Optical fabrication of waveguides in a volume is limited by diffraction in the writing beams. We demonstrate the use of nondiffracting waves in the form of Bessel beams to fabricate scalable optical wiring through direct writing in a photosensitive volume. Experiments are performed in paraelectric potassium-lithium-tantalate-niobate (KLTN), where writing occurs through photogenerated space charge while guiding and electro-optic functionality are supported by the quadratic electro-optic effect. The method allows components to be integrated sequentially without interfering with each other during fabrication, an intrinsic superposition property that is used to realize single, double, and multiple waveguides, and $1\times 2$, $1\times 3$, and $1\times 4$ splitters, and electrically controlled optical switching.

Trapped-ion quantum-information processors offer many advantages for achieving high-fidelity operations on a large number of qubits, but current experiments require bulky external equipment for classical and quantum control of many ions. We demonstrate the cryogenic operation of an ion trap that incorporates monolithically integrated high-voltage complementary metal-oxide semiconductor (CMOS) electronics ($\pm 8\mathrm{V}$ full swing) to generate surface-electrode control potentials without the need for external analog voltage sources. A serial bus programs an array of 16 digital-to-analog converters (DACs) within a single chip that apply voltages to segmented electrodes on the chip to control ion motion. Additionally, we present the incorporation of an integrated circuit that uses an analog switch to reduce voltage noise on trap electrodes due to the integrated amplifiers by over 50 dB. We verify the function of our integrated electronics by performing diagnostics with trapped ions and find noise and speed performance similar to those that we observe using external control elements.

Mask-based pattern generation is a crucial step in microchip production. The next-generation extreme-ultraviolet- (EUV) lithography instruments with a wavelength of 13.5 nm are currently under development. In principle, this should allow patterning down to a resolution of a few nanometers in a single exposure. However, there are many technical challenges, including those due to the very high energy of the photons. Lithography with metastable atoms has been suggested as a cost-effective, less-complex alternative to EUV lithography. The great advantage of atom lithography is that the kinetic energy of an atom is much less than that of a photon for a given wavelength. However, until now no method has been available for making masks for atom lithography that can produce arbitrary, high-resolution patterns. Here we present a solution to this problem. First, traditional binary holography is extended to near-field binary holography, based on Fresnel diffraction. By this technique, we demonstrate that it is possible to make masks that can generate arbitrary patterns in a plane in the near field (from the mask) with a resolution down to the nanometer range using a state-of-the-art metastable-helium source. We compare the flux of this source with that of an established EUV source (NXE:3100, ASML) and show that patterns can potentially be produced at comparable speeds. Finally, we present an extension of the grid-based holography method for a grid of hexagonally shaped subcells. Our method can be used with any beam that can be modeled as a scalar wave, including other matter-wave beams such as helium ions, electrons, or acoustic waves.

We demonstrate the sensitivity of a sensor based on an optically pumped radio-frequency (rf) atomic magnetometer to the polarization state of the detected rf magnetic field and measure $>36$ dB difference in amplitude sensitivity for opposite circular-field polarizations. This sensitivity could be used to create sensors that would allow signal detection while suppressing unwanted rf fields using polarization rejection, in contrast to traditional gradiometry configurations. Additionally, such a sensor will be orientation-sensitive, as the phase of the detected signal is shown to depend on the angle between the sensor’s detection axis and the direction to the transmitter.

Non-Hermitian Hamiltonians can give rise to exceptional points (EPs), which have been extensively explored with nominally identical coupled resonators. Here, a non-Hermitian electromechanical system is developed, which hosts vibration modes that differ massively in their spatial profile, frequency, and even the sign of their dissipation. An optomechanical-like modulation is employed to parametrically couple two of these disparate modes whose dynamics are then probed via frequency spectroscopy. The resultant experimental responses are numerically simulated, to enable the underlying eigenvalues of the electromechanical system to be extracted, which reveal the nondegenerate modes real components undergo parametric normal mode splitting, while their imaginary parts coalesce. These results suggest that virtual EPs can be accessed in systems composed of highly mismatched resonators while still maintaining access to the nontrivial phenomena in their proximity, as recently demonstrated for topological operations, thus enabling non-Hermitian singularities to be more widely exploited with realistic physical systems.

We predict strong interface multiferroicity at $\mathrm{bcc}\text{−}\mathrm{Fe}/\mathrm{Bi}\mathrm{Fe}{\mathrm{O}}_3(001)$ heterointerfaces by using first-principles calculations. For the identified stable atomic structure, we quantify the changes in the orientation of the magnetic moments of bcc $\mathrm{Fe}$ due to the reversal of the electric polarization of $\mathrm{Bi}\mathrm{Fe}{\mathrm{O}}_3$. By determining the magnetoelectric tensor, we find that the magnetoelectric coupling of the present ferromagnetic-multiferroic interface is an order of magnitude larger than that of a ferromagnetic-ferroelectric interface, $\mathrm{bcc}\text{−}\mathrm{Fe}/\mathrm{Ba}\mathrm{Ti}{\mathrm{O}}_3(001)$.

Magnetic sensors are important for detecting nuclear magnetization signals in nuclear magnetic resonance (NMR). As a complementary analysis tool to conventional high-field NMR, zero- to ultralow-field (ZULF) NMR detects nuclear magnetization signals in the submicrotesla regime. Current ZULF NMR systems are always equipped with high-quality magnetic shields to ensure that ambient magnetic-field noise does not dwarf the magnetization signal. An alternative approach is to separate the magnetization signal from the noise based on their differing spatial profiles, as can be achieved using a magnetic gradiometer. Here, we present a gradiometric ZULF NMR spectrometer with a magnetic-field-gradient noise of $17\mathrm{fT}/\mathrm{cm}{\mathrm{Hz}}^{1/2}$ in the frequency ranging from 100 to 400 Hz, based on a single vapor cell ($0.7\times 0.7\times 1.0{\mathrm{cm}}^3$). With applied white magnetic-field noise, we show that the gradiometric spectrometer achieves 13-fold enhancement in the signal-to-noise ratio (SNR) compared to the single-channel configuration. By reducing the influence of the common-mode magnetic-field noise, this work enables the use of compact and low-cost magnetic shields. Gradiometric detection also proves to be beneficial for eliminating systematic errors in ZULF-NMR experiments searching for exotic spin-dependent interactions and molecular parity violation.

We investigate the dynamical control of the heat flux exchanged in the near-field regime between a membrane made with a phase-change material and a substrate when the temperature of the membrane is tuned around its critical value. We show that in interaction with an external source of thermal radiation, this system is multistable and behaves as a thermal transistor, being able to dynamically modulate and even amplify super-Planckian heat fluxes. This behavior could be used to dynamically control heat fluxes exchanged at the nanoscale in systems out of thermal equilibrium and to process thermal information employing suspended membranes.

Superconducting circuits are a versatile platform to implement a multitude of Hamiltonians that perform quantum computation, simulation, and sensing tasks. A key ingredient for realizing a desired Hamiltonian is the irradiation of the circuit by a strong drive. These strong drives provide an in situ control of couplings, which cannot be obtained by near-equilibrium Hamiltonians. However, as shown in this paper, out-of-equilibrium systems are easily plagued by complex dynamics, leading to instabilities. The prediction and prevention of these instabilities is crucial, both from a fundamental and application perspective. We propose an inductively shunted transmon as the elementary circuit optimized for strong parametric drives. Developing a numerical approach that avoids the built-in limitations of perturbative analysis, we demonstrate that adding the inductive shunt significantly extends the range of pump powers over which the circuit behaves in a stable manner.

We theoretically investigate the critical current of a thermally biased superconductor-insulator-superconductor (S-I-S) Josephson junction formed by electrodes made from different Bardeen-Cooper-Schrieffer (BCS) superconductors. The response of the device is analyzed as a function of the asymmetry parameter, $r=T_{c_1}/T_{c_2}$. We highlight the appearance of jumps in the critical current of an asymmetric junction, namely, when $r\ne 1$. In fact, in such a case, at temperatures at which the BCS superconducting gaps coincide, the critical current suddenly increases or decreases. In particular, we thoroughly discuss the counterintuitive behavior of the critical current, which increases by enhancing the temperature of one lead, instead of monotonically reducing. In this case, we find that the largest jump of the critical current is obtained for moderate asymmetries, $r\simeq 3$. In view of these results, the discussed behavior can be speculatively proposed as a temperature-based threshold single-photon detector with photon-counting capabilities, which operates nonlinearly in the nondissipative channel.

Oocyte activation deficiency is considered to be the principal factor underlying fertilization failure after intracytoplasmic sperm injection (ICSI), and consequently exhibits a lack of cytosolic calcium (${\mathrm{Ca}}^{2+}$) oscillations in oocytes. Traditional artificial activation methods are usually proposed to induce an intracellular ${\mathrm{Ca}}^{2+}$ transient in oocytes. However, these current methods either cannot mimic the precise physiological processes of mammalian oocyte activation or there still exists controversy concerning their activation mechanisms. Here, we present a report on the potential of using nanosecond pulsed electric fields (nsPEFs) with a 10-ns duration not only to achieve a high activation rate of mouse oocytes, but also to significantly improve the developmental ability of parthenogenetic embryos. More importantly, in the exploration of activation mechanisms, we find that nsPEFs can regulate three different patterns of ${\mathrm{Ca}}^{2+}$ oscillation via mobilizing both ${\mathrm{Ca}}^{2+}$ influx from the outside and efflux from the endoplasmic reticulum (ER), and can even induce spontaneous ${\mathrm{Ca}}^{2+}$ oscillations. Furthermore, a nsPEFs-mediated ${\mathrm{Ca}}^{2+}$-channel kinetic model is introduced, and the simulation results agree well with our experiments. Our model predicts that nsPEFs could regulate ${\mathrm{Ca}}^{2+}$ oscillations via the direct effects on the openness of ${\mathrm{Ca}}^{2+}$ channels by simultaneously mobilizing extracellular and intracellular ${\mathrm{Ca}}^{2+}$. Therefore, as an effective and controllable method, nsPEFs provide a valuable tool for potential artificial activation treatment in the future.

We argue that a high-purity $\mathrm{Yb}$-doped silica glass can potentially be cooled via anti-Stokes-fluorescence optical refrigeration. In order to achieve net solid-state optical refrigeration, it is necessary for the cooling efficiency to be positive. This requires the pump wavelength to be greater than the mean fluorescence wavelength and the internal quantum efficiency as well as the absorption efficiency to be near unity. Our conclusion is reached by showing, using reasonable assumptions for the host-material properties, that the nonradiative decay rate of $\mathrm{Yb}$ ions can be made substantially smaller than the radiative decay rate. Therefore, an internal quantum efficiency of near unity can be obtained. Moreover, the background absorption coefficient in high-quality silica glass lies in an acceptable range to guarantee a near-unity absorption efficiency at room temperature. Using spectral measurements of the fluorescence from a $\mathrm{Yb}$-doped silica optical fiber at a range of temperatures, we estimate the minimum achievable temperature in $\mathrm{Yb}$-doped silica glass for different values of the internal quantum efficiency.

Nematodes have evolved to swim in highly viscous environments. Artificial mechanisms that mimic the locomotory functions of nematodes can be efficient viscous pumps. We experimentally simulate the motion of the head segment of Caenorhabditis elegans by introducing a reciprocating and rocking blade. We show that the bioinspired motion of the blade not only induces a flow structure similar to that of the worm, but also mixes the surrounding fluid by generating a circulatory flow. When confined between two parallel walls, the blade causes a steady Poiseuille flow through closed circuits. The pumping efficiency is comparable with the swimming efficiency of the worm. If implanted in a sealed chamber and actuated remotely, the blade can provide pumping and mixing functions for microprocessors cooled by polymeric flows and microfluidic devices.

Understanding the physical origin of noise affecting quantum systems is important for nearly every quantum application. Quantum-noise spectroscopy has been used in various quantum systems, such as superconducting qubits, nitrogen-vacancy centers, and trapped ions. Traditional spectroscopy methods are usually efficient in measuring noise spectra with mostly monotonically decaying contributions. However, there are important scenarios in which the noise spectrum is broadband and nonmonotonous, thus posing a challenge to existing noise-spectroscopy schemes. Here we compare several methods for noise spectroscopy: spectral decomposition based on the Carr-Purcell-Meiboom-Gill sequence, the recently presented dynamic sensitivity control (DYSCO) sequence, and a modified DYSCO sequence with a Gaussian envelope (gDYSCO). The performance of the sequences is quantified by analytic and numeric determination of the frequency resolution, bandwidth, and sensitivity, revealing a supremacy of gDYSCO to reconstruct nontrivial features. Using an ensemble of nitrogen-vacancy centers in diamond coupled to a high-density ${}^{13}\mathrm{C}$-nuclear-spin environment, we experimentally confirm our findings. The combination of the schemes presented offers potential to record high-quality noise spectra as a prerequisite to generate quantum systems unlimited by their spin-bath environment.

Spiking neural networks (SNNs) offer an event-driven and more-biologically-realistic alternative to standard artificial neural networks based on analog information processing. This can potentially enable energy-efficient hardware implementations of neuromorphic systems that emulate the functional units of the brain; namely, neurons and synapses. Recent demonstrations of ultrafast photonic computing devices based on phase-change materials (PCMs) show promise for addressing limitations of electrically driven neuromorphic systems. However, scaling these stand-alone computing devices to a parallel in-memory computing primitive is a challenge. In this work, we use the optical properties of the PCM ${\mathrm{Ge}}_2{\mathrm{Sb}}_2{\mathrm{Te}}_5$ to propose a photonic SNN computing primitive, comprising a nonvolatile synaptic array integrated seamlessly with previously explored “integrate-and-fire” neurons. The proposed design realizes an “in-memory” computing platform that leverages the inherent parallelism of wavelength-division multiplexing. We show that the proposed computing platform can be used to emulate a SNN inferencing engine for image-classification tasks. The proposed design not only bridges the gap between isolated computing devices and parallel large-scale implementation but also paves the way for ultrafast computing and localized on-chip learning.

We propose a magnetic scanning-probe sensor based on a single-planar Josephson junction with a magnetic barrier. The planar geometry together with the high magnetic permeability of the barrier facilitates a double flux-focusing effect, which helps to guide magnetic flux into the junction and thus enhances field sensitivity of the sensor. We fabricate and analyze experimentally sensor prototypes with a superparamagnetic $\mathrm{Cu}\text{−}\mathrm{Ni}$ and a ferromagnetic $\mathrm{Ni}$ barrier. We demonstrate that the planar geometry allows easy miniaturization to nanometer scale and facilitates an effective utilization of the self-field phenomenon for amplification of sensitivity and a simple implementation of a control line for feedback operation over a broad dynamic range. We argue that the proposed sensor can outperform equally sized superconducting quantum-interference devices (SQUIDs) both in terms of magnetic-field sensitivity and spatial resolution, which makes it advantageous for scanning-probe microscopy.

We investigate the influence of Meissner screening and trapped magnetic flux on magnetization dynamics for a ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$ film sandwiched between two thick $\mathrm{Nb}$ layers (100 nm) using broadband (5–20 GHz) ferromagnetic resonance (FMR) spectroscopy. Below the superconducting transition T_c of $\mathrm{Nb}$, significant zero-frequency line broadening (5–6 mT) and dc-resonance field shift (50 mT) to a low field are both observed if the $\mathrm{Nb}$ thickness is comparable to the London penetration depth of $\mathrm{Nb}$ films (≥100 nm). We attribute the observed peculiar behaviors to the increased incoherent precession near the ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}/\mathrm{Nb}$ interfaces and the effectively focused magnetic flux in the middle ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$ caused by strong Meissner screening and (defect-)trapped flux of the thick adjacent $\mathrm{Nb}$ layers. This explanation is supported by static magnetic properties of the samples and comparison with FMR data on thick $\mathrm{Nb}/{\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$ bilayers. Great care should, therefore, be taken in the analysis of FMR response in ferromagnetic Josephson structures with thick superconductors, a fundamental property for high-frequency device applications of spin-polarized supercurrents.

We demonstrate microwave-free eddy-current imaging using nitrogen-vacancy centers in diamond. By detecting the eddy-current+induced magnetic field of conductive samples, we can distinguish between different materials and shapes and identify structural defects. Our technique allows the discrimination of different materials according to their conductivity. The sensitivity of the measurements is calculated as $8\times {10}^5\text{S}/\text{m}\sqrt{\text{Hz}}$ at 3.5 MHz for a cylindrical sample with radius $r_0=1\text{mm}$ and height $h=0.1\text{mm}$ (volume approximately $0.3{\text{mm}}^3$) at a distance of 0.5 mm. In comparison with existing technologies, the diamond-based device exhibits a greater bandwidth and spatial resolution. In particular, we demonstrate a flat frequency response from 0 Hz to 3.5 MHz and a spatial resolution of $348\pm 2\mu \text{m}$.

Despite extensive studies on the insulator-to-metal transition (IMT) in strongly correlated ${\mathrm{VO}}_2$, the fundamental mechanism underlying the current-driven IMT in ${\mathrm{VO}}_2$ is still not well understood. Although it is generally believed that the mechanism is Joule heating leading to a rise in temperature to above the normal transition temperature, there is ample experimental evidence demonstrating that the transition could be driven by nonthermal electronic processes. Here we formulate a phase-field model to demonstrate that the electric current may drive the IMT isothermally via the current-induced electron-correlation weakening. We discover that a current with a large density (on the order of $10{\mathrm{nA}/\mathrm{nm}}^2$) induces ultrafast resistive switching on the order of a few nanoseconds, consistent with experimental measurements. We also construct the temperature-current phase diagram and investigate the influence of the current on domain walls. This work is expected to provide guidance for understanding the current-driven IMT in ${\mathrm{VO}}_2$ and for designing ${\mathrm{VO}}_2$-based electric switching devices.

With first-principles calculations based on density-functional theory, we predict the potential for the unprecedentedly high thermoelectric figure of merit $zT=5$ at 800 K in an $n$-type ${\mathrm{Ba}}_2\mathrm{Bi}\mathrm{Au}$ full-Heusler compound. Such a high efficiency arises from an intrinsically ultralow lattice thermal conductivity coupled with a very high power factor reaching $7\mathrm{mW}{\mathrm{m}}^{-1}{\mathrm{K}}^{-2}$ at 500 K. The high $n$-type power factor originates from a light, sixfold degenerate conduction-band pocket along the $\mathrm{\Gamma }$-$X$ direction. Weak acoustic phonon scattering and sixfold multiplicity combine to yield both high mobility and a high Seebeck coefficient. In contrast, the flat-and-dispersive (or low-dimensional) valence band of ${\mathrm{Ba}}_2\mathrm{Bi}\mathrm{Au}$ fails to generate such high power factors due to strong acoustic phonon scattering. The Lorenz numbers at optimal doping are smaller than the Wiedemann-Franz value, an integral feature for $zT$ enhancement as electrons are the majority heat carriers.