Quantum Computation and Quantum Coherence in Mesoscopic Josephson Junctions

Macroscopic quantum dynamics of Josephson junctions hasattracted recently renewed interest in the context of quantumcomputation. Quantum coherence of the charge states in asingle-Cooper-pair box or the flux states in an rf SQUID canbe used to create charge and flux qubits for quantumcomputation. The aim of this paper is to give a briefintroduction to the basic concepts of quantum computation withJosephson junctions and to discuss the theory of quantumcoherence in the rf-stimulated macroscopic resonanttunneling of flux in SQUID's. The results for resonant fluxtunneling show that the quantum coherent flux oscillationsshould lead to splitting of resonant tunneling peaks,indicating that the resonant tunneling can be a convenienttool for studying macroscopic quantum coherence of flux.