Laser cooling of trapped ions in strongly inhomogeneous magnetic fields

Abstract

Hybrid traps for the simultaneous confinement of neutrals and ions have recently emerged as versatile tools for studying interactions between these species at very low temperatures. Such traps rely on the combination of different types of external fields for the confinement of either species raising the question of interactions between the individual traps. Here, the influence of a strongly inhomogeneous magnetic field used for trapping neutrals on the trapping and laser cooling of a single ${\text{Ca}}^{+}$ ion in a radiofrequency ion trap is studied theoretically using molecular-dynamics simulations based on multilevel rate equations. The inhomogeneous magnetic field couples the different components of the ion motion and introduces position-dependent Zeeman splittings. Nonetheless, laser cooling is still found to work efficiently as the ion samples different magnetic field strengths and directions along its trajectory. Offsetting the centres of the two traps generates a linear magnetic-field gradient so that multiple lasers are required to address the resulting range of Zeeman splittings in order to ensure efficient cooling. The present study yields detailed insights into the ion cooling dynamics in combined magnetic and radiofrequency electric fields relevant for the characterisation and optimisation of hybrid trapping experiments.

GRAPHICAL ABSTRACT

Keywords:

• Radiofreqeuncy ion traps
• magnetic traps
• hybrid traps
• multilevel rate equations
• molecular-dynamics simulations

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The codes used to produce the findings of this study are available on the Zenodo repository with the identifier doi:10.5281/zenodo.7445811.

Correction Statement

This article has been corrected with minor changes. These changes do not impact the academic content of the article.

Additional information

Funding

We acknowledge financial support from the Swiss National Science Foundation (Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung) [grant numbers 200021_204123 and TMAG-2_209193] as well as the University of Basel (Universität Basel).