Photons as Qubits for the Quantum Computer?

We analyze a simple and one of the oldest algorithms for the quantum computer to illustrate its principles and the requirements of its fundamental concept - the quantum bit or qubit. Single photons seem to be possible candidates for qubits: they can be superimposed, they evolve and interfere in a classical optical assembly with lenses, mirrors and optical fibers and they can be entangled in the quantum sense like qubits. The latter peculiarity is already applied for quantum cryptography and teleportation. In addition optical components and gates for the binary computer are well known. We discuss the possibilities of using photons in quantum computing and their limits with the help of the example of the Deutsch-problem and give an introduction into its quantum algorithm. 100