Two-Photon Laser Excitation of Rb Rydberg Atoms in the Magneto-Optical Trap and Vapor Cell

We present our experimental results of two-photon laser excitation 5S1/2 -> 5P3/2 -> nS1/2 of Rb atoms to Rydberg nS1/2 states with a homemade 480 nm laser in the second excitation step. In an experiment with cold Rb atoms, we excited the 42S1/2 state and detected Rydberg atoms with a selective-field-ionization (SFI) detector that provides single-atom resolution. The resonance line shapes well agreed with numerical simulations in a three-level theoretical model. We also studied the multiatom spectra of Rydberg excitation of mesoscopic atom ensembles which are of interest to quantum information processing. In the experiment with hot Rb atoms, we first excited the 30S1/2 state and observed a narrow Rydberg EIT resonance. Its line shape also agreed well with theory. Then, we performed a similar experiment with the higher 41S1/2 state and observed the Autler-Townes splitting of the EIT resonance in the presence of a microwave field, which was in resonance with the microwave transition 41S -> 41P3/2. This allowed us to measure the average strength of the microwave field and, thus, demonstrate the operation of a Rydberg microwave sensor. We may conclude that the developed homemade laser at 480 nm substantially extends our capabilities for further experiments on quantum information and quantum sensing with Rydberg atoms.