Rydberg electromagnetically induced transparency and absorption of strontium triplet states in a weak microwave field

TL;DR

This paper theoretically investigates Rydberg triplet states in strontium atoms under weak microwave fields, revealing narrow spectral features and proposing a new method for detecting weak microwave signals using resonance fluorescence.

Contribution

It introduces a novel approach to microwave sensing using Rydberg triplet states in strontium, highlighting their advantages over alkali atoms and singlet states.

Findings

Narrow transparency and absorption features depend on MW Rabi frequency.

Spectral peaks are linearly proportional to MW field strength in weak regimes.

Resonance fluorescence exhibits narrow peaks modulated by MW fields.

Abstract

We study theoretically laser excitation of Rydberg triplet states of strontium atoms in the presence of weak microwave (MW) fields. Starting from the ground state $5s^2\,^1S_0$, the Rydberg excitation is realized through the metastable, triplet $5s5p\,^3P_1$ state, whose decay rate $\gamma_2$ is $2\pi\times 7.5$ kHz, much smaller than the one in the singlet state or alkali atoms. The influences of $\gamma_2$ on the transparency and absorption spectrum in the electromagnetically induced transparency (EIT), and electromagnetically induced absorption (EIA) regime are examined. Narrow transparent windows (EIT) or absorption peaks (EIA) are found, whose distance in the spectrum depends on the Rabi frequency of the weak MW field. It is found that the spectrum exhibits higher contrast than using the singlet state or alkali atoms in typical situations. Using the metastable intermediate state, we find that resonance fluorescence of Sr gases exhibits very narrow peaks, which are modulated by the MW field. When the MW field is weaker than the probe and control light, the spectrum distance of these peaks are linearly proportional to $\Omega_m$. This allows us to propose a new way to sense very weak MW fields through resonance fluorescence. Our study shows that the Sr triplet state could be used to develop the Rydberg MW electrometry that gains unique advantages.