  We propose an effective scheme for manipulating quantum information stored in
a superconducting nanocircuit. The Josephson qubits are coupled via their
separate interactions with an information bus, a large current-biased Josephson
junction treated as an oscillator with adjustable frequency. The bus is
sequentially coupled to only one qubit at a time. Distant Josephson qubits
without any direct interaction can be indirectly coupled with each other by
independently interacting with the bus sequentially, via exciting/de-exciting
vibrational quanta in the bus. This is a superconducting analog of the
successful ion trap experiments on quantum computing. Our approach differs from
previous schemes that simultaneously coupled two qubits to the bus, as opposed
to their sequential coupling considered here. The significant quantum logic
gates can be realized by using these tunable and selective couplings. The
decoherence properties of the proposed quantum system are analyzed within the
Bloch-Redfield formalism. Numerical estimations of certain important
experimental parameters are provided.
