title: Measurement-Induced State Transitions in a Superconducting Qubit: Beyond the Rotating Wave Approximation.
abstract: Many superconducting qubit systems use the dispersive interaction between the qubit and a coupled harmonic resonator to perform quantum state measurement. Previous works have found that such measurements can induce state transitions in the qubit if the number of photons in the resonator is too high. We investigate these transitions and find that they can push the qubit out of the two-level subspace, and that they show resonant behavior as a function of photon number. We develop a theory for these observations based on level crossings within the Jaynes-Cummings ladder, with transitions mediated by terms in the Hamiltonian that are typically ignored by the rotating wave approximation. We find that the most important of these terms comes from an unexpected broken symmetry in the qubit potential. We confirm the theory by measuring the photon occupation of the resonator when transitions occur while varying the detuning between the qubit and resonator.
authors.affiliation: Google Inc., Santa Barbara, California 93117, USA.
authors.forename: Daniel
authors.initials: D
authors.lastname: Sank
authors.affiliation: Department of Physics, University of California, Santa Barbara, California 93106-9530, USA.
authors.forename: Zijun
authors.initials: Z
authors.lastname: Chen
authors.affiliation: Department of Electrical and Computer Engineering, University of California, Riverside, California 92521, USA.|Department of Physics, University of California, Riverside, California 92521, USA.
authors.forename: Mostafa
authors.initials: M
authors.lastname: Khezri
authors.affiliation: Google Inc., Santa Barbara, California 93117, USA.
authors.forename: J
authors.initials: J
authors.lastname: Kelly
authors.affiliation: Google Inc., Santa Barbara, California 93117, USA.
authors.forename: R
authors.initials: R
authors.lastname: Barends
authors.affiliation: Department of Physics, University of California, Santa Barbara, California 93106-9530, USA.
authors.forename: B
authors.initials: B
authors.lastname: Campbell
authors.affiliation: Google Inc., Santa Barbara, California 93117, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Chen
authors.affiliation: Department of Physics, University of California, Santa Barbara, California 93106-9530, USA.
authors.forename: B
authors.initials: B
authors.lastname: Chiaro
authors.affiliation: Department of Physics, University of California, Santa Barbara, California 93106-9530, USA.
authors.forename: A
authors.initials: A
authors.lastname: Dunsworth
authors.affiliation: Google Inc., Santa Barbara, California 93117, USA.
authors.forename: A
authors.initials: A
authors.lastname: Fowler
authors.affiliation: Google Inc., Santa Barbara, California 93117, USA.
authors.forename: E
authors.initials: E
authors.lastname: Jeffrey
authors.affiliation: Google Inc., Santa Barbara, California 93117, USA.
authors.forename: E
authors.initials: E
authors.lastname: Lucero
authors.affiliation: Google Inc., Santa Barbara, California 93117, USA.
authors.forename: A
authors.initials: A
authors.lastname: Megrant
authors.affiliation: Google Inc., Santa Barbara, California 93117, USA.
authors.forename: J
authors.initials: J
authors.lastname: Mutus
authors.affiliation: Google Inc., Santa Barbara, California 93117, USA.
authors.forename: M
authors.initials: M
authors.lastname: Neeley
authors.affiliation: Department of Physics, University of California, Santa Barbara, California 93106-9530, USA.
authors.forename: C
authors.initials: C
authors.lastname: Neill
authors.affiliation: Department of Physics, University of California, Santa Barbara, California 93106-9530, USA.
authors.forename: P J J
authors.initials: PJ
authors.lastname: O'Malley
authors.affiliation: Department of Physics, University of California, Santa Barbara, California 93106-9530, USA.
authors.forename: C
authors.initials: C
authors.lastname: Quintana
authors.affiliation: Google Inc., Santa Barbara, California 93117, USA.
authors.forename: P
authors.initials: P
authors.lastname: Roushan
authors.affiliation: Google Inc., Santa Barbara, California 93117, USA.
authors.forename: A
authors.initials: A
authors.lastname: Vainsencher
authors.affiliation: Google Inc., Santa Barbara, California 93117, USA.
authors.forename: T
authors.initials: T
authors.lastname: White
authors.affiliation: Department of Physics, University of California, Santa Barbara, California 93106-9530, USA.
authors.forename: J
authors.initials: J
authors.lastname: Wenner
authors.affiliation: Department of Electrical and Computer Engineering, University of California, Riverside, California 92521, USA.
authors.forename: Alexander N
authors.initials: AN
authors.lastname: Korotkov
authors.affiliation: Google Inc., Santa Barbara, California 93117, USA.|Department of Physics, University of California, Santa Barbara, California 93106-9530, USA.
authors.forename: John M
authors.initials: JM
authors.lastname: Martinis