A lattice gas model of a single Cooper pair box

Abstract

There exists a large number of experimental and theoretical results supporting the picture of "macroscopic qubits" implemented by nanoscopic Josephson junctions. On the other hand the standard model of such systems given in terms of a single degree of freedom suggests their semiclassical behavior due to a localization mechanism caused by a strong coupling to an environment. Indeed, such a mechanism is observed in an atomic Bose-Einstein condensate (BEC) placed in a double-well potential - a system mathematically equivalent to a Josephson junction. In this note it is shown, on the example of a Cooper pair box, that replacing the BEC-type model for Cooper pairs by a lattice gas model one can reduce the environmental effects of "dequantization" and can explain the experimental data in particular the existing huge differences between the measured values of relaxation times.