AC Stark Shifts of Dark Resonances Probed with Ramsey Spectroscopy

TL;DR

This paper investigates the off-resonant AC Stark shift in CPT resonances using Ramsey spectroscopy, demonstrating experimental and theoretical agreement and identifying conditions where the shift cancels out.

Contribution

It provides a simple theoretical model for the AC Stark shift in CPT Ramsey spectroscopy and confirms its predictions with experimental data on rubidium atoms.

Findings

The shift depends on the relative intensity of the CPT light fields.

The shift is weakly dependent on total light intensity.

Certain interrogation schemes can nullify the off-resonant shift.

Abstract

The off-resonant AC Stark shift for coherent population trapping (CPT) resonances probed with Ramsey spectroscopy is investigated experimentally and theoretically. Measurements with laser-cooled $^{87}$Rb atoms show excellent quantitative agreement with a simple theory. The shift depends on the relative intensity of the two CPT light fields, but depends only weakly on the total intensity. Since the origin of the shift is through couplings of the interrogation light to off-resonant excited state hyperfine levels, the size and sign of the shift depend on the specific interrogation scheme. However, the simple theory shows that for several commonly used interrogation schemes the off-resonant shift goes to zero at specific values of this relative intensity.