Nanostructured lead halide perovskites have received extensive attention due to their potential applications in integrated photonics. Despite many successful realizations of nanoscale coherent-light sources from lead halide perovskites, the role and interplay between excitonic and electron-hole plasma (EHP) states in the stimulated-emission process are not demonstrated yet. In this work, the carrier behavior and dynamics of the stimulated emission in ${\mathrm{Cs}\mathrm{Pb}\mathrm{Br}}_3$ single nanowires are studied with a streak camera under power-dependent one-photon and two-photon excitation at room temperature. A redshift of the lasing gain profile with increasing excitation fluence is observed, suggesting the transition from the excitonic state to EHP state that is responsible for the lasing. Whereas, a blueshift of the gain profile with time decay represents the opposite direction of the former process. Moreover, the individual lasing modes show a blueshift as excitation fluence increases and a redshift as time elapses, due to the carrier-density dependence of the refractive index. This study could provide a comprehensive and deeper understanding of the carrier-density-driven stimulated-emission dynamics in lead halide nanowires and extend their applications in integrated photonics.

The precise and automated calibration of quantum gates is a key requirement for building a reliable quantum computer. Unlike errors from decoherence, systematic errors can in principle be completely removed by tuning experimental parameters. Here, we present an iterative calibration routine, which can remove systematic gate errors on several qubits. A central ingredient is the construction of pulse sequences that extract independent indicators for every linearly independent error generator. We show that decoherence errors only moderately degrade the achievable infidelity due to systematic errors. Furthermore, we investigate the convergence properties of our approach by performing simulations for a specific qubit encoded in a pair of spins. Our results indicate that a gate set with 230 gate parameters can be calibrated in about ten iterations, after which incoherent errors limit the gate fidelity.

We propose how to realize nonreciprocity for a weak input optical field via nonlinearity and synthetic magnetism. We show that the photons transmitted from a linear cavity to a nonlinear cavity (i.e., a linear-nonlinear optical molecule) exhibit nonreciprocal photon blockade but no clear nonreciprocal transmission. Both nonreciprocal transmission and nonreciprocal photon blockade can be observed, when one or two auxiliary modes are coupled to the linear-nonlinear optical molecule to generate an artificial magnetic field. A similar method can be used to create and manipulate nonreciprocal transmission and nonreciprocal photon blockade for photons bidirectionally transport in a nonlinear-nonlinear optical molecule. Additionally, a photon circulator with nonreciprocal photon blockade is designed in cyclic three-nonlinear-mode system. The combination of nonlinearity and synthetic magnetism provides us an effective way towards the realization of quantum nonreciprocal devices, e.g., nonreciprocal single-photon sources and single-photon diodes.

We report the observation of a spin-orbit torque (SOT) originating from the surface Rashba-Edelstein effect. We find that the SOT in a prototypical spin-orbitronic system, a $\mathrm{Pt}$/$\mathrm{Co}$ bilayer, can be manipulated by molecular self-assembly on the $\mathrm{Pt}$ surface. This provides evidence that the Rashba spin-orbit coupling at the $\mathrm{Pt}$ surface generates a sizable SOT, which is hidden by the strong bulk and interface spin-orbit coupling. We show that the molecular tuning of the surface Rashba-Edelstein SOT is consistent with density-functional-theory calculations. These results illustrate the crucial role of the surface spin-orbit coupling in the SOT generation, which alters the landscape of metallic spin-orbitronic devices.

We present a detailed theoretical analysis of the electronic and optical properties of $c$-plane $\mathrm{In}\mathrm{Ga}\mathrm{N}$/$\mathrm{Ga}\mathrm{N}$ quantum-well structures with $\mathrm{In}$ contents ranging from 5% to 25%. Special attention is paid to the relevance of alloy-induced carrier-localization effects to the “green gap” problem. Studying the localization length and electron-hole overlaps at low and elevated temperatures, we find alloy-induced localization effects are crucial for the accurate description of ($\mathrm{In}$,$\mathrm{Ga}$)$\mathrm{N}$ quantum wells across the range of $\mathrm{In}$ content studied. However, our calculations show very little change in the localization effects when moving from the blue to the green spectral regime; that is, when the internal quantum efficiency and wall-plug efficiencies reduce sharply, for instance, the in-plane carrier separation due to alloy-induced localization effects changes weakly. We conclude that other effects, such as increased defect densities, are more likely to be the main reason for the green-gap problem. This conclusion is further supported by our finding that the electron localization length is large, when compared with that of holes, and changes little in the $\mathrm{In}$ composition range of interest for the green-gap problem. Thus, electrons may become increasingly susceptible to an increased (point) defect density in green emitters and as a consequence the nonradiative-recombination rate may increase.

We propose a robust strategy for transforming the Hamiltonian of a metallic structure expressed in a nonorthogonal density-functional-theory (DFT) basis into a low-dimensional space compatible with electron-transport simulations. This mode-space approximation is applied locally to inhomogeneous material stacks including amorphous phases and interfaces. The contacts and periodic parts of the device are transformed into the subspace created, while the active inhomogeneous regions remain represented in real space. The various regions are connected to each other through mode-space–real-space hybrid blocks of the Hamiltonian and overlap matrices. This approach allows harnessing of the full flexibility of DFT combined with the power of the nonequilibrium Green’s function formalism at a moderate cost. In particular, for a realistic resistive random-access memory cell composed of 3390 atoms, a performance improvement by a factor of 136 compared with a pure real-space treatment is demonstrated, with an error of less than 2%.

In the post-Moore era, improving energy efficiency is an urgent requirement for microelectronics moving towards the Internet of Things, artificial intelligence, and 5G. In particular, two-dimensional (2D) materials with natural passivation, gate electrostatics, and high mobility have attracted significant attention for integrated circuits in the race towards next-generation field-effect transistors (FETs). Here, by coupling first-principles and nonequilibrium-Green’s-function approaches, we obtain a physical understanding of the ballistic transport properties of a V-V binary bismuth nitride ($\mathrm{Bi}\mathrm{N}$) material. Promisingly, monolayer $\mathrm{Bi}\mathrm{N}$ has sharp conduction-band and flat valence-band edges, which exhibit disparate effective masses. Simulated sub-10-nm monolayer $\mathrm{Bi}\mathrm{N}$ transistors show potential device performance and fulfill the high-performance and low-power requirements of the goals of the International Technology Roadmap for Semiconductors 2028 with their optimal parameters. Furthermore, by comprehensively analyzing the effective mass, density of states, on-state current, subthreshold swing, etc., we show that materials whose band dispersions have an extreme character have advantages for transistors. Also, benchmarking of the energy-delay product confirms that $\mathrm{Bi}\mathrm{N}$ FETs possess sufficient competitiveness against other 2D FETs. We believe that this could be a guide for designing potential channel materials for next-generation FETs.

The electric double layer (EDL) formed around charged nanostructures at the liquid-solid interface determines their electrochemical activity and influences their electrical and optical polarizability. We experimentally demonstrate that restructuring of the EDL at the nanoscale can be detected by dark-field scattering microscopy. Temporal and spatial characterization of the scattering signal demonstrates that the potentiodynamic optical contrast is proportional to the accumulated charge of polarizable ions at the interface and that its time derivative represents the nanoscale ionic current. The material specificity of the EDL formation is used in our work as a label-free contrast mechanism to image nanostructures and perform spatially resolved cyclic voltammetry on an ion-current density of a few attoamperes, corresponding to the exchange of only a few hundred ions.

We propose a filter method to generate electron beams of high polarization from bubble and blow-out wakefield accelerators. The mechanism is based on the idea of identifying all electron-beam subsets with low polarization and filtering them out with an X-shaped slit placed immediately behind the plasma accelerator. To find these subsets we investigate the dependence between the initial azimuthal angle and the spin of single electrons during the trapping process. This dependence shows that transverse electron spins preserve their orientation during injection if they are initially aligned parallel or antiparallel to the local magnetic field. We derive a precise correlation of the local beam polarization as a function of the coordinate and the electron phase angle. Three-dimensional particle-in-cell simulations, incorporating classical spin dynamics, show that the beam polarization can be increased from 35% to about 80% after spin filtering. The injected flux is strongly restricted to preserve the beam polarization; for example, less than 1 kA in Wen et al. [Phys. Rev. Lett. 122, 214801 (2019)]. This limitation is removed by use of the proposed filter mechanism. The robustness of the method is discussed in terms of drive-beam fluctuations, jitters, the thickness of the filter, and the initial temperature. This idea marks an efficient and simple strategy to generate energetic polarized electron beams on the basis of wakefield acceleration.

Anisotropic two-dimensional materials possess intrinsic angle-dependent physical properties that originate from their low crystal symmetry. Yet, how these properties are affected by external impurities or structural defects in the material is still wholly unclear. Here, we address this question by investigating the electrical transport in the anisotropic layered model system germanium arsenide. First, we show that the ratio of conductivities along the armchair and zigzag crystallographic directions exhibits an intriguing dependence with respect to both temperature and carrier density. Then, by using a conceptually simple model, we demonstrate that this unexpected behavior is directly related to the presence of impurity-induced localized states in the band gap that introduce isotropic hopping conduction. The presence of this conduction mechanism in addition to the intrinsic band conduction significantly influences the anisotropic electrical properties of the material, especially at room temperature, i.e., at application-relevant conditions.

We study the consequences of drying on the internal structure of compressible materials containing pores of different sizes, which may be seen as model systems of sponges or wood. With the help of original techniques, we devise biporous media with different relative amounts of small and large pores, and follow the evolution of the liquid fraction simultaneously in each pore type. We show that in a compressible biporous medium with dispersed large pores (i.e., not directly connected) drying induces the homogeneous emptying of the large pores first, due to their compression, along with some compression of the small-pore matrix. In contrast, when the large pores are connected, they successively empty without compression. In both cases, the small pores start or finish to empty in the next stage, and a constant drying rate is observed during most of the time, thanks to liquid films maintaining the contact of the liquid network with the free surface of the sample.

Electron and hole trapping is studied in the ${\mathrm{Ce}}^{3+}$- and ${\mathrm{Pr}}^{3+}$-doped ${\mathrm{Lu}}_2{\mathrm{Si}}_2{\mathrm{O}}_7$ scintillation single crystals (LPS:$\mathrm{Ce}$ and LPS:$\mathrm{Pr}$) by electron paramagnetic resonance (EPR). Detailed EPR measurements of the x-ray irradiated LPS crystals reveal that holes generated by irradiation are predominantly trapped at oxygen lattice ions creating ${\mathrm{O}}^{-}$ centers. The same x-ray irradiation creates also electron-type centers, which are attributed to ${\mathrm{Lu}}^{2+}$ ions, where the trapped electron at the Lu lattice ion is stabilized by a nearby defect, such as the oxygen vacancy and ${\mathrm{Ir}}^{3+}$ impurity ion. Both the hole and electron centers can be thus considered as a bound small polaron, which makes the charge trapping in a scintillation mechanism quite competitive. The hole ${\mathrm{O}}^{-}$ and electron ${\mathrm{Lu}}^{2+}$ centers show thermal stability well above room temperature. Thermal decays of their concentrations correlate well with the appearance of the thermally stimulated luminescence glow peaks at 470–550 K. The presence of the same intrinsic traps in the $\mathrm{Ce}\text{−}$ and $\mathrm{Pr}$-doped LPS crystals suggests that the difference in the light yield of these crystals is an intrinsic property of the ${\mathrm{Ce}}^{3+}$ and ${\mathrm{Pr}}^{3+}$ activator centers in the LPS lattice. An origin of charge traps in this pyrosilicate structure and their role in the scintillation mechanism is compared with the results previously described in the literature on orthosilicates.

Counterdiabatic driving (CD) offers a fast and robust strategy to manipulate and prepare the quantum state in multibody systems. However, the exact CD term involving the spectral properties of the system is difficult to calculate and generally takes a complicated form for higher-dimensional complex systems. Recently, Sels and Polkovnikov [Proc. Natl. Acad. Sci. U. S. A. 114, E3909 (2017)] proposed a variational method to optimally approximate the CD term with no need for the full spectral information of the original Hamiltonian. Using a nuclear-magnetic-resonance setup, here we report an experimental demonstration of this method to construct available shortcuts to adiabaticity in a nonintegrable spin-$1/2$ chain via only local controls. In this process, the ground state of such a system is rapidly prepared and the final state fidelity is significantly increased compared with the traditional adiabatic method. Our experiments prove the feasibility of this variational method to design CD in practice, and thus it is a promising strategy for fast, high-fidelity quantum-state manipulation in complex and noisy quantum systems.

We report on the dynamics of laser-induced magnetization in magnetic ribbons using the time-resolved magneto-optical Kerr effect. Damped oscillations representing precessional motion of the magnetization vector are observed in a $\mathrm{Co}$-rich ribbon. The frequency and amplitude of these oscillations depend on the fluence of the pump laser pulse and the external magnetic field. With an anisotropy factor defined by the effective field of the magnetic anisotropy, we demonstrate that the frequency of the ferromagnetic mode activated by the laser pulses is close to the frequency of the giant magnetoimpedance response. These findings provide an opportunity to investigate the magnetoimpedance effect in the gigahertz frequency range using ultrashort laser pulses and are particularly interesting for the development of broadband sensor devices. Furthermore, our results link laser-induced magnetization dynamics with magnetoresistive sensing techniques, thus opening up the supergigahertz domain to magnetoimpedance studies.

We present a compact, two-stage atomic beam source that produces a continuous, narrow, collimated, and high-flux beam of rubidium atoms with sub-Doppler temperatures in three dimensions, which features very low emission of near-resonance fluorescence along the atomic trajectory. The atom-beam source originates in a pushed two-dimensional magneto-optical trap ($2{\mathrm{D}}^{+}$ MOT) feeding a slightly off-axis three-dimensional moving optical-molasses stage that continuously cools and redirects the atom beam. The capture velocity of the moving optical molasses is deliberately chosen to be low, approximately $3\mathrm{m}/\mathrm{s}$, to reduce fluorescence, and the cooling light is detuned by several atomic linewidths from resonance to reduce the absorption cross section of cooling-induced fluorescence. Near-resonance light from the $2{\mathrm{D}}^{+}$ MOT and the push beam does not propagate to the output atomic trajectory due to a ${10}^{\circ }$ bend in the atomic trajectory. The atomic beam emitted from the two-stage source has a flux up to $1.6(3)\times {10}^9\mathrm{atoms}/\mathrm{s}$, with an optimized temperature of $15.0(2)\mu \mathrm{K}$. We employ continuous Raman-Ramsey interference measurements at the atom-beam output to study the sources of decoherence in the presence of continuous cooling, and demonstrate that the atom-beam source effectively preserves high fringe contrast even during cooling. This cold-atom-beam source is appropriate for use in atom interferometers and clocks, where continuous operation eliminates dead time, the slow atom-beam velocity (6–16 m/s) improves sensitivity, the narrow 3D velocity distribution improves fringe contrast, and the low reabsorption of scattered light mitigates decoherence caused by the continuous cooling process.

Anisotropic physical properties in two-dimensional (2D) layered semiconductors with low crystal lattice symmetry are of great interest due to the underlying rich physics and potential applications in electronics. Sophisticated transport measurements unveiling the anisotropic effective mass, which is an essential material parameter reflecting the energy band, are still lacking so far. With a focus on the anisotropy with respect to the underlying crystal structure, in this work, we propose a simple strategy to directly probe the carrier effective mass $m^{\ast }$ for 2D semiconductors using tunneling as the sensing tool. The Schottky tunnel transistor is a practically simple device, in which the transport can be electrically tuned to be tunneling dominated. Using such a device as the experimental platform, we extract the anisotropy of the effective mass for both electrons and holes in the low symmetric ${\mathrm{Re}\mathrm{Se}}_2$ from the Fowler-Nordheim tunneling measured at 1.4 K. Furthermore, a colossal conductivity anisotropy of ${10}^3$ is observed for ${\mathrm{Re}\mathrm{Se}}_2$.