Trapping, shaping, and isolating of an ion Coulomb crystal via state-selective optical potentials
Pascal Weckesser, Fabian Thielemann, Daniel Hoenig, Alexander Lambrecht, Leon Karpa, Tobias Schaetz
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 and 1064 nm. We prepare the ions in either the electronic ground ($6{S}_{1/2}$) or one of the metastable excited states ($5{D}_{3/2}$ or $5{D}_{5/2}$) 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.