Controllable coupling of superconducting flux qubits.
We have realized controllable coupling between two three-junction flux qubits by inserting an additional coupler loop between them, containing three Josephson junctions. Two of these are shared with the qubit loops, providing strong qubit-coupler interaction. The third junction gives the coupler a nontrivial current-flux relation; its derivative (i.e., the susceptibility) determines the coupling strength J, which thus is tunable in situ via the coupler's flux bias. In the qubit regime, J was varied from approximately 45 (antiferromagnetic) to approximately -55 mK (ferromagnetic); in particular, J vanishes for an intermediate coupler bias. Measurements on a second sample illuminate the relation between two-qubit tunable coupling and three-qubit behavior.
van der Ploeg
S H W
SH
Institute for Physical High Technology, P.O. Box 100239, D-07702 Jena, Germany.
Izmalkov
A
A
van den Brink
Alec Maassen
AM
Hübner
U
U
Grajcar
M
M
Il'ichev
E
E
Meyer
H-G
HG
Zagoskin
A M
AM