It has recently been shown how computing operations such as high-speed switching, routing, and solving partial differential equations can be performed by exploiting perfect splitting of electromagnetic waves in networks of waveguides from microwaves to the optical regime. Here we propose a technique to achieve perfect splitting of electromagnetic waves using junctions of rectangular waveguides. The structure consists of N air-filled rectangular waveguides interconnected at a junction. They are designed to have their cutoff frequency above the cutoff frequency of a further N waveguides used as inputs. The proposed structure is studied theoretically with use of transmission-line models, and it is demonstrated that perfect splitting can occur at frequencies below the cutoff frequency of the interconnected waveguides (evanescent coupling). Numerical results are used to validate the designs, and it is demonstrated that the theoretical model fits the numerical data well. As examples of computing operations, it is shown how the proposed structure can be used to compare the amplitude of two incident signals (comparison operation) and also for routing of information to different output ports by exploiting the linear superposition of scattered waves excited at the junction of rectangular waveguides, opening new opportunities and possibilities for future exploration and exploitation of electromagnetic waves for high-speed computing.

Pursuing nonradiating sources and radiationless motion for accelerated charged particles has captivated physicists for generations. Nonradiating sources represent intricate current-charge configurations that do not emit radiation beyond their source domain. This study investigates a single nonradiating source comprising a low-index dielectric disk excited by a split-ring resonator. Employing analytical and numerical methods, we demonstrate that this configuration supports an anapole state, exhibiting minimal or no radiation, effectively representing a nonradiating source. The radiation suppression is accomplished through the destructive interference of electric dipoles excited on the metallic and dielectric components of the proposed prototype. Transforming the design into a cost-effective device capable of suppressing radiation, we achieve excellent numerical and experimental agreement, affirming the formation of the anapole state using the lowest-order multipoles. Moreover, the devised anapole device is remarkably compact, constructed from a low-index dielectric, and employs readily available components. As a versatile platform, the proposed device can spearhead anapole research for diverse applications, including sensing, wireless charging, radio frequency identification tags, and other nonlinear applications.

Quantum state readout plays a pivotal role in quantum technologies, spanning applications in sensing, computation, and secure communication. In this work, we introduce an approach for efficiently reading populations of hybrid-spin states in the nitrogen-vacancy center of diamond using a single laser pulse, which utilizes the excited-state-level anticrossing mechanism at around 500 Gs. Reading spin-state populations through this approach achieves the same outcome as traditional quantum state diagonal tomography but significantly reduces the experimental time by an order of magnitude while maintaining fidelity. Moreover, this approach may be extended to encompass full-state tomography, thereby obviating the requirement for a sequence of spin manipulations and mitigating errors induced by decoherence throughout the procedure.

The atomic orbital, as an intrinsic degree of freedom, is critical in improving band-tailoring tactics in condensed-matter physics. In photonics, analogously to atomic orbitals, multiple Mie resonances provide an effective way for photonic band engineering. In this work, we demonstrate the topological phase transitions in photonic Chern insulators imposed by band topology through multiple Mie resonances. By continuously adjusting geometric parameters and the external magnetic field in a two-dimensional gyromagnetic photonic crystal, we present the inversion of Mie resonances together with alterations in the Chern number for the corresponding photonic band. Furthermore, we propose a hetero–photonic structure that combines photonic lattices with distinct Chern numbers and exhibits chiral edge states at the heterointerface. A simple magnetic regulation approach is also provided for effective control of the edge state’s on–off switching. Our work establishes a correlation between the band topology of photonic Chern insulators and Mie resonances, contributing to advancements in higher-band-topology research.

Standard terahertz time-domain spectroscopy uses a relatively slow multidata acquisition process that has hindered the technique’s ability to resolve “fast” dynamics occurring on the microsecond timescale. This timescale, inaccessible to most ultrafast pump-probe techniques, hosts a range of phenomena that has been left unexplored due to a lack of proper real-time monitoring techniques. In this work, chirped-pulse spectral encoding, a photonic time-stretch technique, and high-speed electronics are used to demonstrate time-resolved terahertz detection at a rate up to 1.1 MHz. This configuration relies on a tabletop optical source and a setup able to resolve every terahertz transient generated by the same source. We investigate the performance of this single-pulse terahertz detection system at different acquisition rates in terms of experimental noise, dynamic range, and signal-to-noise ratio. Our results pave the way towards single-pulse terahertz time-domain spectroscopy at arbitrarily fast rates to monitor complex dynamics in real time.

Dicke superradiance is essentially a case of correlated dissipation leading to the macroscopic quantum coherence. Superradiance for arrays of inverted emitters in free space requires interactions far beyond the nearest neighbor, limiting its occurrence to small emitter-emitter distances. Epsilon-near-zero (ENZ) materials, which exhibit infinite effective wavelengths, can mediate long-range interactions between emitters. We investigate the superradiance properties of two ENZ structures, namely plasmonic waveguides and dielectric photonic crystals, and demonstrate their potential to support near-ideal Dicke superradiance across expanded spatial domains. We employ a general method that we have developed to assess the occurrence of superradiance, which is applicable to various coupling scenarios and relies only on the decoherence matrix. Furthermore, by numerically examining the emission dynamics of the few-emitter systems, we distinguish the roles of quantum coherence at different stages of emission for the case of all-to-all interaction, and demonstrate that the maximum quantum coherence in the system can be determined using the maximum photon burst rate. The findings of this work have prospective applications in quantum information processing and light-matter interaction.

Surface acoustic waves (SAWs) coupled to magnons have attracted much attention because they allow for the long-range transport of magnetic information that cannot be achieved by magnon alone. We employed pulsed laser interferometry to visualize the entire spatiotemporal dynamics of a SAW that travels on a nickel ($\mathrm{Ni}$) thin film and is coupled to magnons. It was possible to trace the coupling-induced amplitude reduction and phase shift that occurs as the SAW propagates over a distance of 0.4 mm. The observed changes are consistent with results obtained from conventional radio-frequency transmission measurements, which probe the total SAW absorption due to magnon-phonon coupling. This result verifies that our method can accurately capture the spatiotemporal dynamics of a SAW coupled to magnons across the entire length of the sample. Additionally, we validated our time-resolved profiles by comparing them with theoretical results that take the echo wave due to reflection into account. The impact of the echo wave is significant even when it has propagated over a distance of the order of millimeters. Our imaging results highlight the visualization of the long-range propagation of the SAW coupled to magnons and offer more information about the surface vibration profiles in such devices.

In this study, we demonstrate the management of terahertz pulse attenuation using a metallic structure in the frequency-conversion process with a temporal boundary. During the propagation of a terahertz pulse, rapid optical excitation of the waveguide surface induces a temporal boundary that can cause frequency conversion. The output amplitude of the terahertz pulse varies depending on the timing of the temporal boundary, which is a notable issue in this process. This is attributed to the difference in the attenuation constants before and after the temporal boundary. We fabricated a waveguide with a metal structure consisting of periodically aligned metal lines. This metallic structure decreases the area in which photoexcited carriers are generated and reduces the attenuation constant after the temporal boundary. On the other hand, the attenuation constant before the temporal boundary increased because of the Joule loss of the patterned metal. These effects balance the attenuation constants before and after the temporal boundary. Consequently, regardless of the location of the terahertz pulse within the waveguide at the timing of the temporal boundary, the amplitude of the output terahertz pulse remained constant.

The degeneracy of the Dirac cones in a honeycomb lattice exhibits intriguing electron or photon transport behavior, namely pseudodiffusion, where the phase velocity is locked while the group velocity is ominidirectional. However, this phenomenon is rarely studied in the microwave regime due to the strong interference from boundaries surrounding the bulk material. In this Letter, we propose an open structure exhibiting pseudodiffusive transport in surface waves that creates a highly directional beam. The printed-circuit-board-based design consists of microwave graphene with metallic circular patches, supporting the Dirac mode for surface waves below the light cone. The pseudodiffusive mode is excited and preserved by a photonic topological insulator waveguide with Reuleaux-triangle-like patches, taking advantage of the similarity in geometry and mode profile between bulk and insulator. This design features compatibility with common microwave interfaces, serving as a promising candidate for a miniaturized beamformer for future microwave devices.

Topological photonics has established itself as a promising area for the development of photonic integrated circuits due to the robust properties of topological states. In recent years, different logical devices have been proposed to form the fundamental elements of an integrated topological photonic circuit. Despite the rapid theoretical growth of topological photonics, it still lacks experimental foundations concerning logical devices for on-chip integration. For this reason, in this work, we report the design and build of an all-optical photonic switch in a silicon slab working under the higher-order topological spin Hall effect. We have taken advantage of the gapped edge states due to the higher-order topology and combined this feature with changes in the dielectric permittivity of silicon by inducing transitions of free charge carriers. The transitions of charge carriers were realized through the incidence of electromagnetic radiation with a frequency close to the visible-ultraviolet region boundary, making the device operation entirely optical. The behavior of the constructed device has also been numerically simulated and compared with the experimental results obtained. This work contributes to the idea that photonic crystals are a powerful platform for studying topological states and paves the way for the experimental realization of integrated topological optical circuits.

A classical switch or router determines which of several inputs to the device passes through the output. In analogy, a quantum switch that coherently links the input to a superposition of several outputs plays an important role in quantum information processing, especially when operating at the fundamental limit where a single photon can be controlled. The controllable path superposition of propagating photonic qubits enabled by the quantum switch provides the basis for numerous quantum applications, including entanglement generation and distribution, enhanced quantum communication, and quantum random access memory. In this work, we realize such a quantum switch for microwave single photons with superconducting quantum circuits. We use a superconducting qubit to coherently switch the output path of single microwave photons and confirm quantum entanglement between the control qubit and the photons’ propagation path. We further showcase the generation of quantum entanglement between a time-bin-encoded propagating photonic qubit and a superconducting qubit with the quantum switch, thus providing a versatile approach to generate reconfigurable multinode entanglement in one step. As such, our work provides a prime building block for microwave quantum networks and modular superconducting quantum computing.

Reconfigurable intelligent metasurfaces have been proposed as an efficient solution for improving wireless telecommunication systems in multiple-scattering or reverberating media. Concurrently, topology optimization has been successfully used as an inverse-design technique in many fields, and particularly in electromagnetics. In this work, we apply a gradient-based topology optimization for tuning the binary elements of a metasurface for a focusing goal in a complex environment. First, the metasurface unit cells are approximated as point sources and, then, the optimization problem is formulated. Afterwards, the proposed method is applied to find the optimal parameter sets for three distinct environments of increasing complexity, and the resulting focus for each case is demonstrated via numerical simulations. The combination of a reverberating cavity and a metasurface inside the latter is very powerful since everything can be solved analytically for focusing outside the cavity.

Cat state, is not only interesting for testing the fundamentals of quantum mechanics, but also for wide applications ranging from fault-tolerant quantum computation to quantum metrology. Here, we propose a scheme to generate the magnon cat state by the indirect magnon nonlinearity. We show that the effective two-magnon loss process can be induced by the photon parametric coupling, steering the magnon into the cat-state manifold. In our work, the size of the magnon cat state can be easily adjusted, and the large-size cat state can be generated with high fidelity. At the same time, the speed of cat-state generation can be greatly improved by enhancing the photon-magnon interaction with maintaining a larger size of cat state. Further, we find that the effective two-magnon loss process can strongly suppress the decoherence of the environment under appropriate parameter conditions. The lifetime of the magnon cat state can be expected to be $t\sim 3\text{μ}\mathrm{s}$ under the current experimental techniques. This work provides a proposal for the preparation of nonclassical states of magnons without the direct magnon nonlinearity, which is meaningful for the development of quantum technology in the future.

Metasurfaces provide unique capability in guiding surface waves and controlling their polarization and dispersion properties. One way to study their guiding properties is by analyzing their equifrequency contours. Equifrequency contours are the 2D projections of the 3D dispersion diagram. Since they are $\mathbf{k}$-space-map representations of the surface, many of the wave properties can be understood from the equifrequency contours. In this paper, we investigate numerically and experimentally the engineering of equifrequency contours using a C-shaped metasurface design. We show the ability to provide high self-collimation as well as spin-dependent wave splitting for the same metasurface by tuning the frequency of operation. We also show the ability to steer the wave along a defined curved path by rotating the C-shaped unit cells, which results in rotation of its equifrequency contours. This work demonstrates how engineering equifrequency contours can be used as a powerful tool for controlling the surface wave propagation properties.

Recent advances in nonlocal metasurfaces have enabled unprecedented success in shaping the wave front of light with spectral selectivity, offering alternative solutions for many emerging nanophotonics applications. The ability to tune both the spectral and spatial properties of such a class of metasurfaces is highly desirable, but the dynamic nonvolatile control remains elusive. Here, we demonstrate active narrowband wave-front manipulation by harnessing quasi-bound states in the continuum (quasi-BICs) in phase-change nonlocal metasurfaces. The proof-of-principle metasurfaces made of ${\mathrm{Sb}}_2{\mathrm{S}}_3$ allow for nonvolatile, reversible, and tunable spectral control over wave front and switchable spatial response at a given wavelength in the near-infrared regime. The design principle mainly builds upon the combination of the geometry phase of quasi-BICs and the dynamic tunability of phase-change meta-atoms to tailor the spatial response of light at tunable resonant wavelengths. By tuning the crystallization level of ${\mathrm{Sb}}_2{\mathrm{S}}_3$ meta-atoms through controlling the external stimuli, the dynamic nonlocal wave-front-shaping functionalities of beam steering, one-dimensional, and two-dimensional focusing, and holographic imaging are achieved exclusively at resonant wavelengths, with functionally transparent off resonance. This work represents a critical advance towards developing an integrated dynamic nonlocal metasurface for future augmented and virtual reality wearables.

For most comb-based applications, the signal-to-noise ratio (SNR) of the beat note between the comb and the continuous-wave laser is a critical parameter that affects the stability of the system and the accuracy of the measurement. We analyze the SNR model of the beat note and discuss some key aspects of implementing an optimized gated-detection scheme. High-speed balanced detection is introduced to enable detection of more interfering photons, while suppressing optical-intensity-noise interference. The gated detection is achieved by our combining a self-made low-noise, delay-adjustable pulse-generator circuit, which can suppress phase-random white noise. Compared with traditional direct-detection schemes, we demonstrate a 20-dB improvement in performance and achieve a beat-note SNR of more than 60 dB within a 300-kHz resolution bandwidth. Further experiments on frequency-comb locking show that this scheme has high reliability and robustness.

Quantum technologies, holding the promise of exponentially superior performance in comparison to their classical counterparts for certain tasks, have consistently encountered challenges, including instability in quantum light sources, quantum decoherence, and vulnerability to losses that topological photonics happens to adeptly address. Here, we theoretically put forth a quantum Su-Schrieffer-Heeger-type chain designed to greatly enhance single-photon blockade (single PB) effect with topological protection. By designing the deliberate coupling strengths, the quantum level lattices take the form of a one-dimensional array with a topological edge state in single-excitation space and a two-dimensional square breathing lattice with topological corner states in two-excitation space, resulting in enhanced single-photon excitation and the suppression of two-photon transitions. Therefore, the second-order correlation function is diminished by up to 2 orders of magnitude at the cavity resonance frequency, accompanied by stronger brightness. Furthermore, the PB effect is robust to local perturbations in cavity-qubit coupling and qubit frequency, benefitting from topological protection.

The spin-orbit interaction of light has been extensively examined in reflection and refraction at diverse optical interfaces, which results in the discovery of photonic spin Hall effect (SHE). The fundamental physical essence of this effect is attributed to the one-order effect of polarization rotation associated with one-dimensional geometric phase gradient. Here, we report a unified frame of high-order photonic SHE, which is related to the two-order effect in spin-orbit interaction of light and two-dimensional geometric phase gradient. The conventional one-order photonic SHE is associated with the global transport of the wave vector in momentum space, while the high-order photonic SHE is attributed to the local transport. Direct experimental observation of high-order photonic SHE has been demonstrated in three conventional cases of focusing, diffraction, and scattering. Under the focusing and diffraction conditions, the edge-enhanced images based on the high-order photonic SHE can be realized by inserting two crossed polarizers into a nonparaxial optical system. Under the scattering condition, the confocal imaging system is introduced to observe the high-contrast image and motion trajectory of dynamic transparent particles. We believe that the high-order photonic SHE may develop promising image-processing technique and high-contrast microscopy.