Driving alkali Rydberg transitions with a phase-modulated optical lattice

TL;DR

This paper introduces a phase-modulated optical lattice technique for high-precision, Doppler-free spectroscopy of Rydberg-Rydberg transitions in cold rubidium atoms, enabling new quantum control applications.

Contribution

The authors develop a novel spectroscopic method using phase-controlled standing-wave laser fields to probe Rydberg transitions via ponderomotive interactions, expanding accessible frequency ranges without increased laser power.

Findings

Spectroscopic method successfully probes 40-70 GHz Rydberg transitions.

Spectra exhibit Doppler-free, Fourier-limited components.

Measurements align well with theoretical simulations.

Abstract

We develop and demonstrate a spectroscopic method for Rydberg-Rydberg transitions using a phase-controlled and -modulated, standing-wave laser field focused on a cloud of cold $^{85}$Rb Rydberg atoms. The method is based on the ponderomotive (${\bf{A}}^2$) interaction of the Rydberg electron, which has less-restrictive selection rules than electric-dipole couplings, allowing us to probe both $nS_{1/2}\rightarrow nP_{1/2}$ and $nS_{1/2}\rightarrow (n+1)S_{1/2}$ transitions in first-order. Without any need to increase laser power, third and fourth-order sub-harmonic drives are employed to access Rydberg transitions in the 40 to 70 GHz frequency range using widely-available optical phase modulators in the Ku-band (12 to 18 GHz). Measurements agree well with simulations based on the model we develop. The spectra have prominent Doppler-free, Fourier-limited components. The method paves the way for optical Doppler-free high-precision spectroscopy of Rydberg-Rydberg transitions and for spatially-selective qubit manipulation with $\mu$m-scale resolution in Rydberg-based simulators and quantum computers.