Strongly coupled Yb atoms in a high finesse cavity: Lasing and spectral dynamics

Cavity QED with cold atoms plays a crucial role in exploring controllable light-matter interactions enabling advances in active optical clocks, precision measurements and fundamental physics. We report on the investigation of optical gain and lasing emission on a semi-forbidden transition from an ensemble of a few thousand Yb atoms [1]. The atoms are side-pumped on their ¹𝑆₀ −¹𝑃₁ transition at 399 nm and ¹𝑆₀ −³𝑃₁ intercombination transition at 556 nm in a magneto-optical trap configuration inside a high finesse cavity. We have analyzed this two-photon, continuous wave lasing process using heterodyne detection techniques and modeled an empirical framework based on the Bloch equations [2]. Employing a trapping scheme solely on the intercombination line results in a colder, denser atomic ensemble, facilitating the collective strong coupling regime in cavity QED [3]. In this setting, we observe additional frequency-shifted light scattering outside the lasing regime. We explore the statistics and, by heterodyne analysis, the frequency characteristics of this cavity output as a function of system parameters. We developed a mean-field model to describe the complex dynamics of the atom number dependent phenomena that emerge from the strongly nonlinear interactions.

[1] H. Gothe, D. Sholokhov, A. Breunig, M. Steinel, J. Eschner, Phys. Rev. A 99, 013415 (2019)

[2] D. Sholokhov, S. Shaju, K. Li, S. B. Jäger, J. Eschner, arXiv:2404.16765 (2024). 

[3] S. Shaju, D. Sholokhov, S. B. Jäger, J. Eschner, arXiv:2404.12173 (2024).