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Effect of quantum fluctuations on even-odd energy difference in a Cooper-pair box

R. M. Lutchyn

cond-mat.supr-conarXiv:cond-mat/0612473

Abstract

We study the effect of quantum charge fluctuations on the even-odd energy difference for a small superconducting island (Cooper-pair box) connected to a large finite-size superconductor by a tunnel junction. Even-odd energy difference is important for understanding the quasiparticle "poisoning" effect, and determines the activation energy of a trapped quasiparticle in the Cooper-pair box. We find that renormalization of the activation energy due to quantum charge fluctuations depends on the dimensionless normal-state conductance of the junction gT, and becomes strong at gT >> 1.

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