This thesis presents a spectroscopic study of the 7F0 ---t5D0 transition of Eu3+ in EuC13 ·6H2 0,
which is used to evaluate the potential performance of a quantum com puting system implemented in
EuCla·6H2 0 and, more generally, in stoichiometric rare earth crystals.
EuC13 ·6H2 0 has one of the narrowest optical inhomogeneous linewidths of any solid but this
linewidth is shown to be still much larger than that required for practical quantum computing in a
rare earth crystal. To assess the possibility of reducing the linwidth, the contributions of
isotopic impurities to both the optical linewidth and line structure were investigated, and ligand
isotopes were identified as a major source of both inhomogeneous broadening and structure on the
optical transition, suggesting that the linewidth could be substantially reduced by isotopi cally
purifying EuC13 ·6H20. The effect of ligand isotopes on the optical lifetime and coherence time was
also investigated. It was found that fully deuterating the crystal to EuC13·6D20 substantially
improves both the lifetime and coherence time.
The satellite lines formed in the optical spectrum of a rare earth crystal when
it is doped with another rare earth are proposed as qubits. A crucial step in char acterising
EuCla ·6H20 for quantum computing is associating these satellite lines in EuC13 ·6H2 0 with
crystallographic sites. A new method for associating sites with lines, which works for low symmetry
crystals such as EuC13·6H20, is presented. This method involves modelling the splitting of the
ground state hyperfine levels caused by the magnetic dipole-dipole interaction between a Kramers
dopant and the Eu3+ ion. Using this method, most of the outer satellite lines in rare earth doped
EuCla·6H2 0 were assigned to crystallographic sites.
It has been proposed that the electronic interactions between these satellite lines
be used to enact two-qubit gates in a rare earth quantum computer. These interac tions were
measured between a number of different satellite lines using a new two laser spectral holeburning
technique. Interactions of up to 46.081±0.005 MHz were observed, and this was the first time that
electronic interactions between weakly coupled rare earth ions had been measured. The two most
common interactions identified between rare earth ions in solids are electric dipole-dipole and
exchange, but the observed interactions are stronger than expected from a electric dipole-dipole
model and occur at too large a distance to be superexchange.
It is shown that the development of a moderate-sized quantum processor, one
with more than 10 qubits, in a stoichiometric rare earth crystal is feasible provided that the
optical inhomogeneous linewidth is reduced below 1MHz. Demonstrations of three or four qubit
devices should be possible using existing materials