Quantum computation with persistent-current Aharonov-Bohm qubits and qugates

We analyse the possibility of employing mesoscopic or nanoscopic rings of a normal metal in a double degenerate persistent-current state in the presence of the Aharonov-Bohm flux equal to the half flux quantum as entangled quantum bits of information (qu-bits). The third level in a three-state qubit can be effectively used to coherently couple the qu-bit to logical gates for the reversible NOT (in a single qu-bit) and CNOT (in two coupled qu-bits) operations. Further we suggest that a (hypothetic) crystal implementing conducting ring-shaped molecules, or triples of anionic vacancies (similar to F 3-centers in alkali halides) with one trapped electron, in crossed magnetic and electric fields satisfies the requirements of the proposed mechanism and may serve as a new kind of device for universal quantum computation.