Active light shift stabilization in modulated CPT clocks.

This paper demonstrates a simple technique to significantly improve the long-term frequency stability in atomic clocks based on coherent population trapping (CPT). In this technique, a servo is used to control the local oscillator power level in such a way that the optical spectrum generates no net light shift. This ensures that the clock frequency is always given by the atomic resonance frequency that is not perturbed by the incident light fields