A Tunable Coupling Architecture For Josephson Phase Qubits

Previous coupled-qubit experiments with Josephson phase qubits have used a fixed coupling scheme. However, in order to create high-fidelity multi-qubit gates, a tunable coupling scheme is needed. Fixed coupling schemes cannot be used because single-qubit operations on a coupled-qubit system cannot be performed with high fidelity due to the errors induced by always-on coupling. Fixed coupling also allows for crosstalk between coupled qubits during measurement. We show how to implement a tunable-coupling architecture for Josephson phase qubits using simple linear elements. This architecture can be used to vary the interaction strength from fully-off to fully-on allowing us to get around the problems inherent with the use of a fixed coupling scheme.