| Popis: |
In the last years a thorough research effort has been devoted to the experimental realization of the optimal approximations of the quantum cloning and the quantum flipping of an unknown qubit. Even if these two processes are unrealizable in their exact forms, they can be optimally approximated by the universal quantum machines: the universal optimal quantum cloning machine (UOQCM) and the universal‐NOT (U‐NOT) gate. The 1‐>1 U‐NOT gate and the 1‐>2 UOQCM have been experimentally demonstrated by adopting the process of stimulated emission into an optical parametric amplifier and by slightly modifying the quantum state teleportation protocol. In this perspective, a thorough analysis of the spin‐flipping action induced by the Faraday mirror on any qubit realized by a polarization‐encoded single photon has recently been carried out. The results of the theory show that the device acts as a non‐universal NOT gate, in full agreement with quantum mechanical expectations. All theoretical results have been substant... |
