Experimental Observation of Spin-Exchange in Ultracold Fermi Gases

We experimentally study the spin exchange collision in ultracold~(40) K Fermi gases. The quadratic Zeeman shift,trap potential and temperature of atomic cloud will influence on the spin changing dynamics. Dependences of the spin components populations on the external bias magnetic field, the optical trap depth and the temperature of atomic cloud are experimentally investigated. The spin exchange from the initial states to the final state are observed for different initial states. This work shows an interesting process of reaching equilibrium by redistribution among the spin states with the spin exchange collision in an ultracold large-spin Fermi gas.     

39K-87Rb双组分|F=1,mF=-1>态玻色-爱因斯坦凝聚体的实验制备

本文在³⁹K-⁸⁷Rb混合气体的|F=1,mF=-1>态上获得了双组分玻色-爱因斯坦凝聚体(Bose-Einstein condensates,BECs)。由于³⁹K原子气体的背景散射长度是负值,必须利用磁场调节Feshbach共振技术来操控其散射长度,从而实现³⁹K原子气体的有效蒸发冷却。在0～200 G磁场强度范围内,我们分别测量了³⁹K-⁸⁷Rb混合气体的同核和异核Feshbach共振,并确定了它们在|1,-1>态中的散射长度与磁场的对应关系。通过优化³⁹K-⁸⁷Rb混合气体中原子种内和种间的相互作用,进一步比较了在不同磁场区域³⁹K-⁸⁷Rb混合气体的协同蒸发冷却效率。最后,实验上制备出³⁹K-⁸⁷Rb混合气体|1,-1>态的双组分BECs,同时为接下来进一步研究量子液滴等相互作用体系提供了理想的平台...     

摄像机镜头畸变的一种非量测校正方法

为了减少噪声对摄像机镜头畸变的校正结果带来的影响,提出了一种校正摄像机镜头畸变的非量测方法.先找出由直线畸变而成的曲线,再用直线段连接每条曲线的两个端点形成一些闭合曲线.把它们的面积平方和定义为畸变测度,并用遗传算法搜索畸变测度的最小值.以此得到畸变参量.计算表明,该畸变测度具有较好的抗噪声能力,而遗传算法能避免收敛于局部极小值,减少了矫正图像的均方根误差.实验表明,对多幅图像分别和联合校正,相应矫正图像之间的均方根误差较小,计算和实验郜表明该校正方法具有良好的稳健性.     

Active Learning Approach to Optimization of Experimental Control

We present a general machine learning based scheme to optimize experimental control.The method utilizes the neural network to learn the relation between the control parameters and the control goal, with which the optimal control parameters can be obtained.The main challenge of this approach is that the labeled data obtained from experiments are not abundant.The central idea of our scheme is to use the active learning to overcome this difficulty.As a demonstration example, we apply our method to ...     

Interface Width Effect on the Weakly Nonlinear Rayleigh–Taylor Instability in Spherical Geometry

Interface width effect on the spherical Rayleigh–Taylor instability in the weakly nonlinear regime is studied by numerical simulations.For Legendre perturbation mode P_n with wave number K_n and interface half-width L,the commonly adopted empirical linear growth rate formula γ_n^em(L)=γn/√1 + K_nL is found to be sufficient in spherical geometry.At the weakly nonlinear stage,the interface width affects the mode coupling processes.The development o...