Direct Josephson coupling between superconducting flux qubits
  We have demonstrated strong antiferromagnetic coupling between two three-junction flux qubits based on a shared Josephson junction, and therefore not limited by the small inductances of the qubit loops. The coupling sign and magnitude were measured by coupling the system to a high-quality superconducting tank circuit. Design modifications allowing to continuously tune the coupling strength and/or make the coupling ferromagnetic are discussed. 
M. Grajcar, A. Izmalkov, S.H.W. van der Ploeg, S. Linzen, E. Il'ichev,   Th. Wagner, U. Hubner, H.-G. Meyer, Alec Maassen va...