A two-photon optical atomic clock using the ⁸⁷Rb 4D_J state

We investigate the prospects for realizing a portable, all-optical atomic clock with the two-photon 5S_1/2 → 4D_J transition in rubidium, using a combination of infrared and telecom laser wavelengths. The quantum-noise-limited stability is estimated to be below 10^-11/√Hz, with a limit of about 10^-12 under the assumption that the line center can be determined within a factor of 10^-3 of the natural linewidth. Leading clock systematics are expected to be the ac Stark shift resulting from trapping laser light, as well as Zeeman shifts due to applied bias magnetic fields. Our analysis includes calculations of the dynamic polarizabilities of relevant states. From our results, we identify “magic” wavelength conditions for the two-photon clock transition. This proposal benefits from low size, weight, and power (SWaP) requirements, and uncertainties that are comparable to existing rubidium-based microwave and optical clock designs. Our study could be of interest for long-distance clock comparison and quantum-communication protocols, as well as lay a foundation for novel precision measurements of low-lying D states in rubidium.