Symmetric autobalanced Ramsey interrogation for high-performance coherent-population-trapping vapor-cell atomic clock

Abstract

We report a high-performance pulsed coherent population trapping (CPT) Cs cell atomic clock using the implementation of a symmetric auto-balanced Ramsey (SABR) interrogation sequence. The latter method is found to reduce the light-power induced frequency shift by an order of magnitude compared to a previous experiment using a simple auto-balanced Ramsey interrogation. The contribution of this shift to the clock frequency stability is now rejected in the 10−16 range at 104 s averaging time. Additional tricks, including a compensation method to reduce the laser amplitude noise contribution and the generation of novel error signals for local oscillator frequency and phase correction, have been implemented using a FPGA-based digital electronics board in order to improve the clock short-term stability by a of factor 2. The Allan deviation of the SABR-CPT clock, extracted from a selected 3 × 104 s-long dataset, is 2 × 10−13 τ−1∕2 and averages down to the level of 2.5 × 10−15 at 104 s. These results are encouraging to stimulate the development of hot cell CPT-based clocks for industrial, scientific, and instrumentation applications.