Cooling atomic ions with visible and infra-red light

TL;DR

This paper demonstrates a novel method for cooling and detecting calcium ions in a surface electrode trap using only visible and infrared lasers, enabling efficient ion control and detection.

Contribution

It introduces a new laser cooling technique combining quadrupole transition broadening with quenching, compatible with scalable quantum information processing.

Findings

Achieved background-free fluorescence detection at 393 nm.

Successfully transitioned between Doppler and sideband cooling regimes.

Demonstrated reliable recooling and ion loading from thermal atomic beam.

Abstract

We demonstrate the ability to load, cool and detect singly-charged calcium ions in a surface electrode trap using only visible and infrared lasers for the trapped-ion control. As opposed to the standard methods of cooling using dipole-allowed transitions, we combine power broadening of a quadrupole transition at 729 nm with quenching of the upper level using a dipole allowed transition at 854 nm. By observing the resulting 393 nm fluorescence we are able to perform background-free detection of the ion. We show that this system can be used to smoothly transition between the Doppler cooling and sideband cooling regimes, and verify theoretical predictions throughout this range. We achieve scattering rates which reliably allow recooling after collision events and allow ions to be loaded from a thermal atomic beam. This work is compatible with recent advances in optical waveguides, and thus opens a path in current technologies for large-scale quantum information processing. In situations where dielectric materials are placed close to trapped ions, it carries the additional advantage of using wavelengths which do not lead to significant charging, which should facilitate high rate optical interfaces between remotely held ions.