We demonstrate a long-coherent-time coupling between microwave and optical fields through cold atomic ensembles. The phase information of the microwave field is stored in a coherent superposition state of a cold atomic ensemble and is then read out by two optical fields after 12 ms. A similar operation of mapping the phase of optical fields into a cold atomic ensemble and then retrieving by microwave is also demonstrated. These studies demonstrate that long-coherent-time cold atomic ensembles could resonantly couple with microwave and optical fields simultaneously, which paves the way for realizing high-efficiency, high-bandwidth, and noiseless atomic quantum converters.

An elongated trap potential for cold atoms is designed based on a quadrupole-Ioffe configuration. Phase fluctuations in a Bose–Einstein condensate (BEC), which is confined by the trap, are studied. We simulate the atom density distribution induced by fluctuation after time of flight from this elongated trap potential and study the temperature measurement method related to the distribution. Furthermore, taking advantage of the tight confinement and radio frequency dressing technique, we propose a double well potential for splitting BECs. Our results are helpful for improving understanding of low-dimensional quantum gases and provide important guidance for atomic interferometry.

The definitions of strong superadditive deficit for relative entropy coherence and monogamy deficit of measurement-dependent global quantum discord are proposed. The equivalence between them is proved, which provides a useful criterion for the validity of the strong superadditive inequality of relative entropy coherence. In addition, the strong superadditive deficit of relative entropy coherence is proved to be greater than or equal to zero under the condition that bipartite measurement-dependent global quantum discord (GQD) does not increase under the discarding of subsystems. Using the Monte Carlo method, it is shown that both the strong superadditive inequality of relative entropy coherence and the monogamy inequality of measurement-dependent GQD are established under general circumstances. The bipartite measurement-dependent GQD does not increase under the discarding of subsystems. The multipartite situation is also discussed in detail.

Quantum contextuality is one kind of quantumness that distinguishes quantum mechanics from classical theory. As the simplest exclusivity graph, quantum contextuality of the $n$-cycle graph has been reviewed, while only for odd $n$ the quantumness can be revealed. Motivated by this, we propose the degree of non-commutativity and the degree of uncertainty to measure the quantumness in the $n$-cycle graphs. As desired, these two measures can detect the quantumness of any $n$-cycle graph when $n\ge 4$.

In the traditional random-conformational-search model, various hypotheses with a series of meta-stable intermediate states were proposed to resolve the Levinthal paradox in protein-folding time. Here we introduce a quantum strategy to formulate protein folding as a quantum walk on a definite graph, which provides us a general framework without making hypotheses. Evaluating it by the mean of first passage time, we find that the folding time via our quantum approach is much shorter than the one obtained via classical random walks. This idea is expected to evoke more insights for future studies.

An absorption-desorption model with long-ranged interaction is simulated by the dynamic Monte Carlo method. The dynamic process has an inert phase and an active phase that is controlled by the absorption rate. In the active phase, the number of vacancies increases with time exponentially, while in the inert phase the vacant sites will be occupied by adsorbates rapidly. At the critical absorption rate, both the number of vacancies and the time-depending active probability exhibit power-law behavior. We determine the critical absorption rate and the scaling exponents of the power-laws. The effect of the interaction range of desorption on the critical exponents is investigated. In the short-ranged interaction limit, the critical exponents of Schlögl's first model are recovered. The model may describe the stability of the inner Helmholtz layer, an essential component of the electrochemical double-layer capacitor at a nanowire.

Using the Debye shielding model, the effects of plasma shielding on the dielectronic recombination processes of the H-like helium ions are investigated. It is found that plasma shielding causes a remarkable change in the Auger decay rate of the doubly excited $2p^2$ $^3P_2$ state. As a result, the dielectronic recombination cross sections from the doubly excited $2p^2$ $^3P_2$ state increases with the decreasing Debye shielding length.

High-brightness tapered lasers with photonic crystal structures are designed and fabricated. A narrow taper angle is designed for the tapered section. The device delivers an output power of 3.3 W and a maximum wall-plug efficiency of 43%. The vertical beam divergence is around 11$^{\circ}$ at different currents. Nearly diffraction-limited beam qualities for the vertical and lateral directions are obtained. The lateral beam quality factor $M^{2}$ is below 2.5 and the vertical $M^{2}$ value is around 1.5 across the whole operating current range. The maximum brightness is 85 MW$\cdot$cm$^{-2}$sr$^{-1}$. When the current is above 3.3 A, the brightness is still above 80 MW$\cdot$cm$^{-2}$sr$^{-1}$.

A silicon shallow-ridge waveguide integrated superconducting nanowire single photon detector is designed and fabricated. At the bias current of 11.6 $\mu$A, 4% on-chip detection efficiency near 1550 nm wavelength is achieved with the dark count rate of 3 Hz and a timing jitter of 75 ps. This device shows the potential application in the integration of superconducting nanowire single photon detectors with a complex quantum photonic circuit.

Considered to be a candidate for large-size bulk materials used in lasers and other fields, Nd$^{3+}$-doped glass ceramics containing NaYF$_{4}$ nanocrystallites are prepared. Using x-ray diffraction and transmission electron microscopy, we show that pure cubic NaYF$_{4}$ is well precipitated in the glass matrix. To obtain the optical property of this material at 1.06 μm, the fluorescence decay of $^{4}\!F_{3/2}$ energy levels is measured and analyzed. It is found that the fluorescence lifetime decreases first and then increases with the increasing dopant concentration due to the existing but finally weakening energy dissipation. As a result, a long radiation lifetime of about 191–444 μs is obtained at 1.06 μm in the prepared material. It is thus revealed that Nd$^{3+}$-doped glass ceramic containing NaYF$_{4}$ nanocrystallites is a potential candidate as a near-infrared laser material.

We report herein a high-power folded intra-cavity 2.1 μm optical parametric oscillator (ICOPO) which is the first example of an ICOPO that utilizes a wavelength-locked 878.6 nm in-band pumped Nd:YVO$_{4}$ laser as the pump source. The thermal effect of PPMgLN crystal and the divergence angle of the incident laser are considered comprehensively to determine the 2128 nm degenerate temperature. In the experiment, the functions of different output coupler transmittances and different repetition rates on the parametric laser output power are studied, respectively. The temperature versus parametric laser output power in an in-band pumped non-wavelength-locked 880 nm laser diode (LD) and in a wavelength-locked 878.6 nm LD is compared. A maximum output power of 5.87 W is obtained at the pump power of 56.9 W when the repetition rate is 80 kHz. The corresponding conversion efficiency is 14.55%, with a linewidth of 73.65 nm and pulse width of 3.62 ns. The wavelength-locked 878.6 nm LD in-band pumping technology can stabilize the 2.1 μm laser output power of Nd:YVO$_{4}$ crystal effectively in the environment of intense temperature change.

We investigate the influence of coating layer on acoustic wave propagation in a dispersed random medium consisting of coated fibers. In the strong-scattering regime, the characteristics of wave scattering resonances are found to evolve regularly with the properties of the coating layer. By theoretical calculation, frequency gaps are found in acoustic excitation spectra in a random medium. The scattering cross section results present the evolution of scattering resonances with the properties of the coating layer, which offers a good explanation for the change of the frequency gaps. The velocity of the propagation quasi-mode is also shown to depend on the filling fraction of the coating layer. We use the generalized coherent potential-approximation approach to solve acoustic wave dispersion relations in a complicated random medium consisting of coating-structure scatterers. It is shown that our model reveals subtle changes in the behavior of the acoustic wave propagating quasi-modes.

The oscillation and migration of bubbles within an intensive ultrasonic field are important issues concerning acoustic cavitation in liquids. We establish a selection map of bubble oscillation mode related to initial bubble radius and driving sound pressure under 20 kHz ultrasound and analyze the individual-bubble migration induced by the combined effects of pressure gradient and acoustic streaming. Our results indicate that the pressure threshold of stable and transient cavitation decreases with the increasing initial bubble radius. At the pressure antinode, the Bjerknes force dominates the bubble migration, resulting in the large bubbles gathering toward antinode center, whereas small bubbles escape from antinode. By contrast, at the pressure node, the bubble migration is primarily controlled by acoustic streaming, which effectively weakens the bubble adhesion on the container walls, thereby enhancing the cavitation effect in the whole liquid.

Microturbulence excited by ion temperature gradient (ITG)-dominant and trapped electron mode (TEM)-dominant instabilities is compared in the fusion plasmas using gyrokinetic simulations based on the realistic equilibrium data from DIII–D discharges. Collisions make a difference between two plasmas and give rise to similar results to those found in previous research experiments [Chin. Phys. Lett. 35 (2018) 105201]. The mode structures and frequency spectrum of the most unstable modes characterized by the ITG-dominant and TEM-dominant instabilities are excited in the lower and higher $T_{\rm e}$ plasmas in the linear simulations. In the nonlinear simulations, contour plots of the perturbed potential are shown in the saturated stage, with the radial correlation lengths being microscopic on the order of the ion thermal gyroradius $\rho_{\rm i}$ in both the ITG and the TEM microturbulences. The dominant mode wavelengths of the perturbed potential increase when evolving from linear to nonlinear stages in both simulations, with the fluctuation energy spreading from the linearly dominant modes to the nonlinearly dominant modes. The radial correlation lengths are about 4$\rho_{\rm i}$ and the electron density fluctuation intensities are about 0.85% in the nonlinear saturated stage, which are in agreement with the experimental results.

The diamond anvil cell-based high-pressure technique is a unique tool for creating new states of matter and for understanding the physics underlying some exotic phenomena. In situ sensing of spin and charge properties under high pressure is crucially important but remains technically challenging. While the nitrogen-vacancy (NV) center in diamond is a promising quantum sensor under extreme conditions, its spin dynamics and the quantum control of its spin states under high pressure remain elusive. In this study, we demonstrate coherent control, spin relaxation, and spin dephasing measurements for ensemble NV centers up to 32.8 GPa. With this in situ quantum sensor, we investigate the pressure-induced magnetic phase transition of a micron-size permanent magnet Nd$_{2}$Fe$_{14}$B sample in a diamond anvil cell, with a spatial resolution of $\sim$2 μm, and sensitivity of $\sim$20 $\mu$T/Hz$^{1/2}$. This scheme could be generalized to measure other parameters such as temperature, pressure and their gradients under extreme conditions. This will be beneficial for frontier research of condensed matter physics and geophysics.

Simple molecular solids have been an important subject in condensed matter physics, particularly for research of pressure-induced molecular dissociation. We re-explore the structural changes of element bromine through pressure-induced decomposition of solid HBr. The phase changes in HBr are investigated by Raman spectroscopy and synchrotron x-ray diffraction up to 125 GPa at room temperature. By applying pressure, HBr decomposes into solid bromine in the pressure range of 18.7–38 GPa. The solid bromine changes from molecular phase to incommensurate phase at 81 GPa, and finally to monatomic phase at 91 GPa. During the process of pressure-induced molecular dissociation, the intermediate incommensurate phase of element bromine is confirmed for the first time from the x-ray diffraction studies. The decomposition of HBr is irreversible since HBr cannot form again upon pressure decompression.

Fractional quantum Hall systems are often described by model wave functions, which are the ground states of pure systems with short-range interaction. A primary example is the Laughlin wave function, which supports Abelian quasiparticles with fractionalized charge. In the presence of disorder, the wave function of the ground state is expected to deviate from the Laughlin form. We study the disorder-driven collapse of the quantum Hall state by analyzing the evolution of the ground state and the single-quasihole state. In particular, we demonstrate that the quasihole tunneling amplitude can signal the fractional quantum Hall phase to insulator transition.

Recently, $\theta$-TaN was proposed to be a topological semimetal with a new type of triply degenerate nodal points. Here, we report studies of pressure dependence of transport, Raman spectroscopy and synchrotron x-ray diffraction on $\theta$-TaN up to 61 GPa. We find that $\theta$-TaN becomes superconductive above 24.6 GPa with $T_{\rm c}$ at 3.1 K. The $\theta$-TaN is of n-type carrier nature with carrier density about $1.1\times 10^{20}$/cm$^{3}$ at 1.2 GPa and 20 K, while the carrier density increases with the pressure and saturates at about 40 GPa in the measured range. However, there is no crystal structure transition with pressure up to 39 GPa, suggesting the topological nature of the pressure induced superconductivity.

GaN-based micro light emitting diodes (micro-LEDs) on silicon (Si) substrates with 40 μm in diameter are developed utilizing standard photolithography and inductively coupled plasma etching techniques. From current-voltage curves, the relatively low turn-on voltage of 2.8 V and low reverse leakage current in the order of 10$^{-8}$ A/cm$^{2}$ indicate good electrical characteristics. As the injection current increases, the electroluminescence emission wavelength hardly shifts at around 433 nm, and the relative external quantum efficiency slightly decays, because the impact of quantum-confined Stark effect is not serious in violet-blue micro-LEDs. Since GaN-LEDs are cost effective on large-area Si and suitable for substrate transfer or vertical device structures, the fabricated micro-LEDs on Si should have promising applications in the fields of high-resolution display and optical communication.