Investigation of quantum information storage in rare earth doped materials
Following the explosion of interest in quantum information processing the field has now reached the point where a quantum memory is becoming a real necessity for further improvements. A quantum memory is fundamentally different from a classical memory due to the "Superposition" principle. Unlike classical information no measurement can be made on the quantum information when it is to be stored. Quantum information is also difficult to store due to its fragile nature and the need to isolate it from the surrounding environment. This thesis describes work that was carried out both to investigate and demonstrate the utility of rare earth ion dopants for quantum memories. Rare earth ion dopants are obvious choices for a quantum memory. Long coherence times in both the optical and hyperfine levels have been observed as well as optical manipulation of the nuclear spin states. The rare earth ions of interest also possess a linear Stark shift which is essential for the quantum memory under investigation here. The scheme investigated here for a quantum memory involves reversible inhomogeneous broadening achieved via macroscopic electric field gradients. The advantage that this scheme has over its competitors is its simplicity. The scheme presented here requires no optical coupling beams and t he only light interacting with the sample is the light to be stored. For that reason the scheme inherently suffers less from noise than other quantum memory proposals. These advantages meant that it was possible to demonstrate the first optical memory using reversible inhomogeneous broadening via macroscopic electric field gradients. The experiments performed in this thesis were in two main areas. The first was characterisation of the hyperfine structure of rare earth ion materials. The second area was demonstrations of reversible inhomogeneous broadening as an optical memory.
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