title: Strong coupling of a quantum oscillator to a flux qubit at its symmetry point.
abstract: A flux qubit biased at its symmetry point shows a minimum in the energy splitting (the gap), providing protection against flux noise. We have fabricated a qubit of which the gap can be tuned fast and have coupled this qubit strongly to an LC oscillator. We show full spectroscopy of the qubit-oscillator system and generate vacuum Rabi oscillations. When the gap is made equal to the oscillator frequency ν(osc) we find the largest vacuum Rabi splitting of ∼0.1 ν(osc). Here being at resonance coincides with the optimal coherence of the symmetry point.
authors.affiliation: Kavli Institute of Nanoscience, Delft University of Technology, PO Box 5046, 2600 GA Delft, The Netherlands. fedoroar@phys.ethz.ch
authors.forename: A
authors.initials: A
authors.lastname: Fedorov
authors.forename: A K
authors.initials: AK
authors.lastname: Feofanov
authors.forename: P
authors.initials: P
authors.lastname: Macha
authors.forename: P
authors.initials: P
authors.lastname: Forn-Díaz
authors.forename: C J P M
authors.initials: CJ
authors.lastname: Harmans
authors.forename: J E
authors.initials: JE
authors.lastname: Mooij