Identification of Resonantly Coupled Ion Pairs in Eu3+:Y2SiO5

Abstract

Rare-earth-ion-doped crystals are being increasingly studied for quantum information, due to their highly coherent and long-lived optical and spin levels. In these systems, interactions between dopants form the basis of quantum computation. However, these interactions remains poorly understood at small inter-ion distances. In particular, there has been little work toward understanding off-diagonal interactions, which delocalise the excited states of the two interacting ions. This thesis presents an experimental investigation into the off-diagonal resonant coupling interaction that arises between symmetry-related pairs of Eu3+ ions in Eu3+:Y2SiO5, to investigate both its strength and extent. The strength determines the variation of the coupled ion properties from their uncoupled counterparts, while the extent informs on the number of impacted ions. This thesis presents two new methods for the identification of resonantly coupled ion pairs in rare-earth-ion-doped materials. The first method uses variations in both the frequency and homogeneity of the optical and hyperfine transitions to identify ion pairs with strong resonant coupling interactions. Using this method, I have identified three resonantly coupled ion pairs. The second method uses the change in the permanent electric dipole moment due to the delocalisation of the excited states to identify ion pairs with weaker resonant coupling interactions. Using this method, I identified an additional two resonantly coupled ion pairs. The strength of the resonant coupling interaction can theoretically be deduced from this method. I present the first steps to this analysis, and highlight the current limitations to this approach. The strength of the interaction is additionally investigated through changes to the transition selection rules that are induced by the delocalisation of the excited states. Using this method, I determine the interaction strength for one resonantly coupled ion pair and provide an estimate for the remaining pairs. The number of observed resonantly coupled ion pairs is used to produce a lower bound on the extent of the interaction.