title: Circuit QED with a nonlinear resonator: ac-Stark shift and dephasing.
abstract: We have performed spectroscopic measurements of a superconducting qubit dispersively coupled to a nonlinear resonator driven by a pump microwave field. Measurements of the qubit frequency shift provide a sensitive probe of the intracavity field, yielding a precise characterization of the resonator nonlinearity. The qubit linewidth has a complex dependence on the pump frequency and amplitude, which is correlated with the gain of the nonlinear resonator operated as a small-signal amplifier. The corresponding dephasing rate is found to be close to the quantum limit in the low-gain limit of the amplifier.
authors: Service de Physique de l'État Condensé (CNRS URA 2464), IRAMIS, DSM, CEA-Saclay, Gif-sur-Yvette, France.
authors: F R
authors: FR
authors: Ong
authors: M
authors: M
authors: Boissonneault
authors: F
authors: F
authors: Mallet
authors: A
authors: A
authors: Palacios-Laloy
authors: A
authors: A
authors: Dewes
authors: A C
authors: AC
authors: Doherty
authors: A
authors: A
authors: Blais
authors: P
authors: P
authors: Bertet
authors: D
authors: D
authors: Vion
authors: D
authors: D
authors: Esteve