Sub-Doppler magneto-optical trap temperatures measured using Rydberg tagging

We present measurements of polarization-gradient cooling in a Cs magneto-optic trap (MOT). The temperature in the MOT is found to vary linearly with the light shift. The slope gives a value of C-sigma=0.25 +/- 0.05 while the minimum temperature T-0=3.8 +/- 3.3 mu K, in agreement with measurements done in the absence of a magnetic field. The temperature is determined by using a nondestructive method which uses Rydberg time-of-flight velocity distributions of trapped atoms.