Realization of two-stage crossed beam cooling and the comparison with Delta-kick cooling in experiment

We report the first experimental realization of the two-stage crossed beam cooling (TSCBC) method that we proposed in 2013 [L. Wang et al., J. Phys. B: At., Mol. Opt. Phys. 46, 195302 (2013)]. With the ⁸⁷Rb Bose-Einstein condensation apparatus and electromagnet coils providing the magnetic levitation to counteract the gravitation, we simulated the micro-gravity environment and realized the TSCBC with 4 × 10^{4 87}Rb atoms. We estimated that the lowest temperature of atoms can be at 3.56 nK with a new method and verified that the cooling process is adiabatic enough with time-of-flight images. According to analysis, we believed that the noise of magnetic field was the main obstacle that hinders the further cooling of the atomic ensemble. Under the same experimental conditions, we carried out the Delta-kick cooling method and got a lowest temperature of 23.3 nK also with 4 × 10^{4 87}Rb atoms. According to the results of comparing experiments, we can see that the TSCBC method is more effective.