The bull’s-eye structure in the terahertz (THz) frequency region has ample applications owing to its ability to focus free-propagating waves into subwavelength apertures, resulting in enhanced transmission, that is, extraordinary transmission. However, its coupling properties have been primarily discussed in terms of the normal plane-wave incidence to the structure. In this study, we investigate the multiple resonances in extraordinary transmission with normal and oblique incident waves. The experiment using a widely tunable and high-power THz wave source revealed two types of resonances. The main resonance split depends on the incident angle, and the other corresponds to the side lobe of the main resonances. The results are explained by a simple analytical model using a finite number of scattering media. The analysis is supported by the full-wave simulation using the finite-element method, which agrees with the experimental results. The coupling mechanisms will be applicable to design devices, such as THz biosensing devices or THz antennas for rapid communication systems.

Orbital-angular-momentum (OAM) complex-valued spectrum reconstruction routinely necessitates the measurements of a complete set of observables, which is rather time consuming and inefficient for high-dimensional OAM superposition state. Here we break this barrier to realize the full reconstruction of a high-dimensional OAM complex-valued spectrum via only a single-shot measurement, which benefits from the use of a residual convolutional neural network for learning the diffraction behaviors. In our experiment, the high-dimensional OAM states are diffracted by a simple aperture of pentagram that breaks the OAM conjugate symmetry. We achieve fidelity over 97.8% and 92.1% for high-dimensional pure and mixed OAM states (up to $d=15$), respectively. We also confirm the excellent robustness under strong noise environment. Our method will find potential applications in high-dimensional information encoding, such as large-alphabet communications, quantum imaging, and real-time quantum sensing.

Non-Markovian noise presents a particularly relevant challenge in understanding and combating decoherence in quantum computers, yet is challenging to capture in terms of simple models. Here we show that a simple phenomenological dynamical model known as the post-Markovian master equation (PMME) accurately captures and predicts non-Markovian noise in a superconducting qubit system. The PMME is constructed using experimentally measured state dynamics of an IBM Quantum Experience cloud-based quantum processor, and the model thus constructed successfully predicts the non-Markovian dynamics observed in later experiments. The model also allows the extraction of information about crosstalk and measures of non-Markovianity. We demonstrate definitively that the PMME model predicts subsequent dynamics of the processor better than the standard Markovian master equation.

Optomechanical systems offer unique opportunities to explore macroscopic quantum state and related fundamental problems in quantum mechanics. Here, we propose a quantum optomechanical system involving exchange interaction between spin angular momentum of light and a torsional oscillator. We demonstrate that this system allows coherent control of the torsional quantum state of a torsional oscillator on the single-photon level, which facilitates efficient cooling and squeezing of the torsional oscillator. Furthermore, the torsional oscillator with a macroscopic length scale can be prepared in Schrödinger catlike state. Our work provides a platform to verify the validity of quantum mechanics in macroscopic systems on the micrometer and even centimeter scale.

Differential absorption spectroscopy techniques serve as powerful techniques to study the excited species in organic solar cells. However, it has always been challenging to employ these techniques for characterizing thick-junction organic solar cells, especially when a reflective top contact is involved. In this work, we present a detailed and systematic study on how a combination of the presence of the interference effect and a nonuniform charge-distribution profile, severely manipulates experimental spectra and the decay dynamics. Furthermore, we provide a practical methodology to correct these optical artifacts in differential absorption spectroscopies. The results and the proposed correction method generally apply to all kinds of differential absorption spectroscopy techniques and various thin-film systems, such as organics, perovskites, kesterites, and two-dimensional materials. Notably, it is found that the shape of differential absorption spectra can be strongly distorted, starting from 150-nm active-layer thickness; this matches the thickness range of thick-junction organic solar cells and most perovskite solar cells and needs to be carefully considered in experiments. In addition, the decay dynamics of differential absorption spectra is found to be disturbed by optical artifacts under certain conditions. With the help of the proposed correction formalism, differential spectra and the decay dynamics can be characterized on the full device of thin-film solar cells in transmission mode and yield accurate and reliable results to provide design rules for further progress.

The nonlinear dynamics of microelectromechanical resonators has recently garnered significant attention for their potential use in high-precision detection and information processing. In this paper, we report resonant excitation as a powerful tool for generating nonlinear mode coupling in a cantilever microresonator. It is discovered that resonant driving at its second flexural mode $f_2$ under moderate driving amplitude gives rise to blue and red sidebands due to mode coupling between the fundamental mode and the second flexural mode. Detuning the driving frequency enables a continuous shift in the frequencies of the blue and red sidebands with a frequency span of 220 Hz. Further increase in the drive amplitude at $f_2$ mode splitting, and broadband acoustic frequency comb with a frequency span exceeding 500 kHz. Our findings pave the way towards parametric control based on injection locking for manipulating multimode mechanical resonator systems.

Versatile twisted optical bottles (TOBs) generated from a series of abruptly autofocusing beams are derived numerically and experimentally. This kind of TOB beam utilizes dual-autofocus, optical-vortex, and astigmatic phase properties to structure one or more three-dimensional closed dark regions, the bottle space. Closed off-axis multiple optical bottles are generated and observed experimentally. The twist angles can individually affect the rotation of the TOB. The experimental results agree well with our numerical simulations. The relationships between the astigmatic phase, the length of the TOB, the topological order of the vortex, and the width of the TOB are determined. Additionally, stable mesocarbon particles trapped by TOB beams are observed in side view successfully. These TOBs offer more possibilities to trap, sort, and clean microparticles or nanoparticles and improve optical manipulation systems in the future.

The frequency band 1–15 GHz provides exciting prospects for resonant axion haloscopes as indicated by cosmological and astrophysical arguments. Among the challenges currently addressed to reach the required sensitivity, the development of high-quality factor cavities that tolerate multitesla fields plays a central role. We report a three-dimensional resonator based on a right-circular copper cavity with hollow cylinders that confine higher-order modes around the cylinder axis. Its effective volume at 10.3 GHz is $3.4\times {10}^{-2}$ l, and under an 8-T field we measure an internal quality factor of more than nine million. A fine-tuning system limited to approximately $1$-MHz range is tested, useful for understanding the conditions required to run a haloscope with a cavity exceeding the axion quality factor. The cavity parameters we report demonstrate the potential of this unique resonator to probe galactic dark-matter axion at scan rates exceeding 2 MHz/day when the cavity is readout by a quantum-limited receiver.

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.