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 10 4 s averaging time. Additional tricks, including a compensation method to reduce the laser AM noise contribution and the generation of novel error signals for LO 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 factor 2. The Allan deviation of the SABR-CPT clock, extracted from a selected 3 × 10 4 s-long dataset, is 2 × 10 −13 τ −1/2 and averages down to the level of 2.5 × 10 −15 at 10 4 s. These results are encouraging to stimulate the development of hot cell CPT-based clocks for industrial, scientific, and instrumentation applications.

Combined error signal in Ramsey spectroscopy of clock transitions

“…The implementation of this approach can lead to significant improvement of the accuracy and long-term stability for a variety of types of atomic clocks. Also, it will be interesting to experimentally compare the one-loop CES/GCES method with the two-loop ABRS [37][38][39]. We believe that both methods have comparable efficiency for frequency stabilization, but CES/ GCES is technically simpler because only one feedback loop is required.…”

“…Auto-balanced Ramsey spectroscopy (ABRS) is another effective approach that was first experimentally demonstrated in a 171 Yb + ion clock [37]. This intuitive approach was rigorously substantiated and generalized theoretically in [38], and also recently realized in a CPT atomic clock [39]. For ABRS, in addition to the stabilization of the clock frequency ω, a second loop controls a variable second (concomitant) parameter ξ, which is an adjustable property of the first and/or second Ramsey pulses.…”

General Methods for Suppressing the Light Shift in Atomic Clocks Using Power Modulation

“…Thus, we have shown that the PM-ACS method always leads to zero shift of the stabilized frequency ω in an atomic clock,δ clock = 0. Note that in the general case the convergence of the joint iterative procedures (16) and (17) to the values (20) FIG. 5.…”

“…This condition, when applied to both operating powers, P 1 and P 2 , is equivalent to Eqs. (19)- (20).…”

“…This approach was rigorously substantiated and generalized in Ref. [18], and also recently realized in atomic clocks based on coherent population trapping (CPT) [19][20][21]. In ABR spectroscopy, two Ramsey sequences with different Ramsey times are used.…”