Quantum spin-flipping by the Faraday mirror

The paper gives a thorough analysis of the spin-flipping action induced by the Faraday mirror on any qubit realized by a polarization-encoded single photon. The results of the theory show that the device acts as a nonuniversal NOT gate, in full agreement with quantum mechanical expectations. Furthermore, the universal optical compensation method devised by Martinelli, of common use in long distance quantum-cryptography, has been analyzed. All theoretical results are substantiated experimentally by the modern methods of quantum state tomography and entanglement-assisted quantum process tomography.