qubits in superconducting quantum circuits. Following this approach, we implement a
tunable coupling scheme between two flux qubits. The qubits are coupled parametrically
under microwave driving via the nonlinear inductance of a third qubit. The measured on-
state coupling as well as the off-state residual coupling depends on the coupler bias and
agrees quantitatively with a calculation of transition matrix elements of a three-qubit …