Cold Optical Rubidium Atomic Frequency Standard

Vescent Photonics in collaboration with ColdQuanta proposes to design, build, and deliver a portable atomic clock capable of meeting the Army’s requirements for frequency stability as well as size, weight, and power (SWaP). The proposed Cold Optical Rubidium Atomic Frequency Standard (CORAFS) will provide a precision timing and frequency reference for deployment on mobile platforms, where it is uniquely qualified to synchronize advanced communications networks and enable assured positioning, navigation, and timing in GPS-denied environments. CORAFS improves upon existing cold atom microwave clocks by interrogating the two-photon optical clock transition at 778 nm in a cold sample of rubidium (Rb) atoms to achieve a higher quality factor, and hence better stability, than afforded by probing the conventional microwave clock transition. Hot vapor-cell-based optical clocks based on the two-photon Rb clock transition have previously been demonstrated and validated by the AFRL to have instabilities of <4e-13 in one second. Further improvements to this clock can be made by probing a cold atom sample rather than a hot vapor, but, until recently, the requisite technologies for realizing a fieldable cold-atom optical clock were not mature enough to meet requirements for operational reliability and size, weight, and power (SWaP). Technology and product development efforts by both Vescent and ColdQuanta have significantly evolved the critical infrastructure needed for bringing cold-atom optical clocks from the laboratory to the field. For instance, Vescent has already commercially developed and demonstrated the necessary low-SWaP laser systems critical to CORAFS, namely the optical frequency comb and the trapping/cooling lasers, and ColdQuanta, a recognized leader in compact integrated systems for cold matter applications, has proven expertise in building ruggedized ultracold Rb physics packages for atomic clocks. For this development effort, the two companies will bring together highly skilled experts in cold-atom and optical clocks to integrate their existing component technologies into a novel portable atomic clock that is capable of <3e-13 fractional instability in 1 second and reaching an expected flicker floor at <1e-14 instability.