  Starting from the reduced dynamical model of a two-junction quantum
interference device, a quantum analog of the system has been exhibited, in
order to extend the well known properties of this device to the quantum regime.
By finding eigenvalues of the corresponding Hamiltonian operator, the
persistent currents flowing in the ring have been obtained. The resulting
quantum analog of the overdamped two-junction quantum interference device can
be seen as a supercurrent qubit operating in the limit of negligible
capacitance and finite inductance.
