  A quantum computer is a machine that can perform certain calculations much
faster than a classical computer by using the laws of quantum mechanics.
Quantum computers do not exist yet, because it is extremely difficult to
control quantum mechanical systems to the necessary degree. What is more, we do
at this moment not know which physical system is the best suited for making a
quantum computer (although we have some ideas). It is likely that a mature
quantum information processing technology will use (among others) light,
because photons are ideal carriers for quantum information. These notes are an
expanded version of the five lectures I gave on the possibility of making a
quantum computer using light, at the Summer School in Theoretical Physics in
Durban, 14-24 January, 2007. There are quite a few proposals using light for
quantum computing, and I can highlight only a few here. I will focus on
photonic qubits, and leave out continuous variables completely. I assume that
the reader is familiar with basic quantum mechanics and introductory quantum
computing.
