In the fields of geology, materials and biomedical engineering, the noninvasive and accurate estimation of the dynamic mechanical properties of the soft matter enclosed in a rigid shell induced by a low-frequency vibration is worthy of exploration. The addition of fluidity on the basis of viscoelasticity to describe the properties of the soft matter, especially when containing a large amount of water, may be of great value in the detection of crustal movement, material structure, and early cerebral diseases. In the biomedical field, since the influence of the skull on ultrasound is unknown for viewing the propagation of the transcranial shear wave, it is challenging to obtain the mechanical properties of the brain tissue with the skull using the transcranial ultrasound. In this study, the propagations of the transcranial shear wave within the brain tissue induced by an external low-frequency vibration are presented by finite-element-method simulation. This experiment achieved a transcranial ultrasound estimation and differentiation of viscoelasticity and fluidity of brain phantoms enclosed in the skull using the low-frequency vibration and Kelvin-Voigt fractional derivative modeling, and the estimation results are consistent with the nontranscranial ones. These results represent a great potential in the estimation of viscoelasticity and fluidity of the soft matter under different boundary constraints in various areas.

The dipole response of helium exposed to attosecond extreme ultraviolet (EUV) pulses and a femtosecond near-infrared (NIR) laser field is investigated. The optical interference between the EUV pulse and nonlinear wave-mixing signals leads to fringes in the transmitted spectrum above the single ionization threshold. Perturbation theory suggests that such fringes record the self-convolution of complex-valued NIR pulse in the frequency domain, allowing direct characterization of a broadband optical pulse without the need of reconstruction algorithms. We apply this in situ interferometric scheme to diagnose a few-cycle laser pulse.

Spintronic diodes (STDs) are emerging as a technology for the realization of high-performance microwave detectors. The key advantages of such devices are their high sensitivity, capability to work at low input power, and compactness. In this work, we show a possible use of STDs for neuromorphic computing to expand the realm of their functionalities for the implementation of analog multiplication, which is a key operation in convolutional neural networks (CNNs). In particular, we introduce the concept of degree of rectification (DOR) in injection-locked STDs. Micromagnetic simulations are used to design and identify the working range of the STDs for the implementation of the DOR. Previous experimental data confirm the applicability of the proposed solution, which is tested in image processing and in a CNN that recognizes handwritten digits.

In contrast to artificial metamaterials, natural two-dimensional (2D) hyperbolic materials are able to support higher electromagnetic confinement and stronger photonic density of states. This means natural 2D hyperbolic materials have fascinating potential for applications in thermal photonics. In this work, we investigate mechanisms of near-field thermal radiation (NFTR) in a ${\mathrm{T}}_d$–${\mathrm{WTe}}_2$ single layer at the nanoscale using the fluctuation-dissipation theorem and density-functional theory. The results show that NFTR of ${\mathrm{T}}_d$–${\mathrm{WTe}}_2$ can be 3 orders of magnitude larger than the blackbody limit. By using the photonic tunneling coefficient and the plasmon dispersion, we present a comprehensive study of plasmonic properties of ${\mathrm{T}}_d$–${\mathrm{WTe}}_2$. Moreover, our first-principles calculations predict that application of a certain amount of mechanical stress can trigger topological transition between the elliptic and the hyperbolic surface states by regulating the Fermi surface and interband excitation threshold. Lastly, we systematically exhibit the evolution of surface plasmon polaritons in ${\mathrm{T}}_d$–${\mathrm{WTe}}_2$ under mechanical stress and analyze the performance of using mechanical stress to modulate the corresponding NFTR. Our work explores the great potential of tunable radiative heat flux in ${\mathrm{T}}_d$–${\mathrm{WTe}}_2$, which is explained here through the peculiar nature of hyperbolic surface plasmons.

Two-dimensional (2D) metal-particle focusing is an essential task for various fabrication processes. While acoustofluidic devices can manipulate particles in two-dimensions, the production of these devices often demands a cleanroom environment. Therefore, acoustically excited glass capillaries present a cheap alternative to labor-intensive cleanroom production. Here, we present 2D metal microparticle focusing in a round glass capillary using bulk acoustic waves. Excitation of the piezoelectric transducer at specific frequencies leads to mode shapes in the round capillary, concentrating particles toward the capillary center. We experimentally investigate the particle line width for different particle materials and concentrations. We demonstrate the focus of copper particles approximately $1\mu \mathrm{m}$ in diameter down to a line of width $60.8\pm 7.0\mu \mathrm{m}$ and height $45.2\pm 9.3\mu \mathrm{m}$, corresponding to a local concentration of 4.5% v/v, which is $90$ times higher than the concentration of the initial solution. Further, we achieve the focusing of 1-$\mu \mathrm{m}$ polystyrene particles, which is usually prevented due to acoustic streaming. Through numerical analysis, we reveal the mechanism enabling the manipulation of particles in the low-micrometer range. Due to a transition of the acoustic streaming patterns from two dominant vortices in the lower half to two dominant vortices in the upper half, the streaming velocity exhibits a local minimum while the overall acoustic energy density stays at a sufficiently high level for particle focusing, leading to a lower critical particle radius than in conventional rectangular microchannels. Finally, we use our method to eject copper particles through a tapered round capillary with an opening of $25\mu \mathrm{m}$ in diameter, which would not be possible without particle focusing. Our setup can be utilized for various applications that otherwise might suffer from abrasion, clogging, and limited resolution.

Insulator-metal phase oscillations driven by direct voltages in strongly correlated materials, which can naturally emulate nonlinear neural behavior, have hitherto been realized largely as extrinsic charging and discharging cycles of capacitors with limited frequencies. Here, based on an experimentally validated physical phase-field description of the insulator-metal transition, we demonstrate an intrinsic noncapacitive insulator-metal phase oscillation in a prototypical strongly correlated material, ${\mathrm{VO}}_2$, near room temperature, which can be generic in Mott insulators. Such intrinsic phase oscillations exhibit frequencies $1$–$2$ orders of magnitude higher than the typical frequencies of the extrinsic capacitive phase oscillations. They manifest themselves as electronically driven automatic growth and shrinkage of conduction filaments in contrast to the usual suggestion of thermally driven growth. The discovery of intrinsic phase oscillations has important implications for exploring the intrinsic nonlinear electronic dynamics in strongly correlated materials and advances the realization of high-frequency Mott electronic oscillators for neuromorphic computing.

In the presence of Rashba-Dresselhaus coupling, strong spin-orbit interactions in liquid-crystal optical cavities result in a distinctive spin-split entangled dispersion. Spin coherence between such modes gives rise to an optically persistent spin helix. In this paper, we introduce optical gain in such a system, by dispersing a molecular dye in a liquid-crystal microcavity, and demonstrate an optically persistent spin-helix lasing in the Rashba-Dresselhaus regime.

Mott insulators are a class of strongly correlated materials with emergent properties important for modern electronics applications, such as artificial neural networks. Under an electric field, these compounds undergo a resistive switching that may be used to build up artificial neurons. However, the mechanism of this resistive switching is still under debate and may depend on the Mott material involved. Some works suggest an electronic avalanche phenomenon, while others propose an electrothermal scenario. As electric pulses produce both Joule heating and hot carriers, disentangling their respective roles requires the use of another external stimulus. Here, an ultrashort light pulse is used to tune the number of photogenerated carriers and the energy provided to the system. In these pump-pump-probe experiments, a crystal of the Mott insulator ${\mathrm{Ga}\mathrm{Ta}}_4{\mathrm{Se}}_8$ is simultaneously excited by electric and laser pulses while an electric probe monitors its conductivity. The study shows that the resistive switching is affected by the number of generated photocarriers rather than by the accumulation of energy deposited by the femtosecond laser. It supports therefore a mechanism driven by generation of hot carriers. Finally, our work opens the possibility to build up an artificial electro-optical “Mott” neuron tuned by a femtosecond laser pulse.

On-chip mode conversion is beneficial in photonic integrations and enables many functionalities for optical signal processing, however, it is still challenging to achieve a robust solution with broadband working wavelengths. Here, by exploring an interesting coupling effect between triplet and singlet waveguides, we propose and realize a robust mode conversion based on an undistributed breathing mode in the waveguide triplet supercell. It is well demonstrated with high efficiency and robustness in the silicon waveguide platform, which shows further extensions to higher-order mode conversions by connecting more elements together. Our approach makes good use of the undisturbed breathing modes in a three-level system for robust mode conversions, which is proved to be an effective means and promises further functional elements in photonic integrations.

Terahertz electromagnetic radiation is one of the hottest research topics thanks to its promising applications in diverse scientific and technological fields. Using a uniformly moving electron beam to interact with a metallic or dielectric surface is an efficient tool for the generation of high-power terahertz waves. In the present paper, we demonstrate enhanced coherent terahertz emission theoretically and experimentally by using a metasurface formed by an array of Fabry-Perot-like resonators to obliquely intercept a low-energy flat electron beam. We illustrate that the mechanism is one of modified coherent Smith-Purcell radiation rather than the expected transition radiation. More notably, this metasurface overcomes the inherent restriction imposed by the decay length in conventional beam-wave interactions, greatly enhancing the radiation efficiency and intensity. This emission promises an attractive way of developing high-power terahertz sources.

When midinfrared light interacts with nanoscale polar dielectric structures, optical phonon propagation cannot be ignored, leading to a rich nonlocal phenomenology that we have only recently started to uncover. In properly crafted nanodevices this includes the creation of polaritonic excitations with hybrid longitudinal-transverse nature, which are predicted to allow energy funneling from longitudinal electrical currents to far-field transverse radiation. In this work we study the physics of these longitudinal-transverse polaritons in a dielectric nanolayer in which the nonlocality strongly couples epsilon-near-zero modes to longitudinal phonons. After having calculated the system’s spectrum solving Maxwell’s equations, we develop an analytical polaritonic theory able to transparently quantify the nonlocality-mediated coupling as a function of the system parameters. Such a theory provides a powerful tool for the study of longitudinal-transverse polariton interactions and we use it to determine the conditions required for the hybrid modes to appear.

The ability to engineer high-fidelity gates on quantum processors in the presence of systematic errors remains the primary barrier to achieving quantum advantage. Quantum optimal control methods have proven effective in experimentally realizing high-fidelity gates, but they require exquisite calibration to be performant. We apply robust trajectory optimization techniques to suppress gate errors arising from system parameter uncertainty. We propose a derivative-based approach that maintains computational efficiency by using forward-mode differentiation. Additionally, the effect of depolarization on a gate is typically modeled by integrating the Lindblad master equation, which is computationally expensive. We employ a computationally efficient model and utilize time-optimal control to achieve high-fidelity gates in the presence of depolarization. We apply these techniques to a fluxonium qubit and suppress simulated gate errors due to parameter uncertainty below ${10}^{-7}$ for static parameter deviations of the order of 1%.

Periodic arrays of nanoholes perforated in metallic thin films interact strongly with light and produce large electromagnetic near-field enhancements in their vicinity. As a result, the optical response of these systems is very sensitive to changes in their dielectric environment, thus making them an exceptional platform for the development of compact optical sensors. Given that these systems already operate at the shot-noise limit when used as optical sensors, their sensing capabilities can be enhanced beyond this limit by probing them with quantum light, such as squeezed or entangled states. Motivated by this goal, here, we present a comparative theoretical analysis of the quantum enhanced sensing capabilities of metallic nanohole arrays with one and two holes per unit cell. Through a detailed investigation of their optical response, we find that the two-hole array supports resonances that are narrower and stronger than its one-hole counterpart, and therefore have a higher fundamental sensitivity limit as defined by the quantum Cramér-Rao bound. We validate the optical response of the analyzed arrays with experimental measurements of the reflectance of representative samples. The results of this work advance our understanding of the optical response of these systems and pave the way for developing sensing platforms capable of taking full advantage of the resources offered by quantum states of light.

Distinct non-Hermitian dynamics has demonstrated its advantages in improving measurement precision over traditional sensing protocols. Multimode non-Hermitian lattice dynamics can provide exponentially enhanced quantum sensing where the quantum Fisher information (QFI) per photon increases exponentially with the lattice size. However, it has also been shown that the quintessential non-Hermitian skin effect does not provide any true advantage. In this paper, we demonstrate the importance of optimizing the phase of the coherent drive and the position of the injection and detection in multimode non-Hermitian quantum sensing. The QFI per photon can be exponentially enhanced or exponentially reduced depending on the parameters of the drive and detection. Specifically, it is demonstrated that for large amplification, by choosing appropriate coherent drive parameters, the non-Hermitian skin effect can provide exponentially enhanced quantum sensing. Moreover, in the regime beyond linear response, the skin effect can also provide a clear advantage as compared to the local perturbation and the proposed protocol is robust in tuning the amplification factor.

For nitride-based blue and green light-emitting diodes (LEDs), the forward voltage $V_{\mathrm{for}}$ is larger than expected, especially for green LEDs. This is mainly due to the large barriers to vertical carrier transport caused by the total polarization discontinuity at multiple quantum well and quantum barrier interfaces. The natural random alloy fluctuation in quantum wells has proven to be an important factor reducing $V_{\mathrm{for}}$. However, this does not suffice in the case of green LEDs because of their larger polarization-induced barrier. V-shaped defects (V-defects) have been proposed as another key factor in reducing $V_{\mathrm{for}}$ to allow lateral injection into multiple quantum wells, thus bypassing the multiple energy barriers incurred by vertical transport. In this paper, to model carrier transport in the whole LED, we consider both random-alloy and V-defect effects. A fully two-dimensional drift-diffusion charge-control solver is used to model both effects. The results indicate that the turn-on voltages for blue and green LEDs are both affected by random alloy fluctuations and the V-defect density. For green LEDs, $V_{\mathrm{for}}$ decreases more due to V-defects, where the smaller polarization barrier at the V-defect sidewall is the major path for lateral carrier injection. Finally, we discuss how the V-defect density and size affects the results.

Phase slip is the intrinsic fluctuation of the order parameter and leads to the dissipation of superconductors. Here we propose a photon-assisted phase-slip model in superconducting nanowires to explain the phase-slip rate under photon irradiation. In this phenomenological model, incident photons destroy large quantities of Cooper pairs and reduce the free-energy barrier of phase slips, resulting in proliferation in the phase-slip events and leading to superconducting transition. The switching rates from the superconducting state of a niobium nitride nanowire under various photon irradiation (4.4 mW/m${}^2$–4.4 W/m${}^2$) and temperatures (2.3–3.7 K) are investigated through the distribution of switching currents in the experiment. The experimental data can be well fitted by our deduced expression of phase-slip rate after eliminating the influence of external noise. Our model develops the phase-slip theory under incident photons and is promising to reveal the intrinsic detection mechanism of the superconducting nanowire single-photon detector.

2DEG systems formed in quantum wells of semiconductor heterostructures have been instrumental in advancing science and technology for many decades. Here, we report two unique transport properties of 2DEG formed at the interface of two perovskite oxides ${\mathrm{La}\mathrm{In}\mathrm{O}}_3$ ($\mathrm{LIO}$) and ${\mathrm{Ba}\mathrm{Sn}\mathrm{O}}_3$ ($\mathrm{BSO}$): the peculiar $\mathrm{LIO}$ thickness dependence of the high two-dimensional (2D) carrier density ($n_{2{\rm{D}}}$) and the very narrow width of the quantum well. We analyze, via Poisson-Schrödinger simulation, how the various materials parameters affect the 2D carrier density and its profile when using the “interface-polarization” model in which the polarization exists only near the interface. Our simulations show that the known material parameters of $\mathrm{LIO}$ and $\mathrm{BSO}$ are capable of generating a deep and narrow quantum well as suggested by the experimental transport properties and reveal some distinct features of the $\mathrm{LIO}$/$\mathrm{BSO}$ interface from the conventional 2DEGs. Furthermore, they predict how the $\mathrm{LIO}$/$\mathrm{BSO}$ 2DEG will evolve as the defect density decreases.

We investigate the dynamics of the spin-exchange relaxation-free (SERF) comagnetometer for rotation sensing. The transient and steady-state models of the rotation response are established by solving a set of Bloch equations. The transient responses of the comagnetometer with inertial rotation input and magnetic field input are compared. The effects of the pump-laser power density on the transient response are studied and the results indicate that the transient response reaches the fastest when the pumping rate equals the product of the gyromagnetic ratio and polarization field factor of the electron spins. The measuring range of the comagnetometer is investigated by experiment and simulation, which suggests that the measuring range can be improved by increasing the relaxation rates of the electron spins and nuclear spins and the ratio of the Fermi-contact field of the electron spins to that of the nuclear spins. The theory and method presented here pave the way for the practical application of SERF comagnetometers for rotation sensing.

We theoretically analyze band-to-band tunneling (BTBT) in highly mismatched, narrow-gap dilute nitride and bismide alloys, and quantify the impact of the $\mathrm{N}$- or $\mathrm{Bi}$-induced perturbation of the band structure—due to band anticrossing (BAC) with localized impurity states—on the electric-field-dependent BTBT generation rate. For this class of semiconductors, the assumptions underpinning the widely employed Kane model of BTBT break down, due to strong band-edge nonparabolicity resulting from BAC interactions. Via numerical calculations based on the Wentzel-Kramers-Brillouin approximation we demonstrate that BAC leads, at fixed band gap, to reduced (increased) BTBT current at low (high) applied electric field compared to that in a conventional ${\mathrm{In}\mathrm{As}}_{1-x}{\mathrm{Sb}}_x$ alloy. Our analysis reveals that BTBT in ${\mathrm{In}\mathrm{N}}_x{\mathrm{As}}_{1-x}$ and ${\mathrm{In}\mathrm{As}}_{1-x}{\mathrm{Bi}}_x$ is governed by a field-dependent competition between the impact of $\mathrm{N}$ ($\mathrm{Bi}$) incorporation on (i) the dispersion of the evanescent Bloch band linking the valence and conduction band edges, which dominates at low field strengths, and (ii) the conduction- (valence-) band-edge density of states, which dominates at high field strengths. The implications of our results for applications in long-wavelength avalanche photodiodes (APDs) and tunneling field-effect transistors (TFETs) are discussed. For APDs, we describe that leakage currents in ideal dilute nitride and bismide devices are likely comparable to those in devices based on conventional III-V materials, but that the expected reduction of the hole impact ionization rate in ${\mathrm{In}\mathrm{As}}_{1-x}{\mathrm{Bi}}_x$ is promising from the perspective of obtaining low excess noise factor. For TFETs, we describe that $\mathrm{Bi}$ incorporation provides the potential to obtain both reduced subthreshold swing and increased on-state current, making ${\mathrm{In}\mathrm{As}}_{1-x}{\mathrm{Bi}}_x$ of interest for the development of low-power, high-speed devices.