Abstract
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 , which thus is tunable in situ via the coupler’s flux bias. In the qubit regime, was varied from (antiferromagnetic) to (ferromagnetic); in particular, vanishes for an intermediate coupler bias. Measurements on a second sample illuminate the relation between two-qubit tunable coupling and three-qubit behavior.
- Received 16 August 2006
DOI:https://doi.org/10.1103/PhysRevLett.98.057004
©2007 American Physical Society