Unlike ferromagnets, collinear antiferromagnets have two precession modes exhibiting opposite chirality, which enables the use of the polarization degree of freedom of magnons. In this study, we experimentally measure the polarization-selective spectra of magnetic resonance in perpendicularly magnetized synthetic antiferromagnets using a wideband crossed microstrip circuit. The magnetic resonances with right-handed and left-handed precession modes are directly detected, and theoretical analysis and numerical simulations explain the measurement results by considering the difference in the perpendicular magnetic anisotropy and damping constant between the top and bottom ferromagnetic layers. We also show that magnetic excitations with different polarization types can be excited under degeneracy between the two precession modes. Our work suggests that perpendicularly magnetized synthetic antiferromagnet structures provide an attractive platform for manipulating the polarization degree of freedom of magnons.

Long-distance spin transport through antiferromagnetic insulators (AFMIs) is a long-standing goal of spintronics research. Unlike conventional spintronics systems, monolayer graphene in the quantum Hall regime (QH) offers an unprecedented tuneability of spin-polarization and charge-carrier density in QH edge states. Here, using gate-controlled QH edges as spin-dependent injectors and detectors in an all-graphene electrical circuit, we demonstrate a selective tuning of ambipolar spin transport through graphene ν = 0 AFMIs. By modulating polarities of the excitation bias, magnetic fields, and charge carriers that host opposite chiralities, we show that the difference between spin chemical potentials of adjacent edge channels in the spin-injector region is crucial in tuning spin transport observed across graphene AFMI. We demonstrate that nonlocal response vanishes upon reversing directions of the co-propagating edge channels when the spin filters in our devices are no longer selective for a particular spin polarization. Our results establish a versatile set of methods to tune pure spin transport via an antiferromagnetic media and open a pathway to explore their applications for a broad field of antiferromagnetic spintronics research.

The nontrivial shape of colloidal particles creates complex elastic distortions and topological defects in liquid crystals and plays a key role in governing their electrophoretic propulsion through the medium. Here, we report experimental results on defects and the electrophoretic transport of anisometric (snowman-shaped) polystyrene particles subjected to an alternating electric field perpendicular to the director in a nematic liquid crystal. We demonstrate that the shape asymmetry gives rise to defect polymorphism by nucleating point or ring defects at multiple locations on the particle and controls the direction as well as the magnitude of the electrophoretic propulsion. Unlike spherical particles, quadrupolar anisometric particles can be transported in multiple directions in the plane perpendicular to the applied field. Our findings provide an alternative degree of freedom in translocating microparticles in liquid crystals for applications in microfluidics, controlled transport, and directed assembly.

We propose and verify a method for controlling the frequency dependence of the group delay of electromagnetic waves over a broad frequency range using the Brewster effect in single-layer metamaterials with finite thickness, here referred to as metafilms. When the reflectance of the metafilm vanishes regardless of the incident frequency, the group delay can be large near its resonance frequency while maintaining the transmittance close to unity regardless of the incident frequency. Furthermore, when several reflectionless metafilms are stacked together, the total group delay should be given as the sum of the individual group delays. In this study, we realize reflectionless metafilms by arranging the meta-atoms so that the Brewster effect occurs regardless of the incident frequency. We evaluate in numerical simulations and experiments the frequency dependence of the transmittance and of the group delay of a three-layer metamaterial composed of reflectionless metafilms with different resonance frequencies and find that the total transmittance and group delay of this metamaterial agree, respectively, with the product of the transmittances and the sum of the group delays of the constituent metafilms.

We propose the design of a vibrational energy-absorption device based on the concept of inertial amplification, by utilizing coupling between translational and rotational motions. A compact and lightweight device, with dimensions being only 10–20 cm and weighing less than 1 kg, can achieve ultralow-frequency resonance response at seismic frequency range, i.e., 0.5–5 Hz. Resonators that can respond at such a low-frequency range are usually bulky structures on the civil-engineering scale; our compact design offers flexibility and options for practical applications. Fabricated functional prototypes verify the very large inertial-amplification factor, up to 137, through vibrational characterizations. Experimentally measured data are consistent with our analytical modeling of the inertial-amplification mechanism. Furthermore, we propose a structurally refined device configuration and demonstrate, through simulations, its capability of vibrational total absorption with a comparatively broadband working frequency range. Our design can be easily adapted for resonance frequencies up to 100 Hz, via further miniaturization of the device dimension and lowering of the inertial-amplification factor. The inertial-amplified resonator represents an unconventional solution to the difficult problem of ultralow frequency vibration mitigation, with compact and lightweight devices that can fit into limited space.

We study mutual synchronization in double nanoconstriction-based spin Hall nano-oscillators (SHNOs) under weak in-plane magnetic fields (${\mu }_0{H}_{\mathrm{IP}}=30–40$ mT) and also investigate its angular dependence. We compare SHNOs with different nanoconstriction spacings of 300 and 900 nm. In all devices, mutual synchronization occurs below a certain critical angle, which is higher for the 300 nm spacing than for the 900 nm spacing, reflecting the stronger coupling at shorter distances. Alongside the synchronization, we observe a strong second harmonic consistent with predictions that the synchronization may be mediated by the propagation of second-harmonic spin waves. However, although Brillouin light scattering microscopy confirms the synchronization, it fails to detect any related increase of the second harmonic. Micromagnetic simulations instead explain the angular-dependent synchronization as predominantly due to magnetodipolar coupling between neighboring SHNOs.

Magnetic skyrmions are promising candidates for logic-in-memory applications, intrinsically merging high-density nonvolatile data storage with computing capabilities, owing to their nanoscale size, fast motion, and mutual repulsions. However, concepts proposed so far suffer from reliability issues as well as inefficient conversion of magnetic information to electrical signals. In this paper, we propose a logic-in-memory device, which exploits skyrmion confinement and channeling using anisotropy energy barriers to achieve reliable data storage and synchronous shift in racetracks combined with cascadable and reprogrammable logics relying purely on magnetic interactions. The device combines a racetrack shift register based on skyrmions confined in nanodots with full-adder (FA) gates. The designed FA is reprogrammable and cascadable and can also be used to perform simple logic operations such as and, or, not, nand, xor, and nxor. The monolithic design of the logic gate and the absence of any complex electrical contacts makes the device ideal for integration with conventional CMOS circuitry.

We propose a numerical technique for modeling quantum multimodal light scattering by a perfectly conducting body. Using the special quantization technique, we develop the quantum adaptation of the characteristic mode approach widely used in classical electrodynamics. The method is universal with respect to the body’s configuration, as well as its dimensions relative to the wavelength. Using this method and calculating the first- and second-order field correlation functions, we demonstrate how scattering affects quantum-statistical features of the field. As an example, we consider the scattering of two single-photon incident Gaussian beams on a cylinder with a circular cross section. We show that the scattering is accompanied by two-photon interference and demonstrates the Hong-Ou-Mandel effect. It is shown that the scattered two-photon field and its correlations manifest directive propagation, which is controllable by various means (angles of incidence, configuration of the body, relations between its dimensions and the wavelength). We expect that this method will be useful for designing quantum-optical devices.

We introduce a nonlinear photonic system that enables asymmetric localization and unidirectional transfer of an electromagnetic wave through the second-harmonic generation process. Our proposed scattering setup consists of a noncentrosymmetric nonlinear slab with nonlinear susceptibility ${\chi }^{(2)}$ placed to the left side of a one-dimensional periodic linear photonic crystal with an embedded defect. We engineered the linear lattice to allow the localization of a selected frequency $2{\omega }_{\star }$ while frequency ${\omega }_{\star }$ is in the gap. Thus in our proposed scattering setup, a left-incident coherent transverse electric wave with frequency ${\omega }_{\star }$ partially converts to frequency $2{\omega }_{\star }$ and becomes localized at the defect layer while the unconverted remaining field with frequency ${\omega }_{\star }$ exponentially decays throughout the lattice and gets reflected. For a right-incident wave with frequency ${\omega }_{\star }$ there will not be any frequency conversion and the incident wave gets fully reflected. Our proposed structure will find application in designing optical components such as optical sensors, switches, transistors, and logic elements.

We theoretically propose and experimentally demonstrate a parallel electromagnetically induced transparency (parallel EIT) cooling technique for ion crystals in the Paul trap. It breaks the stringent cooling requirements of the standard EIT cooling, thus allowing, in principle, to simultaneously cool the motional mode spectrum with an arbitrary range. Experimentally a large cooling range over 5 MHz is proved by using a single trapped ${}^{40}{\mathrm{Ca}}^{+}$ ion. We also observe simultaneous near-ground-state cooling for all motional modes of a 4-ion chain with the best average phonon number of about 0.2. For cooling a large number of modes, we only need to modulate the probe beam of the standard EIT cooling with several rf frequencies. This cooling scheme has no selectivity for the types of ions (e.g., ${}^{171}{\mathrm{Yb}}^{+}$, ${}^{40}{\mathrm{Ca}}^{+}$), therefore it would be a powerful tool for initialization of all kinds of operational trapped-ion quantum computers or simulators.

We present a theory to compute the stable gap (interparticle) distance between particle chains collected in the pressure node of an acoustic standing wave. The primary and secondary acoustic radiation forces are the two competing forces that act on the particles during the particle chain formation. The stable equilibrium distance between two chains is reached when both forces are in balance. Most interestingly, the density scattering coefficient appears to the second power in the theoretical prediction of the gap distance, indicating that the particle-chain formation occurs for both particles heavier than the surrounding medium and, notably, also for buoyant particles. Experimentally, the gap distance is evaluated for several different media and particle material combinations and the particle-chain formation is observed for both buoyant particles and particles heavier than the surrounding medium. The theory agrees well with experiments in the cases where the material properties of the medium and the particles are well known.

The determination of relative stopping power (RSP) via proton computed tomography (pCT) of a patient is dependent in part on the knowledge of the incoming proton kinetic energies; the uncertainty in these energies is in turn determined by the proton source—typically a cyclotron. Here, we show that reducing the incident proton beam energy spread may significantly improve RSP determination in pCT. We demonstrate that the reduction of beam energy spread from the typical 1.0% (at 70 MeV) down to 0.2% can be achieved at the proton currents needed for imaging at the Paul Scherrer Institut 250-MeV cyclotron. Through a simulated pCT imaging system, we find that this effect results in RSP resolutions as low as 0.2% for materials such as cortical bone, up to 1% for lung tissue. Several materials offer further improvement when the beam (residual) energy is also chosen such that the detection mechanisms used provide the optimal RSP resolution.

A Kerr nonlinear parametric oscillator (KPO) can stabilize a quantum superposition of two coherent states with opposite phases, which can be used as a qubit. In a universal gate set for quantum computation with KPOs, an $R_x$ gate, which interchanges the two coherent states, is relatively hard to perform owing to the stability of the two states. We propose a method for a high-fidelity $R_x$ gate by exciting the KPO outside the qubit space with parity-selective transitions, which can be implemented by only adding a driving field. In this method, the utilization of higher effective excited states leads to a faster $R_x$ gate, rather than states near the qubit space. The proposed method can realize a continuous $R_x$ gate and thus is expected to be useful for, e.g., recently proposed variational quantum algorithms.

Memristors hold great promise as building blocks for future computing architectures where memory and logic are combined at the hardware level. However, scaling down the dimensions of memristive devices has been limited by high leakage currents, thus inhibiting further progress. Recent studies have demonstrated memristors with monolayers of ${\mathrm{Mo}\mathrm{S}}_2$ and large high-to-low resistance ratios. Defects combined with metallic ion migrations are often seen as a possible explanation for this behavior. A detailed understanding of the switching mechanisms, in particular the role of metal ion diffusion into vacancy sites and crystal defects, remains elusive. Here we investigate how defect densities affect the performance of monolayer ${\mathrm{Mo}\mathrm{S}}_2$ memristors. We experimentally demonstrate that the resistive switching ratio becomes larger if the defect density in ${\mathrm{Mo}\mathrm{S}}_2$ is increased. Furthermore, by means of ab initio quantum transport simulations, we reveal the existence of an optimum range of defect densities and explore the theoretical limits of monolayer ${\mathrm{Mo}\mathrm{S}}_2$ memristors. Our results highlight the importance of defect engineering and control in transition metal dichalcogenides memristors.

Atmospheric aerosols, such as water droplets in fog, interfere with laser propagation through scattering and absorption. Femtosecond optical filaments have been shown to clear foggy regions, improving the transmission of subsequent pulses. However, the detailed fog-clearing mechanism had yet to be determined. Here, we directly measure and simulate the dynamics of water droplets with a radius of about $5\mu \mathrm{m}$, typical of fog, under the influence of optical and acoustic interactions that are characteristic of femtosecond filaments. We find that, for filaments generated by the collapse of collimated near-infrared femtosecond pulses, the main droplet-clearing mechanism is optical shattering by laser light. For such filaments, the single-cycle acoustic wave launched by filament-energy deposition in air leaves droplets intact and drives negligible transverse displacement, and therefore, negligible fog clearing. Only for tightly focused nonfilamentary pulses, where local energy deposition greatly exceeds that of a filament, do acoustic waves significantly displace aerosols.

Theoretical studies of coherent atom transport have as yet mainly been restricted to one-dimensional model systems with harmonic trapping potentials. Here we investigate this important phenomenon—a prerequisite for a variety of quantum-technology applications based on cold neutral atoms—under much more complex physical circumstances. More specifically yet, we study fast atomic transport in a moving double-well optical lattice, whose three-dimensional (anharmonic) potential is nonseparable in the $x$-$y$ plane. We first propose specific configurations of acousto-optic modulators that give rise to the moving-lattice effect in an arbitrary direction in this plane. We then determine moving-lattice trajectories that enable single-atom transport using two classes of quantum-control methods: shortcuts to adiabaticity (STA), here utilized in the form of inverse engineering based on a quadratic-in-momentum dynamical invariant of Lewis-Riesenfeld type, and their recently proposed modification termed enhanced STA (eSTA). Subsequently, we quantify the resulting single-atom dynamics by numerically solving the relevant time-dependent Schrödinger equations and compare the efficiency of STA- and eSTA-based transport by evaluating the respective fidelities. We show that—except for the regime of shallow lattices—the eSTA method consistently outperforms its STA counterpart. This study has direct implications for neutral-atom quantum computing based on collisional entangling two-qubit gates and quantum sensing of constant homogeneous forces via guided-atom interferometry.

The detection dead zones and heading errors induced by light shifts are two important problems in optically pumped scalar magnetometry. We introduce an atomic-orientation-based single-beam magnetometry scheme to simultaneously solve these problems, using a polarization-reversing and path-bending Herriott cavity. Here, a reflection mirror is inserted into the cavity to bend the optical paths in the middle and divide them into two separated orthogonal regions to avoid the detection dead zone. Moreover, half-wave plates are added in the center of each optical region, so that the light polarization is flipped each time it passes the wave plates and the light-shift effects are spatially averaged out. This operation is demonstrated to eliminate the unnoticed heading errors induced by ac light shifts. The methods developed in this paper are robust to use and easy to apply other atomic devices.

Ferroelectricity is promising in emulating the synaptic characteristics of human brains. Utilizing ferroelectricity for brain-inspired computing is proposed as a feasible route to address technical challenges in memory and computing. Here, we demonstrate the use of a ferroelectric van der Waals (vdW) halide perovskite for synaptic emulation. The two-terminal ferroelectric synapse based on the vdW material (R)-(−)-1-cyclohexylethylammonium)${\mathrm{PbI}}_3$ (R-CYHEA${\mathrm{PbI}}_3$) exhibits voltage-pulse-dependent weight modulation with a total on:off ratio of 50 and good endurance up to ${10}^7$ cycles. The energy consumption per synaptic operation for both short-term plasticity and long-term plasticity reaches the picojoule level. The device also shows reasonable write linearity and small cycle-to-cycle variation, as well as promising spike-timing-dependent plasticity and a paired-pulse-facilitation function. Numerical simulations with the R-CYHEA${\mathrm{PbI}}_3$-synapse-based neural network suggest the potential of R-CYHEA${\mathrm{PbI}}_3$ synapses for pattern recognition. Ferroelectric vdW halide perovskites provide opportunities for exploiting their dimensionality, superior optoelectronic properties, and mild material-processing conditions for engineering of the synaptic device performance.

Structural symmetry breaking, which could lead to exotic physical properties, plays a crucial role in determining the functions of a system, especially for two-dimensional (2D) materials. Here, we demonstrate that multiple functionalities of 2D chromium-based materials can be achieved by breaking inversion symmetry via replacing $Y$ atoms in one face of pristine $\mathrm{Cr}$Y (Y = $\mathrm{P}$, $\mathrm{As}$, $\mathrm{Sb}$) monolayers with $\mathrm{N}$ atoms, i.e., forming Janus ${\mathrm{Cr}}_2\mathrm{N}Y$ monolayers. The functionalities include gapless spin, very low work function, inducing carrier doping, and catalytic activity, which are predominately ascribed to the large intrinsic dipole of Janus ${\mathrm{Cr}}_2\mathrm{N}Y$ monolayers, giving them great potential for various applications. Specifically, ${\mathrm{Cr}}_2\mathrm{NSb}$ is found to be a spin-gapless semiconductor, ${\mathrm{Cr}}_2\mathrm{NP}$ and ${\mathrm{Cr}}_2\mathrm{NHPF}$ can simultaneously induce n- and p-type carrier doping for two graphene sheets with different concentrations (forming an intrinsic p-n vertical junction), and ${\mathrm{Cr}}_2\mathrm{N}Y$ exhibits excellent electrocatalytic hydrogen-evolution activity, even superior to that of benchmark $\mathrm{Pt}$. The results confirm that breaking symmetry is a promising approach for the rational design of multifunctional 2D materials.