title: Decoherence in Josephson qubits from dielectric loss.
abstract: Dielectric loss from two-level states is shown to be a dominant decoherence source in superconducting quantum bits. Depending on the qubit design, dielectric loss from insulating materials or the tunnel junction can lead to short coherence times. We show that a variety of microwave and qubit measurements are well modeled by loss from resonant absorption of two-level defects. Our results demonstrate that this loss can be significantly reduced by using better dielectrics and fabricating junctions of small area . With a redesigned phase qubit employing low-loss dielectrics, the energy relaxation rate has been improved by a factor of 20, opening up the possibility of multiqubit gates and algorithms.
authors.affiliation: Department of Physics, University of California, Santa Barbara, California 93106, USA.
authors.forename: John M
authors.initials: JM
authors.lastname: Martinis
authors.forename: K B
authors.initials: KB
authors.lastname: Cooper
authors.forename: R
authors.initials: R
authors.lastname: McDermott
authors.forename: Matthias
authors.initials: M
authors.lastname: Steffen
authors.forename: Markus
authors.initials: M
authors.lastname: Ansmann
authors.forename: K D
authors.initials: KD
authors.lastname: Osborn
authors.forename: K
authors.initials: K
authors.lastname: Cicak
authors.forename: Seongshik
authors.initials: S
authors.lastname: Oh
authors.forename: D P
authors.initials: DP
authors.lastname: Pappas
authors.forename: R W
authors.initials: RW
authors.lastname: Simmonds
authors.forename: Clare C
authors.initials: CC
authors.lastname: Yu