Direct Josephson coupling between superconducting flux qubits

Grajcar, M.; Izmalkov, A.; van der Ploeg, S. H. W.; Linzen, S.; Il'ichev, E.; Wagner, Th.; Hubner, U.; Meyer, H. -G.; Brink, Alec Maassen van den; Uchaikin, S.; Zagoskin, A. M.

Direct Josephson coupling between superconducting flux qubits

Authors

Grajcar, M.

Izmalkov, A.

van der Ploeg, S. H. W.

Brink, Alec Maassen van den

Uchaikin, S.

Description

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.
REVTeX 4, 4 pages, 5 figures; v2: completely rewritten, added finite-temperature results and proposals for ferromagnetic galvanic coupling