  In quantum information and communication, optical schemes provide simple and
intuitive experimental implementations. Of particular importance is quantum
state preparation. In this thesis, the creation of polarisation entanglement
using a particular class of optical circuits is studied. I give a mathematical
description of this class of circuits in terms of Hermite polynomials. In this
context, single photon resolution and single photon sensitivity detectors are
discussed and compared with detector cascading. In addition, I study
applications of state preparation such as quantum teleportation and quantum
lithography.
