Background-free detection of trapped ions

TL;DR

This paper presents a background-free detection method for trapped ions that significantly reduces scattered laser light background while maintaining high fluorescence, beneficial for surface-proximate ion trapping experiments.

Contribution

A novel detection scheme using selective fluorescence filtering that suppresses laser scatter and enhances signal in ion trapping experiments.

Findings

Background count rate reduced to 1 per second

Fluorescence signal maintained at 29,000 per second

Effective cooling with minimal background noise

Abstract

We demonstrate a Doppler cooling and detection scheme for ions with low-lying D levels which almost entirely suppresses scattered laser light background, while retaining a high fluorescence signal and efficient cooling. We cool a single ion with a laser on the 2S1/2 to 2P1/2 transition as usual, but repump via the 2P3/2 level. By filtering out light on the cooling transition and detecting only the fluorescence from the 2P_3/2 to 2S1/2 decays, we suppress the scattered laser light background count rate to 1 per second while maintaining a signal of 29000 per second with moderate saturation of the cooling transition. This scheme will be particularly useful for experiments where ions are trapped in close proximity to surfaces, such as the trap electrodes in microfabricated ion traps, which leads to high background scatter from the cooling beam.