Single barium ion spectroscopy: light shifts, hyperfine structure, and progress on an optical frequency standard and atomic parity violation

Abstract

Single trapped ions are ideal systems in which to test atomic physics at high precision: they are effectively isolated atoms held at rest and largely free from perturbing interactions. This thesis describes several projects developed to study the structure of singly-ionized barium and more fundamental physics.First, we describe a spin-dependent 'electron-shelving' scheme that allows us to perform single ion electron spin resonance experiments in both the ground 6S1/2 and metastable 5D 3/2 states at precision levels of 10-5. We employ this technique to measure the ratio of off resonant light shifts (or ac-Stark effect) in these states to a precision of 10-3 at two different wavelengths. These results constitute a new high precision test of heavy-atom atomic theory. Such experimental tests in Ba+ are in high demand since knowledge of key dipole matrix elements is currently limited to about 5%. Ba + has recently been the subject of theoretical interest towards a test of atomic parity violation for which knowledge of dipole matrix elements is an important prerequisite. We summarize this parity violation experimental concept and describe new ideas.During the study of the nuclear spinless (I = 0) isotope of Ba+, we discovered several worthwhile experimental goals for an isotope with nuclear spin, 137Ba+ ( I = 3/2). The hyperfine structure of the metastable 5D 3/2 state is currently known to a precision 10-4. We show how our rf spin-flip spectroscopy scheme could measure this structure to parts in 10-8 or better, allowing a determination of the nuclear magnetic dipole, electric quadrupole, and perhaps magnetic octopole moments.Finally, the hyperfine structure of 137Ba+ yields an optical transition with unique advantages in a single ion optical frequency reference. Namely, the 2051 nm 6S1/2, F = 2 ↔ 5D3/2, F' = 0 transition is effectively free of quadrupole (or gradient) Stark shifts which may plague competing ion frequency references at the 10 -16 level. We describe the performance and frequency narrowing of a diode-pumped solid state 2051 nm laser, and the observation of transitions in Ba+. We also estimate all known systematic effects on this transition and conclude that the realization of a frequency standard with long-term precision of < 10-17 is possible at cryogenic temperatures.