title: Dephasing of a superconducting qubit induced by photon noise.
abstract: We have studied the dephasing of a superconducting flux qubit coupled to a dc-SQUID based oscillator. By varying the bias conditions of both circuits we were able to tune their effective coupling strength. This allowed us to measure the effect of such a controllable and well-characterized environment on the qubit coherence. We can quantitatively account for our data with a simple model in which thermal fluctuations of the photon number in the oscillator are the limiting factor. In particular, we observe a strong reduction of the dephasing rate whenever the coupling is tuned to zero. At the optimal point we find a large spin-echo decay time of .
authors.affiliation: Quantum Transport Group, Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg, Delft, The Netherlands.
authors.forename: P
authors.initials: P
authors.lastname: Bertet
authors.forename: I
authors.initials: I
authors.lastname: Chiorescu
authors.forename: G
authors.initials: G
authors.lastname: Burkard
authors.forename: K
authors.initials: K
authors.lastname: Semba
authors.forename: C J P M
authors.initials: CJ
authors.lastname: Harmans
authors.forename: D P
authors.initials: DP
authors.lastname: DiVincenzo
authors.forename: J E
authors.initials: JE
authors.lastname: Mooij