Integrated optical circuits for polarisation-entangled photons

Photons are excellent candidates for benchmarking in experiments the innovative concepts and potentials of Quantum Information (QI) theory, as they are practically immune from decoherence. Experimental realizations of complex quantum optical schemes with bulk elements suffer however from severe limitations as far as stability and physical size are concerned. Integrated photonic circuits, on the contrary, due to their compact monolithic structure, easily overcome all these problems and can pave the way to out-of-lab applications of QI ideas. Anyway, they were demonstrated so far only operating with path-encoded qubits and fixed polarisation state of the photons [1,2].