A compact microchip atomic clock based on all-optical interrogation of ultra-cold trapped Rb atoms

Abstract

We propose a compact atomic clock that uses all-optical interrogation of ultra-cold Rb atoms that are magnetically trapped near the surface of an atom microchip. The interrogation scheme, which combines electromagnetically induced transparency with Ramsey’s method of separated oscillatory fields, can achieve an atomic shot-noise-level performance better than $10^{-13}/\sqrt{\tau}$ for 10⁶ atoms. A two-color Mach–Zehnder interferometer can detect a 100-pW probe beam at the optical shot-noise level using conventional photodetectors. This measurement scheme is nondestructive and therefore can be used to increase the operational duty cycle by reusing the trapped atoms for multiple clock cycles. Numerical calculations of the density matrix equations are used to identify realistic operating parameters at which AC Stark shifts are eliminated. By considering fluctuations in these parameters, we estimate that AC Stark shifts can be canceled to a level better than 2×10⁻¹⁴. An overview of the apparatus is presented with estimates of cycle time and power consumption.