  Josephson qubits without direct interaction can be effectively coupled by
sequentially connecting them to an information bus: a current-biased large
Josephson junction treated as an oscillator with adjustable frequency. The
coupling between any qubit and the bus can be controlled by modulating the
magnetic flux applied to that qubit. This tunable and selective coupling
provides two-qubit entangled states for implementing elementary quantum logic
operations, and for experimentally testing Bell's inequality.
