The control of nonthermal all-optical magnetization switching, under a regime of a train of identical laser pulses, opens up opportunities for ultrafast magnetic recording. Here, we investigate the photomagnetic back-switching capabilities of the write and erase magnetic domain pattern using double-pump pulse excitations in an iron-garnet film with pure cubic magnetocrystalline symmetry. It is essential to note that forward and backward magnetization switching is achievable in two distinctive scenarios: using identical linearly polarized laser pulses and with pulses having orthogonal polarization planes. By observing the switch of magnetization at domains independent of the initial state, one can nonthermally toggle the magnetization, equivalent to the xor logic operation, at frequencies reaching up to 50 GHz.

We report the experimental observation of large spin-pumping signals in the YIG/Pt system driven by broad-wave-vector spin-wave spin current. 280-nm-wide microwave inductive antennas offer broad-wave-vector excitation, which, in combination with the quasiflatband of YIG, allows a large number of magnons to participate in spin pumping at a given frequency. Through comparison with ferromagnetic resonance spin pumping, we attribute the enhancement of the spin current to the multichromatic magnons. The high efficiency of spin-current generation enables us to uncover nontrivial propagating properties in ultralow power regions. Additionally, our study achieves the spatially separated detection of magnons, allowing the direct extraction of the decay length. The synergistic combination of the capability of broad-wave-vector excitation, enhanced voltage signals, and nonlocal detection provides an alternative avenue for the electrical exploration of spin-wave dynamics.

We explore the transient response of a gain-embedded cavity magnon polariton system using time-domain measurements. The intricate interplay of gain, loss, and the light-matter interaction gives rise to distinctive dynamic behaviors, which can be categorized as damping, zero damping, and antidamping. The antidamping state triggers a unique exponential decay process, with the decay rate experiencing exponential amplification over time. This dynamic behavior results in an exceptionally swift decline in polariton amplitude, exceeding the pace of conventional constant-exponential decay processes. These findings have significant implications for advancing polariton devices, facilitating the rapid initiation of monochromatic microwave and light emission, and amplification in pulsed-mode operation.

Superparamagnetic tunnel junctions (SMTJs) are promising sources of randomness for compact and energy-efficient implementations of probabilistic computing techniques. Augmenting an SMTJ with electronic circuits, to convert the random telegraph fluctuations of its resistance state to stochastic digital signals, gives a basic building block known as a probabilistic bit or $p$-bit. Though scalable probabilistic computing methods connecting $p$-bits have been proposed, practical implementations are limited by either minimal tunability or energy-inefficient microprocessors in the loop. In this work, we experimentally demonstrate the functionality of a scalable analog unit cell, namely a pair of $p$-bits with programmable electrical coupling. This tunable coupling is implemented with operational amplifier circuits that have a time constant of approximately $1\text{μ}\text{s}$, which is faster than the mean dwell times of the SMTJs over most of the operating range. Programmability enables flexibility, allowing both positive and negative couplings, as well as coupling devices with widely varying device properties. These tunable coupling circuits can achieve the whole range of correlations from $-1$ to 1, for both devices with similar time scales, and devices whose time scales vary by an order of magnitude. This range of correlation allows such circuits to be used for scalable implementations of simulated annealing with probabilistic computing.

Unbiased sources of true randomness are critical for the successful deployment of stochastic unconventional computing schemes and encryption applications in hardware. Leveraging nanoscale thermal magnetization fluctuations provides an efficient and almost costfree means of generating truly random bitstreams, distinguishing them from predictable pseudorandom sequences. However, existing approaches that aim to achieve randomness often suffer from bias, leading to significant deviations from equal fractions of 0 and 1 in the bitstreams and compromising their inherent unpredictability. This study presents a hardware approach that capitalizes on the intrinsic balance of phase noise in an oscillator injection-locked at twice its natural frequency, leveraging the stability of this naturally balanced physical system. We demonstrate the successful generation of unbiased and truly random bitstreams through extensive experimentation. Our numerical simulations exhibit excellent agreement with the experimental results, confirming the robustness and viability of our approach.

An ideal toolset to diagnose diabetes consists of an in-hand portable device that can effectively detect glucose concentration in the blood in real time without having to perforate the skin. However, existing glucose monitoring systems are invasive, and those that are noninvasive have low accuracy. Here, we explore an alternative approach for noninvasive monitoring of the glucose concentration in blood. We excite Mie-like resonances within highly lossy media by introducing active loads, uniformly applied within the inner circumference of a dielectric ring structure. Our study opens a possible way of developing portable glucose monitoring systems that can detect the glucose concentration with a noninvasive approach and improved accuracy compared with existing techniques.

In recent years there has been significant progress in the development of artificial ion-pumping membranes. Ion pumps based on asymmetric nanopores have been shown to operate as ionic current rectifiers, thus pumping a net ion flux against a concentration gradient even when driven with unbiased ac signals. However, since ion transport relies on charged nanopores, it is selective to either cations or anions, and thus cannot pump both cations and anions simultaneously. In this paper, we present a model for an electronically active membrane which is based on a flashing ratchet mechanism. The model includes adjacent electrolyte reservoirs and ion-ion interactions, which were not accounted for in prior similar models, and thus provides a better understanding of the driving mechanism and potential capabilities and limitations. It is shown that, unlike most other proposed ion pumps, the ratchet-based ion pump (RBIP) drives both cations and anions in the same direction and up a concentration gradient. This process, referred to as ambipolar ion pumping, is shown to be highly robust for many electrolyte compositions and input signals. The membrane is composed of alternating conductive thin layers (electrodes), separated by insulating layers in an asymmetric design. With insulating layer thicknesses of 70 and 30 nm and an input signal amplitude of 0.5 V, the device drives a salt flux of 0.03 mol/(${\mathrm{m}}^2$ s) in a mildly saline solution (10 mM). Thus, RBIPs may pave the way for many exciting future applications involving ambipolar ion pumping, most notably for desalination.

Advances in silicon photonics technology have enabled the field of neuromorphic photonics, where analog neuron-like processing elements are implemented in silicon photonics technology. Accurate and scalable simulation tools for photonic integrated circuits are critical for designing neuromorphic photonic circuits. This is especially important when designing networks with recurrent connections, where the dynamics of the system may give rise to unstable and oscillatory solutions which need to be accurately modeled. These tools must simultaneously simulate the analog electronics and the multichannel (wavelength-division multiplexed) photonics contained in a photonic neuron to accurately predict on-chip behavior. In this paper, we utilize a Verilog-A model of the photonic neural network to investigate the dynamics of recurrent integrated circuits. We begin by reviewing the theory of continuous-time recurrent neural networks as dynamical systems and the relation of these dynamics to important physical features of photonic neurons such as cascadability. We then present the neural dynamics of systems of one and two neurons in the simulated Verilog-A circuit, which are compared to the expected dynamics of the abstract continuous-time recurrent neural network model. Due to the presence of parasitic circuit elements in the Verilog-A simulation, it is seen that there is a topological equivalence, but not an exact isomorphism, between the theoretical model and the simulated model. The implications of these discrepancies for the design of neuromorphic photonic circuits are discussed. Our findings pave the way for the practical implementation of large-scale silicon photonic recurrent neural networks.

Future quantum technologies such as quantum communication, quantum sensing, and distributed quantum computation, will rely on networks of shared entanglement between spatially separated nodes. In this work, we provide improved protocols and policies for entanglement distribution along a linear chain of nodes, both homogeneous and inhomogeneous, that take practical limitations into account. For a wide range of parameters, our policies improve upon previously known policies, such as the “swap-as-soon-as-possible” policy, with respect to both the waiting time and the fidelity of the end-to-end entanglement. This improvement is greatest for the most practically relevant cases, namely, for short coherence times, high link losses, and highly asymmetric links. To obtain our results, we model entanglement distribution using a Markov decision process, and then we use the $Q$-learning reinforcement-learning (RL) algorithm to discover alternative policies. These policies are characterized by dynamic, state-dependent memory cutoffs, and collaboration between the nodes. In particular, we quantify this collaboration between the nodes. Our quantifiers tell us how much “global” knowledge of the network every node has, specifically, how much knowledge two distant nodes have of each other’s states. In addition to the usual figures of merit, these quantifiers add an extra dimension to the performance analysis and practical implementation of quantum repeaters. Finally, our understanding of the performance of large quantum networks is currently limited by the computational inefficiency of simulating them using RL or other optimization methods. The other main contribution of our work is to address this limitation. We present a method for nesting policies in order to obtain policies for large repeater chains. By nesting our RL-based policies for small repeater chains, we obtain policies for large repeater chains that improve upon the swap-as-soon-as-possible policy, and thus we pave the way for a scalable method for obtaining policies for long-distance entanglement distribution under practical constraints.

This study presents a measurement method for determining the figure of merit for transverse thermoelectric conversion ($z_{\mathrm{T}}T$) in thin-film forms. Leveraging the proposed methodology, we comprehensively investigate the transverse thermoelectric coefficient ($S_{\rm T}$), in-plane electrical conductivity (${\sigma }_{yy}$), and out-of-plane thermal conductivity (${\kappa }_{xx}$) in epitaxial and polycrystalline $\mathrm{Fe}/\mathrm{Pt}$ metallic multilayers. Multilayers with a number of stacking repetitions (N) of 200 have ${\kappa }_{xx}$ values that are lower than those of $\mathrm{Fe}\mathrm{Pt}$ alloy films, indicating that the multilayer structure effectively contributes to the suppression of ${\kappa }_{xx}$. $z_{\mathrm{T}}T$ is found to increase with increasing N, which remarkably reflects the N-dependent enhancement of the $S_{\mathrm{T}}$ values. Notably, $S_{\mathrm{T}}$ and ${\sigma }_{yy}$ are significantly larger in the epitaxial multilayers than in the polycrystalline counterparts, whereas negligible differences in ${\kappa }_{xx}$ are observed between the epitaxial and polycrystalline multilayers. The present measurement technique reveals the transverse thermoelectric properties inherent to multilayers.

Here, we present a study investigating the effects of spin-wave coupling in a structure composed of parallel-oriented magnonic stripes fabricated from thin films of yttrium-iron garnet. The structure consists of two parallel stripes separated by a sufficiently small gap to enable dipolar coupling, while a third stripe is positioned atop the lateral system, forming an asymmetric three-dimensional (3D) coupler geometry. Through the utilization of Brillouin light-scattering spectroscopy, we experimentally demonstrate the transport of spin waves along the asymmetric 3D coupler. Additionally, by employing experimental techniques, we explore the nonreciprocal propagation of spin waves in the considered structure by reversing the polarity of the external magnetic field. To gain further insights, we employ micromagnetic modeling and the finite-element method to obtain the eigenmode spectra of the asymmetric 3D coupler. Our results show that reversing the polarity of the external magnetic field induces coupling between the magnetic stripes. We elucidate the characteristics of lateral and vertical spin-wave transport, as well as nonreciprocal spin-wave propagation within the investigated structure. Notably, in the asymmetric 3D coupler, the coupling length diminishes, offering the potential to enhance the density of functional elements in the design of three-dimensional magnonic networks.

Light-field microscopy (LFM) is a three-dimensional microscopy technique whereby volumetric information of a sample is gained by simultaneously capturing both the position and momentum information of light illuminating the sample. Conventional LFM designs generally require a trade-off between position and momentum resolution, requiring one to sacrifice resolving power for increased depth of field (DOF). In this work, we demonstrate a LFM design that does not require this trade-off by utilizing the inherent correlations between spatial-temporal entangled photon pairs. Here, one photon from the pair is used to illuminate a sample from which the position information of the photon is captured directly by a camera. By virtue of the momentum anticorrelation between the two photons, the momentum information of the illumination photon can be inferred by measuring the momentum of its entangled partner. By using a wave-optics approach for the light-field reconstruction, we demonstrate that a resolving power of up to $5\text{μ}\mathrm{m}$ can be maintained with a DOF of approximately $500\text{μ}\mathrm{m}$, approximately 10 times that of a conventional LFM or $>100$ times that of a bright-field microscope. In the extreme, at a resolving power of $100\text{μ}\mathrm{m}$, it is possible to achieve near infinite DOF.

Parametric amplifiers play a crucial role in modern quantum technology by enabling the enhancement of weak signals with minimal added noise. Traditionally, Josephson junctions have been the primary choice for constructing parametric amplifiers. Nevertheless, high-kinetic inductance thin films have emerged as viable alternatives to engineer the necessary nonlinearity. In this work, we introduce and characterize a kinetic inductance parametric amplifier (KIPA) built using high-quality $\mathrm{Nb}\mathrm{N}$ superconducting thin films. The KIPA addresses some of the limitations of traditional Josephson-based parametric amplifiers, excelling in dynamic range, operational temperature, and magnetic field resilience. We demonstrate a quantum-limited amplification ($>20$ dB) with a 20-MHz gain-bandwidth product, operational at fields up to 6 T and temperatures as high as 850 mK. Harnessing kinetic inductance in $\mathrm{Nb}\mathrm{N}$ thin films, the KIPA emerges as a robust solution for quantum signal amplification, enhancing research possibilities in quantum information processing and low-temperature quantum experiments. Its magnetic field compatibility and quantum-limited performance at high temperatures make it an invaluable tool, promising advancements in quantum research.

A continuous-variable quantum key distribution (CV QKD) using a true local (located at the receiver) oscillator (LO) has been proposed to remove any possibility of side-channel attacks associated with transmission of the LO as well as reduce the cross-pulse contamination. Here we report an implementation of true LO-CV QKD using “off-the-shelf” components and conduct QKD experiments using the fiber optical network at Oak Ridge National Laboratory. A phase reference and quantum signal are time multiplexed and then wavelength division multiplexed with the classical communications that “coexist” with each other on a single optical network fiber. This is the first demonstration of CV QKD with a receiver-based true LO over a deployed fiber network, a crucial step for its application in real-world situations.

The continuous scaling of semiconductor-based technologies to micrometer and submicrometer regimes has resulted in higher device density and lower power dissipation. Many physical phenomena such as self-heating or current leakage become significant at such scales, and mapping current densities to reveal these features is decisive for the development of modern electronics. However, advanced noninvasive technologies either offer low sensitivity or poor spatial resolution and are limited to two-dimensional spatial mapping. Here we use near-surface nitrogen-vacancy centers in diamond to probe Oersted fields created by current flowing within a multilayered integrated circuit in predevelopment. We show the reconstruction of the three-dimensional components of the current density with a magnitude down to about ≈10 µA/µ${\mathrm{m}}^2$ and submicrometer spatial resolution at room temperature. We also report the localization of currents in different layers and observe anomalous current flow in an electronic chip. Our method therefore provides a decisive step toward three-dimensional current mapping in technologically relevant nanoscale electronics chips.

Superconducting parametric amplifiers play a crucial role in the preparation and readout of quantum states at microwave frequencies, enabling high-fidelity measurements of superconducting qubits. Most existing implementations of these amplifiers rely on the nonlinearity from Josephson junctions, superconducting quantum interference devices, or disordered superconductors. Additionally, frequency tunability arises typically from either flux or current biasing. In contrast, semiconductor-based parametric amplifiers are tunable by local electric fields, which impose a smaller thermal load on the cryogenic setup than current and flux biasing and lead to vanishing crosstalk to other on-chip quantum systems. In this work, we present a gate-tunable parametric amplifier that operates without Josephson junctions, using a proximitized semiconducting nanowire. This design achieves near-quantum-limited performance, featuring more than 20-dB gain and a 30-MHz gain-bandwidth product. The absence of Josephson junctions results in advantages, including substantial saturation powers of $-120$ dBm, magnetic field compatibility up to $500\mathrm{mT}$, and frequency tunability over a range of 15 MHz. Our realization of a parametric amplifier supplements efforts towards gate-controlled superconducting electronics, further advancing the abilities for high-performing quantum measurements of semiconductor-based and superconducting quantum devices.

Using three-dimensional kinetic Monte Carlo simulations, we systematically investigate the effect of dilution with an inert material on the current density in unipolar sandwich-type disordered organic semiconductor devices. Such a dilution technique was studied experimentally by Abbaszadeh et al. [Nat. Mater. 15, 628 (2016)], who observed a dilution-induced increase of the current density. The authors explained the effect as a result of a reduced density of trapped charges (“trap dilution”), assuming an exponential density of trap states. Our simulations support this explanation, and show under which conditions this trap-dilution-induced increase of the current density becomes more than outweighed by the negative effect of the dilution-induced decrease of the mobility. The effect is studied for sets of systematically varied material parameters, including systems with a Gaussian shape of the host and trap DOS.

Atomic engineering in a solid-state material has the potential to functionalize the host with novel phenomena. STM-based lithographic techniques have enabled the placement of individual phosphorus atoms at selective lattice sites of silicon with atomic precision. Here we show that by placing four phosphorus donors spaced 10–15 nm apart from their neighbors in a linear chain, one can realize coherent spin coupling between the end dopants of the chain, analogous to the superexchange interaction in magnetic materials. Since phosphorus atoms are a promising building block of a silicon quantum computer, this enables spin coupling between their bound electrons beyond nearest neighbors, allowing the qubits to be separated by 30–45 nm. The added flexibility in architecture brought about by this long-range coupling not only reduces gate densities but can also reduce correlated noise between qubits from local noise sources that are detrimental to error-correction codes. We base our calculations on a full-configuration-interaction technique in the atomistic tight-binding basis, solving the four-electron problem exactly, over a domain of a million silicon atoms. Our calculations show that superexchange can be tuned electrically through gate voltages where it is less sensitive to charge noise and donor-placement errors.

We report on the use of an optically trapped microsphere as an acoustic transducer. A model for the hydrodynamic coupling between the microsphere and the surrounding acoustic fluid flow is combined with thermomechanical calibration of microsphere-position tracking to enable quantitative acoustic measurements. We describe our technique in detail, including the self-noise, the sensitivity, and the minimum detectable signals, using a model appropriate for both liquid and gas environments. We then test our approach in an air-based experiment and compare our measurements with two state-of-the-art commercially available acoustic sensors. Piezoelectrically driven bursts of pure tones and laser ablation provide two classes of test sounds. We find that accurate measurements with a bandwidth of 1 MHz are possible using our technique, improving by several orders of magnitude the bandwidth of previous flow measurements based on optically trapped microspheres.

The formation and dissolution of silver nanowires plays a fundamental role in a broad range of resistive-switching devices, which fundamentally rely on the electrochemical-metallization phenomenon. It has been shown that resistive switching may also appear in pure metallic nanowires lacking any silver-ion-hosting embedding environment but this pure atomic switching mechanism differs fundamentally from the conventional electrochemical-metallization-based resistive switching. To facilitate the quantitative description of the former phenomenon, we investigate a broad range of $\mathrm{Ag}$ atomic junctions, with a special focus on the frequency dependence and the fundamentally stochastic cycle-to-cycle variation of the switching-threshold voltage. These devices are established in an ultrahigh-purity environment in which electrochemical metallization can be excluded. The measured characteristics are successfully described by a vibrational-pumping model, yielding consistent predictions for the weak frequency dependence and the large variance of the switching-threshold voltage. We also demonstrate that electrochemical-metallization-based resistive switching and pure atomic switching may appear in the same device structure and therefore the proper understanding of the pure atomic switching mechanism has a very relevant importance in silver-based electrochemical-metallization cells.