# Superposition of two mesoscopically distinct quantum states : coupling a Cooper-pair box to a large superconducting island

Marquardt, F. and Bruder, C.. (2001) Superposition of two mesoscopically distinct quantum states : coupling a Cooper-pair box to a large superconducting island. Physical Review B, Vol. 63, H. 5 , 054514, 6 S..

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Official URL: http://edoc.unibas.ch/dok/A5252854

We consider a system of two superconducting islands, each of which is coupled to a bulk superconductor via Josephson tunneling. One of the islands represents a Cooper-pair box, i.e., it is an effective two-level system. The other island has a smaller charging energy and approximates a harmonic oscillator. A capacitive interaction between the islands results in a dependence of the oscillator frequency on the quantum state of the box. Placing the latter in a coherent superposition of its eigenstates and exciting coherent oscillations in the large island will lead to a phase shift of these oscillations depending on the box quantum state, thereby producing a coherent superposition of two mesoscopically distinct quantum states in the large island.