Laser-plasma accelerators represent a promising technology for future compact accelerating systems, enabling the acceleration of tens of pC to above $1\mathrm{Ge}\mathrm{V}$ over just a few centimeters. Nonetheless, these devices currently lack the stability, beam quality, and average current of conventional systems. While many efforts have focused on improving acceleration stability and quality, little progress has been made in increasing the beam’s average current, which is essential for future laser-plasma-based applications, such as three-dimensional X-ray tomography for cargo inspection. In this paper, we investigate a laser-plasma acceleration regime aimed at increasing the beam average current with energies up to few MeVs, efficiently enhancing the beam charge. We present experimental results on configurations that allow reaching charges of 5–30 nC and a maximum conversion efficiency of around 14%. Through comprehensive particle-in-cell simulations, we interpret the experimental results and present a detailed study on electron dynamics. From our analysis, we show that most electrons are not trapped in a plasma wave; rather, they experience ponderomotive acceleration. Thus, we prove the laser pulse as the main driver of the particles’ energy gain process.

To promote the development of the next generation of nanospintronic devices, it is of great significance to tune the valley degree of freedom in two-dimensional (2D) materials. Here, we propose a mechanism for manipulating the valley and nonlinear Hall effect using a 2D ferroelectric substrate. Monolayer ${\mathrm{Mn}}_2{\mathrm{P}}_2{\mathrm{S}}_3{\mathrm{Se}}_3$ is a robust antiferromagnetic, valley polarized semiconductor. Importantly, the valley polarized metal-semiconductor phase transition of ${\mathrm{Mn}}_2{\mathrm{P}}_2{\mathrm{S}}_3{\mathrm{Se}}_3$ can be effectively tuned by switching the ferroelectric polarization of ${\mathrm{Sc}}_2{\mathrm{CO}}_2$. We reveal the microscopic mechanism of the phase transition, which originates from charge transfer and band alignment. Additionally, we find that the reversed polarization direction of ${\mathrm{Sc}}_2{\mathrm{CO}}_2$ can flexibly manipulate the Berry curvature dipole. Based on this discovery, we present the detection of the valley polarized metal-semiconductor transition using nonlinear Hall effect devices. These findings not only offer a scheme to tune the valley degree of freedom but also provide a promising platform for designing nonlinear Hall effect devices.

Octave-spanning soliton frequency combs generated by microresonators present a compact and low-noise tool for high-resolution time and distance measurements through self-referencing. While these soliton combs have been observed on various photonic platforms, their practical deployment is often hindered by complex control mechanisms, resulting in a low yield of useful devices. To address these challenges, we have optimized a dual-mode soliton scheme by incorporating heaters directly onto ${\mathrm{Si}}_3{\mathrm{N}}_4$ microresonators. The thermal control, achieved by adjusting the electrical power supplied to the heaters, effectively tunes the mode separation to a favorable level (∼100 pm for a 1 THz resonator), facilitating efficient thermal compensation and improving the yield of functional dual-mode resonators. Kerr solitons can be deterministically generated by simply reducing the heater voltage via either slow sweeping or fast pulse tuning with the pump wavelength and power fixed. Additionally, bidirectional voltage scanning enables a smooth transition from multisoliton to single-soliton states, optimizing both the bandwidth and comb power. The integrated heater allows for fine-tuning of both the repetition rate and carrier-envelope offset frequency of the soliton comb with slopes of −21.18 MHz/mW and +0.35 GHz/mW, respectively. We have successfully generated octave-spanning solitons across multiple resonators with different repetition rates (∼1 THz and ∼390 GHz). Additionally, a systematic dual-mode design strategy is explored for future optimization. These improvements mark a significant advancement toward cost-effective and practical Kerr frequency combs for applications such as optical clocks and frequency synthesizers.

Electrometry based on electromagnetically induced transparency (EIT) in alkali Rydberg vapor cells may suffer reduced sensitivity due to spurious line broadening effects, caused by surface charges, contaminant gases, or other manufacturing defects. To draw conclusions about the deleterious effects of potential contaminant gases inside Rydberg electrometry vapor cells, we revisit collisional broadening and shifts of both the $D_2$ line and Rydberg levels of rubidium. Specifically, we measure the broadening and shifts of the $5S_{1/2}\to 5P_{3/2}$ (i.e., the $D_2$ line) and $5S_{1/2}\to 5P_{3/2}\to (25D,27S,30D,32S,35D,37S)$ transitions of ${}^{85}\mathrm{Rb}$ due to $\mathrm{He}$, $\mathrm{Ne}$, ${\mathrm{N}}_2$, and $\mathrm{Ar}$. By combining these measurements with observations of velocity-changing collisions in the sub-Doppler spectrum of the $D_2$ line, we conclude the following: (1) contaminant gases are most likely not the cause of irregular line shapes or shifts of Rydberg transitions due to the high pressures required, and (2) the sub-Doppler spectrum of the $D_2$ line, through its accompanying loss of contrast at high pressures, can validate that a vapor cell is sufficiently free of contaminant gas for EIT electrometry. We use the theory of Omont [J. Phys. France 38, 1343 (1977)] to extend our results to a wide variety of possible contaminant gases, and further derive scaling laws applicable to all gases.

Ferroelectric polarization provides the possibility for electrically modulating photoconductance gain in low-dimensional optoelectronic devices. The utilization of ferroelectric polymers to manipulate the photocarrier dynamics in ${\mathrm{Sn}\mathrm{S}}_2$ films has not yet been investigated, although it has become highly desired for facilitating the photodetection application of ${\mathrm{Sn}\mathrm{S}}_2$. To reveal the potential regulating advantages of ferroelectric P(VDF-TrFE) polymer on ${\mathrm{Sn}\mathrm{S}}_2$ film, the two-dimensional coupling structure of ${\mathrm{Sn}\mathrm{S}}_2$/P(VDF-TrFE) is designed. Benefiting from the ultrahigh residual electrostatic field after voltage polarization, the photoluminescence effect in adjacent ${\mathrm{Sn}\mathrm{S}}_2$ film is substantially adjusted. Significantly, the as-fabricated ferroelectric-integrated ${\mathrm{Sn}\mathrm{S}}_2$ device exhibits a tunable photodetection capability to light of wavelength 405 nm upon varying the polarization direction. The photocurrent under positive polarization is increased by two times compared with that for the unpolarized state, whereas the dark current is depressed by five orders of magnitude under negative polarization. The surface-potential characterizations from theoretical calculations confirmed that the ferroelectric polarization could modulate the Fermi level, channel carrier concentration, and photocarrier dynamics in ${\mathrm{Sn}\mathrm{S}}_2$ film. This study provides an alternative method for electrically modulating exciton excitation and photocurrent enhancement for ${\mathrm{Sn}\mathrm{S}}_2$, which also demonstrates a promising material platform for research of ferroelectric-tuned optoelectronic devices.

Motivated by recent advancements highlighting $\mathrm{Ta}$ as a promising material in low-loss superconducting circuits and showing long coherence times in superconducting qubits, we have explored the effect of cryogenic temperatures on the growth of $\mathrm{Ta}$ and its integration in superconducting circuits. Cryogenic growth of $\mathrm{Ta}$ using a low-temperature molecular beam epitaxy (MBE) system is found to stabilize single-phase $\alpha$-$\mathrm{Ta}$ on several different substrates, which include ${\mathrm{Al}}_2{\mathrm{O}}_3(0001)$, $\mathrm{Si}$(001), $\mathrm{Si}$(111), ${\mathrm{Si}\mathrm{N}}_x$, and $\mathrm{Ga}\mathrm{As}$(001). The substrates are actively cooled down to cryogenic temperatures and remain <20 K during the $\mathrm{Ta}$ deposition. X-ray $\theta$-$2\theta$ diffraction (XRD) after warming to room temperature indicates the formation of polycrystalline $\alpha$-$\mathrm{Ta}$. The 50-nm $\alpha$-$\mathrm{Ta}$ films grown on ${\mathrm{Al}}_2{\mathrm{O}}_3(0001)$ at a substrate manipulator temperature of 7 K have a room temperature resistivity (${\rho }_{300\mathrm{K}}$) of $13.4\text{μ}\mathrm{\Omega }\mathrm{cm}$, a residual resistivity ratio (RRR) of 17.3 and a superconducting transition temperature ($T_C$) of 4.14 K, which are comparable to bulk values. In addition, atomic force microscopy (AFM) indicates that the film grown at 7 K with an rms roughness of 0.45 nm was significantly smoother than the one grown at room temperature. Similar properties are found for films grown on other substrates. Results for films grown at higher substrate manipulator temperatures show higher ${\rho }_{300\mathrm{K}}$, lower RRR and $\mathrm{Tc}$, and increased $\beta$-$\mathrm{Ta}$ content. Coplanar waveguide resonators with a gap width of $3\text{μ}\mathrm{m}$ fabricated from cryogenically grown $\mathrm{Ta}$ on $\mathrm{Si}$(111) and ${\mathrm{Al}}_2{\mathrm{O}}_3(0001)$ show low-power $Q_i$ of 1.9 million and 0.7 million, respectively, indicating polycrystalline $\alpha$-$\mathrm{Ta}$ films may be promising for superconducting qubit applications even though they are not fully epitaxial.

Integrated and fiber-packaged magnetic field sensors with a sensitivity sufficient to sense electric pulses propagating along nerves and a spatial resolution fine enough to resolve their propagation directions will trigger tremendous steps ahead in medical diagnostics and research. Nitrogen-vacancy centers in diamond are best suitable for such sensing tasks under ambient conditions. Current research on uniting a good sensitivity and high spatial resolution is facilitated by scanning or imaging techniques. However, these techniques employ moving parts or bulky microscopes. Both approaches cannot be miniaturized to build robust, adjustment-free, hand-held devices. In this work, we introduce concepts for spatially resolved magnetic field sensing and two-dimensional gradiometry with an integrated magnetic field camera. The camera utilizes infrared absorption optically detected magnetic resonance (IRA ODMR) mediated by perpendicularly intersecting infrared and pump laser beams forming a pixel matrix. We demonstrate our scalable $3\times 3$ pixel sensor’s capability to reconstruct the position of an electromagnet. In a reference measurement, we show an IRA ODMR sensitivity of $44\mathrm{nT}{\mathrm{Hz}}^{-1/2}$.

We propose a unified description of dual radiative heat engines (RHEs), consisting of two facing optoelectronic components (diodes) and capable of generating electrical power from heat. They can operate in three regimes depending on the applied biases, namely in thermoradiative-negative electroluminescent (TRNEL), thermoradiative-photovoltaic, or thermophotonic regimes (TPX, consisting of a light-emitting diode and a photovoltaic cell). They have access to operating conditions that are unachievable by single RHEs such as thermophotovoltaic systems: at the radiative limit, TRNEL devices can reach the Carnot efficiency for any bandgap, while TPX devices achieve large power outputs by means of electroluminescent enhancement. The influence of nonradiative losses is also investigated, revealing the importance for dual engines to operate close to the radiative limit to clearly outperform single engines. Expressions of the maximum power output and related efficiency achieved by dual engines at the radiative limit are derived analytically, and reveal that the power output of TPX engines is not bounded. A comparison to usual efficiency bounds also highlights the impact of thermalization losses, and the subsequent interest of spectral filtering to extend the operating region. This work provides a common framework and guidelines for the study of RHEs, which represent a promising solution for reliable and scalable energy conversion.

Finding optimal wave sampling methods has far-reaching implications in wave physics, such as seismology, acoustics, and telecommunications. A key challenge is surpassing the Whittaker-Nyquist-Shannon (WNS) aliasing limit, establishing a frequency below which the signal cannot be faithfully reconstructed. However, the WNS limit applies only to periodic sampling, opening the door to bypassing aliasing by aperiodic sampling. In this work, we investigate the efficiency of a recently discovered family of aperiodic monotile tilings, the hat family, in overcoming the aliasing limit spatially sampling a wave field. By analyzing their spectral properties, we show that aperiodic monotile seismic (AMS) arrays, based on a subset of the hat tiling family, efficiently surpass the WNS sampling limit. Our investigation leads us to propose AMS arrays as a design principle for seismic arrays. We show that AMS arrays can outperform regular and other aperiodic arrays in realistic beamforming scenarios using single and distributed sources, including station-position noise and station failures. While current seismic arrays optimize beamforming or imaging applications using spiral or regular arrays, AMS arrays can accommodate both, as they share properties with both periodic and aperiodic arrays. More generally, our work suggests that aperiodic monotiles can be an efficient design principle in various fields requiring wave sampling.

Gate-all-around architecture provides the ultimate solution for controlling carriers in ultrascaled transistors. However, the complex all-around interface between $\mathrm{Si}$ and amorphous ${\mathrm{Si}\mathrm{O}}_2$, especially at the inevitable corners, becomes detrimental to device performance. Here, we endeavor to unveil the properties of interface and corner states in gate-all-around field-effect transistors (GAAFETs) by first building real all-around interfaces between silicon and amorphous ${\mathrm{Si}\mathrm{O}}_2$, and then conducting large-scale (up to 2796 atoms) first-principles calculations on them. Results show that the interface states are not only contributed by the widely known dangling bonds, but also by the scarcely recognized corner strains and interface dipoles. They present asymmetric densities near the conduction and valence bands, and show distinct spatial distributions across the channel cross section. Fortunately, the interface states turn out to be tunable by changing the channel size, orientation, and geometry. This research is very meaningful because it can explain several experimental observations, including the performance degradation of sub-4-nm channel devices, the extremely low hole mobility in GAAFETs, the degradation of drain-induced barrier lowering in small-size GAAFETs, and the superior performance of nanosheet channels over nanowire ones. Based on these results, it is suggested that we should pay special attention to the quality of corner interfaces during device fabrication, and keep focusing on nanosheet GAAFETs instead of nanowire ones at this stage.

Progress of state-of-the-art and next-generation thin-film photovoltaic devices is often stymied by open-circuit voltage ($V_{\mathrm{oc}}$) that is significantly lower than theoretical and practical limits. Yet, effectively diagnosing the primary sources of voltage loss remains challenging. Herein, a sequence of device-level characterization techniques and simulations are employed to identify and rank loss mechanisms. For the research-based $\mathrm{Cd}(\mathrm{Se},\mathrm{Te})$ device under study, most of the loss was at the front semiconductor heterointerface due to a clifflike conduction-band offset that lowered the recombination activation energy. Additional losses due to band tails were quantified by photoluminescence analysis. The latter provided the absorption coefficient and activation energy reduction associated with band tails as inputs to device models. Simulations showed that alleviating front-interface issues would improve $V_{\mathrm{oc}}$, but it would then be limited by bulk recombination. Further improvement of the bulk would then lead to back-contact limitations. Reducing band tails is beneficial in any circumstance. This analysis provides guidance for reaching toward the radiative $V_{\mathrm{oc}}$ limit.

We realize a high-performance compact optically pumped cesium beam atomic clock utilizing the Faraday laser simultaneously as the pumping and detection lasers. The Faraday laser, which is frequency stabilized by the modulation transfer spectroscopy (MTS) technique, has a narrow linewidth and superior frequency stability. Measured by the optical heterodyne method between two identical systems, the linewidth of the Faraday laser is 2.5 kHz after MTS locking, and the fractional frequency stability of the Faraday laser is optimized to $1.8\times {10}^{-12}/\sqrt{\tau }$. Based on this high-performance Faraday laser, the cesium beam clock realizes a signal-to-noise ratio of 39 600 in 1-Hz bandwidth when the cesium oven temperature is $130{}^{\circ }\mathrm{C}$. Compared with hydrogen maser, the fractional frequency stability of the Faraday-laser-pumped cesium beam clock can reach $1.3\times {10}^{-12}/\sqrt{\tau }$ and decreases to $1.4\times {10}^{-14}$ at 10 000 s when the cesium oven temperature is set at $110{}^{\circ }\mathrm{C}$. This Faraday-laser-pumped cesium beam clock demonstrates its excellent performance and its great potential in the fields of timekeeping, navigation, and communication. Moreover, as a high-performance optical frequency standard, the Faraday laser can contribute to the development of other applications in quantum metrology, precision measurement, and atomic physics.

Entanglement-based quantum key distribution (QKD) protocols require robust and stable photon-pair sources in terms of high heralding efficiencies or photon-pair generation rates even under harsh environmental conditions, e.g., when operated in the field. Here we report on a type-0 spontaneous parametric down-conversion photon source in periodically poled crystals based on simultaneous operation of second harmonic generation and spontaneous parametric down-conversion (SPDC) in a double-pass configuration within the same nonlinear crystal, further simplifying the hardware requirements of SPDC photon sources. Our source is flexible, tunable, alignment-free, relatively broadband, and completely fiber coupled. Its rack-compatible and modular setup allows a straightforward plug-and-play integration of coding modules, e.g., interferometers to enable various QKD protocols such as phase or phase-time coding. We compare the double-pass configuration with our single-pass type-II and type-0 SPDC source configurations. To evaluate the conversion efficiencies of our modules, we use data postprocessing to remove artifacts from detector after-pulsing and dead times of the detectors.

In this study, we employed a quantum computer to solve a low-energy effective Hamiltonian for spin defects in diamond (so-called nitrogen-vacancy centres) and wurtzite-type aluminium nitride, which are anticipated to be qubits. The probabilistic imaginary-time evolution (PITE) method, designed for use in a fault-tolerant quantum computer era, was employed to calculate the ground and excited states of the spin singlet state, as represented by the effective Hamiltonian. It is difficult to compute the spin singlet state correctly using density functional theory, which should be described by multiple Slater determinants. To mitigate the effects of quantum errors inherent in current quantum computers, we implemented a $\text{⟦}n+2,n,2\text{⟧}$ quantum error detection (QED) code called the Iceberg code. Despite the inevitable destruction of the encoded state resulting from the measurement of the ancilla qubit at each PITE step, we were able to successfully re-encode and recover the logical success state. In the implementation of the PITE, it was observed that the effective Hamiltonian comprises large diagonal components and relatively small nondiagonal components, which is frequently the case with quantum chemistry calculations. An efficient implementation of Hamiltonian simulations, in which the diagonal components dominate, was developed on a quantum computer based on the second-order Trotter-Suzuki decomposition. This is the first instance of an encoded PITE circuit being executed on a trapped-ion quantum computer. Our results demonstrate that QED effectively reduces quantum errors and that we successfully obtained both the ground and excited states of the spin singlet state. Our demonstration clearly indicates that ${\mathrm{Zr}}_{\mathrm{Al}}{\mathrm{V}}_{\mathrm{N}}$, ${\mathrm{Ti}}_{\mathrm{Al}}{\mathrm{V}}_{\mathrm{N}}$, and ${\mathrm{Hf}}_{\mathrm{Al}}{\mathrm{V}}_{\mathrm{N}}$ defects have a high potential as spin qubits for quantum sensors.

The coherence established in a Rydberg medium through the electromagnetically induced transparency (EIT) process is significantly modified with the inclusion of a microwave (MW) field, leading to a dramatic change in the susceptibility. However, the majority of existing studies focus on the impact of the MW electric field (E-field) on the absorptive properties, while little experimental progress has been made in studying the MW-induced optical phase shift (MIOPS), a feature derived from the MW-dressed refractive index. Here we investigate this coherent effect by measuring the MIOPS of the probe laser in a Rydberg-EIT system in a ${}^{87}\mathrm{Rb}$ vapor cell. We illustrate the optical phase shift as a function of the MW E-field strength under various conditions and achieve a shift of 0.18 rad in the optical phase (corresponding to a variation of $4.5\times {10}^{-7}$ in the refractive index) with a MW E-field strength of 8 mV/cm. Moreover, we develop a MW sensor based on MIOPS and achieve a sensitivity of $92.4\mathrm{nV}{\mathrm{cm}}^{-1}{\mathrm{Hz}}^{-1/2}$ or $279.5\text{μ}\mathrm{V}{\mathrm{cm}}^{-1}{\mathrm{Hz}}^{-1/2}{n}^2$ when scaling the quantum number $n$ of the Rydberg states. Our experiment demonstrates a promising platform for studying nonlinear quantum optics in a MW-dressed Rydberg medium and opens the avenue for developing next-generation MW electrometry.