Quantum zeno effect in Cooper-pair transport through a double-island Josephson system

Motivated by recent experiments, we analyze transport of Cooper pairs through a double-island Josephson qubit. At low bias in a certain range of gate voltages, coherent superpositions of charge states play a crucial role. Analysis of the evolution of the density matrix allows us to cover a wide range of parameters, including situations with degenerate levels, when dissipation strongly affects the coherent eigenstates. At high noise levels, the so-called Zeno effect can be observed, which slows down the transport. Our analysis explains certain features of the I-V curves, in particular, the visibility and shape of resonant peaks and lines. (C) 2003 MAIK "Nauka / Interperiodica".