Microwave Spectroscopy of Ultracold Rydberg Atoms

We have used microwave resonance techniques to measure the resonant frequencies of ns-np, ns-(n+1)s,np-(n+1)p, and nd-(n+1)d millimeter wave transitions of cold Rydberg atoms in MOT for n 27-37 in spite of the 10G/cm magnetic field gradients in the trap. We are able to observe transform limited 125kHz transition linewidths for the two photon transitions, and we have improved the quantum defects for the s,p and d states by an order of magnitude. In addition to this spectroscopic application, these narrow linewidth transitions should be a powerful tool for the study of cold dense samples of Rydberg atoms, and we are presently exploring broadening in cold dense Rydberg atom samples.