second-order elastic TI (SETI), made of a perforated metaplate with a series of etched C-shaped slots, to achieve dual-band topological corner states. The etched slots in the metaplate form a type of cantileverlike oscillator, the multimodal bending resonances of which couple with the flexural vibration modes of the metaplate, resulting in multiple locally resonant band gaps. Judiciously configuring these slots in a $C_{4v}$-symmetric lattice enables topologically distinct metastructures and creates a SETI. We numerically and experimentally observe the dual-band corner states in two broad topological band gaps. Our platform for observing the topological effects in a perforated metaplate greatly simplifies the fabrication of metastructures for implementing locally resonant elastic TIs, benefiting applications of TIs at the subwavelength scale such as elastic wave trapping and energy amplification.