Quantum information processing and quantum optics devices

This chapter presents the basic concepts necessary to use photons as physical implementations of qubits. It starts with a traditional field quantization approach in the optical domain, where it puts an emphasis on how to obtain field modes which can be used as single localizable qubits. After quickly touching on several ways of generating single photon states, it moves to more technical aspects of parametric down conversion, which up to now has been the workhorse for most of the demonstration experiments involving two or a few more qubits in entangled states of high purity. The reader should be able to understand most aspects of contemporary sources of this type. The chapter then finishes by touching upon a few qubit operations with photons, exploring the high temporal correlation of down converted photon pairs, which also allow for at least a partial Bell state analysis.