Development of a Portable Microwave Atomic Clock Using Pulsed Coherent Population Trapping

We propose to develop a low SWaP, portable microwave Rb-87 cold atomic clock using pulsed coherent population trapping (CPT). The SWaP goal is to achieve a volume of <1 liter, weight of <1 kG, and a power consumption of <5 Watts. The performance goal is a stability of 10^(-12) at 1 sec, <5x10^(-15) at 1 day. The specific approach we will pursue entails the following features: (a) Use pulsed CPT in the D1 manifold of trapped Rb-87 atoms, (b) Use magnetically insensitive Zeeman sublevels for the clock transition (c) Use a pi-polarized auxiliary beam to keep all atoms optically pumped into the clock levels for maximum signal, (d) use the proprietary all-glass miniature cell developed by Honeywell under the Darpa IMPACT program, with magnetic shielding added, (e) Use large trapping beam diameters to increase the signal, and (f) Suppress light-shift by saturating the CP transition during the first pulse. Honeywell and Northwestern University will be subcontractors on this project. During Phase I, we will use a conventional magneto-optic trap loaded from Rb getters to demonstrate the functionality of the clock, and produce the design for a miniaturized clock based on the Honeywell glass cell, meeting the SWaP requirements. During Phase II, we will realize the miniaturized clock, and demonstrate meeting the short and long term stability goals via studies of errors sources and mitigations thereof.