Studying near-valence-band ($E_{\mathrm{V}}$) defects at the insulator–$n$-type $4H$-$\mathrm{Si}\mathrm{C}$ interface is challenging due to the low minority carrier concentration. Herein, we present a technique for characterizing the border traps near $E_{\mathrm{V}}$ in an $n$-type $4H$-$\mathrm{Si}\mathrm{C}$ MOS capacitor by generating holes using above-band-gap optical excitation (OE). A rise in capacitance was observed under OE (due to hole capture by border traps), remaining stable long after the optical stimulus was removed, resulting in a persistent photocapacitance effect. We show the dynamics of the capture process and perform a quantification of the captured holes in samples with thermally grown oxide and different postoxidation annealing treatments.

Efficiently exciting and controlling phonons in diamond nanoresonators represents a fundamental challenge for quantum applications. Here, we theoretically demonstrate the possibility of exciting mechanical modes within a double hybrid cavity (DHC), formed by adjoining to a diamond cavity a second cavity made of aluminum nitride. The latter is piezoelectric and serves as a microwave-to-phonon transducer, activating mechanical modes in the entire DHC. We show the process of matching the cavities’ phononic properties, making them work coordinately in the DHC and obtaining a well-confined mode. In the diamond part of the cavity, this mode replicates the fundamental mode of the individual diamond cavity, showing that the piezoelectric transducer does not alter the diamond individual fundamental mode. In the piezoelectric part, the strong confinement of stress and electric field results in a high piezoelectric coupling rate, demonstrating the effectiveness of a phononic cavity as a transducer. The study is contextualized in the framework of a quantum networking application, where the DHC serves as a spin qubit, exploiting the spin-mechanical coupling within diamond color centers.

The spectral properties of electrons confined in a wirelike quasi-one-dimensional (1D) elongated quantum dot coupler between silicon qubits are investigated with a valley-augmented unrestricted Hartree-Fock (VAUHF) method, generalized to include the valley degree of freedom treated as an isospin, allowing calculations for a large number of electrons. The lower-energy symmetry-broken solutions of the self-consistent generalized Pople-Nesbet equations exhibit, for a confinement that has been modeled after an experimentally fabricated one in silicon, the formation of Wigner-molecule polymeric (longitudinal) chains, which are initiated through charge accumulation at the edges of the finite-length quasi-1D wire. An increasing number of parallel zigzag chains form as the number of electrons loaded into the confinement is increased, with the formation of newly added chains determined by the strength of the transverse harmonic confinement. The broken-symmetry VAUHF solutions, subsequently augmented by the quantum mechanically required parity restoration, go beyond the VAUHF single-determinant solution, predicting the formation of entangled Wigner-molecule chains, the charge distributions of which obliterate the zigzag organization of the broken-symmetry solutions. The symmetry-restored VAUHF methodology enables systematic investigations of multielectron-complex nanoscale confined structures that could be targeted for future imaging-microscopy experiments in silicon and other materials (e.g., 1D domain walls in transition-metal dichalcogenide materials) and quantum information utilization.

We investigate the peripheral circuits required to enable ideal performance for a high-gain traveling-wave parametric amplifier (TWPA) based on three-wave mixing . By embedding the TWPA in a network of superconducting diplexers, hybrid couplers, and impedance matching networks, the amplifier can deliver a high stable gain with near-quantum-limited noise performance, with suppressed gain ripples, while eliminating the reflections of the signal, the idler and the pump as well as the transmission of all unwanted tones. We also demonstrate a configuration where the amplifier can isolate. We call this technique wideband idler filtering (WIF). The theory is supported by simulations that predict over 20 dB gain in the 4–8 GHz band with 10 dB isolation for a single amplifier and 30 dB isolation for two cascaded amplifiers. We demonstrate how the WIF-TWPAs can be used to construct controllable isolators with over 40 dB isolation over the full 4–8 GHz band. Finally, we look at nonidealities and show how certain nonidealities can be devastating for both the gain and the idler filtering, especially a cutoff imbalance or a flux imbalance, and discuss how to compensate for them.

Nuclear reactors have long been a favored source for antineutrino measurements for estimates of power and burnup. With appropriate detector parameters and background rejection, an estimate of the reactor power can be derived from the measured antineutrino event rate. Antineutrino detectors are potentially attractive as a safeguards technology that can monitor reactor operations and thermal power from a distance. Advanced reactors have diverse features that may present challenges for current safeguards methods. By comparison, neutrino detectors offer complementary features, including a remote, continuous, unattended, and near-real-time monitoring capability, that may make them useful for safeguarding certain classes of advanced reactors. This study investigates the minimum depth and size of an antineutrino detector for a small modular reactor to meet safeguards needs for advanced reactors. Extrapolating performance from several prior reactor antineutrino experiments, this study uses an analytical approach to develop a possible design for a remote antineutrino-based monitoring device.

In quantum computation, control signals are adversely affected by distortion due to nonidealities in control chains. In order to implement high-fidelity digital and analog quantum operations, one must characterize the distortion and compensate for it. Here, we propose and experimentally verify an extensible method to model the behavior of control lines with the system function and correct it with digital filters. We correct the distortion of the superconducting-qubit flux control lines within a precision of $1\times {10}^{-3}$, which ensures gate fidelity free of the limit of pulse distortion. For the purpose of more accurate and scalable parameter extraction of the low-temperature line response, we employ an optimization-based protocol and the convergence is fast by setting the result of adjacent control lines with the same setup as the initial values. The techniques presented here improve distortion calibration efficiency and enable distortion-free operations, which paves the way for high-precision control of quantum computation and quantum simulation.

Continuous-variable quantum key distribution protocol using coherent states and heterodyne detection, called the no-switching protocol, is widely used in practical systems due to the simple experimental setup without basis switching and easy assessment to phase information. The security of an ideal no-switching protocol has been proved against general attacks in the finite-size regime and composable security framework, whose heterodyne detector consists of a beam splitter with transmittance of $50\mathrm{\%}$ and two ideal homodyne detectors. However, the transmittance of a beam splitter is inaccurate and the two detectors always have different quantum efficiency and electronic noise, which introduce asymmetry into the heterodyne detection, and further lead to the mismatch between the ideal protocol and practical systems, thereby overestimating the secret key rate and resulting in a practical security loophole. In this paper, we close this loophole by proposing a modified no-switching protocol with biased quadrature detection, where the asymmetry of the heterodyne detection is modeled to match the practical systems, and the security of the protocol is analyzed in asymptotic and finite-size regimes. Further, an optimization strategy is proposed to achieve the optimal secret key rate by adjusting the transmittance of the beam splitter. Simulation results show the necessity of considering the asymmetry in heterodyne detection and the effectiveness of the optimization, which provides a promising way to realize a practical secure and high-performance no-switching system.

We suggest using a device called the bootstrap superconducting quantum interference device (BS SQUID) to break the reciprocity in charge transport. This device uses magnetic flux backaction to create a nonreciprocal current-voltage characteristic, which results in a supercurrent rectification coefficient of up to approximately 95%. The BS SQUID works as a quasi-ideal supercurrent diode (SD) and maintains its efficiency up to about 40% of its critical temperature. The external magnetic flux can be used to adjust or reverse the rectification polarity. Finally, we discuss the finite-voltage operation regime of the SD and present a possible application of our device as a half- and full-wave signal rectifier in the microwave regime.

Spin-motive force induced by standing spin waves under nonlinear magnon scattering in a permalloy strip is investigated numerically. When the power of an applied microwave field is increased above a threshold under ferromagnetic resonance, spin waves with finite wave numbers are excited via four-magnon scattering, leading to standing spin waves in real space. We calculate the spin-motive force induced by the spin waves with finite wave numbers in a permalloy strip and estimate the electric voltage due to the spin-motive force. We demonstrate the increase of electric voltage as a result of steep magnetization modulation of the nonlinearly excited spin waves and the nonlinear spin waves produced.

A recently proposed fully passive quantum key distribution (QKD) removes all source modulator side channels. In this work, we combine fully passive sources with measurement-device-independent (MDI) QKD to simultaneously remove side channels from source modulators and detectors. We show a numerical simulation of passive MDI QKD, and we obtain an acceptable key rate while achieving much better implementation security, as well as ease of implementation, compared with a recently proposed fully passive twin-field QKD, paving the way towards more secure and practical QKD systems. We prove that a fully passive protocol is compatible with MDI QKD and we propose a novel idea that can improve the sifting efficiency.

Salt crystallization in composite layered porous materials such as wall paintings, frescoes, tiles, and ceramics can lead to cracks or delamination of the upper layers (paintings and glaze). The resulting open surface areas induce asymmetrical flow of liquid and ions from the heart of the material towards the delaminated evaporative region. By performing drying experiments in truncated cone–shaped sandstone samples as a model system for such flow, we show that for a given volume and a given salt concentration, the size of the evaporative surface (i.e., the large base and the small base) leads to different drying kinetics and salt-crystallization patterns of $\mathrm{Na}\mathrm{Cl}$. By characterizing the temporal evolution of the ion-concentration profiles by NMR in the liquid during evaporation and by determining the Péclet number over time, we explain this different behavior and the resulting adhesive or nonadhesive efflorescence and subflorescence when the truncated cone–shaped sandstones are dried with either the large base or the small base as the evaporative surface. Fluid transport from a larger region beneath the surface to a smaller, localized evaporative area occurs faster as the surface is approached. This, in turn, combined with the evaporation rate induces greater ion advection, resulting in salt precipitation as nonadhesive efflorescence at the surface. As the damaged area increases, subsurface crystallization interlaced with the efflorescence leads to an adhesive salt crust at the surface. The latter can increase subsequently the chance of mechanical damaging with time. These findings bring new insight into why with aging and the progress of delamination areas the risk of accelerating the deterioration of artworks will also increase.

Multifunctional integrated optical sensors have attracted considerable attention for their fast response and high precision. However, it remains a challenge to decouple the crosstalk on the multisensory in a single sensor to enhance reliability and practicality. Here, we present a generic strategy for introducing multiple optical parameters, a fluorescence intensity ratio, and a lifetime to monitor alterations of temperature and strain synergistically. An ultrasensitive sensing platform with suitable multiple emissions was constructed by designing luminescent metal halides to realize versatile energy transfer channels between intrinsic self-trapped excitons and dopants’ emission centers. Thus, the flexible fiber was fabricated and committed to monitoring temperature and strain in real-time working conditions with precision and repeatability. Moreover, the decoupling of temperature and strain sensing can be performed by the fluorescence intensity ratio and the lifetime of the ${\mathrm{Mn}}^{2+}$ ions. This work paves the way for emerging luminescent metal halides with multiple emissions applied in advanced multifunctional optical sensors and provides the solution for decoupling the crosstalk on the multisensory to enhance its reliability and practicality.

Due to a strong zero-phonon-line emission, narrow inhomogeneous broadening, and stable optical transition frequencies, the quantum system consisting of negatively charged silicon-vacancy ($\mathrm{Si}\text{−}V$) centers in diamond is highly anticipated for application in the development of universal quantum computation. We propose to implement quantum computation using $\mathrm{Si}\text{−}V$ centers placed in a one-dimensional phononic waveguide, for which quantum gates are realized in a nonadiabatic geometric way and protected by dynamical decoupling (DD). The scheme has the feature of geometric quantum computation, which is robust for controlling errors, and the advantage of DD, which is insensitive to environmental impact. Furthermore, the encoding of qubits in long-lifetime ground states of silicon-vacancy centers can reduce the effect of spontaneous emission. Numerical simulations demonstrate the practicability of the $\mathrm{Si}\text{−}V$-center system for quantum computation and the robustness improvement of quantum gates by DD pulses. This scheme may provide a promising path toward high-fidelity geometric quantum computation in solid-state systems.

A quantum-limited amplifier enables the amplification of weak signals while introducing minimal noise dictated by the principles of quantum mechanics. Such amplifiers serve a broad spectrum of applications in quantum computing, including fast and accurate readout of superconducting qubits and spins, as well as various uses in quantum sensing and metrology. Parametric amplification, primarily developed with use of Josephson junctions, has evolved into the leading technology for highly effective microwave measurements within quantum circuits. Despite their significant contributions, these amplifiers face fundamental limitations, such as their inability to handle high powers, their sensitivity to parasitic magnetic fields, and particularly their limitation to operate only at millikelvin temperatures. To tackle these challenges, here we experimentally develop a novel quantum-limited amplifier based on superconducting kinetic inductance and present an extensive theoretical model to describe this nonlinear coupled-mode system. Our device surpasses the conventional constraints associated with Josephson-junction amplifiers by operating at much higher temperatures up to 4.5 K. With two distinct spectral modes and tunability through bias current, this amplifier can operate selectively in both the single-mode-amplification regime and the double-mode-amplification regime near the quantum noise limit. Using a nonlinear thin film exhibiting kinetic inductance, our device attains gain exceeding 50 dB in a single-mode configuration and 32 dB in a double-mode configuration, while adding 0.82 input-referred noise quanta. Importantly, this amplifier eliminates the need for Josephson junctions, resulting in the capability to handle significantly higher powers than Josephson junction–based amplifiers. It also demonstrates resilience in the presence of magnetic fields, offers a straightforward design, and increases reliability. This positions the amplifier as a versatile solution for quantum applications and facilitates its integration into future superconducting quantum computers.

In this paper, we present a detailed simulation of the antineutrino emissions from an advanced gas-cooled reactor (AGR) core, benchmarked with input data from the United Kingdom Hartlepool reactors. An accurate description of the evolution of the antineutrino spectrum of reactor cores is needed to assess the performance of antineutrino-based monitoring concepts for nonproliferation, including estimations of the sensitivity of the antineutrino rate and spectrum to fuel content and reactor thermal power. The antineutrino spectral variation we present, while specific to AGRs, are different from studies published previously and help provide insight into the likely behavior of other reactor designs that use a similar refueling approach, such as those used in the RBMK ( – “high-power channel-type reactor”), CANDU (Canada Deuterium Uranium), and other reactors.

High-fidelity quantum gates are an essential prerequisite for large-scale quantum computation. When manipulating practical quantum systems, environmentally and operationally induced errors are inevitable, and thus, in addition to being fast, it is preferable that operations should be intrinsically robust against different errors. Here, we propose a general protocol for constructing geometric quantum gates with on-demand trajectories by modulating the applied pulse shapes that define the system’s evolution trajectory. Our scheme adopts reverse engineering of the target Hamiltonian using smooth pulses, which also eliminates the difficulty of calculating geometric phases for an arbitrary trajectory. Furthermore, because a particular geometric gate can be induced by various different trajectories, we can further optimize the gate performance under different scenarios; the results of numerical simulations indicate that this optimization can greatly enhance the quality of the gate. In addition, we present an implementation of our proposal using superconducting circuits, showcasing substantial enhancements in gate performance compared with conventional schemes. Our protocol thus presents a promising approach for high-fidelity and strong-robust geometric quantum gates for large-scale quantum computation.

In this paper, we apply a tabletop, ultrafast, high-harmonic generation (HHG) source to measure the element-specific ferromagnetic resonance (FMR) in ultrathin magnetic alloys and multilayers on an opaque $\mathrm{Si}$ substrate. We demonstrate a continuous-wave bandwidth up to 62 GHz, with a promise to extend it to 100 GHz or higher. This laboratory-scale instrument detects the FMR using ultrafast, extreme-ultraviolet (EUV) light, with photon energies spanning the M-edges of the most relevant magnetic elements. A radiofrequency frequency comb generator is used to produce a microwave excitation that is intrinsically synchronized to the EUV pulses with a timing jitter of 1.1 ps or better. We apply this system to measure the dynamics in a multilayer system as well as $\mathrm{Ni}$-$\mathrm{Fe}$ and $\mathrm{Co}$-$\mathrm{Fe}$ alloys. Since this instrument operates in reflection mode, it is a milestone toward measuring and imaging the dynamics of the magnetic state and spin transport of active devices on arbitrary substrates on a tabletop. The higher bandwidth also enables measurements of materials with high magnetic anisotropy, as well as ferrimagnets, antiferromagnets, and short-wavelength (high-wavevector) spin waves in nanostructures or nanodevices. Furthermore, the coherence and short wavelength of the EUV will enable extending these studies using dynamic nanoscale lensless imaging techniques such as coherent diffractive imaging, ptychography, and holography.