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.
Highlights
Coulomb crystals are an intriguing form of matter
The ions are typically trapped in Paul [2] and Penning traps [3], which combine electrostatic with radio-frequency fields or magnetic fields, respectively
We demonstrate that the ensemble remains a onedimensional Coulomb crystal in the optical trap and reveal access to the axial motional modes
Summary
Coulomb crystals are an intriguing form of matter. On the one hand, it is believed that they make up the core of white dwarves and the surface of neutron stars [1]. Motion close to zero [12], but, even when assuming perfect compensation of stray electric fields, driven motion remains inevitable if ions are intrinsically displaced from the trap center, e.g., in a 2D or 3D crystal [1,13], or during the interaction with neutral atoms [14,15] In these cases, the kinetic energy of the driven motion exceeds the residual thermal energy by orders of magnitude. The kinetic energy of the driven motion exceeds the residual thermal energy by orders of magnitude This makes it challenging to extend the unique level of control and isolation available for single ions and linear chains of ions to Coulomb crystals of larger size and dimensionality. We demonstrate that the ensemble remains a onedimensional Coulomb crystal in the optical trap and reveal access to the axial motional modes
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