Dark-state suppression and optimization of laser cooling and fluorescence in a trapped alkaline-earth-metal single ion

TL;DR

This paper investigates dark state formation in a single trapped 88Sr+ ion, analyzing how to suppress these states to optimize laser cooling and fluorescence detection, with theoretical and experimental insights.

Contribution

It provides a detailed numerical and experimental analysis of dark states in trapped ions, offering methods to prevent them and enhance ion cooling and detection efficiency.

Findings

Dark states reduce scattering rates but can be suppressed.

Laser linewidths and ion motion influence dark state formation.

Experimental results agree with numerical simulations.

Abstract

We study the formation and destabilization of dark states in a single trapped 88Sr+ ion caused by the cooling and repumping laser fields required for Doppler cooling and fluorescence detection of the ion. By numerically solving the time-dependent density matrix equations for the eight-level system consisting of the sublevels of the 5s 2S1/2, 5p 2P1/2, and 4d 2D3/2 states, we analyze the different types of dark states and how to prevent them in order to maximize the scattering rate, which is crucial for both the cooling and the detection of the ion. The influence of the laser linewidths and ion motion on the scattering rate and the dark resonances is studied. The calculations are then compared with experimental results obtained with an endcap ion trap system located at the National Research Council of Canada and found to be in good agreement. The results are applicable also to other alkaline earth ions and isotopes without hyperfine structure.