Trapping, Shaping and Isolating of Ion Coulomb Crystals via State-selective Optical Potentials

TL;DR

This paper demonstrates state-dependent optical trapping of ion Coulomb crystals, enabling selective removal and purification of ions based on electronic states, which enhances control over ion arrangements in quantum experiments.

Contribution

It introduces experimental methods for using optical dipole potentials to trap, shape, and isolate ions in specific electronic states within Coulomb crystals, improving ion manipulation techniques.

Findings

State-dependent optical potentials were characterized at 532 nm and 1064 nm.

Selective removal of ions from Coulomb crystals was achieved.

Reliable isolation of single ions within Coulomb crystals was demonstrated.

Abstract

For conventional ion traps, the trapping potential is close to independent of the electronic state, providing confinement for ions dependent primarily on their charge-to-mass ratio $Q/m$. In contrast, storing ions within an optical dipole trap results in state-dependent confinement. Here we experimentally study optical dipole potentials for $^{138}\mathrm{Ba}^+$ ions stored within two distinctive traps operating at 532 nm and 1064 nm. We prepare the ions in either the $6\mathrm{S}_{\mathrm{1/2}}$ electronic ground or the $5\mathrm{D}_{\mathrm{3/2}}$/ $5\mathrm{D}_{\mathrm{5/2}}$ metastable excited state and probe the relative strength and polarity of the potential. On the one hand, we apply our findings to selectively remove ions from a Coulomb crystal, despite all ions sharing the same $Q/m$. On the other hand, we deterministically purify the trapping volume from parasitic ions in higher-energy orbits, resulting in reliable isolation of Coulomb crystals down to a single ion within a radio-frequency trap.