Progress towards an EIT-based cold rubidium-87 clock

We plan to study the use of electromagnetically induced transparency (EIT) interrogation of a rubidium-87 optical molasses as a stable two-photon optical frequency reference. Ladder-type EIT addressing lower-lying Rydberg levels may exhibit a reduction in clock instability due to narrow natural linewidth while also realizing reduced Doppler broadening due to sub-Doppler temperatures in the optical molasses. We plan a comparison of stability and linewidth of EIT spectra for different upper levels of the ladder system: 5D_5/2 and 15D/16P/16D. High-duty-cycle measurement of the EIT spectrum is made possible by rapid alternation between optical cooling and EIT pulses. We plan studies of the optimization of up-time performance and light shift effects. These results will inform on the merits of further studies of EIT spectroscopy and low-Rydberg spectroscopy for cold-atom clock applications.