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<jats:title>Abstract</jats:title> <jats:p>A dual functional terahertz metasurface based on VO<jats:sub>2</jats:sub> and graphene is proposed in this paper. It consists of gold layer embedded with VO<jats:sub>2</jats:sub> patches, SiO<jats:sub>2</jats:sub> spacer layer, VO<jats:sub>2</jats:sub> layer, graphene and SiO<jats:sub>2</jats:sub> spacer substrate. When the bottom VO<jats:sub>2</jats:sub> is in metallic state, the designed metasurface can achieve absorption function. As the top VO<jats:sub>2</jats:sub> patches are metallic state, the proposed metasurface can be used as single band absorber with terahertz absorptance of 99.7 % at 0.736 THz. When the top VO<jats:sub>2</jats:sub> patches are in insulating state, the designed structure behaves as dual band absorber with the absorptance of 98.9 % at 0.894 THz and 99.9 % at 1.408 THz. In addition, the absorber is polarization insensitive and keeps good performance at large incident angle. When the bottom VO<jats:sub>2</jats:sub> is in insulated state, the metasurface serves as electromagnetically induced transparency. The transparent window can be dynamically regulated by controlling the chemical potential of graphene. The proposed metasurface exhibits the advantages of terahertz absorption, electromagnetic induced transparency and dynamic control, which provides more options for the design of terahertz devices in the future.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>As a fundamental thermodynamic variable, pressure can alter bonding patterns and drive phase transitions, leading to the creation of new high-pressure phases with exotic properties that are inaccessible at ambient pressure. Using swarm-intelligence structural prediction method, a phase transition of TiF<jats:sub>3</jats:sub>, from <jats:italic>R</jats:italic>-3<jats:italic>c</jats:italic> to <jats:italic>Pnma</jats:italic> phase, is predicted at high pressure, accompanied by the destruction of TiF<jats:sub>6</jats:sub> octahedra and formation of TiF<jats:sub>8</jats:sub> square antiprismatic units. Particularly, through laser-heated diamond anvil cell technique, the predicted <jats:italic>Pnma</jats:italic> phase of TiF<jats:sub>3</jats:sub> is confirmed by high-pressure X-ray diffraction experiment. Furthermore, the in-situ electrical measurement indicates that the newly found <jats:italic>Pnma</jats:italic> phase has a semiconducting character, which is also consistent with electronic band structure calculations. We further show that this pressure-induced phase transition is a general phenomenon in ScF<jats:sub>3</jats:sub>, VF<jats:sub>3</jats:sub>, CrF<jats:sub>3</jats:sub> and MnF<jats:sub>3</jats:sub>, offering valuable insights on the high-pressure phases in transition metal trifluorides.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A single-beam leaky-wave antenna (LWA) with wide-scanning-angle and high-scanning-rate transmission line (TL) is proposed based on spoof surface plasmon polariton (SSPP) in this paper. The SSPP TL is etched with periodically arranged circular patches which can convert the slow-wave mode into the fast-wave region for radiation. The proposed LWA is designed, fabricated, and tested. The simulated results imply that the proposed LWA can not only achieve high radiation efficiency about 81.4% and high scanning rate of 12.12, but also has a large scanning angle with 176deg over a narrow operation bandwidth of 8.3-9.6 GHz (for |S<jats:sub>11</jats:sub>| &amp;#60; −10 dB). In addition, the simulated average gain of the LWA can reach 10.9dBi. The measured scanning angle range is 175deg in the operation band of 8.2-9.6 GHz, and the measured average gain is 10.6dBi. The experimental results are consistent with the simulation, which validate its good performance. The antenna with high radiation efficiency, wide scanning angle range, and high scanning rate has great application potential in radar and wireless communication systems.</jats:p>

<jats:p>The Loschmidt echo is a useful diagnostic for the perfection of quantum time-reversal process and the sensitivity of quantum evolution to small perturbations. The main challenge for measuring the Loschmidt echo is the time reversal of a quantum evolution. In this work, we demonstrate the measurement of the Loschmidt echo in a superconducting 10-qubit system using Floquet engineering and discuss the imperfection of an initial Bell-state recovery arising from the next-nearest-neighbor (NNN) coupling present in the qubit device. Our results show that the Loschmidt echo is very sensitive to small perturbations during quantum-state evolution, in contrast to the quantities like qubit population that is often considered in the time-reversal experiment. These properties may be employed for the investigation of multiqubit system concerning many-body decoherence and entanglement, etc., especially when devices with reduced or vanishing NNN coupling are used.</jats:p>

<jats:p>The semiclassical method based on Feynman’s path-integral is in favor of uncovering the quantum tunneling effect, the classical trajectory description of the electron, and the quantum phase information, which can present an intuitive and transparent physical image of electron’s propagation in comparison with the <jats:italic>ab initio</jats:italic> time-dependent Schrödinger equation. In this review, we introduce the basic theoretical concepts and development of several semiclassical methods as well as some of their applications in strong-field physics. Special emphasis is placed on extracting time delay on attosecond scale by the combination of the semiclassical method with phase of phase method. Hundreds of millions of trajectories are generally adopted to obtain a relatively high-resolution photoelectron spectrum, which would take a large amount of time. Here we also introduce several optimization approaches of the semiclassical method to overcome the time-consuming problem of violence calculation.</jats:p>

<jats:p>To measure and control the electron motion in atoms and molecules by the strong laser field on the attosecond time scale is one of the research frontiers of atomic and molecular photophysics. It involves many new phenomena and processes and raises a series of questions of concepts, theories, and methods. Recent studies show that the Coulomb potential can cause the ionization time lag (about 100 attoseconds) between instants of the field maximum and the ionization-rate maximum. This lag can be understood as the response time of the electronic wave function to the strong-field-induced ionization event. It has a profound influence on the subsequent ultrafast dynamics of the ionized electron and can significantly change the time–frequency properties of electron trajectory (an important theoretical tool for attosecond measurement). Here, the research progress of response time and its implications on attosecond measurement are briefly introduced.</jats:p>

<jats:p>We systematically investigate the power distribution characteristics of microjets generated by prismatic scatterers with different shapes at sub-THz region (<jats:italic>λ</jats:italic> = 8.57 mm). Among these prismatic scatterers, the hexagonal-type one shows better focusing feature than the others. Aiming at the hexagonal-type one, we propose a double-layer scatterer composed of a Teflon hexagonal prism as an outer layer and a semiconductor cuboid as an inner layer. Aiming at the double-layer scatterer, we further study the effects of refractive index, size, and shape of the inner cuboid on microjet’s features. The study allows us to present an optimized double-layer scatterer, which has a side length <jats:italic>λ</jats:italic>/2 (<jats:italic>λ</jats:italic>) and a refractive index 2.0 (1.4) for the inner (outer) layer. We show that the optimized scatterer can produce an ultra-strong, ultra-narrow microjet with a power enhancement of ∼ 30 and a full width at half maximum (FWHM) of ∼ 0.26<jats:italic>λ</jats:italic>, and the microjet is just located at the output face. The microjet keeps compact within the distance range of <jats:italic>λ</jats:italic> from the output face. These features and effects are explained from the viewpoint of ray optics theory. According to the optimized double-layer scatterer, we further study the multi-frequency focusing features of the microjets, and find that the microjet remains good features at harmonic frequencies 2<jats:italic>f</jats:italic> <jats:sub>0</jats:sub> and 3<jats:italic>f</jats:italic> <jats:sub>0</jats:sub>. In addition, we investigate the effect of an Au sphere presence in the center of the microjet on the power distribution. The results show that a spherical dark spot with a size similar to that of the Au sphere emerges in the area where the Au sphere is placed. The feature can be used to measure the size of a metallic particle.</jats:p>

<jats:p>A secure encryption scheme for color images based on channel fusion and spherical diffraction is proposed in this paper. In the proposed encryption scheme, a channel fusion technology based on the discrete wavelet transformation is used to transform color images into single-channel grayscale images, firstly. In the process of transformation, the hyperchaotic system is used to permutate and diffuse the information of red–green–blue (RGB) channels to reduce the correlation of channels. Then the fused image is encrypted by spherical diffraction transform. Finally, the complex-valued diffraction result is decomposed into two real parts by the improved equal module decomposition, which are the ciphertext and the private key. Compared with the traditional color image encryption schemes that encrypt RGB channels separately, the proposed scheme is highly secure and robust.</jats:p>

<jats:p>The 808-nm vertical cavity surface emitting laser (VCSEL) with strained In<jats:sub>0.13</jats:sub>Ga<jats:sub>0.75</jats:sub>Al<jats:sub>0.12</jats:sub>As/Al<jats:sub>0.3</jats:sub>Ga<jats:sub>0.7</jats:sub>As quantum wells is designed and fabricated. Compared with the VCSELs with Al<jats:sub>0.05</jats:sub>Ga<jats:sub>0.95</jats:sub>As/Al<jats:sub>0.3</jats:sub>Ga<jats:sub>0.7</jats:sub>As quantum wells, the VCSEL with strained In<jats:sub>0.13</jats:sub>Ga<jats:sub>0.75</jats:sub>Al<jats:sub>0.12</jats:sub>As/Al<jats:sub>0.3</jats:sub>Ga<jats:sub>0.7</jats:sub>As quantum wells is demonstrated to possess higher power conversion efficiency (PCE) and better temperature stability. The maximum PCE of 43.8% for 10-μm VCSEL is achieved at an ambient temperature of 30 °C. The size-dependent thermal characteristics are also analyzed by characterizing the spectral power and output power. It demonstrates that small oxide-aperture VCSELs are advantageous for temperature-stable performance.</jats:p>

<jats:p>We experimentally engineer a high-spectral-purity single-photon source using a single-interferometer-coupled silicon microring. By the reconfiguration of the interferometer, different coupling conditions can be obtained, corresponding to different quality factors for the pump and signal/idler. The ratio between the quality factor of the pump and signal/idler ranges from 0.29 to 2.57. By constructing the signal–idler joint spectral intensity, we intuitively demonstrate the spectral correlation of the signal and idler. As the ratio between the quality factor of the pump and signal/idler increases, the spectral correlation of the signal and idler decreases, i.e., the spectral purity of the signal/idler photons increases. Furthermore, time-integrated second-order correlation of the signal photons is measured, giving a value up to 94.95 ± 3.46%. Such high-spectral-purity photons will improve the visibility of quantum interference and facilitate the development of on-chip quantum information processing.</jats:p>