On-chip thermoelectric generation is of vital importance and is attracting wide attention as an option for implementing green microelectronics. We achieve temperature sensing and energy harvesting using the anomalous Nernst effect (ANE) in ${\mathrm{[IrMn/magnetic\; metal]}}_n$ multilayers, which can be used as on-chip temperature sensors and thermoelectric generators. An increase of 103% (1356%) in the voltage (power) generation coefficient is achieved by increasing the number of periods ($n$) from 1 to 7, due to the enhanced interfacial spin-orbit-coupled scattering. The voltage and power generation coefficients of an optimized ${\mathrm{[IrMn/NiFe]}}_5$ sample with geometric dimensions of $1800\mu \mathrm{m}\times 120\mu \mathrm{m}$ reach $1.3\mu \mathrm{V}{\mathrm{K}}^{-1}$ and $1.7\mathrm{pW}{\mathrm{K}}^{-2}$, respectively. Meanwhile, the exchange bias field introduced by Ir-Mn enables an ANE voltage and power output without an external field. Both features can advance the thermopower applications of ${\mathrm{[IrMn/magnetic\; metal]}}_n$ multilayers, especially the ${\mathrm{[IrMn/NiFe]}}_n$ system, for energy-efficient microelectronics.

As a secondary structure of DNA, DNA tetrahedra exhibit intriguing charge-transport phenomena and provide a promising platform for wide applications like biosensors, as shown in recent electrochemical experiments. Here, we study charge transport in a multiterminal DNA tetrahedron, finding that its charge-transport properties strongly depend upon the interplay of contact position, on-site energy disorder, and base-pair mismatch. Our results indicate that this multiterminal DNA tetrahedron behaves as a nanoscale charge splitter when the source is contacted at the top vertex. Besides, we find that the charge-transport efficiency is nearly independent of the contact position in the weak disorder regime, and is dramatically declined by the occurrence of a single base-pair mismatch between the source and the drain, in accordance with experimental results [J. Am. Chem. Soc. 134, 13148 (2012); Chem. Sci. 9, 979 (2018)]. By contrast, the charge-transport efficiency will be enhanced monotonically by shifting the source toward the drain in the strong disorder regime, and be increased when the base-pair mismatch takes place exactly at the contact position. In particular, when the source moves successively from the top vertex to the drain, the charge transport through the tetrahedral DNA device can be separated into three regimes, ranging from disorder-induced linear decrement of conductance to disorder-insensitive charge transport, and to disorder-enhanced charge transport. Finally, we predict that the DNA tetrahedron functions as a more efficient spin filter compared to double-stranded DNA and as a nanoscale spin splitter with opposite spin polarization observed at different drains. These results could be readily checked by electrochemical measurements and help for designing intriguing DNA tetrahedron-based molecular nanodevices.

We present an experimental study of local magnetic imaging in order to visualize the current flow in superconducting networks. We track the evolution of the spatial distribution of the current flow as the network is driven from fully superconducting to fully normal phases. Our results highlight the factors that contribute to the disordered flow in superconducting networks during their collapse, and demonstrate that the current is never uniformly distributed in the network. These results can assist the design and development of circuits based on superconductors and Josephson junctions.

In this work, we introduce an interconnected nano-optoelectronic spiking artificial neuron emitter-receiver system capable of operating at ultrafast rates (about $100\mathrm{ps}/$optical spike) and with low-energy consumption (< pJ/spike). The proposed system combines an excitable resonant tunneling diode (RTD) element exhibiting negative differential conductance, coupled to a nanoscale light source (forming a master node) or a photodetector (forming a receiver node). We study numerically the spiking dynamical responses and information propagation functionality of an interconnected master-receiver RTD node system. Using the key functionality of pulse thresholding and integration, we utilize a single node to classify sequential pulse patterns and perform convolutional functionality for image feature (edge) recognition. We also demonstrate an optically interconnected spiking neural network model for processing of spatiotemporal data at over 10 Gbit/s with high inference accuracy. Finally, we demonstrate an off-chip supervised learning approach utilizing spike-timing-dependent plasticity for the RTD-enabled photonic spiking neural network. These results demonstrate the potential and viability of RTD spiking nodes for low footprint, low-energy, high-speed optoelectronic realization of spike-based neuromorphic hardware.

An optical unitary converter (OUC) that can convert a set of $N$ mutually orthogonal optical modes into another set of arbitrary $N$ orthogonal modes is expected to be a key device in diverse applications, including optical communication, deep learning, and quantum computing. While various types of OUC have been demonstrated on photonic integration platforms, the sensitivity against a slight deviation in waveguide dimensions has been the crucial issue in scaling $N$. Here, we demonstrate that an OUC based on the concept of multiplane light conversion (MPLC) shows outstanding robustness against waveguide deviations. Moreover, it becomes more and more insensitive to fabrication errors as we increase $N$, which is in clear contrast to the conventional OUC architecture, composed of $2\times 2$ Mach-Zehnder interferometers. The physical origin behind this unique robustness and scalability is studied by considering a generalized OUC configuration. As a result, we reveal that the number of coupled modes in each stage plays an essential role in determining the sensitivity of the entire OUC. The maximal robustness is attained when all-to-all-coupled interferometers are employed, which are naturally implemented in a MPLC-based OUC.

Impurities in silicon are fundamental to a variety of modern nanoscale technologies working in both classical and quantum regimes of operation. The aggressive miniaturization of electronic devices has reduced their size to the nanometer scale, where the exact count and positioning of a few impurity atoms dictates their overall operation and performance. In the emerging area of quantum hardware development, single-impurity spins in silicon form excellent qubits and identifying their exact locations is important to engineer two-qubit interactions for high-fidelity quantum operations and the associated quantum control systems. This work reports a theoretical framework for the spatial metrology of single-impurity atoms in silicon with exact atomic precision for impurity depths approaching the bulk limit. The application of a carefully designed electric field pulls the impurity wave functions toward the surface, leading to spatially resolved scanning tunneling microscope images of electronic states exhibiting features that distinctly depend on the exact locations of the impurity atoms beneath the silicon surface. After verification of the developed metrology technique for individual atom positions, we train a machine-learning algorithm that can autonomously perform the metrology with high throughput in the presence of noise commensurate with experimental measurements. A future experimental implementation of the established capability for impurity-atom characterization is anticipated to play an important role in the design of a wide range of electronic and quantum devices.

The current autotuning approaches for quantum dot (QD) devices, while showing some success, lack an assessment of data reliability. This leads to unexpected failures when noisy or otherwise low-quality data is processed by an autonomous system. In this work, we propose a framework for robust autotuning of QD devices that combines a machine learning (ML) state classifier with a data quality control module. The data quality control module acts as a “gatekeeper” system, ensuring that only reliable data are processed by the state classifier. Lower data quality results in either device recalibration or termination. To train both ML systems, we enhance the QD simulation by incorporating synthetic noise typical of QD experiments. We confirm that the inclusion of synthetic noise in the training of the state classifier significantly improves the performance, resulting in an accuracy of $95.0(9)\mathrm{\%}$ when tested on experimental data. We then validate the functionality of the data quality control module by showing that the state classifier performance deteriorates with decreasing data quality, as expected. Our results establish a robust and flexible ML framework for autonomous tuning of noisy QD devices.

Nitrogen-vacancy (N-$V$) diamonds have attracted keen interest for nanoscale sensing and spin manipulation. In particular, the nonequilibrium electron spin polarization after optical excitation of single N-$V$ centers has successfully been transferred to nuclear spin baths in the surrounding of defects. However, these experiments need to be extended to N-$V$ ensembles that have promising practical applications in the hyperpolarization of bulk sample volumes for NMR signal enhancement. Here, we use a dense, shallow ensemble of N-$V$ centers to demonstrate polarization transfer to nuclear spins in a well-defined composite diamond sample system. This allows us to address three different types of nuclear spins in different positions with respect to the N-$V$ polarization source: from the close proximity of ${}^{13}\mathrm{C}$ inside the diamond lattice to the self-assembled molecular system consisting of ${}^1\mathrm{H}$ and ${}^{19}\mathrm{F}$ spins outside the diamond and over multiple interfaces. We show that ensemble N-$V$ experiments face problems different from single N-$V$ experiments. In particular, using spinlock pulses, the inhomogeneously broadened electron spin resonance line of the N-$V$ ensemble limits the minimal resonance linewidth with which the transfer protocol can occur. Furthermore, we compare the N-$V$ spin-polarization losses and polarization transfer rates to the different nuclear baths and discuss the role of spin diffusion as detrimentally affecting the direct observation of nuclear polarization buildup within the detection volume of nanoscale N-$V$-NMR experiments.

Most applications of metasurfaces require excitation and control of both electric and magnetic surface currents. For such purposes, the metasurface must have a finite thickness to handle magnetic surface currents. For metasurface sheets of negligible thickness that offer only electric response, coherent illumination can compensate the need to create discontinuities of the tangential electric field component using magnetic surface currents. Most of the known coherent metasurfaces are space uniform and can control only plane-wave absorption and specular reflection. However, it is also known that periodical space-modulated (inhomogeneous) metasurfaces can be used to realize anomalous reflection, refraction, and other useful effects. In this paper, we propose the concept of a coherently illuminated space-modulated metasurface that functions as a coherent asymmetric absorber. We study its behavior under nonideal illumination and suggest applications related to sensing.

Measurement of the absolute value of the applied pressure in high-pressure muon and neutron experiments is a complicated task. It often requires the presence of a calibration material inside the sample volume, and could also cause additional time to obtain the response of the calibrant. Here we describe the use of optical calibrants for precise determination of the pressure value inside the piston-cylinder clamp cells. Utilizing the concept of separate volumes for the sample and the optical media, a setup for conducting in situ pressure measurements is successfully tested. Pressures in both the “sample” and the “optical” volumes are proved to be the same within experimental accuracy. The use of ${\mathrm{Sr}\mathrm{B}}_4{\mathrm{O}}_7:(0.01{\mathrm{Sm}}^{2+},0.03{\mathrm{Eu}}^{2+})$ as a pressure calibrant allows for a high accuracy of pressure determination by considering up to eight fluorescence lines.

Transmission asymmetry in reciprocal systems offers an appealing alternative to bulkier nonreciprocal implementations for certain applications. Common reciprocal routes to transmission asymmetry of linearly polarized light involve a rotation of its polarization. Here, we explore a different route with a linear all-dielectric metagrating that preserves polarization, while lacking inversion symmetry along the surface-normal direction. Our all-angle transmission calculations reveal an abrupt transition from a symmetric to an asymmetric transmission response that traces the Bragg critical wavelength of higher-order beam emergence as a function of the incident angle. By adopting an analogy between scattering from a multiport network and the metagrating paradigm we establish why the only necessary condition for transmission symmetry breaking in this class of systems is the emergence of any higher-order Bragg diffracted beam. We further show how such a transmission symmetry breaking is consistent with reciprocity and also demonstrate the underpinning symmetry-breaking mechanism with a first-principles numerical experiment. Finally, we shed light on some previous misconceptions regarding transmission symmetry breaking related to the role of the substrate or need for change of diffraction order number at each interface. Our proposed metagrating can exhibit a strong transmission asymmetry, with contrast that can be as high as approximately 75%, thus underlining its potential as a blueprint for passive asymmetric or nonlinear self-biasing nonreciprocal metasurfaces relevant to integrated and active photonics.

Many computational problems are intractable through classical computing and, as Moore’s law is drawing to a halt, demand for finding alternative methods in tackling these problems is growing. Here, we realize a liquid light machine for the NP-hard max-3-cut problem based on a network of synchronized exciton-polariton condensates. We overcome the binary limitation of the decision variables in Ising machines using the continuous-phase degrees of freedom of a coherent network of polariton condensates. The condensate network dynamical transients provide optically fast annealing of the $XY$ Hamiltonian. We apply the Goemans and Williamson random hyperplane technique, discretizing the $XY$ ground-state spin configuration to serve as ternary decision variables for an approximate optimal solution to the max-3-cut problem. Applications of the presented coherent network are investigated in image-segmentation tasks and in circuit design.

Multipartite entanglement is one of the core concepts in quantum information science with broad applications that span from condensed matter physics to quantum physics foundation tests. Although its most studied and tested forms encompass two-dimensional systems, current quantum platforms technically allow the manipulation of additional quantum levels. We report the experimental demonstration and certification of a high-dimensional multipartite entangled state in a superconducting quantum processor. We generate the three-qutrit Greenberger-Horne-Zeilinger state by designing the necessary pulses to perform high-dimensional quantum operations. We obtain the fidelity of $76\mathrm{\%}\pm 1\mathrm{\%}$, proving the generation of a genuine three-partite and three-dimensional entangled state. To this date, only photonic devices have been able to create and certify the entanglement of these high-dimensional states. Our work demonstrates that another platform, superconducting systems, is ready to exploit genuine high-dimensional entanglement and that a programmable quantum device accessed on the cloud can be used to design and execute experiments beyond binary quantum computation.

The high performance of hybrid perovskite-based devices is attributed to its excellent bulk transport properties. However, carrier dynamics, especially at the metal-perovskite interface, and their influence on device operation are not widely understood. This work presents the dominant transport mechanisms in methylammonium lead iodide (MA${\mathrm{Pb}\mathrm{I}}_3$) perovskite-based asymmetric metal electrode lateral devices. The device operation is studied with interelectrode lengths varying from 4 µm to 120 µm. Device characteristics indicate distinct ohmic and space-charge-limited current regimes that are controlled by the interelectrode length and applied bias. The electric-potential mapping using Kelvin-probe microscopy across the device indicates minimal ion-screening effects and the presence of a transport barrier at the metal-MA${\mathrm{Pb}\mathrm{I}}_3$ junction. Furthermore, photocurrent imaging of the channel using near-field excitation-scanning microscopy reveals dominant recombination and charge-separation zones. These lateral devices exhibit photodetector characteristics with a responsivity of about 51 mA/W in self-powered mode and 5.2 A/W at 5 V bias in short-channel devices (4 µm). The low device capacitance enables a fast light-switching response of approximately 12 ns.

Metagratings are periodic arrays of subwavelength scatterers, or atoms, engineered to refract or reflect waves toward anomalous directions with unit efficiency. Here, we design and build a metagrating to control the reflection direction of waterborne ultrasound waves impinging on a rigid or free surface. The grating and its atoms are designed to cancel the specular reflection and to redirect acoustic power toward a negative-reflection direction, through the first-negative-order Floquet mode. Despite a simple design, based on C-shaped brass particles acting as Helmholtz resonators, the grating is efficient ($>90\mathrm{\%}$) over a relatively broad range of frequencies (74–103 kHz) for a broad range of incidence angles (${14}^{\circ }$–${54}^{\circ }$). This good performance is obtained by tuning the distance between the atoms and the reflective surface. A multiple-scattering analytical model is presented to explain the phenomenon and a finite-element model is developed to further investigate the performance of the proposed design. Predictions from the model are confirmed experimentally in a water tank. The simplicity, reconfigurability, and scalability of the design, as well as its high efficiency, broadband behavior, and robustness to the incidence angle are all features that make the grating potentially useful for various applications in underwater acoustics, such as telemetry, communication, or noise mitigation.