  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.
