We demonstrate an inertially sensitive atomic interferometer based on a continuous, rather than pulsed, atomic beam at sub-Doppler temperatures in three dimensions. We measure 30% fringe contrast in continuous, inertially sensitive interference fringes at interrogation time $T=6.7\mathrm{ms}$ and a short-term phase measurement noise of $530\mu \mathrm{rad}/\sqrt{\mathrm{Hz}}$ as inferred from interference measurements. Atoms are delivered to the interferometer by a cold-rubidium source that produces a high flux of atoms at temperature $\le 15\mu \mathrm{K}$ in three dimensions while reducing near-resonance fluorescence in the downstream path of the atoms. We describe the optimization of the interrogating Raman beams to achieve high contrast, and validate interferometer operation through comparison with measurements by commercial accelerometers. We further provide a demonstration of zero-dead-time phase-shear readout of atom interferometer phase, achieving a measurement rate up to 160 Hz. This demonstration lays the groundwork for future gyroscope/accelerometer sensors that measure continuously, with both high bandwidth and high sensitivity, and on dynamic platforms.

Moisture transport and/or storage in clothes plays a major role on the comfort or discomfort they procure due to the resulting wetness or heat loss along the skin. Our current knowledge of these complex processes, which involve both vapor transport and water sorption in the solid structure, is limited. This is, in particular, due to the open questions concerning the sorption dynamics at a local scale (for modeling), which lead to complex nonvalidated models, and to the challenge that constitutes the direct observation of these transports (for measurements). Here, through unique experiments, we directly observe the bound-water transport in a model textile sample during drying with the help of an original magnetic resonance imaging technique. Despite the various physical effects involved, this transport appears to follow a diffusionlike process. We then demonstrate theoretically that this process is described in detail (at a local scale) by a simple model of vapor transport through the structure assuming instantaneous sorption equilibrium and without any parameter fitting, which finally brings a simple response to modeling. This, in particular, allows us to quantify, as a function of simply measurable material parameters and air-flux impact, the characteristic time during which the evaporation of sweat is accelerated by sorption, the time during which a textile constitutes a barrier against ambient humidity, or the conditions of mask humidification. These results open the way to a full characterization and prediction of fabric properties under different conditions, and to direct formulation of high-performance materials by adjusting the material constituents.

Metamaterials can enable peculiar static and dynamic behavior (such as negative effective mass density, dynamical stiffness, and Poisson’s ratio) due to their geometry rather than their chemical composition. The geometry of these metamaterials can be thought of as the phase of the material, which is usually fixed once the material is fabricated. While there exist many theoretical and numerical studies of metamaterials that can change phase, or reprogram, experimental realizations remain limited due to challenges in manufacturability, the destructive nature of the reprogramming, and inherent nonlinearities. Through a combination of analytical, numerical, and experimental analyses, we utilize tunable, self-assembled, nonlinear magnetic lattices to realize metamaterials with reversible phase transitions. Our metamaterials are composed of free-floating disks, with embedded permanent magnets, confined within magnetic boundaries. We exploit the nondestructive nature of the adjustable magnetic boundaries to create a set of reprogrammable metamaterials to control the propagation of sound waves. Furthermore, we demonstrate a robust, real-time tunable wave filter at ultralow frequencies. Our findings can expand the metamaterials horizon into functional and tunable devices.

Mott materials such as vanadium oxides, when subject to a strong applied voltage, present an inhomogeneous insulator-to-metal transition with formation of metallic filaments within the insulating bulk. This property is enabling the development of compact and power-efficient neuromorphic devices known as Mott neurons. However, the nature of the transition has not been fully understood yet, as it may be attributed to different effects, including Joule self-heating and hot-carrier injection. Moreover, the experimental determination of the threshold voltage needed to induce the transition has proven to be challenging, as the transition becomes increasingly unpredictable when the threshold is approached. The physical understanding of these issues would not only deepen our understanding of Mott insulators, but would also be an important step toward the realization of neuromorphic devices based on such materials. In this work we use numerical simulations based on the Mott resistor network model to study the nature of the filament incubation and formation process. We show that both electronic and thermal effects, in the form of current density focusing and Joule self-heating, respectively, contribute to the filamentary incubation and growth. Remarkably, we find that the percolation of the metallic filaments near the threshold is intrinsically stochastic, qualitatively similar to the familiar Arrhenius activated behavior and to the stochastic firing of biological neurons. More precisely, we characterize the filament percolation as a Poisson point process, which has the same probability distribution as mathematical models of neuronal firing with an exponential escape rate. Finally, we support the numerical simulation results by performing experiments in ${\mathrm{VO}}_2$ that are in agreement with the exponential escape rate behavior. Thus, we establish a functionality of Mott insulators that opens a path toward implementing neuromorphic hardware with quantum materials.

We use electromigration (EM) to tune the oxygen content of ${\mathrm{Y}\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$ (YBCO) nanowires. During EM, the dopant oxygen atoms in the nanowire are moved under the combined effect of electrostatic force and Joule heating. The EM current can be tuned to either deplete or replenish nanowires with oxygen, allowing fine tuning of its hole-doping level. Electrical transport measurements and Kelvin probe microscopy corroborate good homogeneity of the doping level along the electromigrated nanowires. Thus, EM provides an effective method to study transport properties of YBCO in a wide doping range at the nanoscale in one and the same device.

Internal bias in ferroelectric materials is a well-known phenomenon that offsets the ferroelectric polarization hysteresis loop along the electric-field axes. Control over this degree of freedom could lead to alternative classes of ferroelectric devices, as with control over the analogous concept of exchange bias in ferromagnetic devices. Currently, there lacks a systematic approach to engineering internal bias by design that allows for device-by-device control over this parameter, leading to difficulty in translating these concepts to the large-scale integration of ferroelectric electronics. In this work, the flexoelectric effect is used to engineer internal bias through the controlled deposition of stressed thin films onto ferroelectrics. Large strain gradients are generated near the surface of ferroelectric $\mathrm{Pb}({\mathrm{Mg}}_{1/3}{\mathrm{Nb}}_{2/3}{)}_{0.71}{\mathrm{Ti}}_{0.29}{\mathrm{O}}_3$ single crystals through the deposition of stressed thin film strain gauges with increasing film force (film stress × film thickness). Using this technique, it is possible to continuously tune internal bias to control ferroelastic strain applied by the ferroelectric versus applied electric field, thereby achieving control of ferroelastic nonvolatility. Flexoelectric control of internal bias is verified by density functional theory and finite element analysis using a model with no free parameters, which matches both the expected magnitude and directionality of the flexoelectric field, and then further confirmed by piezoresponse force microscopy. This stress-induced flexoelectric effect utilizes popular strain engineering techniques already widely adopted by commercial complementary metal-oxide-semiconductor (CMOS) industrial fabrication processes, therefore sharing its advantages in scalability and reliability. Utilizing these techniques may lead to device-by-device level control of nonvolatility in ferroelectric field-effect or straintronic devices.

Twin-field quantum key distribution (TFQKD) systems have shown great promise for implementing practical long-distance secure quantum communication due to its measurement-device-independent nature and its ability to offer fundamentally superior rate-loss scaling than point-to-point QKD systems. A surge of research and development effort in the last two years has produced many variants of protocols and experimental demonstrations. In terms of hardware topology, TFQKD systems interfering quantum signals from two remotely phase-locked laser sources are in essence giant Mach-Zehnder interferometers (MZIs) requiring active phase stabilization. Such configurations are inherently unsuitable for a TFQKD network, where more than one user pair share the common quantum measurement station, because it is practically extremely difficult, if not impossible, to stabilize MZIs of largely disparate path lengths, a situation that is inevitable in a multi-user-pair TFQKD network. On the other hand, Sagnac interferometer-based TFQKD systems exploiting the inherent phase stability of the Sagnac ring can implement asymmetric TFQKD, and are therefore eminently suitable for implementing a TFQKD network. In this work, we experimentally demonstrate a proof-of-principle multi-user-pair Sagnac TFQKD network where three user pairs sharing the same measurement station can perform pairwise TFQKD through time multiplexing, with channel losses up to $58.00$ dB, and channel loss asymmetry up to $15.00$ dB. In some cases, the secure key rates still beat the rate-loss bound for point-to-point repeaterless QKD systems, even in this network configuration. Our demonstration of this multi-user-pair TFQKD network is a step in advancing quantum-communication network technologies.

One of the big challenges of current electronics is the design and implementation of hardware neural networks that perform fast and energy-efficient machine learning. Spintronics is a promising catalyst for this field with the capabilities of nanosecond operation and compatibility with existing microelectronics. Considering large-scale, viable neuromorphic systems however, variability of device properties is a serious concern. In this paper, we show an autonomously operating circuit that performs hardware-aware machine learning utilizing probabilistic neurons built with stochastic magnetic tunnel junctions. We show that in situ learning of weights and biases in a Boltzmann machine can counter device-to-device variations and learn the probability distribution of meaningful operations such as a full adder. This scalable autonomously operating learning circuit using spintronics-based neurons could be especially of interest for standalone artificial-intelligence devices capable of fast and efficient learning at the edge.

Measurements that occur within the internal layers of a quantum circuit—midcircuit measurements—are a useful quantum-computing primitive, most notably for quantum error correction. Midcircuit measurements have both classical and quantum outputs, so they can be subject to error modes that do not exist for measurements that terminate quantum circuits. Here we show how to characterize midcircuit measurements, modeled by quantum instruments, using a technique that we call quantum instrument linear gate set tomography (QILGST). We then apply this technique to characterize a dispersive measurement on a superconducting transmon qubit within a multiqubit system. By varying the delay time between the measurement pulse and subsequent gates, we explore the impact of residual cavity photon population on measurement error. QILGST can resolve different error modes and quantify the total error from a measurement; in our experiment, for delay times above $1000\mathrm{ns}$ we measure a total error rate (i.e., half diamond distance) of ${ϵ}_{\diamond }=8.1\pm 1.4\mathrm{\%}$, a readout fidelity of $97.0\pm 0.3\mathrm{\%}$, and output quantum-state fidelities of $96.7\pm 0.6\mathrm{\%}$ and $93.7\pm 0.7\mathrm{\%}$ when measuring $0$ and $1$, respectively.

Quantum nano-optics aims at transposing the concepts of quantum optics at the nanoscale. In this context, nitrogen-vacancy color centers in nanodiamonds are particularly interesting model sources as they emit single photons one by one with a broad spectral distribution between 600 and 800 nm. We deposit such quantum emitters at the extremities of silicon nanowires and analyze the effects of this interaction via spectrally resolved confocal microscopy. We demonstrate that the single-photon emission can be guided over several microns under conservation of their quantum statistics, while the silicon nanowires act as spectral filters for the quantum emission. Numerical simulations are in very good agreement with experiments, and indicate that the modal landscape of these nanowaveguides and the according coupling efficiencies with quantum emitters can be designed such that only light from emitters of specific orientations is efficiently guided through the nanowire, enabling a unique quantum state selectivity at a micrometer length scale. Our work opens the door to a genuine modal control of single-photon transfer in subwavelength waveguides, paving the way to future fundamental studies and toward integrated and multiwavelength photonics applications in quantum nano-optics.

Stimuli-responsive materials are designed for self-sustained soft robots. Using a photothermally responsive hydrogel cantilever as a model system, this paper investigates the mechanism and energy flow in self-excited oscillation under a constant light source. Based on an analytical model, we show that a periodic photomoment, produced by nonuniform water concentration across the cantilever’s thickness driven by diffusion, is imposed on the cantilever by the ever-switching light incidence between the top and bottom surfaces. The synergy between the photomoment and oscillation ensures positive work input to the cantilever when the diffusion timescale is comparable to the period of free oscillation. When the input energy is higher than the damping energy, the oscillation amplitude increases, while, when the input energy is lower, the amplitude decreases. Based on dimensional energy analysis, we determine the stable oscillation amplitude and construct phase diagrams for the increase and decrease of the oscillation amplitude, which are further confirmed experimentally. A mass-spring-damper system subjected to a displacement-dependent excitation force is developed to investigate the features in generalized self-excited oscillating systems. This work lays a solid foundation for understanding self-excited oscillation and provides design guidelines for self-sustainable soft robots.

In recent years, the ability to propagate topological solitons in mechanical metamaterials has unlocked unpaved paths towards potential applications in wave propagation, mechanical logic, and shape morphing. Here, we demonstrate how a multistable metamaterial can harness topological solitons with coupled rotational and translational components and become, itself, a crawling robot. We start by characterizing the topological solitons via experimental measurements and analysis. We then use their rotational component to produce a favorable gradient of friction between the metamaterial and the underlying substrate. This, in turn, creates locomotion. Previously proposed crawling robots usually require complex control of multiple actuators. In contrast, our robot can be powered by a single actuator, and all features needed for locomotion are embedded in the mechanics and activated by the topological solitons.

Ferrite microwave circulators allow one to control the directional flow of microwave signals and noise, and thus play a crucial role in present-day superconducting quantum technology. They are typically viewed as a black box, with their internal structure neither specified nor used as a quantum resource. In this work, we show a low-loss waveguide circulator constructed with single-crystalline yttrium iron garnet in a three-dimensional cavity, and analyze it as a multimode hybrid quantum system with coupled photonic and magnonic excitations. We show the coherent coupling of its chiral internal modes with integrated superconducting niobium cavities, and how this enables tunable nonreciprocal interactions between the intracavity photons. We also probe experimentally the effective non-Hermitian dynamics of this system and its effective nonreciprocal eigenmodes. The device platform provides a test bed for implementing nonreciprocal interactions in open-system circuit QED.

Tunable two-qubit couplers offer an avenue to mitigate errors in multiqubit superconducting quantum processors. However, most couplers achieve this by fine tuning circuit parameters and often target specific couplings, such as the spurious $ZZ$ interaction. We introduce a superconducting coupler that alleviates these limitations by suppressing all two-qubit interactions with an exponentially large on:off ratio and without the need for fine tuning. Our approach is based on a bus mode supplemented by an ancillary nonlinear resonator mode. Driving the ancillary mode leads to a coupler-state-dependent field displacement in the resonator that, in turn, results in an exponential suppression of real and virtual two-qubit interactions with respect to the drive power. A superconducting circuit implementation supporting the proposed mechanism is presented.

In this work we introduce a modular self-assembled microswimmer whose propulsion mechanism along a fluid interface is based on the decoupling between the dynamics exhibited by the component particles and the assembly. The velocity, direction, and structure of the array can be dynamically adjusted by altering the applied field and understood in terms of hydrodynamics. We also show how these small micromotors can act as building blocks of more complex designs, which can be used for the precise and long-range transport of hydrophilic, hydrophobic, or amphiphilic molecules and cargos along various fluid interfaces.

We address an outstanding problem that represents a critical roadblock in the development of the Majorana-based topological qubit using semiconductor-superconductor hybrid structures: the quantitative characterization of disorder effects generated by the unintentional presence of charge impurities within the hybrid device. Given that disorder can have far-reaching consequences for the Majorana physics but is intrinsically difficult to probe experimentally in a hybrid structure, providing a quantitative theoretical description of disorder effects becomes essential. To accomplish this task, we develop a microscopic theory that (i) provides a quantitative characterization of the effective potential generated by a charge impurity embedded inside a semiconductor wire proximity coupled to a superconductor layer by solving self-consistently the associated three-dimensional Schrödinger-Poisson problem, (ii) describes the low-energy physics of the hybrid structure in the presence of $s$-wave superconductivity, spin-orbit coupling, Zeeman splitting, and disorder arising from multiple charge impurities by using the results of (i) within a standard free-fermion approach, and (iii) links the microscopic results to experimentally observable features by generating tunneling differential-conductance maps as a function of the control parameters (e.g., Zeeman field and chemical potential). We find that charge impurities lead to serious complications regarding the realization and observation of Majorana zero modes, which have direct implications for the development of Majorana-based qubits. More importantly, our work provides a clear direction regarding what needs to be done for progress in the field, including specific materials-quality and semiconductor-purity targets that must be achieved to create a topological qubit.

We investigate the temporal response of constriction-based spin Hall nano-oscillators driven by pulsed stimuli using time-resolved Brillouin light scattering microscopy. The growth rate of the magnetization auto-oscillations, enabled by spin Hall effect and spin-orbit torque, is found to vary with the amplitude of the input voltage pulses, as well as the synchronization frequency set by an external microwave input. The combination of voltage and microwave pulses allows us to generate auto-oscillation signals with multilevel amplitude and frequency in the time domain. Our findings suggest that the lead time of processes such as synchronization and logic using spin Hall nano-oscillators can be reduced to the nanosecond timescale.

The genuine concurrence is a standard quantifier of multipartite entanglement, detection, and quantification of which still remains a difficult problem from both the theoretical and experimental points of view. Although many efforts have been devoted to the detection of multipartite entanglement (e.g., using entanglement witnesses), measuring the degree of multipartite entanglement, in general, requires some knowledge about the exact shape of a density matrix of the quantum state. An experimental reconstruction of such a density matrix can be done by full state tomography, which amounts to having the distant parties share a common reference frame and well-calibrated devices. Although this assumption is typically made implicitly in theoretical works, establishing a common reference frame, as well as aligning and calibrating measurement devices in experimental situations, are never trivial tasks. It is therefore an interesting and important question whether the requirements of having a shared reference frame and calibrated devices can be relaxed. In this work, we study both theoretically and experimentally the genuine concurrence for the generalized Greenberger-Horne-Zeilinger states under randomly chosen measurements on individual qubits without a shared frame of reference and calibrated devices. We present the relation between genuine concurrence and the so-called nonlocal volume, a recently introduced indicator of nonlocality.

An understanding of nano- and microscale crystal strain in chemical-vapor-deposition diamond is crucial to the advancement of diamond quantum technologies. In particular, the presence of such strain and its characterization presents a challenge to diamond-based quantum sensing and information applications—as well as for future dark-matter detectors, where the directional information about incoming particles is encoded in crystal strain. Here, we exploit nanofocused scanning x-ray diffraction microscopy to quantitatively measure crystal deformation from defects in diamond with high spatial and strain resolution. The combination of information from multiple Bragg angles allows stereoscopic three-dimensional modeling of strain-feature geometry; the diffraction results are validated via comparison to optical measurements of the strain tensor based on spin-state-dependent spectroscopy of ensembles of nitrogen-vacancy centers in the diamond. Our results demonstrate both strain and spatial resolution sufficient for directional detection of dark matter via x-ray measurement of crystal strain and provide a promising tool for diamond growth analysis and improvement of defect-based sensing.

We use spin torque ferromagnetic resonance and ferromagnetic-resonance-driven spin pumping to detect spin-charge interconversion at room temperature in heterostructure devices that interface an archetypal Dirac semimetal, ${\mathrm{Cd}}_3{\mathrm{As}}_2$, with a metallic ferromagnet, ${\mathrm{Ni}}_{0.80}{\mathrm{Fe}}_{0.20}$ (permalloy). Angle-resolved photoemission directly reveals the Dirac-semimetal nature of the samples prior to device fabrication and high-resolution transmission electron microscopy is used to characterize the crystalline structure and the relevant heterointerfaces. We find that the spin-charge interconversion efficiency in ${\mathrm{Cd}}_3{\mathrm{As}}_2/$permalloy heterostructures is comparable to that in heavy metals and that it is enhanced by the presence of an interfacial oxide. Spin torque ferromagnetic resonance measurements reveal an in-plane spin polarization regardless of an oxidized or pristine interface. We discuss the underlying mechanisms for spin-charge interconversion by comparing our results with first principles calculations and conclude that extrinsic mechanisms dominate the observed phenomena. Our results indicate a need for caution in interpretations of spin-transport and spin-charge conversion experiments in ${\mathrm{Cd}}_3{\mathrm{As}}_2$ devices that seek to invoke the role of topological Dirac and Fermi arc states.