NASA’s Cold Atom Lab (CAL): system development and ground test status

False color absorption images of 87Rb and 39K after 3？ms of expansion from an atom chip trap at five different stages of microwave-induced evaporation of rubidium and the corresponding sympathetic cooling of potassium. Higher temperature/atom number data are shown for illustrative purposes. The 39K atoms loaded onto the chip are initially so diffuse that our imaging fails to detect them. The last stage shows 70,000 39K atoms at a temperature of 1.6？μK and phase space density (PSD) of 0.05. 87Rb numbers in the final stage are 155,000 atoms at a temperature of 1.6？μK and a PSD of 0.02