The temporal evolutions of electron density and plasma diameter of 1 kHz femtosecond laser filament in air are experimentally investigated by utilizing a pump-probe longitudinal diffraction method.A model based on scalar diffraction theory is proposed to extract the spatial phase shift of the probe pulse from the diffraction patterns by the laser air plasma channel.The hydrodynamic effect on plasma evolution at 1 kHz filament is included and analyzed.The measured initial peak electron density of~10^(18)cm^(-3) in our experimental conditions decays rapidly by nearly two orders of magnitude within200 ps.Moreover,the plasma channel size rises from 90μm to 120μm as the delay time increases.The experimental observation is in agreement with numerical simulation results by solving the rate equations of the charged particles.
The experiment of PCD cutter and YG6X cutter milling SiCp/Al matrix composites was conducted, and the effect of tool material and machining parameters on cutting force and surface roughness was investigated, and the milling process of PCD tool was simulated with finite element software. The results showed that the axial thrust force was larger than the other two while precision milling 45% volume SiCp/Al matrix composites by YG6X tool, which resulting from great compressive strength of the material. The cutting force of PCD tool was much smaller than that of the YG6X, and the surface roughness of PCD tool was also smaller. Considering the cutting force and machining surface quality, YG6X should be used for rough machining, and PCD should be used for precision machining. The results of finite element simulation of PCD tools were in good agreement with experimental results, which can provide basis for production.
Cloud-based quantum computing is anticipated to be the most useful and reachable form for public users to experience with the power of quantum. As initial attempts, IBM Q has launched influential cloud services on a superconducting quantum processor in 2016, but no other platforms has followed up yet. Here,we report our new cloud quantum computing service – NMRCloud Q(http://nmrcloudq.com/zh-hans/),where nuclear magnetic resonance, one of the pioneer platforms with mature techniques in experimental quantum computing, plays as the role of implementing computing tasks. Our service provides a comprehensive software environment preconfigured with a list of quantum information processing packages,and aims to be freely accessible to either amateurs that look forward to keeping pace with this quantum era or professionals that are interested in carrying out real quantum computing experiments in person. In our current version, four qubits are already usable with in average 99.10% single-qubit gate fidelity and 97.15% two-qubit fidelity via randomized benchmaking tests. Improved control precisions as well as a new seven-qubit processor are also in preparation and will be available later.
High-strain InGaAs/GaAs quantum wells （QWs） are grown by low-pressure metal-organic chemical vapor deposition （LP-MOCVD）. Photoluminescence （PL） at room temperature is applied for evaluation of the optical property. The influence of growth temperature, V/III ratio, and growth rate on PL characteristic are investigated. It is found that the growth temperature and V/III ratio have strong effects on the peak wavelength and PL intensity. The full-width at half-maximum （FWHM） of PL peak increases with higher growth rate of InGaAs layer. The FWHM of the PL peak located at 1039 nm is 20.1 meV, which grows at 600 ℃ with V/ III ratio of 42.7 and growth rate of 0.96 μm/h.
