Metasurfaces, the artificially planar electromagnetic structures, have exhibited strong potential for arbitrary electromagnetic wave-scattering control; however, most of the existing low-scattering metasurfaces are based on spatial phase redistributions to generate diffusive backscattering, leaving time dimension unexploited. The time-modulated mechanism provides an attractive alternative to realize backscattering control but still lacks experimental demonstration for realization of radar cross-section reduction in microwave frequencies. Here, we propose a broadband spatiotemporal metasurface approach for arbitrary scattering control and provide experimental evidence of reshaping scattering patterns in the spatial and spectral domains simultaneously. The metasurface is composed of broadband high-efficiency meta-atoms incorporating electric p-i-n diodes, which ensures independent and dynamic phase-response modulation over time under external voltage control in an octave working band from 3.4 to 7.7 GHz. The measured results demonstrate that the metasurface could redirect incidence to various spatial directions and harmonic frequencies, achieving broadband spatial and spectral control of the backward scattering. The proposed metasurface may offer promising applications in radar detection and camouflage.

Doubly parametric quantum transducers, such as electro-optomechanical devices, show promise for providing the critical link between quantum information encoded in highly disparate frequencies such as in the optical and microwave domains. This technology would enable long-distance networking of superconducting quantum computers. Rapid experimental progress has resulted in impressive reductions in decoherence from mechanisms such as thermal noise, loss, and limited cooperativities. However, the fundamental requirements on transducer parameters necessary to achieve quantum operation have yet to be characterized. In this work we find simple, protocol-independent expressions for the necessary and sufficient conditions under which doubly parametric transducers in the resolved-sideband, steady-state limit are capable of entangling optical and microwave modes. Our analysis treats the transducer as a two-mode bosonic Gaussian channel capable of both beamsplitter-type and two-mode squeezing-type interactions between optical and microwave modes. For the beamsplitter-type interaction, we find parameter thresholds that distinguish regions of the channel’s separability, capacity for bound entanglement, and capacity for distillable entanglement. By contrast, the two-mode squeezing-type interaction always produces distillable entanglement with no restrictions on temperature, cooperativities, or losses. Counterintuitively, for both interactions, we find that achieving quantum operation does not require either a quantum cooperativity exceeding one, or ground-state cooling of the mediating mode. Finally, we discuss where two state-of-the-art implementations are relative to these thresholds and show that current devices operating in either mode of operation are in principle capable of entangling optical and microwave modes.

We measure the spin-orbit torques (SOTs), current-induced switching, and domain wall (DW) motion in synthetic ferrimagnets consisting of $\mathrm{Co}$/$\mathrm{Tb}$ layers with differing stacking order grown on a $\mathrm{Pt}$ underlayer. We find that the SOTs, magnetic anisotropy, compensation temperature, and SOT-induced switching are highly sensitive to the stacking order of $\mathrm{Co}$ and $\mathrm{Tb}$ and to the element in contact with $\mathrm{Pt}$. Our study further shows that $\mathrm{Tb}$ is an efficient SOT generator when in contact with $\mathrm{Co}$, such that its position in the stack can be adjusted to generate torques additive to those generated by $\mathrm{Pt}$. With optimal stacking and layer thickness, the dampinglike SOT efficiency reaches 0.3, which is more than twice that expected from the $\mathrm{Pt}$/$\mathrm{Co}$ bilayer. Moreover, the magnetization can be easily switched by the injection of pulses with current density of about (0.5–$2)\times {10}^7\mathrm{A}/{\mathrm{cm}}^2$ despite the extremely high perpendicular magnetic anisotropy barrier (up to 7.8 T). Efficient switching is due to a combination of large SOTs and low saturation magnetization owing to the ferrimagnetic character of the multilayers. We observe current-driven DW motion in the absence of any external field, which is indicative of homochiral Néel-type DWs stabilized by the interfacial Dzyaloshinkii-Moriya interaction. These results show that the stacking order in transition metal/rare-earth synthetic ferrimagnets plays a major role in determining the magnetotransport properties relevant for spintronic applications.

We explore the possibility offered by magnetic materials with cubic anisotropy to realize reconfigurable magnonic crystals with a very simple geometry working at zero magnetic field. As a proof of concept, we use micromagnetic simulations to calculate the static and dynamic magnetic configurations of a squared antidot lattice made with ${\mathrm{Co}}_2\mathrm{Mn}\mathrm{Si}$ Heusler alloy having an anisotropy constant of about 17 × ${10}^3{\mathrm{J}/\mathrm{m}}^3$. We show that the cubic anisotropy allows very different magnetic states to be obtained at remanence as a function of the direction of a saturation magnetic field, including quasiuniform remanent states that cannot be obtained in materials with the same magnetic parameters but without crystal anisotropy. This leads to the possibility to excite or extinct several quantized spin-wave modes whose frequencies can be tuned with the antidot dimensions. Reconfigurable magnetic states are demonstrated for antidot sizes in the range 300–350 nm for a ratio between the antidot size and spacing equal to 1/3. The transition between two different remanent states can be obtained with low-amplitude magnetic field (down to 3.5 mT) and with a switching time faster than 1 ns, which is of great interest for applications. Oppositely, for a particular orientation of the antidot lattice with respect to the cubic anisotropy axes, we also obtain a single stable remanent state independent of the saturation field direction. Finally, propagation properties and frequency band gaps in an antidot lattice with lateral antidot size of 100 nm are studied for frequency-filtering applications at remanence. Both magnetostatic surface waves and magnetostatic backward-volume wave configurations are explored for different positions of the microwave excitation with respect to the magnonic crystal.

Hole spins confined in semiconductor quantum dot systems have gained considerable interest for their strong spin-orbit interactions (SOIs) and relatively weak hyperfine interactions. Here, we experimentally demonstrate a tunable SOI in a double quantum dot in a germanium ($\mathrm{Ge}$) hut wire (HW), which could help to enable fast all-electric spin manipulations while suppressing unwanted decoherence. Specifically, we measure the transport spectra in the Pauli-spin-blockade regime in the double-quantum-dot device. By adjusting the interdot tunnel coupling, we obtain an electric-field-tuned spin-orbit length of $l_{\mathrm{SO}}$= 2.0–48.9 nm. This tunability of the SOI could pave the way toward the realization of high-fidelity qubits in $\mathrm{Ge}$ HW systems.

We present experimental results using a single-electron resolution skipper CCD running above ground level to demonstrate the potential of this technology for its use in reactor neutrino observations and other low-energy particle-interaction experiments. Operating conditions and event-selection criteria are provided to decouple most of the background rate at low energies. The majority of this background comes from interactions in the inactive silicon surrounding the active detector volume that ends up in the readout register of the sensor. Our final results are compared with other low-threshold technologies showing a good control of the background for low ionization energies down to five electron-hole pairs. This demonstrates that the skipper CCD proves to be among the best options to measure low-energy and weakly interacting particles at ground level.

Rapid heating is highly sought-after for compositional control in the sintering-annealing process of materials containing volatile elements. Although several innovative approaches have been reported, suitable processes for the rapid annealing of thin films are still very rare. Herein, we develop a high-temperature rapid heating method for thin-film preparation through employing an indium tin oxide (ITO)/mica-based flexible transparent heater (FTH). The ITO/mica FTH shows an extremely fast thermal response (2 s), high saturation temperature (>830 °C), and high heating-cooling rates (>${10}^4$ °C ${\min }^{-1}$). Thermodynamic analysis reveals that the excellent heating performance can be largely attributed to the high heat-transfer coefficient and the low thickness of the mica substrates. The remarkable potential of our ITO/mica FTH for practical use is unambiguously evident by the demonstration of water heating and rapid thermal annealing of ferroelectric oxide thin films.

We present a quantitative study of the nonlinear optical response of layered perovskites placed inside planar photonic microcavities in the regime of strong light-matter coupling, when excitonic and photonic modes hybridize and give rise to cavity polaritons. Two sources of nonlinearity are specified, the saturation of the excitonic transition with increase of the optical pump and Coulomb interaction between the excitons. It is demonstrated that a peculiar form of the interaction potential, specific to the multilayer structure of organic perovskites, is responsible for the substantial increase of the exciton binding energy and Rabi splitting with respect to conventional semiconductor systems. This results in a dominant contribution of the Rabi splitting quench effect in the nonlinear optical response. Moreover, due to the tightly bound character of excitons, the density of Mott transition is essentially higher, allowing extremely large polariton blueshifts of about 20 meV to be reached, which is an order of magnitude higher than in conventional semiconductors.

Digital signatures can guarantee the unforgeability and transferability of the message. Differently from classical digital signatures, whose security depends on computational complexity, quantum digital signatures (QDSs) can provide information-theoretic security. We propose a general method of random-pairing QDS, which can drastically increase QDS efficiency. In a way, our random-pairing method provides a tightened result for the security level of QDS. In the method, the parity value of each pair is used for the outcome-bit value. We present general formulas for the fraction of untagged bits and error rates of the outcome bits. Random pairing can be applied as a fundamental method to increase the QDS efficiency for all existing quantum key distribution (QKD) protocols. We take the QDS with sending-or-not-sending protocol and the QDS with side-channel-free protocol as examples to demonstrate the advantage of random pairing through numerical simulation. A similar advantage with random pairing is also found with decoy-state measurement-device-independent QKD and also the decoy-state BB84 protocol. We study the random-pairing QDS with sending-or-not-sending protocol considering effects of finite data size through optimization. The numerical simulation results show that the signature rate can be increased by more than $100\mathrm{\%}$ under a noisy channel using our random-pairing method.

Quantum annealing (QA) was originally intended for accelerating the solution of combinatorial optimization tasks that have natural encodings as Ising models. However, recent experiments on QA-hardware platforms have demonstrated that, in the operating regime corresponding to weak interactions, the QA hardware behaves like a noisy Gibbs sampler at a hardware-specific effective temperature. This work builds on those insights and identifies a class of small hardware-native Ising models that are robust to noise effects and proposes a procedure for executing these models on QA hardware to maximize Gibbs-sampling performance. The experimental results indicate that the proposed protocol results in high-quality Gibbs samples from a hardware-specific effective temperature. Furthermore, we show that this effective temperature can be adjusted by modulating the annealing time and energy scale. The procedure proposed in this work provides an approach to using QA hardware for Ising-model sampling presenting potential opportunities for applications in machine learning and physics simulation.

Supercapacitors exhibit immense potential in electric vehicles and national grids due to their high power density. The power and energy density of supercapacitors largely depend on the design of electrodes and the composition of electrolytes, which dominate the capacitive charging process. However, the availability of only a few mathematical models for capacitive charging in bulk porous electrodes has limited the rational design of a supercapacitor in practice. Herein, a mathematical model is proposed to predict the charging process in a porous electrode and is then experimentally validated. In this model, the dependence of capacitive behavior on the conductivity of both the electrode and electrolyte, as well as the porosity and thickness of electrode, are systematically discussed. Moreover, different charging modes, e.g., potentiostatic charging, potentiodynamic charging, and galvanostatic charging, are studied. The results of this model indicate that the conductivity of the electrolyte (even though it is an aqueous electrolyte) is the bottleneck that limits the charging rate of a supercapacitor, in particular, in thick electrode films. This mathematical model could be a powerful tool for optimizing the design of both electrodes and electrolytes for high-performance supercapacitors.

Photophoretic forces are induced when light causes a net momentum exchange between a particle and a surrounding gas. Such forces have been shown to be a robust means for trapping and guiding particles in air over long distances. Here, we apply the concept of an optical funnel for the delivery of bioparticles to the focus of an x-ray free-electron laser (XFEL) for femtosecond x-ray diffractive imaging. We provide the experimental demonstration of transversely compressing a high-speed beam of aerosolized viruses via photophoretic forces in a low-pressure gas environment. Relative temperature gradients induced on the viruses by the laser are estimated via particle-velocimetry measurements. The results demonstrate the potential for an optical funnel to improve particle-delivery efficiency in XFEL imaging and spectroscopy.

Vacuum-gap and orthogonally aligned double-gate geometry is employed in a nanowire-based electromechanical resonator device to independently control two nearly degenerate orthogonal vibration modes. In the device, piezoresistance is the dominant mechanism of motion-induced conductance variation, which provides an efficient scheme for the self-transduction of vibrational motion into an electric signal. Two simultaneously applied gate voltages induce an opposite combined effect on the frequency shift between two vibration modes, which is well explained by model calculations. Using the opposite double-gate effect, we demonstrate vectorial control of two mode frequencies, which is not possible with single-gate geometry.

We introduce a diffraction-theory-inspired analytical description of the metasurface comprising an array of graphene subwavelength hemispheres. Our theory describes light interaction with the random metasurface, in which the periodicity is broken by accidentally damaged meta-atoms in the nodes of a two-dimensional periodic lattice. Both numerical modeling and experiments show that such a nanometer-thin metasurface possesses giant broadband absorption in the terahertz spectral range that remains intact, even when a substantial portion of meta-atoms, i.e., graphene hemispheres, is damaged. Moreover, defective fabrication of graphene free-standing metasurface may enhance the absorptive properties.

The inhomogeneous magnetization distribution in antiskyrmions helps in nullifying the unwanted skyrmion Hall effect generally found in the current driven motion of skyrmions. At present, the observation of room-temperature antiskyrmion phase is limited to only a very few materials. Here, we present the evidence of a tunable antiskyrmion phase in the $D_{2d}$-symmetry-based tetragonal Heusler system ${\mathrm{Mn}}_{2+x}{\mathrm{Ni}}_{1-x}\mathrm{Ga}$. With the help of dc magnetization, ac susceptibility, and topological Hall effect measurements, we demonstrate that the potential antiskyrmion phase can be tuned over a wide compositional range with magnetic ordering temperature of above 600 K. In addition, we find the existence of multiple topological phase transitions for a certain Mn/Ni ratio where the magnetic anisotropy attains its maxima. Our micromagnetic simulations suggest that the transition from antiskyrmionium and antiskyrmion pockets to the conventional antiskyrmion phase at the optimal value of magnetic anisotropy might be responsible for the observed multiple topological transitions in the present materials. The expected small size of antiskyrmions in the present low magnetic-moment-based ferrimagnetic system gives a great advantage over other skyrmion and antiskyrmion hosting materials for their potential application in racetrack-based memory devices.