Since the introduction of transformation optics and experimental demonstration using microwave metamaterials in 2006, a variety of electromagnetic invisibility cloaking techniques and physical realizations based on coordinate transformations, scattering cancellation, and control of reflected and transmitted waves have been reported from microwaves to visible. However, existing cloaking methodologies face challenges in reducing cloak thicknesses, concealing large volumes, and cloaking free-standing objects. Here, we design, fabricate, and experimentally validate a unidirectional, single-layer printed metasurface cloak for free-standing cylindrical objects in the microwave regime. Based on a spatially modulated reactance surface, the printed metasurface converts an incident plane wave on the lit side into a surface wave, which carries power to the shadow side before reconstructing the incident wave behind the object. Using a subwavelength-thin printed circuit prototype, the cloaking function is experimentally confirmed, demonstrating a thin, passive cloak that conceals a large, free-standing object.

Basal-plane dislocations (BPDs) pose a great challenge to the reliability of bipolar power devices based on the 4H silicon carbide (4H-SiC). It is well established that heavy nitrogen ($\mathrm{N}$) doping promotes the conversion of BPDs to threading edge dislocations (TEDs) and improves the reliability of $4\mathrm{H}$-$\mathrm{SiC}$-based bipolar power devices. However, the interaction between $\mathrm{N}$ and BPDs, and the effect of $\mathrm{N}$ on the electronic properties of BPDs are still ambiguous, which significantly hinder the understanding on the electron-transport mechanism of $4\mathrm{H}$-$\mathrm{SiC}\text{−}$based bipolar power devices. Combining molten-alkali etching and the Kelvin probe force microscopy (KPFM) analysis, we demonstrate that BPDs create acceptorlike states in undoped $4\mathrm{H}$-$\mathrm{SiC}$, while acting as donors in $\mathrm{N}$-doped $4\mathrm{H}$-$\mathrm{SiC}$. First-principles calculations verify that BPDs create occupied defect states above the valence band maximum (VBM) and unoccupied defect states under the conduction-band minimum (CBM) of undoped $4\mathrm{H}$-$\mathrm{SiC}$. The electron transfer from the defect states of intrinsic defects and native impurities to the unoccupied defect states of BPDs gives rise to the acceptorlike behavior of BPDs in undoped $4\mathrm{H}$-$\mathrm{SiC}$. Defect formation energies indicate that $\mathrm{N}$ atoms can spontaneously decorate BPDs during the $\mathrm{N}$ doping of $4\mathrm{H}$-$\mathrm{SiC}$. The binding between $\mathrm{N}$ and BPD is strong against decomposition. The accumulation of $\mathrm{N}$ dopants at the core of BPDs results in the accumulation of donorlike states at the core of BPDs in $\mathrm{N}$-doped $4\mathrm{H}$-$\mathrm{SiC}$. This work not only enriches the understanding on the electronic behavior of BPDs in $\mathrm{N}$-doped $4\mathrm{H}$-$\mathrm{SiC}$, but also helps understand the electron transport mechanism of $4\mathrm{H}$-$\mathrm{SiC}$-based bipolar power devices.

Semiconducting monolayer $\mathrm{Mo}\mathrm{Si}$${}_2$$\mathrm{N}$${}_4$ and monolayer $\mathrm{WSi}$${}_2$$\mathrm{N}$${}_4$ have recently been fabricated and a number of two-dimensional (2D) materials with the same chemical formula and symmetry have been predicted, the mechanical, optical, and thermoelectric properties of which have been investigated. However, research regarding device applications of this 2D family have been very limited so far. Here, we propose a photodetector based on a 2D $\mathrm{VSi}$${}_2$$\mathrm{N}$${}_4$/$\mathrm{WSi}$${}_2$$\mathrm{N}$${}_4$/$\mathrm{VSi}$${}_2$$\mathrm{N}$${}_4$ lateral heterojunction, and investigate the transport properties of the photocurrent by using quantum transport simulations. The dependence of the photocurrent on the incident angle $\alpha$ and on the light-polarization angle $\theta$ is formulated. A robust photogalvanic effect is generated under the illumination of linearly polarized light due to the noncentrosymmetric $C_{2v}$ symmetry of the photodetector. The photocurrent has a $\cos (2\theta )$ and $\cos (2\alpha )$ dependence on the light polarization and on the incident angle, respectively. A pure spin current, a perfect spin-filtering effect, and an excellent spin-valve effect can be achieved at zero bias for a broad photon energy range with an appropriate polarization angle at both normal and horizontal incidence. Moreover, at horizontal incidence, the photocurrent is highly polarization sensitive with an extinction ratio of up to ${10}^4$. These results suggest that the 2D $\mathrm{WSi}$${}_2$$\mathrm{N}$${}_4$ family has promising multifunctional applications in low-power optoelectronics and spintronics.

A Schottky barrier, formed in the contact of a two-dimensional (2D) semiconductor and metal electrode, seriously degrades device performance. Herein, we propose a dipole-engineering strategy to regulate the electronic contact properties of a 2D polar $\mathrm{Sb}$X (X = $\mathrm{P}$, $\mathrm{As}$, $\mathrm{Bi}$) and graphene ($\mathrm{Gr}$) van der Waals interface. Owing to the mirror asymmetry of $\mathrm{Sb}$X, we construct seven vertical heterostructures in the form of X$\mathrm{Sb}$-$\mathrm{Gr}$ and $\mathrm{Sb}$X$\text{−}\mathrm{Gr}$. Tunable Schottky barrier height and contact type can be obtained by using different atomic terminals to contact with $\mathrm{Gr}$. Based on the first-principles calculations, the dipole and its associated potential step are found to be responsible for the regulating effect. Moreover, owing to the remarkable properties of the $\mathrm{Sb}\mathrm{Bi}$-$\mathrm{Gr}$ heterostructure, such as Ohmic contact and low tunneling barrier, we design an optoelectronic field-effect transistor, which exhibits considerable responsivity (0.089 ${\mathrm{AW}}^{-1}$) and external quantum efficiency (28.57%). Our findings further confirm that regulating the electronic contact properties by the dipole in the heterostructure is a feasible strategy, which provides meaningful guidance for designing high-performance electronic and optoelectronic devices.

Electrically addressing spin systems is predicted to be a key component in developing scalable semiconductor-based quantum-processing architectures, to enable fast spin-qubit manipulation and long-distance entanglement via microwave photons. However, single spins have no electric dipole, and therefore a spin-orbit mechanism must be integrated in the qubit design. Here, we propose to couple microwave photons to atomically precise donor spin-qubit devices in silicon using the hyperfine interaction intrinsic to donor systems and an electrically induced spin-orbit coupling. We characterize a one-electron system bound to a tunnel-coupled donor pair (1P-1P) using the tight-binding method, and then estimate the spin-photon coupling achievable under realistic assumptions. We address the recent experiments on double quantum dots (DQDs) in silicon and indicate the differences between DQD and 1P-1P systems. Our analysis shows that it is possible to achieve strong spin-photon coupling in 1P-1P systems in realistic device conditions without the need for an external magnetic field gradient.

Single spin qubits based on phosphorus donors in silicon are a promising candidate for a large-scale quantum computer. Despite long coherence times, achieving uniform magnetic control remains a hurdle for scale-up due to challenges in high-frequency magnetic field control at the nanometre scale. Here, we present a proposal for a flopping-mode electric dipole spin resonance qubit based on the combined electron and nuclear spin states of a double phosphorus donor quantum dot. The key advantage of utilizing a donor-based system is that we can engineer the number of donor nuclei in each quantum dot. By creating multidonor dots with antiparallel nuclear spin states and multielectron occupation we can minimize the longitudinal magnetic field gradient, known to couple charge noise into the device and dephase the qubit. We describe the operation of the qubit and show that by minimizing the hyperfine interaction of the nuclear spins we can achieve $\pi /2-X$ gate error rates of about ${10}^{-4}$ using realistic noise models. We highlight that the low charge noise environment in these all-epitaxial phosphorus-doped silicon qubits will facilitate the realization of strong coupling of the qubit to superconducting microwave cavities, allowing for long-distance two-qubit operations.

Color centers in silicon carbide are emerging candidates for distributed spin-based quantum applications due to the scalability of host materials and the demonstration of integration into nanophotonic resonators. Recently, silicon vacancy centers in silicon carbide have been identified as a promising system with excellent spin and optical properties. Here, we fully study the spin-optical dynamics of the single silicon vacancy center at hexagonal lattice sites, namely V1, in 4H-polytype silicon carbide. By utilizing resonant and above-resonant sublifetime pulsed excitation, we determine spin-dependent excited-state lifetimes and intersystem-crossing rates. Our approach to inferring the intersystem-crossing rates is based on all-optical pulsed initialization and readout scheme, and is applicable to spin-active color centers with similar dynamics models. In addition, the optical transition dipole strength and the quantum efficiency of V1 defect are evaluated based on coherent optical Rabi measurement and local-field calibration employing electric field simulation. The measured rates well explain the results of spin-state polarization dynamics, and we further discuss the altered photoemission dynamics in resonant enhancement structures such as radiative lifetime shortening and Purcell enhancement. By providing a thorough description of the V1 center’s spin-optical dynamics, our work provides deep understanding of the system, which guides implementations of scalable quantum applications based on silicon vacancy centers in silicon carbide.

Quantum nonreciprocal devices have received extensive attention in recent years because they can be used to realize unidirectional quantum routing and noise isolation. In this work, we show that the shift of resonance frequencies of propagating phonons induced by spin-orbit interactions of phonons in a rotating acoustic ring cavity can be used to realize nonreciprocal phonon blockade. When driving the cavity from different directions, nonreciprocal single-, two-phonon blockade, and phonon-induced tunneling can take place by varying the parameters of the system to an appropriate value. To realize phonon blockade, a two-level system is employed to induce self-interactions of phonons in the cavity. We also show the possibility of this proposal for designing nonreciprocal phonon routing. This work provides a way to achieve acoustic nonreciprocal devices, such as directional acoustic switches and quantum noise isolation, which may help acoustic information network processing.

Second-order photonic topological insulators (SPTIs) with topologically protected corner states possess extraordinary abilities of robust light steering in lower dimensions. However, previous SPTIs are difficult for multiband on-chip applications. To overcome this challenge, we design, via the inverse design method, a SPTI supporting four highly localized corner states within four sizeable band gaps that are robust to bulk impurities. Importantly, the designed SPTI is made of fully connected dielectric materials, which can be readily fabricated in nanoscale via electron-beam lithography and integrated into on-chip circuits. Our work offers potential applications in designing multiband on-chip photonic integrated devices with high efficiency, high capacity, and high robustness for both linear and nonlinear optical processing.

Here, we demonstrate the generation and manipulation of hyperentanglement in polarization and time-energy degrees of freedom. The hyperentangled photon pairs are generated by cascaded second-harmonic generation and spontaneous parametric down-conversion processes in a high-efficiency periodically poled lithium niobate (PPLN) waveguide in a fiber Sagnac loop. The states achieve the maximum value of Clauser-Horne-Shimony-Holt Bell inequality of $S=2.76\pm 0.03$ with two-photon interference visibility of higher than 99% for polarization entanglement and the Franson-type two-photon interference visibility of 98.5% for time-energy entanglement. In addition, the polarization maximally entangled states can be fast switched to each other by using a PPLN on insulator chip through the electro-optic effect. After the entanglement manipulation, the two-photon interference visibility for polarization entanglement is still higher than 97% while keeping the quantum characteristics of time-energy degrees of freedom maintained. Our system paves a way toward reducing the complexity of quantum systems and has potential applications in many quantum-information tasks like fast superdense coding and teleportation.

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.