Optical trapping of ion Coulomb crystals

TL;DR

This paper demonstrates trapping multiple ions in an optical dipole trap without radio-frequency fields, forming one-dimensional Coulomb crystals and enabling studies of collective motion and many-body physics.

Contribution

It introduces a novel optical trapping method for ions that avoids driven motion, allowing for stable Coulomb crystals and new avenues for quantum many-body experiments.

Findings

Successfully trapped and ordered up to six ions in a single-beam optical trap.

Measured normal modes and confirmed the formation of a linear Coulomb crystal.

Demonstrated the system's potential for studying quantum phase transitions.

Abstract

The electronic and motional degrees of freedom of trapped ions can be controlled and coherently coupled on the level of individual quanta. Assembling complex quantum systems ion by ion while keeping this unique level of control remains a challenging task. For many applications, linear chains of ions in conventional traps are ideally suited to address this problem. However, driven motion due to the magnetic or radio-frequency electric trapping fields sometimes limits the performance in one dimension and severely affects the extension to higher dimensional systems. Here, we report on the trapping of multiple Barium ions in a single-beam optical dipole trap without radio-frequency or additional magnetic fields. We study the persistence of order in ensembles of up to six ions within the optical trap, measure their temperature and conclude that the ions form a linear chain, commonly called a one-dimensional Coulomb crystal. As a proof-of-concept demonstration, we access the collective motion and perform spectrometry of the normal modes in the optical trap. Our system provides a platform which is free of driven motion and combines advantages of optical trapping, such as state-dependent confinement and nano-scale potentials, with the desirable properties of crystals of trapped ions, such as long-range interactions featuring collective motion. Starting with small numbers of ions, it has been proposed that these properties would allow the experimental study of many-body physics and the onset of structural quantum phase transitions between one- and two-dimensional crystals.