| dc.description.abstract | Trapped ions are at the forefront of the quantum information processing field. This platform has demonstrated some of the highest native gate fidelities, in addition to offering fully connected qubits with incredibly long coherence and trapping lifetimes. Among the trapped ion candidates, barium is emerging as one of the top contenders. Barium has a long lived metastable state, which can either be exploited to greatly increase the fidelity of processes like state preparation or can be used to store information in additional hyperfine levels. This attractive atomic structure, combined with the fact that many transitions fall within the visible wavelength spectrum, eases optical design and makes barium an ideal trapped ion candidate to move the technology forward.
Researchers have been working with barium ions for decades, but quickly trapping long chains of this element is more of a challenge compared with other species because it reacts in the atmosphere forming oxides and salts. Furthermore, the two most promising isotopes of barium, 137Ba+ and 133Ba+, have their own added barriers, with the former being a mere 11% naturally abundant and the latter usable in only microgram quantities due to its radioactivity. Improving the loading efficiency of these isotopes will be key to reliably generating long chains of these ions, and realizing quantum information processing with barium in the most complex trapped ion platforms the technology has to offer. To this end, we demonstrate the use of an autoionizing transition to increase our loading rate of Ba+ by a factor of 7 compared with a non-resonant photoionization scheme. We utilize the largest experimentally measured photoionization cross-section in barium, which is the most power efficient scheme that exists for generating Ba+ from neutral atoms in an isotope-selective manner. This is the first reported use of an autoionizing transition to trap Ba+ and this scheme is applicable to all isotopes of barium.
In order to further aid in trapping of the most elusive isotope, 133Ba+, methods for fabricating microgram quantity targets for ablation loading trapped ions are also presented. Loading an ion trap with microgram materials of any element is incredibly difficult, and even more so when it only exists as a salt, as is the case with 133Ba+. Heat-treatment of these salt ablation targets is shown to increase the consistency of neutral barium production as well as the lifetime of the ablation target, which will make trapping more predictable.
The work surrounding the use of a novel photoionization scheme and testing of ablation targets was done in order to facilitate the reliable trapping of long chains of Ba+ in a surface trap. The design and initial construction of an ultra-high vacuum system and the supporting optical infrastructure for eventually trapping Ba+ in a chip trap is detailed and evaluated as well. This vacuum chamber prioritizes optical access for individual addressing ions to drive laser-based gates and allow imaging of ion chains, while still maintaining sufficient optical access for multiple global addressing zones.
This chamber and experiment will serve as a platform to further probe Ba+ as a front running candidate for quantum simulation and information processing in one of the most sophisticated surface trap that exists. Finally, studies of an alternative approach for driving amplitude-modulated entangling gates between ion pairs in chains is numerically simulated. This technique leverages existing practices found in signal processing for driving spin-spin interactions in ion pairs via their collective motional modes. The purpose of this numerical project is to provide a basis for creating pulse-shapes that will entangle ions and act as a resource for when the platform has the capability to manipulate qubits. | en |
