Dick effect in a pulsed atomic clock using Coherent Population Trapping

TL;DR

This paper analyzes the Dick effect in a pulsed CPT atomic clock, revealing its unique sensitivity function, comparing it with two-level systems, and demonstrating improved stability through oscillator optimization.

Contribution

It provides a detailed analysis of the Dick effect in pulsed CPT clocks, including a new sensitivity function formula and stability improvements.

Findings

CPT clock exhibits higher phase noise sensitivity than two-level systems.

Numerical and experimental results align well, validating the model.

Optimized quartz oscillator improves clock stability to 3.2×10⁻¹³ at 1s.

Abstract

The Dick effect can be a limitation of the achievable frequency stability of a passive atomic frequency standard when the ancillary frequency source is only periodically sampled. Here we analyze the Dick effect for a pulsed vapor cell clock using coherent population trapping (CPT). Due to its specific interrogation process without atomic preparation nor detection outside of the Ramsey pulses, it exhibits an original shape of the sensitivity function to phase noise of the oscillator. Numerical calculations using a three-level atom model are successfully compared with measurements; an approximate formula of the sensitivity function is given as an easy-to-use tool. A comparison of our CPT clock sensitivity to phase noise with a clock of the same duty cycle using a two-level system reveals a higher sensitivity in the CPT case. The influence of a free-evolution time variation and of a detection duration lengthening on this sensitivity is studied. Finally this study permitted to choose an adapted quartz oscillator and allowed an improvement of the clock fractional frequency stability at the level of 3.2x10-13 at 1s