High-mobility field-effect transistors (FETs) can serve as resonant detectors of terahertz radiation due to excitation of plasmons in the channel. The modeling of these devices previously relied either on approximate techniques or on complex time-consuming full-wave simulations. In this paper, we obtain an exact solution for driven electrical oscillations in a plasmonic FET with realistic contact geometry. The solution obtained highlights the importance of evanescent plasma waves excited near the contacts, which qualitatively modify the detector responsivity spectra. We also derive the boundary condition on the ac floating electrodes that generalizes the open-circuit (Dyakonov-Shur) and short-circuit (fixed-voltage) conditions and reduces to them in limting cases. In both limits, the FET photovoltage has resonant fringes; however, the absolute value of the voltage is greater in the open-circuit case.

We evaluate the sensitivity of large gadolinium-doped water detectors to antineutrinos released by nuclear-fission explosions, using updated signal and background models and taking advantage of the capacity for seismic observations to provide an analysis trigger. Under certain realistic conditions, the antineutrino signature of a 250-kton pure-fission explosion could be identified several hundred kilometers away, in a detector about the size of the largest module currently proposed for a basic physics experiment. In principle, such an observation could provide rapid confirmation that the seismic signal coincided with a fission event, possibly useful for international monitoring of nuclear-weapon tests. We discuss the limited potential for seismically cued antineutrino observations to constrain fission yield, differentiate pure fission from fusion-enhanced weapon tests, indicate that the seismic evidence of an explosion had been intentionally masked, or verify the absence of explosive testing in a targeted area. We conclude that advances in seismic monitoring and neutrino physics have made the detection of explosion-derived antineutrinos more conceivable than previously asserted, but the size and cost of sufficiently sensitive detectors continue to limit applications.

Intersubband (ISB) transitions are of high significance for light-emitting and light-detecting devices in the infrared and, when involving large electron densities, for plasmonics and strong light-matter coupling physics. Here it is observed that the simultaneously occurring fundamental and excited-state ISB transitions in highly-doped, m-plane $\mathrm{Zn}\mathrm{O}/{\mathrm{Mg}}_x{\mathrm{Zn}}_{1-x}\mathrm{O}$ multiple quantum wells, couple into a single collective oscillation: the multisubband plasmon (MSP). With 2D electron densities up to $4\times {10}^{13}{\mathrm{cm}}^{-2}$, an outstanding regime is reached in which the observed MSP frequency is three times larger than that of the fundamental ISB transition as a result of depolarization. This effect is analyzed using a dielectric tensor for $\mathrm{Zn}\mathrm{O}$ including the interaction of the light with the lattice, the in-plane free electrons, and the off-plane MSP. The impact of the broadening of the MSP and its interaction with phonons is discussed. The results presented here show the potential of $\mathrm{Zn}\mathrm{O}/{\mathrm{Mg}}_x{\mathrm{Zn}}_{1-x}\mathrm{O}$ for infrared optoelectronic applications, which can be extended to the THz range with appropriate design of the quantum wells.

Thermal runaway occurs when a rise in system temperature results in heat-generation rates exceeding dissipation rates. Here, we demonstrate that thermal runaway occurs in radiative (photon) systems given a sufficient level of negative-differential thermal emission. By exploiting the insulator-to-metal phase transition of vanadium dioxide, we show that a small increase in heat generation (e.g., $10\mathrm{nW}/{\mathrm{mm}}^2$) results in a large change in surface temperature (e.g., ∼35 K), as the thermal emitter switches from high emittance to low emittance. While thermal runaway is typically associated with catastrophic failure mechanisms, detailed understanding and control of this phenomenon may give rise to new opportunities in infrared sensing, camouflage, and rectification.

Boolean algebra, the branch of mathematics in which variables can assume only true or false values, is the theoretical basis of classical computation. The analogy between Boolean operations and electronic switching circuits, highlighted by Shannon in 1938, paved the way for modern computation based on electronic devices. The growth in the computational power of such devices, after an exciting exponential—Moore’s trend—is nowadays blocked by heat dissipation due to computational tasks, which are very demanding due to the miniaturization of chips. Heat is often a detrimental form of energy which increases the system’s entropy, decreasing the efficiency of logic operations. Here, we propose a physical system that is able to perform thermal-logic operations by reversing the old heat-disorder epitome into a heat-order paradigm. We lay the foundations of heat computation by encoding logic state variables in temperature and introducing the thermal counterparts of electronic logic gates. Exploiting quantum effects in thermally biased Josephson junctions (JJs), we propound a possible realization of a functionally complete logic. Our architecture ensures high operational stability and robustness, with switching frequencies reaching the GHz range.

${\mathrm{Ga}}_2{\mathrm{O}}_3$ and $({\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}{)}_2{\mathrm{O}}_3$ alloys are promising materials for solar-blind UV photodetectors and high-power transistors. Basic key parameters in the device design, such as band-gap variation with alloy composition and band offset between ${\mathrm{Ga}}_2{\mathrm{O}}_3$ and $({\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}{)}_2{\mathrm{O}}_3$, are yet to be established. Using density-functional theory with the Heyd-Scuseria-Ernzerhof hybrid functional, we compute formation enthalpies, band gaps, and band-edge positions of $({\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}{)}_2{\mathrm{O}}_3$ alloys in the monoclinic ($\beta$) and corundum ($\alpha$) phases. We find the formation enthlapies of $({\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}{)}_2{\mathrm{O}}_3$ alloys are significantly lower than of $({\mathrm{In}}_x{\mathrm{Ga}}_{1-x}{)}_2{\mathrm{O}}_3$, and that $({\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}{)}_2{\mathrm{O}}_3$ with $x=0.5$ can be considered as an ordered compound $\mathrm{Al}\mathrm{Ga}{\mathrm{O}}_3$ in the monoclinic phase, with $\mathrm{Al}$ occupying the octahedral sites and $\mathrm{Ga}$occupying the tetrahedral sites. The band gaps of the alloys range from 4.69 to 7.03 eV for $\beta \text{−}({\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}{)}_2{\mathrm{O}}_3$ and from 5.26 to 8.56 eV for $\alpha \text{−}({\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}{)}_2{\mathrm{O}}_3$. Most of the band offset of the $({\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}{)}_2{\mathrm{O}}_3$ alloy arises from the discontinuity in the conduction band. Our results are used to explain the available experimental data, and consequences for designing MODFETs based on $({\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}{)}_2{\mathrm{O}}_3/{\mathrm{Ga}}_2{\mathrm{O}}_3$ are discussed.

We present a straightforward and computationally cheap method to obtain the phonon-assisted photocurrent in large-scale devices from first-principles transport calculations. The photocurrent is calculated using the nonequilibrium Green’s function with light-matter interaction from the first-order Born approximation, while electron-phonon coupling (EPC) is included through special thermal displacements. We apply the method to a silicon solar-cell device and demonstrate the impact of including EPC in order to properly describe the current due to the indirect band-to-band transitions. The first-principles results are successfully compared to experimental measurements of the temperature and light-intensity dependence of the open-circuit voltage of a silicon photovoltaic module. Our calculations illustrate the pivotal role played by EPC in photocurrent modeling to avoid underestimation of the open-circuit voltage, short-circuit current, and maximum power. This work represents a recipe for computational characterization of future photovoltaic devices including the combined effects of light-matter interaction, phonon-assisted tunneling, and the device potential at finite bias from the level of first-principles simulations.

Developing fast, accurate, and scalable techniques for quantum-state readout is an active area in semiconductor-based quantum computing. Here, we present results on dispersive sensing of silicon corner state quantum dots coupled to lumped-element electrical resonators via the gate. The gate capacitance of the quantum device is placed in parallel with a superconducting spiral inductor resulting in resonators with loaded $Q$ factors in the 400–800 range. We utilize resonators operating at 330 and 616 MHz, and achieve charge sensitivities of 7.7 and $1.3\mu e/\sqrt{\mathrm{Hz}}$, respectively. We perform a parametric study of the resonator to reveal its optimal operation points and perform a circuit analysis to determine the best resonator design. The results place gate-based sensing on a par with the best reported radio-frequency single-electron transistor sensitivities while providing a fast and compact method for quantum-state readout.

Soft and highly-strain-hardening metals such as iron, aluminum, and tantalum, often called “gummy,” are notoriously difficult to cut. This is due to their tendency to exhibit redundant, unsteady plastic flow with large-amplitude folding, which results also in macroscale defects on the cut surface and large energy dissipation. In this work, we demonstrate that this difficulty can be overcome by merely coating the initial metal surface with common adhesive chemical media such as glues and inks. Using high-speed in situ imaging, we show that the media act by coupling unsteady surface-plastic-flow modes with interface energetics—a mechanochemical action—thereby effecting a ductile-to-brittle transition, locally. Consequently, the unsteady plastic flow with folding transitions to a periodic segmentation-type flow in the presence of the surface media, with near absence of defects on the cut surface and significantly lower energy dissipation (a reduction of up to 80%). This mechanochemical effect is controllable and not material specific, with the chemical media demonstrating comparable efficacy across different metal systems. This makes it quite distinct from other well-known mechanochemical effects, such as liquid-metal embrittlement and stress-corrosion cracking, that are both highly material specific and catastrophic. An analytic model incorporating local flow dynamics, stability of dislocation emission, and surface-media energetics is found to correctly predict the onset of the plastic-flow transition. The benign nature and simplicity of the media suggest wide-ranging opportunities for improving the performance of cutting and deformation processes for metals and alloys in practical settings.

Decoherence remains a major challenge in quantum computing hardware, and a variety of physical-layer controls provide opportunities to mitigate the impact of this phenomenon through feedback and feed-forward control. In this work, we compare a variety of machine-learning algorithms derived from diverse fields for the task of state estimation (retrodiction) and forward prediction of future qubit-state evolution for a single qubit subject to classical, non-Markovian dephasing. Our approaches involve the construction of a dynamical model capturing qubit dynamics via autoregressive or Fourier-type protocols using only a historical record of projective measurements. A detailed comparison of achievable prediction horizons, model robustness, and measurement-noise-filtering capabilities for Kalman filters (KFs) and Gaussian process regression (GPR) algorithms is provided. We demonstrate superior performance from the autoregressive KF relative to Fourier-based KF approaches and focus on the role of filter optimization in achieving suitable performance. Finally, we examine several realizations of GPR using different kernels and discover that these approaches are generally not suitable for forward prediction. We highlight the linkages between predictive performance and kernel structure, and we identify ways in which forward predictions are susceptible to numerical artifacts.

We present a porous electrode theory for capacitive deionization with electrodes containing nanoparticles that consist of a redox-active intercalation material. A geometry of a desalination cell is considered which consists of two porous electrodes, two flow channels, and an anion-exchange membrane, and we use the Nernst-Planck theory to describe ion transport in the aqueous phase in all these layers. A single-salt solution is considered, with unequal diffusion coefficients for anions and cations. Similar to previous models for capacitive deionization and electrodialysis, we solve the dynamic two-dimensional equations by assuming that the flow of water, and thus the advection of ions, is zero in the electrode, and in the flow channel only occurs in the direction along the electrode and membrane. In all layers, diffusion and migration are only considered in the direction perpendicular to the flow of water. Electronic as well as ionic transport limitations within the nanoparticles are neglected, and instead the Frumkin isotherm (or regular solution model) is used to describe local chemical equilibrium of cations between the nanoparticles and the adjacent electrolyte, as a function of the electrode potential. Our model describes the dynamics of key parameters of the CDI process with intercalation electrodes, such as effluent salt concentration, the distribution of intercalated ions, cell voltage, and energy consumption.

We report on the conversion to telecommunication wavelengths of single photons emitted by a nitrogen-vacancy (NV) defect in diamond. By means of difference frequency generation, we convert spin-selective photons at 637 nm, associated with the coherent NV zero-phonon line, to the target wavelength of 1588 nm in the $L$-telecommunication band. The successful conversion is evidenced by time-resolved detection revealing a telecommunication-photon lifetime identical to that of the original 637-nm photon. Furthermore, we show by second-order correlation measurements that the single-photon statistics are preserved. The overall efficiency of this one-step conversion reaches 17% in our current setup, along with a signal-to-noise ratio of approximately 7 despite the low probability $(<{10}^{-3})$ of an incident 637-nm photon. This result shows the potential for efficient telecommunication-photon–NV-center interfaces and marks an important step towards future long-range entanglement-based quantum networks.

Transparent semiconducting oxides (TSO) are promising candidates for the fabrication of flexible and low-cost electronic devices, as they contain only abundant materials, are nontoxic, and exhibit high carrier mobilities. The formation of rectifying Schottky-barrier contacts is a prerequisite for devices, such as rectifiers, photodetectors, and metal-semiconductor field-effect transistors, and it was found that the presence of oxygen plays an essential role during the formation of the Schottky contacts. With electrical measurements on Pt/zinc-tin-oxide (ZTO) and ${\mathrm{PtO}}_x/\mathrm{ZTO}$ Schottky-barrier contacts and depth-resolved x-ray photoelectron spectroscopy measurements we demonstrate the important role of oxygen at the interface between TSOs and the metal contact for the rectifying behavior of diodes. In the vicinity of the interface, ${\mathrm{PtO}}_x$ is reduced to Pt in a two-step process. $\mathrm{Pt}{(\mathrm{OH})}_4$ is reduced within one day, whereas the reduction of PtO takes place over a time period of several weeks. The reduction results in improved rectification compared to $\mathrm{Pt}/\mathrm{ZTO}$, due to a filling of oxygen vacancies, which leads to a reduction of the free-carrier concentration in the vicinity of the ${\mathrm{PtO}}_x/\mathrm{ZTO}$ interface. This increases the depletion layer width and subsequently reduces the tunneling current, resulting in a higher rectification ratio. The time scale of the permanent performance improvement can be shortened significantly by applying a reverse bias to the diode. The described mechanism is most likely also present at other transparent-semiconducting-oxide–metal interfaces.

Similar to its electromagnetic counterpart, magnetic cloaking also has very important technological applications. However, the traditional method to build a static magnetic cloak requires the use of superconducting materials as the diamagnetic component, which seriously limits the practical potential because of the cryogenic condition. We show that a diamagnetic active current boundary combined with a high-permeability magnetic inner shell (MIS) can be designed to solve this problem, rendering an ideal magnetic cloaking effect at zero frequency. We first theoretically prove that a current boundary could magnetically behave as a superconductor to external observers. Based on this phenomena, we introduce a high-permeability MIS made of magnetically ultrasoft metallic sheets (permeability $\mu >{10}^3$) and experimentally prove that the bilayer combination can exactly balance out the disturbance to the external probing field and, meanwhile, have a large invisible inner space. We also show that the active boundary currents can be accordingly configured to overcome the permeability and frequency band limits, leading to a robust cloak over the entire quasistatic frequency region. Our work creates an efficient way to circumvent the traditional limits of metamaterials to build magnetic cloaks for ultralow frequencies. The active-passive hybrid approach could be generally extended to yield other artificial magnetic devices or systems as well.

Electrical power generation from a moderate-temperature thermal source by means of direct conversion of infrared radiation is important and highly desirable for energy harvesting from waste heat and micropower applications. Here, we demonstrate direct rectified power generation from an unbiased large-area nanoantenna-coupled tunnel diode rectifier called a rectenna. Using a vacuum radiometric measurement technique with irradiation from a temperature-stabilized thermal source, a generated power density of $8\mathrm{nW}/{\mathrm{cm}}^2$ is observed at a source temperature of $450°\mathrm{C}$ for the unbiased rectenna across an optimized load resistance. The optimized load resistance for the peak power generation for each temperature coincides with the tunnel diode resistance at zero bias and corresponds to the impedance matching condition for a rectifying antenna. Current-voltage measurements of a thermally illuminated large-area rectenna show current zero crossing shifts into the second quadrant indicating rectification. Photon-assisted tunneling in the unbiased rectenna is modeled as the mechanism for the large short-circuit photocurrents observed where the photon energy serves as an effective bias across the tunnel junction. The measured current and voltage across the load resistor as a function of the thermal source temperature represents direct current electrical power generation.

When performing precision measurements, the quantity being measured is often perturbed by the measurement process itself. Such measurements include precision frequency measurements for atomic clock applications carried out with Ramsey spectroscopy. With the aim of eliminating probe-induced perturbations, a method of generalized autobalanced Ramsey spectroscopy (GABRS) is presented and rigorously substantiated. The usual local-oscillator frequency control loop is augmented with a second control loop derived from secondary Ramsey sequences interspersed with the primary sequences and with a different Ramsey period. This second loop feeds back to a secondary clock variable and ultimately compensates for the perturbation of the clock frequency caused by the measurements in the first loop. We show that such a two-loop scheme can lead to perfect compensation for measurement-induced light shifts and does not suffer from the effects of relaxation, time-dependent pulse fluctuations and phase-jump modulation errors that are typical of other hyper-Ramsey schemes. Several variants of GABRS are explored based on different secondary variables including added relative phase shifts between Ramsey pulses, external frequency-step compensation, and variable second-pulse duration. We demonstrate that a universal antisymmetric error signal, and hence perfect compensation at a finite modulation amplitude, is generated only if an additional frequency step applied during both Ramsey pulses is used as the concomitant variable parameter. This universal technique can be applied to the fields of atomic clocks, high-resolution molecular spectroscopy, magnetically induced and two-photon probing schemes, Ramsey-type mass spectrometry, and the field of precision measurements. Some variants of GABRS can also be applied for rf atomic clocks using coherent-population-trapping-based Ramsey spectroscopy of the two-photon dark resonance.

Universal quantum gates and quantum error correction (QEC) lie at the heart of quantum-information science. Large-scale quantum computing depends on a universal set of quantum gates, in which some gates may be easily carried out, while others are restricted to certain physical systems. There is a unique three-qubit quantum gate called the Deutsch gate [$\mathbb{D}(\theta )$], from which a circuit can be constructed so that any feasible quantum computing is attainable. We design an easily realizable $\mathbb{D}(\theta )$ by using the Rydberg blockade of neutral atoms, where $\theta$ can be tuned to any value in $[0,\pi ]$ by adjusting the strengths of external control fields. Using similar protocols, we further show that both the Toffoli and controlled-not gates can be achieved with only three laser pulses. The Toffoli gate, being universal for classical reversible computing, is also useful for QEC, which plays an important role in quantum communication and fault-tolerant quantum computation. The possibility and speed of realizing these gates shed light on the study of quantum information with neutral atoms.

We investigate the interaction of guided surface acoustic modes (GSAMs) in unconsolidated granular media with a metasurface, consisting of an array of vertical oscillators. We experimentally observe the hybridization of the lowest-order GSAM at the metasurface resonance, and note the absence of mode delocalization found in homogeneous media. Our numerical studies reveal how the stiffness gradient induced by gravity in granular media causes a down-conversion of all the higher-order GSAMs, which preserves the acoustic energy confinement. We anticipate these findings to have implications in the design of seismic-wave protection devices in stratified soils.

Quantum computers require interfaces with classical electronics for efficient qubit control, measurement, and fast data processing. Fabricating the qubit and the classical control layer using the same technology is appealing because it will facilitate the integration process, improving feedback speeds and offering potential solutions to wiring and layout challenges. Integrating classical and quantum devices monolithically, using complementary metal-oxide-semiconductor (CMOS) processes, enables the processor to profit from the most mature industrial technology for the fabrication of large-scale circuits. We demonstrate a CMOS single-electron memory cell composed of a single quantum dot and a transistor that locks charge on the quantum-dot gate. The single-electron memory cell is conditionally read out by gate-based dispersive sensing using a lumped-element $LC$ resonator. The control field-effect transistor (FET) and quantum dot are fabricated on the same chip using fully depleted silicon-on-insulator technology. We obtain a charge sensitivity of $\delta q=95\times {10}^{-6}e{\mathrm{\text{Hz}}}^{-1/2}$ when the quantum-dot readout is enabled by the control FET, comparable to results without the control FET. Additionally, we observe a single-electron retention time on the order of a second when storing a single-electron charge on the quantum dot at millikelvin temperatures. These results demonstrate first steps towards time-based multiplexing of gate-based dispersive readout in CMOS quantum devices opening the path for the development of an all-silicon quantum-classical processor.

Fast-gated avalanche photodiodes (APDs) are the most commonly used single photon detectors for high-bit-rate quantum key distribution (QKD). Their robustness against external attacks is crucial to the overall security of a QKD system, or even an entire QKD network. We investigate the behavior of a gigahertz-gated, self-differencing (In,Ga)As APD under strong illumination, a tactic Eve often uses to bring detectors under her control. Our experiment and modeling reveal that the negative feedback by the photocurrent safeguards the detector from being blinded through reducing its avalanche probability and/or strengthening the capacitive response. Based on this finding, we propose a set of best-practice criteria for designing and operating fast-gated APD detectors to ensure their practical security in QKD.