An EIT-based cold rubidium-87 clock using a low-lying Rydberg level

Here we present the progress in studying the efficacy of a two-photon rubidium-87 clock utilizing the 5S_1/2 → 5P_3/2 → 18S_1/2 electromagnetically induced transparency (EIT) ladder state. A laser-cooled rubidium molasses is prepared for interrogation using red-detuned cooling beams and a polarization gradient cooling stage to reach sub-Doppler temperatures. A D₂ probe laser and a 490 nm control beam locked to a high-finesse optical cavity are used to create the EIT state. A high duty-cycle clock measurement is planned by rapidly alternating between the EIT and optical cooling pulses, ideally optimizing the recapture vs. clock cycle readout time. We also plan to study alternative upper-level EIT states and decay paths that may affect stability and linewidth; higher level Rydberg states are more susceptible to the deleterious effects of black-body radiation (BBR).