Quantum geometry provides an intrinsic framework for characterizing the geometric structure of quantum states. It highlights its relevance to various aspects of fundamental physics. However, its direct implications for magnetic phenomena remain largely unexplored. Here, we report the observation of electric-field-induced nonlinear magnetization in the nonmagnetic semimetal WTe$_2$ by using a second-harmonic magneto-optical Kerr effect (SMOKE) spectroscopy. We observe a robust nonlinear SMOKE signal that scales quadratically with current and persists up to 200 K. Theoretical modeling and scaling analysis indicate that this nonlinear magnetization is dominated by the orbital contribution and is intrinsically linked to the quantum Christoffel symbol. Just as the Christoffel symbol is a fundamental quantity encoding spacetime geometry in Einstein's general relativity, our work establishes a direct link between quantum geometry and nonlinear magnetization, and provides a geometric perspective for designing future orbitronic devices.

Coherent control of light with electron spins represents a fundamental goal across multiple research fields, such as opto-spintronics, chiroptics, quantum information. In a magnetic-ordered material, coherent magnon gives rise to temporally and spatially modulated spin structure that may stimulate intriguing spin-photon interactions as well as opto-spintronic applications. However, the development of such magnon-photon interface is hampered due to the lack of magnetic photonic structure that embraces strong light-matter interaction. Here, we present such magnon-photon interface in a CrSBr metasurface by showing the formation of a magnetic exciton polariton bound states in the continuum, whose energy and the radiative properties can be tuned with an external magnetic field. We further show that the exciton polaritons are modulated by the coherent magnon excitation, exhibiting a nontrivial magnon mode- and k-dependent behavior which suggests the formation of hybrid magnon-exciton polariton states. Our results shed light on the interplay of spin, magnon and photon in the magnetic metasurface and provide a new platform for exploring spin functional photonic and quantum devices. This work creates a magnon-photon interface from a 2D magnetic semiconductor metasurface. It demonstrates both the static and ultrafast control of exciton polaritons with spins and coherent magnons, paving the way for spin-based photonic devices.

The quantum geometry of Bloch wavefunctions underpins a wealth of emergent phenomena in quantum materials. Its imaginary part, the Berry curvature, has long been recognized as a key source for hallmark effects such as quantum Hall and topological phenomena, etc. The real part of quantum geometry, the quantum metric, has recently garnered considerable attention due to predictions of a range of unconventional nonlinear and nonequilibrium responses. Such responses usually vanish in centrosymmetric systems, largely restricting relevant studies to non-centrosymmetric materials. Here we challenge this convention by revealing that the vanished quantum metric response can survive in a hidden form. Using a non-local photovoltaic scheme in a layered magnetic semiconductor, we spatially separate mutually compensating photocurrents and thereby detect such hidden quantum metric response. We demonstrate this effect across distinct magnetic states and down to the ultrathin limit. Moreover, we realize reconfigurable, nonvolatile and probabilistic photodetection enabled by the quantum metric response. These results not only fundamentally expand the material landscape for quantum geometric physics, but also open new gateway to harvest the quantum geometric contributions for state-of-the-art nonvolatile reprogrammable sensing and computing applications.

Spin-orbit torque (SOT)-induced deterministic control of the magnetization in ferromagnets with perpendicular magnetic anisotropy (PMA) is key to next-generation spintronic applications. However, the tunability of SOT-induced switching still requires further exploration. Here, we investigated the angle-dependent interlayer exchange coupling on all-electric magnetization switching in a Co/Pt/Co trilayer, where the two Co layers exhibit PMA and in-plane magnetic anisotropy, respectively. After pre-magnetizing the in-plane Co layer, all-electric magnetization switching was achieved through interlayer exchange coupling. By changing the pre-magnetization direction, the out-of-plane SOT efficiency in the Co/Pt/Co device can be modulated, which depends on the x-component of the interlayer exchange coupling field. Additionally, a proportional variation in the magnitude of magnetization switching was observed, which corresponds to different current-induced out-of-plane effective fields. Such modulation of SOT switching is attributed to angle-dependent interlayer exchange coupling, which could be important for developing spin devices with enhanced tunability.

We demonstrate the photon-number resolution (PNR) capability of a 1.25 GHz gated InGaAs single-photon avalanche photodiode (APD) that is equipped with a simple, low-distortion ultra-narrowband interference circuit for the rejection of its background capacitive response. Through discriminating the avalanche current amplitude, we are able to resolve up to four detected photons in a single detection gate with a detection efficiency as high as 45％. The PNR capability is limited by the avalanche current saturation, and can be increased to five photons at a lower detection efficiency of 34％. The PNR capability, combined with high efficiency and low noise, will find applications in quantum information processing technique based on photonic qubits.

Afterpulsing noise in InGaAs/InP single photon avalanche photodiodes (APDs) is caused by carrier trapping and can be suppressed successfully through limiting the avalanche charge via sub-nanosecond gating. Detection of faint avalanches requires an electronic circuit that is able to effectively remove the gate-induced capacitive response while keeping photon signals intact. Here we demonstrate a novel ultra-narrowband interference circuit (UNIC) that can reject the capacitive response by up to 80 dB per stage with little distortion to avalanche signals. Cascading two UNIC's in a readout circuit, we were able to enable a high count rate of up to 700 MC/s and a low afterpulsing of 0.5 % at a detection efficiency of 25.3 % for 1.25 GHz sinusoidally gated InGaAs/InP APDs. At a temperature of -30 ∘C, we measured an afterpulsing probability of 1 % at a detection efficiency of 21.2 %.

Enlarging antenna diameter while maintaining an accurate reflective surface is important in the development of next-generation single-dish sub-mm telescopes. In this article, we propose an emulation and optimization method of the active surface system (EOMASS) for large single-dish sub-mm telescopes. The proposed method involves three main steps: 1) building an active surface system model (ASSM) based on the whole finite element model (FEM) of the large single-dish sub-mm telescope, which includes the main reflector, realistic adjustment models of actuators, backup structure and so on; 2) emulating the reflective surface deformation compensation under gravity based on the initial distribution of the actuators with the ASSM, in consideration of the manufacturing error of panels; and 3) further optimizing the number and distribution of actuators based on the illumination function, and predicting the performance of the sub-mm antenna due to the limited number of faulty actuators. As an application example, a 60 m single-dish sub-mm telescope is analyzed under gravity with the proposed EOMASS. The results demonstrate that the proposed EOMASS is an effective and advanced method, providing a feasible precision design of the active surface system for a large single-dish sub-mm telescope.

Versatile memory is strongly desired for end users, to protect their information in the information era. In particular, bit-level switchable memory that can be switched from rewritable to read-only function would allow end users to prevent important data being tampered with. However, no such switchable memory has been reported. We demonstrate that the rewritable function can be converted into read-only function by applying a sufficiently large current pulse in a U-shaped domain-wall memory, which comprises an asymmetric Pt/Co/Ru/AlOx heterostructure with strong Dzyaloshinskii-Moriya interaction. Wafer-scale switchable magnetic domain-wall memory arrays on 4-inch Si/SiO2 substrate are demonstrated. Furthermore, we confirm that the information can be stored in rewritable or read-only states at bit level according to the security needs of end users. Our work not only provides a solution for personal confidential data, but also paves the way for developing multifunctional spintronic devices.

Here we review the spatial self-phase modulation in nonlinear refraction, with a brief introduction of the origin and development of nonlinear optics. With a powerful laser irradiating a nonlinear medium, we can observe bright and dark fringes, namely interference rings, in the far field. In this paper we analyzed the formation mechanisms of interference rings from liquid (water as an example), liquid crystal and low dimensional material suspension. For most liquids, the main reason for the formation of the interference rings is the optical path difference caused by the temperature distribution in the liquid. Because the laser light intensity has a Gaussian distribution, the liquid at different positions is heated differently, so the refractive index of local liquid is no longer the same, resulting in optical path difference (thermal lens effect). The interference rings contain abundant information about the physical properties of materials, while the thermal effect also affects the performance of optical instruments. A thorough understanding of spatial selfphase modulation will help us use or eliminate the thermal lens effect.

We report a novel ultra-narrowband interference circuit (UNIC) for low noise photon counting of 1.25GHz gated InGaAs/InP avalanche photodiodes. We achieve record-low afterpulsing probability of 0.5% at a detection efficiency of 25.3%.

世界总是在不断地变化,今天更是如此.远程医疗、数字支付和工业自动化等新技术发展迅猛,我们还必须努力发展经济、减少碳排放、应对人口老龄化问题以及利用人工智能的力量.

We look into the 2851 ^12 CO molecular clouds harboring ^13 CO structures to reveal the distribution of the projected angular separations and radial velocity separations between their internal ^13 CO structures. The projected angular separations are determined using the minimal spanning tree algorithm. We find that ∼50% of the angular separations fall in a narrow range of ∼3′–7′ with a median of ∼5′, and the corresponding radial velocity separations mainly range from ∼0.3 to 2.5 km s ^−1 . The mean and standard deviation of the angular separations of the internal ^13 CO structures within ^12 CO clouds appear to be universal, independent of the ^12 CO cloud angular areas and the counts of their internal ^13 CO structures. We also reveal a scaling relation between the ^12 CO cloud angular area and its harbored ^13 CO structure count. These results suggest there is a preferred angular separation between ^13 CO structures in these ^12 CO clouds, considering the distance effects. According to that, we propose an alternative picture for the assembly and destruction of molecular clouds: there is a fundamental separation for the internal structures of molecular clouds, the build-up and destruction of molecular clouds proceeds under this fundamental unit.

Large-aperture, single-dish, submillimeter (sub-mm)-wave telescopes are important to our understanding of the universe, but it is a long-term outstanding challenge to make the single-dish sub-mm telescopes larger while keeping a high accuracy of their surfaces. A bottleneck in the context of the size and the operating wavelengths of such telescopes is the deterioration of wavefront errors (phase shift) due to the deformation of reflective surfaces. Here proposed is a phase adaptive stabilization system (PASS), functioning as an adaptive optics system of radio frequency (RF), an essential tool for overcoming the challenge, which is based on a state-of-the-art ultrastable microwave signal distribution (UMSD) technology. The UMSD system with a phase drift of less than 11 fs rms over 600 s, is especially proposed for the PASS, which is an innovation. The results of outfield experiments have shown that the PASS is sufficiently accurate to measure the changes in the excess path length down to the level of $20~\mu \text{m}$ , which is the highest accuracy reported up to now. Our study marks a major step toward the PASS.

20世纪是物理学的时代,以相对论和量子力学为代表的新物理学不仅带来了物理学的革命,更是开辟了科学技术改造自然界和人类社会的新战场,其中影响最大的可能就是半导体科技带来的信息技术革命了.

We report on the spin and occupation noise of a single, positively charged (InGa)As quantum dot emitting photons in the telecommunication C-band. The spin noise spectroscopy measurements are carried out at a temperature of 4.2 K in dependence on intensity and detuning in the regime beyond thermal equilibrium. The spin noise spectra yield in combination with an elaborate theoretical model the hole-spin relaxation time of the positively charged quantum dot and the Auger recombination and the electron-spin relaxation time of the trion state. The extracted Auger recombination time of this quantum dot emitting at 1.55μm is comparable to the typical Auger recombination times on the order of a few μs measured in traditionally grown InAs/GaAs quantum dots emitting at around 900 nm.

In order to meet the requirements of thermostat control in the application of medium temperature calibrations, a cesium heat pipe is fabricated and it is performance under the horizontal state is determined in this work. The effects of heating powers and heating modes on frozen startup and heat transfer characteristics are experimentally examined. Increasing the heating power from 772.5 to 940.9 W, the cesium heat pipe shows the best temperature uniformity with an operating temperature of 413 degrees C and the minimum total thermal resistance of 0.042 K/W at 827.5 W, the shortest frozen startup time of 1175 s at 940.9 W. However, overheating of the cesium heat pipe happens when the heating power is increased to 980.7 W which triggers a capillary limit phenomenon, leads deteriorations of temperature uniformity and heat transfer performance. In addition, the modulated heating mode introduces a better heat transfer performance of heat pipe. For cases with the constant heating mode, the cesium heat pipe shows the effective length of the heat pipe is about 510 mm which is 85% of the total length. Comparatively, the modulated heating mode can avoid the capillary limit phenomenon and improve the operating temperature from 413 to 500 degrees C as the heating power is stepped increased to 1300.9 W. With the increasing of heating power, the vapor flow is drove farther and the effective length of the heat pipe can reach 550 mm (92% of the total length). Simultaneously, the temperature fluctuation at the end of the condenser (p(8)) is depressed for the thickness increasing of condensate film. (C) 2021 Elsevier Ltd. All rights reserved.

After morphological classification of 18,190 12 CO molecular clouds, we further investigate the properties of their internal molecular gas structures traced by the 13 CO ( J = 1−0) line emissions. Using three different methods to extract the 13 CO gas structures within each 12 CO cloud, we find that ∼15% of the 12 CO clouds (2851) have 13 CO gas structures and these 12 CO clouds contribute about 93% of the total integrated flux of 12 CO emission. In each of the 2851 12 CO clouds with 13 CO gas structures, the 13 CO emission area generally does not exceed 70% of the 12 CO emission area, and the 13 CO integrated flux does not exceed 20% of the 12 CO integrated flux. We reveal a strong correlation between the velocity-integrated intensities of 12 CO lines and those of 13 CO lines in both 12 CO and 13 CO emission regions. This indicates the H 2 column densities of molecular clouds are crucial for the 13 CO line emission. After linking the 13 CO structure detection rates of the 18,190 12 CO molecular clouds to their morphologies, i.e., nonfilaments and filaments, we find that the 13 CO gas structures are primarily detected in 12 CO clouds with filamentary morphologies. Moreover, these filaments tend to harbor more than one 13 CO structure. That demonstrates filaments not only have larger spatial scales, but also have more molecular gas structures traced by 13 CO lines, i.e., local gas density enhancements. Our results favor the turbulent compression scenario for filament formation, in which dynamical compression of turbulent flows induces local density enhancements. The nonfilaments tend to be in the low-pressure and quiescent turbulent environments of the diffuse interstellar medium.

现在的中学不讲计算(加减乘除不算的),大学前两年基本上也不涉及计算.很多大学生,包括理工科的大二学生,并不了解现代计算的威力,也不理解我们为什么要强调定性和半定量分析. 我们都听说过"摩尔定律"——信息处理能力每两年翻一番(也许还更快一些),但是很多人并不真的理解这种"指数增长"有多厉害,即使是理工科的大学生,也许还包括研究生,并不知道现代计算的威力.

Exploiting the spin degree of freedom to store and manipulate information provides a paradigm for future microelectronics. The development of van der Waals (vdW) heterostructures has created a fascinating platform for exploring spintronic properties in the two-dimensional (2D) limit. Transition-metal dichalcogenides such as tungsten diselenide (WSe2) have electronic band structures that are ideal for hosting many exotic spin–orbit phenomena. Here, we report the spin-filtering effect in all-vdW heterostructures with WSe2 barrier. Combining 2D-perpendicular magnetic anisotropy Fe3GeTe2 (FGT) with different thicknesses of WSe2, the FGT/WSe2/FGT spin valve shows distinct charge and spin transport behavior. Moreover, the negative magnetoresistance (−4.3%) could be inverted into positive magnetoresistance (up to +25.8%) with decreasing the WSe2 thickness. Furthermore, we proposed a spin-filtering model based on Δ-symmetry electrons tunneling to explain the crossover from negative to positive MR signal through ab initio calculation. These experimental and theoretical results illustrate the rich potential of the families of TMDC materials to control spin currents in 2D spintronic devices.

When white light laser is focused on liquids, colorful interference rings with different shapes, i.e. “coherent rainbows” can be seen. The formation mechanism of such coherent rainbows is described as follows. The laser heating changes the local temperature distribution of the liquid, which affects the refractive index locally and thus the optical path difference, i.e. thermal lens effect which may cause the laser to go off at large angles. The curvature of the laser wavefront and the convection and bubbles in the liquid can also play some roles as reported here. The wave front curvature results in the asymmetry of the coherent rainbows in the near of the focal point because the wave front curvature in front of the focal point is negative and the wave front curvature in the rear of the focal point is positive. The coherent rainbow has an oval shape with up-down asymmetry because convection in the locally heated liquid leads to an asymmetric temperature distribution. We construct a function including wave front curvature and thermal lens effect, and obtain the relationship between the size of the coherent rainbows and the position of the sample. As a result of the liquid instability induced by the laser heating, the temperature distribution in the liquid is no longer axisymmetric, thus, the focal length of the transverse and longitudinal thermal concave lens are no longer the same. The fitting results accord well with the experimental observations that the coherent rainbows change faster (slower) in front of (rear) the focal point and the longitudinal and transverse dimension of the coherent rainbow are different. Many tiny bubbles are generated in water in the center of the laser beam, forming a local “black barrier” which explains the observation that there are diffraction rings and Poisson-type bright spots in the dark area of the coherent rainbows. The coherent rainbows can be observed in many liquids where the shape and number of rings of coherent rainbows depend on liquid properties such as density, viscosity and thermal conductivity.