Comparison of different techniques in optical trap for generating picokelvin 3D atom cloud in microgravity

Pursuing ultralow temperature 3D atom gas under microgravity conditions is one of the popular topics in the field of ultracold research. Many groups around the world are using, or are planning to use, delta-kick cooling (DKC) in microgravity. Our group has also proposed a two-stage crossed beam cooling (TSCBC) method that also provides a path to picokelvin temperatures. In this paper, we compare the characteristics of TSCBC and DKC for producing a picokelvin system in microgravity. Using a direct simulation Monte Carlo (DSMC) method, we simulate the cooling process of 87Rb using the two different cooling techniques. Under the same initial conditions, 87Rb can reach 7 pK in 15 s using TSCBC and 75 pK in 5.1 s with DKC. The simulation results show that TSCBC can reach lower temperatures compared with DKC, but needs more time and a more stable laser.