title: Continuous Quantum Nondemolition Measurement of the Transverse Component of a Qubit.
abstract: Quantum jumps of a qubit are usually observed between its energy eigenstates, also known as its longitudinal pseudospin component. Is it possible, instead, to observe quantum jumps between the transverse superpositions of these eigenstates? We answer positively by presenting the first continuous quantum nondemolition measurement of the transverse component of an individual qubit. In a circuit QED system irradiated by two pump tones, we engineer an effective Hamiltonian whose eigenstates are the transverse qubit states, and a dispersive measurement of the corresponding operator. Such transverse component measurements are a useful tool in the driven-dissipative operation engineering toolbox, which is central to quantum simulation and quantum error correction.
authors.affiliation: Department of Applied Physics and Physics, Yale University, New Haven, Connecticut 06520, USA.
authors.forename: U
authors.initials: U
authors.lastname: Vool
authors.affiliation: Department of Applied Physics and Physics, Yale University, New Haven, Connecticut 06520, USA.
authors.forename: S
authors.initials: S
authors.lastname: Shankar
authors.affiliation: Department of Applied Physics and Physics, Yale University, New Haven, Connecticut 06520, USA.
authors.forename: S O
authors.initials: SO
authors.lastname: Mundhada
authors.affiliation: Department of Applied Physics and Physics, Yale University, New Haven, Connecticut 06520, USA.
authors.forename: N
authors.initials: N
authors.lastname: Ofek
authors.affiliation: Department of Applied Physics and Physics, Yale University, New Haven, Connecticut 06520, USA.
authors.forename: A
authors.initials: A
authors.lastname: Narla
authors.affiliation: Department of Applied Physics and Physics, Yale University, New Haven, Connecticut 06520, USA.
authors.forename: K
authors.initials: K
authors.lastname: Sliwa
authors.affiliation: Department of Applied Physics and Physics, Yale University, New Haven, Connecticut 06520, USA.
authors.forename: E
authors.initials: E
authors.lastname: Zalys-Geller
authors.affiliation: Department of Applied Physics and Physics, Yale University, New Haven, Connecticut 06520, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Department of Applied Physics and Physics, Yale University, New Haven, Connecticut 06520, USA.
authors.forename: L
authors.initials: L
authors.lastname: Frunzio
authors.affiliation: Department of Applied Physics and Physics, Yale University, New Haven, Connecticut 06520, USA.
authors.forename: R J
authors.initials: RJ
authors.lastname: Schoelkopf
authors.affiliation: Department of Applied Physics and Physics, Yale University, New Haven, Connecticut 06520, USA.
authors.forename: S M
authors.initials: SM
authors.lastname: Girvin
authors.affiliation: Department of Applied Physics and Physics, Yale University, New Haven, Connecticut 06520, USA.
authors.forename: M H
authors.initials: MH
authors.lastname: Devoret