Three-laser coherent population trapping in a multi-lambda system: theory, experiment and applications

TL;DR

This paper explores a three-laser coherent population trapping system in a multi-level ion, combining theory and experiments to enhance control and measurement capabilities, including polarization and temperature sensing.

Contribution

It introduces a multi-laser CPT scheme in a multi-level ion system, with a Floquet-based theoretical model and practical applications like vectorial polarimetry and tunable thermometry.

Findings

Extra laser can preserve or decohere dark resonances depending on power.

The Floquet-like model accurately predicts experimental spectra.

Multi-laser spectra enable vectorial polarization measurement and temperature sensing.

Abstract

We present theoretical and experimental results of coherent population trapping spectra on a multi-level $^{40}$Ca$^+$-type configuration, adding a third beam to the standard two-laser $\Lambda$ system to avoid undesired optical pumping. We show that the extra laser can preserve the nature of the dark resonances or introduce decoherence depending on its power. Experiments are carried out using a single trapped $^{40}$Ca$^+$ ion in the $S_{1/2}-P_{1/2}-D_{3/2}$ manifold. Theoretically, the problem is solved with a Floquet-like expansion of the Liouvillian that correctly predicts all of the measured spectra without the need of full time integration. As a first application of the multilaser technique, we show that the richer spectra obtained can be used as a vectorial polarimeter of one of the beams, allowing one to measure the electrical field at the ion position in any spatial direction. We also explain how our setup could realize a thermometer with tunable sensitivity and no laser-linewidth dependence.