Noise and the Measurement Process for a Circular Josephson Array Qubit

Abstract

We discuss a charge qubit consisting of a circular array of Josephson junctions. The two-level system we consider couples the two charge states through a higher order tunneling process thus making it possible to achieve a long relaxation time. Using the spin-boson Hamiltonian, we estimate decoherence due to ohmic as well as 1/f noise. We simulate the quantum mechanical measurement process by studing the density matrix of the qubit and a capacitively coupled single-electron transistor that measures the charge.