PhD Thesis
My PhD Thesis entitled "Non-classical states of light" (2010).
Abstract
Optical quantum computing, quantum information and quantum communication protocols rely on the generation of qubits encoded in optical systems, many of which can be generated via the process of spontaneous parametric down-conversion. In this thesis, we investigate down-converted states in the context of quantum computing and quantum information.
In the high gain regime, a type I down-converted state can be described as a single-mode squeezed vacuum state. We present an analysis of photon-subtracted squeezed vacuum states as a resource for teleportation of coherent state qubits and propose proof-of-principle experiments for the demonstration of coherent-state teleportation and entanglement swapping.
In the low gain regime, the output state of a type II parametric down-converter can be approximated as containing pairs of single photons, which can be used to herald the presence of one- or two-photon Fock states in one mode, conditional on the detection of the same number of photons in the other mode. We explore the effects of spectral filtering and inefficient detection, of the heralding mode, on the count rate, g(2) and purity of the heralded state, as well as the fidelity between the resulting state and an ideal Fock state.
We also develop a technique for controlling the joint spectral profile of the down-converted photons. By exploiting the dependence of the effective nonlinearity of a periodically poled crystal on its poling order, we tailor the nonlinearity profile and therefore the phase matching function of the down-converted photons.
Finally, we consider the validity of the Taylor series expansion of the unitary operator which governs the evolution of the fields within the crystal, in comparison to the strictly correct time-ordered Dyson series expansion.