Photonic crystals (PCs) offer unique ways to control light-matter interactions. The measurement of dispersion relations is a fundamental prerequisite if we are to create various functionalities in PC devices. Angle-resolved spectroscopic techniques are commonly used for characterizing PCs that work in the visible and near-infrared regions. However, the techniques cannot be applied to the mid- and long-wavelength infrared regions due to the limited sensitivity of infrared detectors. Here, we propose an alternative approach to measuring infrared dispersion relations. We construct a high-precision angle-resolved setup compatible with a Fourier-transform spectrometer with an angle resolution as high as ${0.3}^{\circ }$. Hence, the reflection spectra are mapped to the two-dimensional (2D) photonic band structures of In($\mathrm{Ga}$,$\mathrm{Al}$)As/$\mathrm{In}\mathrm{P}$-based PC slabs, which are designed as midinfrared-PC surface-emitting lasers. We identify complex PC modes with the aid of polarization-selection rules derived by group theory. Spectral analysis makes it possible to evaluate the mode quality ($Q$) factors. Therefore, angle-resolved reflection is a useful way of optimizing 2D PC parameters for midinfrared devices.

Nitrogen-vacancy (N-$V$) centers in diamond have developed into a powerful solid-state platform for compact quantum sensors. However, high-sensitivity measurements usually come with additional constraints on the pumping intensity of the laser and the pulse control applied. Here, we demonstrate high-sensitivity N-$V$-ensemble-based magnetic field measurements with low-intensity optical excitation. Direct current magnetometry methods such as continuous-wave optically detected magnetic resonance and continuously excited Ramsey measurements combined with lock-in detection are compared to achieve an optimization. Gradiometry is also investigated as a step towards unshielded measurements of unknown gradients. The magnetometer demonstrates a minimum detectable field of 0.3–0.7 pT in a 73-s measurement when a flux guide with a sensing dimension of 2 mm is applied, corresponding to a magnetic field sensitivity of 2.6–6 $\mathrm{pT}/\sqrt{\mathrm{Hz}}$. Combined with our previous efforts on diamond ac magnetometry, the diamond magnetometer is promising for performing wide-bandwidth magnetometry with picotesla sensitivity and a cubic-millimeter sensing volume under ambient conditions.

Superconducting qubits on a circuit exhibit an always-on state-dependent phase error. This error is due to sub-MHz parasitic interaction that repels computational levels from noncomputational ones. We study a general theory to evaluate the “static” repulsion between seemingly idle qubits as well as the “dynamical” repulsion between entangled qubits under microwave driving gate. By combining qubits of either the same or opposite anharmonicity signs we find the characteristics of static and dynamical $ZZ$ freedoms. The latter universally eliminate the parasitic repulsion, leading us to mitigate high-fidelity gate operation. Our theory introduces the opportunities for making perfect entangled and unentangled states, which is extremely useful for quantum technology.

We study the radiative heat flux between two nanoparticles in close vicinity to the natural hyperbolic material $h$-BN, with its optical axis oriented parallel to the interface. We show that the heat flux between the nanoparticles can be efficiently modulated when rotating the nanoparticles due to the coupling to the highly directional hyperbolic surface modes in $h$-BN. Finally, we discuss the thickness and distance dependence of this effect.

We present a method for measuring the magnetic field that allows hyperfine and Zeeman optical pumping, excitation and detection of magnetic resonance by means of a single laser beam with time-modulated ellipticity. This improvement allows us to significantly simplify the Bell-Bloom magnetometric scheme, while retaining its sensitivity. The method does not require the use of radio-frequency fields, which is essential when creating arrays of sensors. The results of experimental studies demonstrate the efficiency of the proposed method and its potential applicability in most challenging magnetoencephalographic tasks.

For a large liquid-argon time-projection chamber (LArTPC) operating on or near the Earth’s surface to detect neutrino interactions, the rejection of cosmogenic background is a critical and challenging task because of the large cosmic-ray flux and the long drift time of the time-projection chamber. We introduce a superior cosmic background rejection procedure based on the Wire-Cell three-dimensional (3D) event reconstruction for LArTPCs. From an initial 1:20 000 neutrino to cosmic-ray background ratio, we demonstrate these tools on data from the MicroBooNE experiment and create a high-performance generic neutrino event selection with a cosmic contamination of 14.9% (9.7%) for a visible energy region greater than $O(200)$ MeV. The neutrino interaction selection efficiency is 80.4% and 87.6% for inclusive ${\nu }_{\mu }$ charged-current and ${\nu }_e$ charged-current interactions, respectively. This significantly improved performance compared with existing reconstruction algorithms marks a major milestone toward reaching the scientific goals of LArTPC neutrino oscillation experiments operating near the Earth’s surface.

We provide a vectorial model to simulate second-harmonic generation (SHG) in birefringent, transparent media with an arbitrary configuration of nonlinear (${\chi }^{(2)}$) crystalline domains. We apply this model on disordered assemblies of ${\mathrm{Li}\mathrm{Nb}\mathrm{O}}_3$ and ${\mathrm{Ba}\mathrm{Ti}\mathrm{O}}_3$ to identify the influence of the birefringence on the random quasi-phase-matching process. We show that in monodispersed assemblies, the birefringence relaxes the domain size dependence of the SHG efficiency. In polydispersed assemblies with sufficiently large domains, we find that the birefringence introduces a SHG efficiency enhancement of up to 54% compared to isotropic reference crystals. This enhancement is domain size independent in non-phase-matchable materials, while it increases linearly with the domain size if the domains can be phase matched. These two different scaling behaviors are used in Kurtz and Perry’s (KP) powder technique to identify the phase matchability of a material. We show on the example of ${\mathrm{Li}\mathrm{Nb}\mathrm{O}}_3$ and ammonium dihydrogen phosphate that the KP technique cannot be applied to domains smaller than the coherence length, because then the SHG scaling with the domain size becomes material specific.

This study introduces a framework for the design and implementation of acoustic black holes (ABHs) in airfoils. A generalized multiparameter damped-ABH generation function is mapped onto airfoils based on the National Advisory Committee for Aeronautics series. Representative geometries and a uniformly distributed baseline, all with the same mass of structure and damping are fabricated using multimaterial PolyJet three-dimensional printing. Laser Doppler vibrometer measurements along the airfoil chord in response to a broadband 0.1–12 kHz excitation show a decrease in trailing-edge vibrations by as much as 10 dB, a broadband 5-dB reduction across the entire chord, substantial spatial and temporal modulation of flexural waves by ABH foils. Finite-element analysis (FEA) models are developed and validated based on the measured data. Furthermore, a parametric FEA study is performed on a set of comparable designs to elucidate the scope of modulation achievable. These findings are applicable to trailing-edge noise reduction, flow control, structural enhancement, and energy harvesting for airfoils.

Line waves are recently discovered wave entities that are localized along two directions and therefore can be viewed as the one-dimensional counterpart of surface waves. These waves can be supported at discontinuities of the surface reactance and/or resistance of low-dimensional materials such as metasurfaces or graphene. Here, a broader class of non-Hermitian surface-impedance junctions is studied that can support coupled line waves and that allows the investigation of different one-dimensional waveguiding mechanisms in a unified framework. It is theoretically demonstrated that, under parity–time-symmetry conditions, exceptional points can occur in a truly flat-optics scenario, hence endowing these waveguiding systems with the attractive features of both line-wave and exceptional-point physics and shedding further light on the phase transitions existing in these systems. It is also shown that the required surface-impedance parameters are compatible with those attainable with typical models of photoexcited graphene metasurfaces at terahertz frequencies. Besides providing additional understanding in the physics of line waves, which is still in its infancy, these results pave the way toward intriguing developments in the largely unexplored field of non-Hermitian flat optics, with possible applications ranging from sensing to lasing and on-chip optical signal processing.

We experimentally observe a self-injection locking regime of the gain-switched laser to a high-$Q$ optical microresonator. We reveal that the comb generated by the gain-switched laser experiences a dramatic reduction of comb-teeth linewidths in this regime. We demonstrate the Lorentzian linewidth of the comb teeth of sub-kHz scale as narrow as for a nonswitched self-injection locked laser. Such a setup allows generation of high-contrast electrically tunable optical frequency combs with tunable comb-line spacing in a wide range from 10 kHz up to 10 GHz. The characteristics of the generated combs are studied for various modulation parameters—modulation frequency and amplitude, and for parameters, defining the efficiency of the self-injection locking—locking phase, coupling efficiency, and pump frequency detuning.

Snapshot projection optical tomography (SPOT) uses a microlens array (MLA) to simultaneously capture the projection images of a three-dimensional (3D) specimen corresponding to different viewing directions. Compared to other light-field imaging techniques using an MLA, SPOT is dual telecentric and can block high-angle stray rays without sacrificing the light collection efficiency. Using SPOT, we recently demonstrated snapshot 3D fluorescence imaging. Here we demonstrate snapshot 3D absorption imaging of microscopic specimens. For the illumination, we focus the incoherent light from a light-emitting diode onto a pinhole, which is placed at a conjugate plane to the sample plane. SPOT allows us to capture the ray bundles passing through the specimen along different directions. The images recorded by an array of lenslets can be related to the projections of 3D absorption coefficient along the viewing directions of lenslets. Using a tomographic reconstruction algorithm, we obtain the 3D map of absorption coefficient. We apply the developed system to different types of samples, which demonstrates the optical sectioning capability. The transverse and axial resolutions measured with gold nanoparticles are 1.3 and 2.3 $\mu \mathrm{m}$, respectively.

Underwater acoustic stealth is of significance for hiding targets. Since perfect cloaking achieved by carpet cloaks or metasurface carpet cloaks may only be suitable for static targets, here we propose a broadband 2-bit coding metasurface to reduce the scattering cross section (SCS) of an object by the destructive interferences among waves scattered by different coding elements. A simple and easy fabricated design is developed by drilling square holes into a steel plate. Utilizing the antiresonance induced by couplings among four square holes of the unit cell, we achieve an approximate $95.62\mathrm{\%}$ fractional bandwidth of acoustic stealth with the SCS reduction below $-10\mathrm{dB}$, which has been confirmed by both the theoretical prediction and experimental measurement. Compared with the previously proposed underwater acoustic carpet cloaks by the transformation acoustics, the bandwidth of SCS reduction is greatly expanded by the destructive interferences. In addition, simulations have demonstrated that the proposed metasurface may also be suitable for an object with a nonplanar surface.

We propose a floating tunable coupler that does not rely on direct qubit-qubit coupling capacitances to achieve the zero-coupling condition. We show that the polarity of the qubit-coupler couplings can be engineered to offset the otherwise constant qubit-qubit coupling and attain the zero-coupling condition when the coupler frequency is above or below the qubit frequencies. We experimentally demonstrate these two operating regimes of the tunable coupler by implementing symmetric and asymmetric configurations of the superconducting pads of the coupler with respect to the qubits. Such a floating tunable coupler provides flexibility in designing large-scale quantum processors while reducing the always-on residual couplings.

The operation of random lasers (RLs) is possible due to multiple light scattering, which provides optical feedback inside the gain medium. No conventional optical cavity is required for the operation of RLs and, therefore, RLs provide the best evidence to defy the conventional view that disorder is an unwanted phenomenon when present in physical systems. Mirrorless lasers demonstrate that the degree of disorder, associated with the spatial distribution of scattering particles, is the main factor responsible for generating a light source with low spatial coherence; this is reason why RLs are so attractive for modern imaging systems. Here, we demonstrate how to optimize the performance of typical diffusive RLs by exploiting a different degree of randomness in the system, which is loaded onto an induced disorder in the transverse intensity and wave-vector distributions of the light pattern that pumps the random-lasing medium. Quantitative analyses show that the RL’s intensity emission and threshold fluence can be optimized by more than 20 times, when excited by an optical field presenting a random spatial-intensity distribution, with high speckle contrast, becoming an efficient methodology to induce high photon degeneracy in RLs required for high sensitivity applications.

Next-generation millimeter-wave $(>30\mathrm{GHz})$ telecommunications electronics must be compact, energy efficient, and have good thermal management. Tunable materials may play a role in meeting these requirements for millimeter-wave front-end devices, but there are few models or even measurements of tunable dielectrics at these frequencies. Here, we report on the adaptation and development of high-frequency dielectric spectroscopy techniques for composition-spread thin films from 100 MHz to 110 GHz. Our comprehensive technique sequentially probes the composition, frequency, and electric field dependence of the complex permittivity in a combinatorial thin film library, which provides a platform to rapidly explore functional materials for emerging telecommunications electronics. This is achieved by modifying existing on-wafer transmission line permittivity measurement techniques to obtain a compact set of test devices that can be patterned to extract the complex permittivity in multiple regions of a thin film. We demonstrate this technique by applying it to composition-spread ${\mathrm{Ba}}_{1-x}{\mathrm{Sr}}_x{\mathrm{Ti}\mathrm{O}}_3$ thin films spanning compositions from $x=0$ to $x=1.$ The systematic approach to materials growth inherent in combinatorial synthesis allows for a comprehensive picture of the ${\mathrm{Ba}}_{1-x}{\mathrm{Sr}}_x{\mathrm{Ti}\mathrm{O}}_3$ system. Our continuous, quantitative measurements provide an encompassing view of the composition- and voltage-dependent trends in the room temperature dielectric properties at millimeter-wave frequencies—from strong, few-picosecond relaxations to no relaxation, and from large relative tunability ($n_r>50\mathrm{\%}$ at $75\mathrm{k}{\mathrm{V}}_{}\mathrm{c}{\mathrm{m}}^{-1}$) to zero tunability. Our work underscores both the utility of our technique, and the need to discover lower-loss, highly tunable electronic materials for next-generation telecommunications.

In the present paper, we propose and experimentally verify a concept of a magnonic reservoir computer. The system utilizes the nonlinear behavior of propagating magnetostatic surface spin waves in a yttrium-iron garnet thin film and the time delay inherent in the active ring configuration to process time-dependent data streams. Higher reservoir dimensionality is obtained through the time-multiplexing method, whereby inputs to the system are multiplied by a mask to drive complex dynamics in the ring and the output is sampled in time to create a series of “virtual” neurons for each sample. The input mask is implemented as a train of microwave pulses injected to the system. To demonstrate the efficacy of the concept, the reservoir computer is evaluated on the short-term memory and parity-check benchmark tasks, and the physical system parameters are tuned to optimize performance. By incorporating a reference line to mix the input signal directly onto the ring-resonator output, both the amplitude and phase nonlinearity of the spin waves can be exploited. The addition of a second spin-wave delay line increases the delay time of the ring and enhances the fading memory capacity of the system. Configuring the second delay line to transmit backward volume spin waves also partly compensates the dispersive pulse broadening that is present because of the large delay time.

A high-flux entangled-photon source is a key resource for quantum optical study and application. Here, it is realized in a lithium niobate on isolator (LNOI) chip, with 2.79 × ${10}^{11}$ Hz/mW photon-pair rate and 1.53 × ${10}^9$ Hz/(nm mW) spectral brightness. These data are boosted by over 2 orders of magnitude compared with existing technologies. A 160-nm-broad bandwidth is engineered for eight-channel multiplexed energy-time entanglement. Harnessed by high-extinction-frequency correlation and Franson interferences up to 99.17% visibility, such energy-time-entanglement multiplexing further enhances the high-flux data rate and warrants broad application in quantum-information processing on a chip.