Nonlinear phenomena represent one of the central topics in the study of wave-matter interactions and constitute the key blocks for various applications in optical communication, computing, sensing, and imaging. In this work, we show that by employing the interactions between microwave photons and electron spins of nitrogen-vacancy ($\mathrm{N}$-$V$) centers, one can realize a variety of nonlinear effects, ranging from the resonance at the sum or difference frequency of two or more waves to electromagnetically induced transparency from the interference between spin transitions. We further verify the phase coherence through two-photon Rabi-oscillation measurements. The highly sensitive optically detected $\mathrm{N}$-$V$–center dynamics not only provides a platform for studying magnetically induced nonlinearities but also promises novel functionalities in quantum control and quantum sensing.

In the cavity-magnonics system, the coupling between microwave photon and magnon is of beam-splitter (BS) interaction, which in general does not support steady-state entanglement in a vacuum environment. We propose a scheme to generate and enhance steady-state magnon-photon entanglement and one-way steering in cavity-magnonics system. By coupling microwave cavity mode and magnon mode to a common waveguide, the effective dissipative coupling of the cavity-magnonics system is derived. If there is only nondegenerate parametric (NP) dissipative coupling, entanglement is negatively affected by the effective gain of the cavity mode caused by the common waveguide environment. When the coherent coupling exists, effective gain of cavity mode can cancel the intrinsic dissipation. Consequently, the larger the intrinsic dissipation of cavity the better the entanglement. When the effective dissipative coupling with NP and BS coexist, the effective dissipation can be eliminated and the entanglement is significantly improved. In addition, we find that the asymmetric coupling of the two modes to the common waveguide leads to one-way steering, which means that the cavity mode can guide the magnetic mode, and the magnetic mode can not affect the cavity mode through local measurements. This property facilitates the development of the cavity-magnonics system towards quantum information processing.

We investigate the pure dephasing of a Josephson qubit due to the spectral diffusion of two-level systems that are close to resonance with the qubit. We identify the parameter regime in which this pure dephasing rate can be of the order of the energy relaxation rate and, thus, the relation $T_2=2T_1$ is violated for the qubit. This regime is reached if the dynamics of the thermal TLSs responsible for the spectral diffusion is sufficiently slower than the energy relaxation of the qubit. By adding periodic bias modulating the qubit frequency or TLS excitation energies we show that this pure dephasing mechanism can be mitigated, allowing enhancement of superconducting qubits’ coherence time. Mitigating pure dephasing, even if it is subdominant, is of special significance in view of recent suggestions for converting the dominant relaxation process ($T_1$) into erasure errors, leaving pure dephasing as the bottleneck for efficient quantum computation.

Efficient control of antiferromagnetic (AFM) domain switching in thin films is vital for advancing antiferromagnet-based memory devices. In this study, we directly observed the current-driven switching process of $\mathrm{Co}\mathrm{O}$ AFM domains in the $\mathrm{Pt}/\mathrm{Co}\mathrm{O}(001)$ bilayer through the magneto-optical birefringence effect. The observed critical current density for AFM domain switching remains nearly constant across varying $\mathrm{Co}\mathrm{O}$ thicknesses, associated with consistent switching polarity, n ⊥ j—where n and j stand for the Néel vector and current density vector, respectively—suggesting the dominance of the thermomagnetoelastic effect. Further confirmation comes from a similar switching process with n ⊥ j observed in the $\mathrm{Pt}/{\mathrm{Al}}_2{\mathrm{O}}_3/\mathrm{Co}\mathrm{O}$ sample, excluding the contribution of spin-current injection. Remarkably, it was also surprisingly observed that the Néel vector could be further switched parallel to the current direction (n || j) at higher current density. Our findings not only enhance our understanding of current-driven AFM domain switching but also present alternative avenues for manipulating AFM domains.

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.

An optical clock network requires the establishment of an optical frequency transmission link between multiple optical clocks, utilizing narrow-linewidth lasers. Despite achieving link noise levels of ${10}^{-20}$, the final accuracy is limited by the phase noise of the clock laser. Correlation spectroscopy has been developed to transmit frequency information between two optical clocks directly, enabling optical clock comparison beyond the phase noise limit of clock lasers, and significantly enhancing the measurement accuracy or shortening the measurement time. In this article, two compact transportable ${}^{40}\mathrm{Ca}{}^{+}$ clocks are employed to accomplish a correlation spectroscopy comparison, demonstrating a 10-cm level measurement accuracy of chronometric leveling using a mediocre clock laser with linewidth of 200 Hz. The relative frequency instability reaches $6.0\times {10}^{-15}/\sqrt{\tau /s}$, which is about 20 times better than the result with Rabi spectroscopy using the same clock laser. This method circumvents the harsh requirements on the performance of the clock laser, so that an ordinary stable laser can also be employed in the construction of an optical clock network, which is essential for field applications, especially for chronometric leveling.

As promising quantum sensors, nitrogen-vacancy (N-$V$) centers in diamond have been widely used in frontier studies in condensed-matter physics, material science, and life sciences. In practical applications, weak laser excitation is favorable as it reduces the side effects of laser irradiation, such as phototoxicity and heating. Here we report a combined theoretical and experimental study of (near) zero-field optically detected magnetic resonance (ODMR) of N-$V$-center ensembles under weak 532-nm laser excitation. In this region, both the width and splitting of the ODMR spectra decrease with increasing laser power. This power dependence is reproduced with a model that accounts for the laser-induced charge neutralization of $\mathrm{N}\text{−}{V}^{-}$–${\mathrm{N}}^{+}$ pairs, which alters the local electric field environment. These results are useful for the understanding and development of N-$V$-based quantum sensing in light-sensitive applications.

We investigate superradiant enhancements in the refrigeration performance of a set of $N$ three-level systems that are collectively coupled to a hot and a cold thermal reservoir and are additionally subject to collective periodic (circular) driving. Assuming the system-reservoir coupling to be weak, we explore the regime of stronger periodic driving strengths by comparing collective weak driving, Floquet-Lindblad, and Floquet-Redfield master equations. We identify regimes where the power injected by the periodic driving is used to pump heat from the cold to the hot reservoir and derive analytic sufficient conditions for them based on a cycle analysis of the Floquet-Lindblad master equation. In those regimes, we also argue for which parameters collective enhancements like a quadratic scaling of the cooling current with $N$ can be expected and support our arguments by numerical simulations.

Recently, with advances in acoustic metamaterial, the Fano resonance has been widely introduced into the field of noise reduction for simultaneous airborne soundproofing and airflow permeability. The conventional Fano-based mechanism, manifesting as an ultrasharp spectrum, just serves a narrow working-frequency range, which deviates from the demands of broadband sound insulation. Here, we theoretically present and experimentally demonstrate the concept of acoustic consecutive multiple Fano resonances (ACMFRs), unlocking an unprecedented soundproof bandwidth (80%) while maintaining highly efficient ventilation. We first develop an analytical model to analyze the transmission spectra of ACMFRs in the bilayer metamaterial. Owing to the superposition of multiorder Fano resonance modes, the response strength from the discrete and continuum states of ACMFRs remains quasibalanced over a broad frequency range, which can be further interpreted by a consecutive single-negative nature. Subsequently, we implement this concept with an ultraopen helical metamaterial, which yields broadband sound attenuation at 770–1768 Hz and high air permeability (90%) simultaneously. The experimental results coincide with both theoretical and numerical ones, validating the effectiveness of the proposed ACMFRs. Our work lays the groundwork for the next generation of Fano-based metamaterial applications, with far-reaching implications for noise control and related fields.

Motivated by entanglement protection, our work utilizes a resonance effect to enhance optomechanical entanglement in the coherent-state representation. We propose a filtering model to filter out the significant detuning components between a thermal-mechanical mode and its surrounding heat baths in the weak-coupling limit. We reveal that protecting continuous-variable entanglement involves the elimination of degrees of freedom associated with significant detuning components, thereby resisting decoherence. We construct a nonlinear Langevin equation of the filtering model and numerically show that the filtering model doubles the robustness of the stationary maximum optomechanical entanglement to the thermal fluctuation noise and mechanical damping. Furthermore, we generalize these results to an optical cavity array with one oscillating end mirror to investigate the long-distance optimal optomechanical-entanglement transfer. Our study breaks new ground for applying the resonance effect to protect quantum systems from decoherence and advancing the possibilities of large-scale quantum information processing and quantum network construction.

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.

Janus transition metal dichalcogenides (JTMDs) have attracted much attention because of their outstanding electronic and optical properties. The additional out-of-plane dipole in JTMDs can form $n$- and $p$-like contacts, and this may be used in device applications, such as pin diodes and photovoltaic cells. In this study, we exploit this property to design $n$- and $p$-type metal-oxide-semiconductor field-effect transistors (MOSFETs). First, we use density-functional-theory calculations to study the inherent dipole field strength in the trilayer JTMD $\mathrm{Mo}\mathrm{S}\mathrm{Se}$. The intrinsic dipole of $\mathrm{Mo}\mathrm{S}\mathrm{Se}$ causes band bending at both the metal/$\mathrm{SMo}\mathrm{Se}$ and $\mathrm{SMo}\mathrm{Se}$/metal interfaces, resulting in electron and hole accumulation to form $p$-type, $n$-type, and even Ohmic contact regions. We incorporate this property into a two-dimensional finite-element-based Poisson-drift-diffusion solver to perform simulations, based on which we design complementary MOSFETs. Our results demonstrate that JTMDs can be used to make $n$- and $p$-MOSFETs in the same layer without the need for any extra doping.

In this paper, we present an alternative design for an acoustic metasurface with sparse units featuring open-ended pipes located on both sides of a central cavity, which can be tuned by designing the widths and length sizes. Band-stop and band-pass transmission control can be easily attained by alternating these units’ periodic arrangements with and without intervals and can be theoretically computed by the transfer-matrix method. By combining four of these units, the formed coupled metasurface has a subwavelength of 0.127λ and can insulate broadband sound (4.2 cm for approximately 1000–1500 Hz). The working bandwidth is between the resonant frequencies of monopolar and dipolar modes, which correspond to a negative effective bulk modulus and a negative effective-mass density, respectively, whose mechanism is different from conventional ones. To help with the tuning, the acoustic-electrical analogy gives the operating frequency as a function of size parameters. Numerical simulations and experiments are used to verify the ventilated sound insulation and transmission control capabilities. This paper presents a structurally simple, lightweight, and multifunctional design with appropriate arrangements that can be applied to acoustic communications, architectural acoustics, noise control, and other related fields.

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.

Laser-driven manipulation of magnetic skyrmions holds great promise for the development of next-generation information memory devices due to the flexibility of optical modulation. In this study, we theoretically present an approach for generating and manipulating stable topological spin textures using a light-induced radially polarized magnetic field, along with the ability to easily control quasiparticles by adjusting the intensity of the input beam. The generated topological spin textures can shrink into a stabilized quasiparticle with a size significantly smaller than the light-induced radially polarized magnetic field in few picoseconds. Through exploiting the relaxation mechanism of the spin texture at the center of the beam, we demonstrate the creation and stabilization of quasiparticles with higher ring numbers. Furthermore, we investigate the motion of these distinct quasiparticles and discover that the nπ quasiparticles (n > 1) exhibit significantly faster velocities than a traditional skyrmion, with the 4π quasiparticle being the fastest. Our method offers a promising avenue for constructing various topological spin textures with multiring profiles in ultrafast and high-density data-storage devices.