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.

A flux qubit can interact strongly when it is capacitively coupled to other circuit elements. This interaction can be separated into two parts, one acting on the qubit subspaces and one in which excited states mediate the interaction. The first term dominates the interaction between the flux qubit and an $LC$ resonator, leading to ultrastrong couplings of the form ${\sigma }^y(a+a^{†})$, which complement the inductive ${\sigma }^{x}i(a^{†}-a)$ coupling. However, when coupling two flux qubits capacitively, all terms need to be taken into account, leading to complex nonstoquastic ultrastrong interaction of types ${\sigma }_1^y{\sigma }_2^y$, ${\sigma }_1^z{\sigma }_2^z$, and ${\sigma }_1^x{\sigma }_2^x$. Our theory explains all these interactions, describing them in terms of general circuit properties—coupling capacitances, qubit gaps, inductive, Josephson and capacitive energies—that apply to a wide variety of circuits and flux qubit designs.

Diverse external stimuli, such as light irradiation, an electric field, and a stress field, are employed to trigger the large modulation of electronic properties in Mott insulators. Here, we demonstrate that multiple nonvolatile and reversible resistivity evolution can be realized by adjusting the magnitude of ferroelastic strain in voltage-actuated ${\mathrm{LaVO}}_3/0.7\mathrm{Pb}({\mathrm{Mg}}_{1/3}{\mathrm{Nb}}_{2/3}){\mathrm{O}}_3\text{−}0.3{\mathrm{Pb}\mathrm{Ti}\mathrm{O}}_3$ heterostructures. The electrically driven ferroelastic strain tunability of resistivity, with a giant gauge factor of 494, can be effectively modified by light stimulus. Moreover, the visible-light-excited photoresistivity response can be ferroelastically enhanced by up to 65%. This discovery illustrates the strong interplay between the ferroelastic-strain-induced and light-induced effects, mediated by lattice-charge-orbital coupling. Our work implies the potential application of correlated oxide-ferroelectric systems for future low-power high-density versatile electronic storage devices with light-sensing capability.

Acoustic manipulation has been a topic of significant research in recent years. However, the trapping scale in the radiative acoustic field domain is severely limited by the diffraction limit of the classic wave. Here, we report on a simple strategy to create multiple acoustic diffraction-limit-broken spots at different spatial positions in the far-field region for a wide frequency range. The subwavelength acoustic field comes from the interference of the plentiful diffractive beams specific to a quasiperiodic structure plate. We analyze the acoustic radiation force of the gradient field at multiheight plane above the plate for different frequencies and further demonstrate acoustic pushing and ring-shaped trapping of polystyrene particles within this subwavelength region. This work could be envisaged to pave a way for high-resolution manipulation of tiny particles in biomedical and cell research fields.

Demonstrating a quantum computational advantage will require high-fidelity control and readout of multiqubit systems. As system size increases, multiplexed qubit readout becomes a practical necessity to limit the growth of resource overhead. Many contemporary qubit-state discriminators presume single-qubit operating conditions or require considerable computational effort, limiting their potential extensibility. Here, we present multiqubit readout using neural networks as state discriminators. We compare our approach to contemporary methods employed on a quantum device with five superconducting qubits and frequency-multiplexed readout. We find that fully connected feedforward neural networks increase the qubit-state-assignment fidelity for our system. Relative to contemporary discriminators, the assignment error rate is reduced by up to 25% due to the compensation of system-dependent nonidealities such as readout crosstalk, which is reduced by up to one order of magnitude. Our work demonstrates a potentially extensible building block for high-fidelity readout relevant to both near-term devices and future fault-tolerant systems.

An optical dyadic Green’s function framework to describe the transverse electromagnetic fields in a planar perovskite solar-cell stack is coupled to an electronic drift-diffusion model for rigorous treatment of photon recycling in the wave-optics regime for a realistic photovoltaic device. The optical model provides the local reabsorption rate as well as a detailed-balance compatible radiative prefactor, which are used in the electronic model to achieve a self-consistent solution that yields the full optoelectronic device characteristics. The presented approach provides detailed insights into the impact of photon recycling on device performance under different regimes of charge transport and recombination and can help identify the various electronic and optical losses for nonideal, realistic devices. The global efficiency of photon recycling is quantified by defining quantum efficiencies of reabsorbed radiation, while the local efficiency can furthermore be quantified by defining an effective local radiative prefactor. The model introduced here can be used to guide the design of future devices that exploit the full potential of photon recycling.

We use a science-grade skipper charge-coupled device (skipper CCD) operating in a low-radiation background environment to develop a semiempirical model that characterizes the origin of single-electron events in CCDs. We identify, separate, and quantify three independent contributions to the single-electron events, which were previously bundled together and classified as “dark counts”: dark current, amplifier light, and spurious charge. We measure a dark current, which depends on exposure, of $(5.89\pm 0.77)\times {10}^{-4}{e}^{-}/\mathrm{pix}/\mathrm{day}$, and an unprecedentedly low spurious charge contribution of $(1.52\pm 0.07)\times {10}^{-4}{e}^{-}/\mathrm{pix}$, which is exposure independent. In addition, we provide a technique to study events produced by light emitted from the amplifier, which allows the detector’s operation to be optimized to minimize this effect to a level below the dark-current contribution. Our accurate characterization of the single-electron events allows one to greatly extend the sensitivity of experiments searching for dark matter or coherent neutrino scattering. Moreover, an accurate understanding of the origin of single-electron events is critical to further progress in ongoing research and development efforts of skipper and conventional CCDs.

Quantum diamond microscope (QDM) magnetic field imaging is an emerging interrogation and diagnostic technique for integrated circuits (ICs). To date, the ICs measured with a QDM have been either too complex for us to predict the expected magnetic fields and benchmark the QDM performance or too simple to be relevant to the IC community. In this paper, we establish a 555 timer IC as a “model system” to optimize QDM measurement implementation, benchmark performance, and assess IC device functionality. To validate the magnetic field images taken with a QDM, we use a spice electronic circuit simulator and finite-element analysis (FEA) to model the magnetic fields from the 555 die for two functional states. We compare the advantages and the results of three IC-diamond measurement methods, confirm that the measured and simulated magnetic images are consistent, identify the magnetic signatures of current paths within the device, and discuss using this model system to advance QDM magnetic imaging as an IC diagnostic tool.

The transport of tiny particles is of great interest in the field of lab-on-a-chip. Here, by drawing inspiration from electric materials, we introduce magnetometamaterials, which, as opposed to electrons, transport magnetic particles (i.e., matter). The proposed metamaterial is composed of lithographically patterned disk-shaped micromagnets arranged in rows forming linear magnetic tracks on a silicon substrate. It is shown that by applying an external rotating magnetic field with the right frequency, the particles move along the magnetic tracks. The magnetic matter transport rate (i.e., magnetic matter conductivity) is tuned by adjusting the external magnetic field. We show that the particle transport is similar to the classical electron transport through a periodic lattice. At low frequencies, similar to the electrons at low temperatures, the particles move in closed loops around single magnets, resulting in an insulating regime. At higher frequencies, similar to the electrons at higher temperatures, some particles show the same behavior (i.e., move in closed loops); however, some others move along the magnetic tracks (i.e., demonstrate open trajectories). This behavior resembles a magnetic matter semiconductor. At even higher frequencies, all the particles show open trajectories along the magnetic tracks, and the device resembles a magnetic matter conductor. We define the operational ranges, both theoretically and experimentally, for both one- and two-dimensional magnetometamaterials. We show that, in an appropriate vertical bias field, the two-dimensional magnetometamaterials can transport the particles in arbitrary paths. The proposed metamaterial in this work can be used in designing circuits for transporting particles with crucial applications in biomedical engineering.