Active compensation of the AC Stark shift in a two-photon rubidium optical frequency reference using power modulation

TL;DR

This paper presents a feedback method to actively compensate for the AC Stark shift in a rubidium two-photon optical frequency reference, significantly improving its stability and reducing sensitivity to power fluctuations.

Contribution

The authors develop and demonstrate a power modulation feedback protocol that suppresses the AC Stark shift by a factor of 1000, enhancing the stability of rubidium optical clocks.

Findings

Reduced sensitivity to optical power variations by a factor of 1000

Achieved instabilities of 3×10⁻¹⁴ at 1 s and 2×10⁻¹⁴ at 10⁴ s

Identified a stability limit imposed by local oscillator frequency noise

Abstract

We implement a feedback protocol to suppress the AC Stark shift in a two-photon rubidium optical frequency reference, reducing its sensitivity to optical power variations by a factor of 1000. This method alleviates the tradeoff between short-term and long-term stability imposed by the AC Stark shift, enabling us to simultaneously achieve instabilities of $3\times10^{-14}$ at 1 s and $2\times10^{-14}$ at $10^4$ s. We also quantitatively describe, and experimentally explore, a stability limit imposed on clocks using this method by frequency noise on the local oscillator.