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.

Although n-type transparent conducting oxides (TCOs) with visible-light transparency and electric conductivity have been used in industry for decades, their p-type counterparts have not been commercialized. To search for promising p-type TCOs, computational screening was applied by several research groups in the last decade. However, screening of a wide material space is mainly based on the approximated physical quantities, such as underestimated band gaps, and band-alignment techniques. In particular, it is unlikely that band alignments can predict the dopability of a wide range of insulators because they do not include information about the chemical potentials of the constituent elements. In this study, we use optical absorption spectra calculated with dielectric dependent hybrid functionals and the formation energies of oxygen vacancies as screening parameters. Oxygen vacancies are known to act as hole killers when seeking p-type TCOs, and indeed, only 156 out of the 845 oxides are found to have benign oxygen vacancies for p-type doping. As a result, we identify six potential p-type TCOs from 845 oxides: ${\mathrm{Na}}_3{\mathrm{Ag}\mathrm{O}}_2$, ${\mathrm{Rb}}_2{\mathrm{Pb}}_2{\mathrm{O}}_3$, ${\mathrm{Cs}}_2{\mathrm{Pb}}_2{\mathrm{O}}_3$, $\mathrm{Cs}\mathrm{Cu}\mathrm{O}$, ${\mathrm{K}}_2{\mathrm{Pb}}_2{\mathrm{O}}_3$, and ${\mathrm{B}}_6\mathrm{O}$. ${\mathrm{Na}}_3{\mathrm{Ag}\mathrm{O}}_2$, ${\mathrm{Rb}}_2{\mathrm{Pb}}_2{\mathrm{O}}_3$, and ${\mathrm{Cs}}_2{\mathrm{Pb}}_2{\mathrm{O}}_3$ are identified as potential p-type TCOs, while $\mathrm{Cs}\mathrm{Cu}\mathrm{O}$, ${\mathrm{K}}_2{\mathrm{Pb}}_2{\mathrm{O}}_3$, and ${\mathrm{B}}_6\mathrm{O}$ were previously proposed. By analyzing the electronic structures and point-defect properties of ${\mathrm{Na}}_3{\mathrm{Ag}\mathrm{O}}_2$, $\mathrm{Cs}\mathrm{Cu}\mathrm{O}$, and ${\mathrm{K}}_2{\mathrm{Pb}}_2{\mathrm{O}}_3$ in detail, we find that they show p-type conductivity, even without external doping, which validates the use of the formation energies of oxygen vacancies as descriptors of the p-type dopability of oxides.

In this study, the topological valley Hall edge states of elastic waves in phononic crystals are realized based on material differences. A phononic crystal structure with lantern rings is proposed. The results show that differences in the Young’s modulus or density of lantern-ring materials can cause the destruction of the effective spatial inversion symmetry, which causes the valley Hall phase transition; thus, topological edge states emerge at the interface of two domains with topologically dissimilar phases. For valley topological transport, the traditional method to break the spatial inversion symmetry is by changing the dimensional parameters of scatterers in phononic crystals. However, in many cases, the space between scatterers is extremely small, making it difficult to obtain a sufficiently large band gap. Moreover, it is difficult to change the transport path and operating-frequency range of elastic waves after sample fabrication is finished. Here, the above problems are solved by the realization of valley topological transport based on changes to lantern-ring materials. The waveguide path is reconfigurable, that is, it can be altered conveniently, and the operating frequency can be tuned by changing the lantern-ring materials. These factors are very important for the topological transport of elastic waves. Topological valley transport achieved by this method has a good backscattering-suppression ability and obvious robustness to defects. Realization of topological valley Hall edge states by utilizing material differences provides an effective method for obtaining the topological transport of elastic waves, breaking the limitations of those based only on structural parameter changes, and this has good application prospects in elastic wave manipulation and communication.

Electrical detection of nitrogen-vacancy (N-V) centers in diamond is advantageous for developing and integrating quantum information processing devices and quantum sensors and has the potential to achieve a higher collection efficiency than that of optical techniques. However, the mechanism for the electrical detection of N-V spins is not fully understood. In this study, we observe positive contrast in photocurrent detected magnetic resonance (PDMR). Note that negative PDMR contrast is usually observed. To discuss the sign of the PDMR contrast, we numerically analyze the dynamics of photocarrier generation by N-V centers using a seven-level rate model. It is found that the sign of the PDMR contrast depends on the difference in the photocurrent generated from the excited states and the metastable state of N-V centers. Furthermore, we demonstrate ac magnetic field sensing using spin coherence with the PDMR technique. ac magnetic field measurement with the PDMR technique is still challenging because the noise from a fluctuating magnetic environment is greater than the measured signal. Here, we introduce noise suppression using a phase-cycling-based noise-canceling technique. We demonstrate electrically detected ac magnetic field sensing with a sensitivity of 29 nT ${\mathrm{Hz}}^{-1/2}$. Finally, we discuss sensitivity enhancement based on the proposed model.

To date, antineutrino experiments built for the purpose of demonstrating a nonproliferation capability have typically employed organic scintillators situated as close to the core as possible (typically at a distance of a few meters to tens of meters) and have not exceeded a few tons in size. One problem with this approach is that proximity to the reactor core requires accommodation by the host facility. Water Cherenkov detectors located offsite, at distances of a few kilometers or greater, may facilitate nonintrusive monitoring and verification of reactor activities over a large area. As the standoff distance increases, the detector target mass must scale accordingly. This paper quantifies the degree to which a kiloton-scale gadolinium-doped water Cherenkov detector can exclude the existence of undeclared reactors within a specified distance, and remotely detect the presence of a hidden reactor in the presence of declared reactors, by verifying the operational power and standoff distance using a Feldman-Cousins-based likelihood analysis. A 1-kton scale (fiducial) water Cherenkov detector can exclude gigawatt-scale nuclear reactors up to tens of kilometers within a year. When attempting to identify the specific range and power of a reactor, the detector energy resolution is not sufficient to delineate between the two.

Exceptional points, with simultaneous coalescence of eigenvalues and eigenvectors, can be realized with non-Hermitian photonic systems. With the enhanced response, exceptional points have been proposed to improve the performance of photonic sensing. Recently, there are intense debates about the actual sensing advantage of exceptional points. The major concern is that intrinsic noise is also increased at exceptional points. Here, we aim to clarify the contribution of exceptional points for photonic sensing. This is achieved by analyzing the condition to realize divergent quantum Fisher information in linear non-Hermitian photonic systems. We show that the divergence of quantum Fisher information is the result of lasing threshold, instead of exceptional points. However, exceptional points correspond to the condition that lasing threshold is simultaneously achieved across multiple photonic modes. Therefore, exceptional points can further improve the sensitivity on top of lasing threshold. On the other hand, exceptional points alone cannot provide sensing advantage.

In this work, we show a correspondence between linear support vector machines (SVMs) and entanglement witnesses, and use this correspondence to generate entanglement witnesses for bipartite and tripartite qubit (and qudit) target entangled states. An SVM allows for the construction of a hyperplane that clearly delineates between separable states and the target entangled state; this hyperplane is a weighted sum of observables (“features”) whose coefficients are optimized during the training of the SVM. We demonstrate with this method the ability to obtain witnesses that require only local measurements even when the target state is a nonstabilizer state. Furthermore, we show that SVMs are flexible enough to allow us to rank features, and to reduce the number of features systematically while bounding the inference error. This allows us to derive $W$-state witnesses capable of detecting entanglement with fewer measurement terms than the fidelity method dominant in today’s literature. The utility of this approach is demonstrated on quantum hardware furnished through the IBM Quantum Experience.

Memristive devices based on correlated Mott materials have great potential for memory applications, and specifically neuromorphic computations, due to their simple structure, miniaturization capabilities, power efficiency, and operation speeds. For these reasons, many efforts are made to design improved synaptic devices based on Mott materials. This work demonstrates a nonvolatile memristive three-terminal transistor based on the correlated oxide ${\mathrm{VO}}_2$, which has a (Mott) metal-insulator transition near room temperature. An ultrathin ${\mathrm{VO}}_2$ layer is incorporated in a metal-oxide-semiconductor field-effect geometry using alumina as the gate dielectric. A field effect is demonstrated to modify the channel’s resistance in a nonvolatile and reversible fashion. However, only when the gate voltage is applied at the metallic state of the ${\mathrm{VO}}_2$ does the resistance of the insulating state change. Thus, the metallic and insulating states, reached via heating and cooling, act as a write-read switch. Field-induced oxygen motion is the probable mechanism, and a model based on oxygen motion at the ${\mathrm{VO}}_2/{\mathrm{Al}}_2{\mathrm{O}}_3$ interface reproduces the observed results well. This study provides a proof of principle for the development of high-performance electronic synaptic transistors utilizing Mott materials, where the fully solid-state composition simplifies fabrication and enables integration with silicon-based architectures for future applications.

Electrons in two-dimensional materials possess an additional quantum attribute, the valley pseudospin, labeled as $\mathbf{K}$ and ${\mathbf{K}}^{\mathrm{\prime }}$—analogous to the spin up and spin down. The majority of research to achieve valley-selective excitations in valleytronics depends on resonant circularly polarized light with a given helicity. Not only acquiring valley-selective electron excitation but also switching the excitation from one valley to another is quintessential for bringing valleytronics-based technologies in reality. Present work introduces a coherent control protocol to initiate valley-selective excitation, de-excitation, and switch the excitation from one valley to another on the fly within tens of femtoseconds — a timescale faster than any valley decoherence time. Our protocol is equally applicable to both gapped and gapless two-dimensional materials. Monolayer graphene and molybdenum disulfide are used to test the universality. Moreover, the protocol is robust as it is insensitive to significant parameters of the protocol, such as dephasing times, wavelengths, and time delays of the laser pulses. Present work goes beyond the existing paradigm of valleytronics, and opens an alternative realm of valley switch at petahertz rate.

Mesa-shaped structures of the high critical temperature (high-$T_c$) superconductor ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{Ca}\mathrm{Cu}}_2{\mathrm{O}}_{8+\delta }$ contain stacked intrinsic Josephson junctions. As such, they are a promising source of coherent radiation in the “terahertz gap” range, spanning from approximately 0.3 to 2.0 THz. Technological applications of these devices become far more practical if they can be operated at a cryogenic bath temperature of 77 K or higher. Previous works have reported emission from this type of device at high terahertz power levels at lower operating temperatures, 40–60 K, while at $T_{\mathrm{bath}}\ge 77\mathrm{K}$ observed power levels have generally been low. Here we report generation of 130 μW of coherent power at 0.456 THz from a mesa of ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{Ca}\mathrm{Cu}}_2{\mathrm{O}}_{8+\delta }$ doped with 0.16 holes per $\mathrm{Cu}$ atom, at a bath temperature of 77.4 K. We find that the device radiates terahertz power when clearly identifiable cavity modes are excited, and that the frequency and bias voltage corresponding to each of these modes is almost independent of $\mathrm{temperature}$. This is consistent with these modes having terahertz-frequency electric fields with very little dependence on vertical position within the mesa. We also find that the terahertz power radiated from any given mode decreases monotonically as the mesa temperature is increased. On the other hand, the low-frequency modes become inaccessible at low temperatures due to retrapping of the intrinsic Josephson junctions, and the maximum radiation power for the emitting mode is typically achieved at the temperature at which the retrapping voltage reaches the resonance voltage for this mode.

We present a photonic structure in which Mie, Tamm, and surface-plasmon optical modes can be tailored to enhance the brightness of an embedded single-photon emitter. Contrary to most proposals, the structure is designed for excitation and collection through the substrate side. The front surface can be used instead to arrange metal contacts which serve the purpose of both electrical gates and optical mirrors. The design is particularized for $\mathrm{In}\mathrm{Ga}\mathrm{As}$ quantum dots on $\mathrm{Ga}\mathrm{As}$, resulting in an out-coupled single-photon rate exceeding 3 GHz in a cone of narrow numerical aperture ($\mathrm{NA}=0.17$). The fabrication tolerances are also discussed.