Compact cold atom microwave clock for GPS-denied environments

Microwave atomic clocks are near-term solutions for commercial GPS-like timing and holdover services. Cold atoms provide environmental decoupling and lasers eliminate bulky microwave cavities. Our objective is to miniaturize a cold rubidium microwave clock with rapid startup and a design optimized for manufacturability. A magneto-optical trap cools atoms that are probed using a laser-based coherent population trapping technique. To achieve our goal, we fabricated a miniaturized ultra-high vacuum cell, ion pump, atom source, optics, and an integrated control system. The entire device fits into a 25-liter rack mounted chassis. It is tolerant to orientation and acceleration. The electromagnetically induced transparency contrast approaches unity, producing strong Ramsey fringes with widths of tens of Hertz. Frequency stability, better than 10^-11 at one second, is comparable to commercial standards, but with reduced size and weight. This work has set the stage for our development of dramatically more precise optical standards. We demonstrate several two-photon rubidium schemes based on both thermal vapors and cold atoms. For example, our prototype thermal vapor approach yields sub-10^-12 performance at one second and long-term performance near 10^-15 with competitive size and weight characteristics.