Toward a High-Stability Coherent Population Trapping Cs Vapor-Cell Atomic Clock Using Autobalanced Ramsey Spectroscopy

Abstract

Vapor cell atomic clocks are widely appreciated for their excellent short-term fractional frequency stability and their compactness. However, they are known to suffer on medium and long time scales from significant frequency instabilities, generally attributed to light-induced frequency shift effects. In order to tackle this limitation, we investigate the application of the recently proposed auto-balanced Ramsey (ABR) interrogation protocol onto a pulsed hot vapor Cs cell clock based on coherent population trapping (CPT). We demonstrate that the ABR protocol, developed initially to probe the one-photon resonance of quantum optical clocks, can be successfully applied to a two-photon CPT resonance. The applied method, based on the alternation of two successive Ramsey-CPT sequences with unequal free-evolution times and the subsequent management of two interconnected phase and frequency servo loops, is found to allow a relevant reduction of the clock frequency sensitivity to laser power variations. This original ABR-CPT approach, combined with the implementation of advanced electronics laser power stabilization systems, yields the demonstration of a CPT-based Cs cell clock with a short-term fractional frequency stability at the level of 3.1 × 10 −13 τ −1/2 , averaging down to the level of 6 ×10 −15 at 2000 s integration time. These encouraging performances demonstrate that the use of the ABR interrogation protocol is a promising option towards the development of low drift CPT-based frequency standards. Such clocks could be attractive candidates in numerous applications including next-generation satellite-based navigation systems, secure communications, instrumentation or defense systems.

A Dual-Frequency Faraday Laser

“…Utilizing DF laser field, the fractional frequency stability of diode laser can be improved by about one order of magnitude compared to the traditional single-frequency SAS [29], [30]. Secondly, through carefully designing the cavity length of DF Faraday laser, the integer number of FSR can be exactly equal to the hyperfine frequency interval of Cs ground state, such a DF Faraday laser can be used as the coherent light source for CPT atomic clocks [31], [32], [38]. Thirdly, the DF Faraday laser, with potential in transmitting signal from optical domain to microwave domain like the frequency comb, will infuse new elements to optical generation microwave field.…”

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

“…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.…”

Ramsey-coherent population trapping Cs atomic clock based on lin∥lin optical pumping with dispersion detection*

“…Several innovative pumping schemes, including the lin⊥lin, [5] lin lin, [6] and push-pull optical pumping (PPOP) [7,11] schemes, have been demonstrated to obtain high contrast. Recently, the state-ofthe-art performance of a PPOP CPT atomic clock with a frequency stability of 3 × 10 −13 / √ τ up to 2000 s was achieved at Laboratoire National de Métrologie et d'Essais-Systèmes de Référence Temps-Espace (LNE-SYRTE) [12] by implementation of the ABR technique.…”