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.

The ability to manipulate and select optical modes effectively and accurately is strongly desired to enable single-mode operation. Here, we report an optical system consisting of two directly coupled metal-cladded optical resonators that can realize a single-mode peak through control of the tuning between the resonant wavelengths of the two optical resonators. Additionally, the wavelength of the single-mode peak can be chosen via adjusting the angle of incident light. Furthermore, the linewidth and power of the single-mode output can be controlled completely by the thickness of the resonator guide layer and the angle of incident light. This optical system provides a way to realize optical information processing without the need for complex structures and specific materials.

Charge-to-spin conversion is crucial for the application of emerging spintronic devices. A two-dimensional electron gas (2DEG) at a complex oxide interface usually possesses strong Rashba spin-orbit coupling, and spin-momentum locking offers a great possibility for efficient charge-to-spin conversion through the Rashba-Edelstein effect. Here, we report the fabrication of metallic 2DEGs in γ-${\mathrm{Al}}_2{\mathrm{O}}_3/{\mathrm{KTaO}}_3$ spinel/perovskite heterostructures and investigate the charge-to-spin conversion for Py/γ-${\mathrm{Al}}_2{\mathrm{O}}_3/{\mathrm{KTaO}}_3$ devices using the technique of spin-torque ferromagnetic resonance. The sizable spin splitting of the band structure results in a large current-induced spin-orbit torque efficiency with values up to around 3.6 at 5 K and about 1.1 at 300 K, which are more than an order of magnitude higher than those of heavy metals (0.07 for $\mathrm{Pt}$ at 300 K). Moreover, both theoretical and experimental results show that the charge-to-spin conversion is strongly dependent on the position of the Fermi level. These results demonstrate that optimizing the band filling of a ${\mathrm{KTaO}}_3$-based 2DEG is crucial for maximizing the conversion efficiency.

Hyperentanglement, defined as the simultaneous entanglement in several independent degrees of freedom (DOFs) of a quantum system, is a fascinating resource in quantum information processing with its outstanding merits. Here we propose heralded hyperentanglement concentration protocols (hyper-ECPs) to concentrate an unknown partially less polarization-spatial hyperentangled Bell state with available linear optics and common single-photon detectors. By introducing time-delay DOFs, the schemes are highly efficient in that the success of the scheme can be accurately heralded by the detection signatures, and postselection techniques or photon-number-resolving detectors, necessary for previous experiments, are not required. Additionally, our linear optical architectures allow certain states, where concentration fails, to be recyclable, and a trick makes the success probabilities of our schemes higher than those of previous linear optical hyper-ECPs.

Iridium ($\mathrm{Ir}$) is a 5d heavy metal with strong spin-orbit coupling (SOC), which introduces various intriguing phenomena when interacting with a ferromagnetic layer. In this study, we utilize $\mathrm{Ir}$ as an insertion layer in $\mathrm{W}/\mathrm{Ir}(t_{\mathrm{Ir}})/{\mathrm{Co}}_{20}{\mathrm{Fe}}_{60}{\mathrm{B}}_{20}/\mathrm{Mg}\mathrm{O}$ heterostructures to tune SOC and study its influence on the spin-orbit torque (SOT), perpendicular magnetic anisotropy (PMA), and Dzyaloshinskii-Moriya interaction (DMI). The SOT efficiency decreases first and then increases with an increase of $\mathrm{Ir}$ insertion layer thickness because of the opposite spin Hall angle between $\mathrm{W}$ and $\mathrm{Ir}$, and the sign changes when the thickness of $\mathrm{Ir}$ is 1.5 nm, which is close to the spin diffusion length of $\mathrm{Ir}$ of 1.35 nm. Importantly, a 0.25-nm-thick $\mathrm{Ir}$ layer enhances largely the effective PMA by 140%–350% under different annealing temperatures compared with that of a sample without insertion. Meanwhile, the DMI constant is also enhanced. The enhancement of PMA and DMI is likely due to the enhancement of interfacial SOC when $\mathrm{Ir}$ diffuses into ${\mathrm{Co}}_{20}{\mathrm{Fe}}_{60}{\mathrm{B}}_{20}$ and leads to the formation of ${\mathrm{Fe}}_{1-x}{\mathrm{Ir}}_x$. These results provide an effective method to tune SOC by inducing a dusting layer with strong SOC to meet different requirements in spintronic devices like small magnetic tunnel junctions.

We present a scheme for measuring a rotational Doppler frequency shift with only a single-shot measurement. Our protocol benefits from the combination of computational temporal ghost imaging and heterodyne detection of the rotational Doppler effect. Specifically, by multiplexing a series of elaborately designed ring-shaped spatial patterns, we map the temporal rotational Doppler signal into the spatial domain and thus can collect the Doppler signal with a camera in a single-shot exposure. Then, by calculating intensity correlations between the resulting elaborate spatial patterns and the image captured by the camera, we reconstruct the temporal Doppler signal. In our experiments, we succeed in demonstrating fairly good performance for measuring the angular velocity of a real spinning object with a rough surface. Our scheme could find potential applications in remote sensing and could also inspire more attempts to develop protocols for temporal detection and processing on the basis of space-time duality.

Optofluidic force induction (OF2i) is an optical nanoparticle characterization scheme which achieves real-time optical counting with single-particle sensitivity and high throughput. In a recent paper [Šimić et al., Phys. Rev. Appl. 18, 024056 (2022)], we have demonstrated the working principle for standardized polystyrene nanoparticles, and have developed a theoretical model to analyze the experimental data. In this paper we give a detailed account of the model ingredients, including the full working equations, provide additional justification for the assumptions underlying OF2i, and discuss directions for further developments and future research.

Direct measurements of far-field thermal infrared emission become increasingly useful because conventional indirect methods are limited or even unfeasible to characterize state-of-the-art thermal devices with engineered spectra, directionalities, and polarizations. The direct collection of the weak far-field emission from nanoscale infrared devices is also challenging because of their tiny footprints and the relatively large background radiation noises from surroundings. Here, we demonstrate a microscopic lock-in Fourier transform infrared spectrometer (FTIR) system that realizes significant improvement in SNR by combining a microscope and a lock-in amplifier with a FTIR. The lock-in FTIR is ultrasensitive, with a specific detectivity ${10}^6$ times higher than commercial ones, to overcome the optical loss and background noise during the emission light collection. Based on an analytical model of the full signal-detection process, we first employ the combination of the global heating and modulated Joule heating to maximize the potential of our system for noise reduction. Our findings show that, compared to previous studies, more than 3 times lower temperatures are sufficient to generate a measurable signal. Under a heating temperature of around 125 °C, we can achieve a SNR of about 23.7, which is far above the true-signal-threshold (SNR of about 3.0). Furthermore, the system can respond fast enough to record spectral-resolved dynamics of microdevices in the frequency domain. The system together with the analytical signal processing can be beneficial for next-generation thermal infrared material and device development, facilitating their applications in lighting, sensing, imaging, and energy harvesting at a small scale.

Electron-mediated spin torque provides a fast and efficient method to manipulate magnetization; however, electron motion inevitably brings about the generation of Joule heat and corresponding power consumption. Magnon-mediated spin torque, without involving moving electrons, could circumvent the energy dissipation issue. In this work, we fabricate a sandwich structure of topological insulator/antiferromagnetic insulator/ferromagnet with perpendicular magnetic anisotropy. We find that the magnon current with spin angular momentum can traverse a 25-nm-thick antiferromagnetic $\mathrm{Ni}\mathrm{O}$ layer and effectively switch the perpendicular magnetization of $\mathrm{Co}\text{−}\mathrm{Fe}\text{−}\mathrm{B}$ at room temperature with a critical switching current density of 4.1 × ${10}^6\mathrm{A}/{\mathrm{cm}}^2$. The magnon torque efficiency is characterized using spin-torque ferromagnetic resonance measurements to be 0.33 with a magnon diffusion length of 26.6 nm. Our work paves the way for manipulating perpendicular magnetization via magnon torques, facilitating the exploration of magnon-based spintronics with low power consumption.

Certification of quantum systems and their properties has become a field of intensive study. Here, taking advantage of the one-sided device-independent (1SDI) scenario (also known as the quantum steering scenario), we propose a self-testing scheme for all bipartite entangled states using a single family of steering inequalities with the minimal number of two measurements per party. Building on this scheme we then show how to certify all rank-one extremal measurements, including nonprojective $d^2$-outcome measurements, which in turn can be used for certification of the maximal amount of randomness, that is, $2{\log }_2d$ bits. Finally, in the particular case of $d=3$, we propose an extended Bell scenario that transforms a 1SDI scheme to “almost device independent.”

Controlling the spectral response of thermal emitters has become increasingly relevant for a range of energy and sensing applications. Conventional approaches to achieving arbitrary spectrum selectivity in photonic systems have entailed combining multiple resonantly emissive elements together to achieve a range of spectral profiles through numerical optimization, with a universal theoretical framework lacking. Here, we develop a temporal coupled-mode theory for thermal emission from multiple, arbtirarily coupled resonators. We validate our theory against numerical simulations of complex two- and three-dimensional nanophotonic thermal emitters, highlighting the anomalous thermal emission spectra that can emerge when multiple resonators with arbitrary properties couple to each other with varying strengths.

Magnon polaritons (MPs) refer to a light-magnon coupled state, which have the potential to act as information carriers, possibly enabling charge-free computation. However, light-magnon coupling is inherently weak. To achieve sufficiently strong coupling, a large ferromagnet or coupling with a microwave cavity is necessary. Thus, we theoretically propose a 100 nm YIG/1 µm GGG/500 µm YIG structure as a fundamental platform for magnonic and magnon-optical information storage devices to address the aforementioned issues. Furthermore, we discuss the transport properties of the MPs. Owing to the waveguide modes formed by the dielectric constant of the structure, the magnons placed in a nanometer-thin layer are strongly coupled with light. In addition, a longitudinal magnon-magnon coupling between thin and thick magnetic layers yields rich functionalities and a large magnon density to the thick-layer MPs due to the “magnonic antenna effect.” Hence, a large, direction-switchable magnon current in the thin layer is observed. The proposed structure indicates a longer coherence length and suitable figure of merit for the magnonic antenna effect. Therefore, the findings of this study would enable the integration of ferromagnetic micro- and nanostructures for MP-based information devices without any restrictions due to cavities.

Metal photocathodes are an important source of high-brightness electron beams, ubiquitous in the operation of both large-scale accelerators and table-top microscopes. When the surface of a metal is nanoengineered with patterns on the order of the optical wavelength, it can lead to the excitation and confinement of surface-plasmon-polariton waves that drive nonlinear photoemission. In this work, we aim to evaluate gold plasmonic nanogrooves as a concept for producing bright electron beams for accelerators via nonlinear photoemission. We do this by first comparing their optical properties to numerical calculations from first principles to confirm our ability to fabricate these nanoscale structures. Their nonlinear photoemission yield is found by measuring emitted photocurrent as the intensity of their driving laser is varied. Finally, the mean transverse energy of this electron source is found using the solenoid-scan technique. Our data demonstrate the ability of these cathodes to provide a tenfold enhancement in the efficiency of photoemission over flat metals driven with a linear process. We find that these cathodes are robust and capable of reaching sustained average currents over 100 nA at optical intensities larger than $2\mathrm{GW}{\mathrm{cm}}^{-2}$ with no degradation of performance. The emittance of the generated beam is found to be highly asymmetric, a fact we can explain with calculations involving the also asymmetric roughness of the patterned surface. These results demonstrate the use of nanoengineered surfaces as enhanced photocathodes, providing a robust air-stable source of high-average-current electron beams hopefully with great potential for industrial and scientific applications.