  We study an LC-circuit implemented using a current-biased Josephson junction
(CBJJ) as a tunable coupler for superconducting qubits. By modulating the bias
current, the junction can be tuned in and out of resonance and entangled with
the qubits coupled to it. One can thus implement two-qubit operations by
mediating entanglement. We consider the examples of CBJJ and charge--phase
qubits. A simple recoupling scheme leads to a generalization to arbitrary qubit
designs.
