Compact experimental apparatus for producing high-repetition-rate ⁸⁷Rb Bose-Einstein condensation on an atom chip

Abstract

We construct a compact experimental apparatus for producing high-repetition-rate ultra cold ⁸⁷Rb atom based on an external atom chip. Initially, we produce an atomic flux from a 2D⁺ MOT (magneto-optical trap) in a nearly isolated 2D⁺ MOT chamber and improve the flux by adjusting the cooling beam detuning of the 2D⁺ MOT. The flux is trapped in the 3D MOT for 1.2 s and is further cooled by performing compressing the MOT for 20 ms and using polarization gradient cooling for 6.2 ms. After optical pumping into the 5S F = 2 (m _F = 2) ground state, we transport atoms toward the chip surface by performing external Z coil trapping. At 1 mm below the chip surface, the external Z coil trap is completely switched to an atom chip trap by using a Z wire and a dimple wire on the chip with external bias fields. The transport and the switching take totally 520 ms. The number of atoms trapped on the atom chip is measured to be about 2 × 10⁷. After the atoms has been compressed for 100 ms to increase trap frequencies, we perform RF evaporative cooling in the RF frequency range from 32 MHz to 6.82 MHz for 2.4 seconds. The final number of atoms in the atomic cloud after RF cooling is 1.2 × 10⁵ atoms, and we are able to observe some Bose-Einstein condensation. The repetition rate for producing the condensation is 0.234 Hz. In this paper, we describe our experimental apparatus and processes.