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.

We propose a quantum annealing protocol that effectively probes the dynamics of a single qubit on D-Wave’s quantum annealing hardware. This protocol uses D-Wave’s $h$-gain schedule functionality, which allows the rapid suppression of the longitudinal magnetic field at arbitrary points during the anneal. This feature enables us to distinguish between open and closed-system dynamics as well as the presence and absence of longitudinal magnetic field noise. We show that thermal fluctuations alone are not sufficient to explain the system’s dynamics and that a prominent role is played by magnetic field fluctuations, which need to be included in an open quantum system description. Moreover, our protocol only requires single-qubit measurements, which makes it suitable as an exploration and calibration tool for large-scale quantum annealing hardware.

We introduce magic measures to quantify the nonstabilizerness of multiqubit quantum gates and establish lower bounds on the $T$ count for fault-tolerant quantum computation. First, we introduce the stabilizer nullity of multiqubit unitary, which is based on the subgroup of the quotient Pauli group associated with the unitary. This unitary stabilizer nullity extends the state-stabilizer nullity by Beverland et al. [Quantum Sci. Technol. 5, 035009 (2020)] to a dynamic version. In particular, we show this nonstabilizerness measure has desirable properties, such as subadditivity under composition and additivity under tensor product. Second, we prove that a given unitary’s stabilizer nullity is a lower bound for the $T$ count, utilizing the above properties in gate synthesis. Third, we compare the state and the unitary stabilizer nullity, proving that the lower bounds for the $T$ count obtained by the unitary stabilizer nullity are never less than the state-stabilizer nullity. Moreover, we show an explicit $n$-qubit unitary family of unitary stabilizer nullity $2n$, which implies that its $T$ count is at least $2n$. This gives an example where the bounds derived by the unitary stabilizer nullity strictly outperform the state-stabilizer nullity by a factor of 2. We finally showcase the advantages of unitary stabilizer nullity in estimating the $T$ count of quantum gates with interests.

Hybrid heterostructure-based phototransistors are attractive owing to their high gain induced by the photogating effect. However, the absence of an in-plane built-in electric field in the single-channel-layer transistor results in a relatively higher dark current and requires a large operating gate voltage of the device. Here, we report air-stable cesium lead iodide/tungsten di-sulfide (${\mathrm{Cs}\mathrm{Pb}\mathrm{I}}_3/{\mathrm{WS}}_2$) mixed-dimensional heterostructure-based photo-field-effect-transistors (photo-FETs) with asymmetric metal electrodes ($\mathrm{Cr}/{\mathrm{WS}}_2/\mathrm{Au}$), exhibiting extremely low dark current (approximately ${10}^{-12}$ A) with a responsivity of approximately ${10}^2$ A/W at zero gate bias. The Schottky-barrier- (${\mathrm{WS}}_2/\mathrm{Au}$ interface) induced rectification characteristics in the channel accompanied by the excellent photogating effect from solution-processed α-phase ${\mathrm{Cs}\mathrm{Pb}\mathrm{I}}_3$ nanocrystal sensitizers, resulting in gate-tunable broadband photodetection with a very high responsivity (approximately ${10}^4$ A/W) and excellent sensitivity (approximately ${10}^6$). Most interestingly, the device shows superior performance even under high-humidity (50–65%) conditions owing to the formation of cubic α-phase ${\mathrm{Cs}\mathrm{Pb}\mathrm{I}}_3$ nanocrystals with a relatively smaller lattice constant (a = 6.2315 Å) and filling of surface vacancies (${\mathrm{Pb}}^{2+}$ centers) with the sulphur atoms from the ${\mathrm{WS}}_2$ layer, thus protecting it from environmental degradation. These results emphasize an exciting strategy for developing mixed-dimensional hybrid heterostructure-based phototransistors for futuristic integrated nano-optoelectronic systems.

A fault-tolerant quantum computer will be supported by a classical decoding system interfacing with quantum hardware to perform quantum error correction. It is important that the decoder can keep pace with the quantum clock speed, within the limitations on communication that are imposed by the physical architecture. To this end, we propose a local “predecoder,” which makes greedy corrections to reduce the amount of syndrome data sent to a standard matching decoder. We study these classical overheads for the surface code under a phenomenological phase-flip noise model with imperfect measurements. We find substantial improvements in the run time of the global decoder and the communication bandwidth by using the predecoder. For instance, to achieve a logical-failure probability of $f={10}^{-15}$ using qubits with physical error rate $p={10}^{-3}$ and a distance $d=22$ code, we find that the bandwidth cost is reduced by a factor of 1000 and that the time taken by a matching decoder is sped up by a factor of 200. To achieve this target failure probability, the predecoding approach requires a 50% increase in the qubit count compared with the optimal decoder.

Quantum correlation between two parties serves as a useful resource in the surging applications of quantum information. The Bell nonlocality and quantum steering have been proposed to describe nonclassical correlations against local-hidden-variable and local-hidden-state theories, respectively. To characterize the two types of nonclassical correlations, various nonlocality and steering inequalities have been established, and the amount of inequality violation serves as a helpful indicator for many entanglement-based tasks. Quantum state tomography has been employed for measuring quantum states, while the method requires intensive computation and does not directly verify either nonlocality or steering over the full domain independent of established theories. Here, we experimentally map the full-domain correlation with bipartite states for nonlocality and quantum steering in Clauser-Horne-Shimony-Holt scenarios. The measurement of the maps automatically accounts for detection imperfections. Furthermore, we demonstrate the application of the correlation maps in the entanglement-based quantum key distribution protocol with arbitrary bipartite states. The correlation maps show direct measurements and simple interpretations that can answer fundamental questions about nonlocality and quantum steering as well as contribute to quantum information applications in a straightforward manner.

We numerically study how to enhance reservoir computing performance by thoroughly extracting the spin-wave device potential for higher-dimensional information generation. The reservoir device has a 1-input exciter and 120-output detectors on the top of a continuous magnetic garnet film for spin-wave transmission. For various nonlinear and fading-memory dynamic phenomena distributing in the film space, small in-plane magnetic fields are used to prepare stripe domain structures and various damping constants at the film sides and bottom are explored. The ferromagnetic resonant frequency and relaxation time of spin precession clearly characterizes the change in spin dynamics with the magnetic field and damping constant. The common input signal for reservoir computing is a 1-GHz cosine wave with random 6-valued amplitude modulation. A basic 120-dimensional reservoir output vector is obtained from time-series signals at the 120-output detectors under each of three magnetic field conditions. Then, 240- and 360-dimensional reservoir output vectors are also constructed by concatenating two and three basic ones, respectively. In nonlinear autoregressive moving average (NARMA) prediction tasks, the computational performance is enhanced as the dimension of the reservoir output vector becomes higher and a significantly low prediction error is achieved for the tenth-order NARMA task using the 360-dimensional vector and optimum damping constant. The results are clear evidence that the collection of diverse output signals efficiently increases the dimensionality of the integrated reservoir state vector (i.e. reservoir-state richness) and thereby contributes to high computational performance. This paper demonstrates that performance enhancement through various configuration settings is a practical approach for on-chip reservoir computing devices with small numbers of real output nodes.