title: A Schrödinger cat living in two boxes.
abstract: Quantum superpositions of distinct coherent states in a single-mode harmonic oscillator, known as "cat states," have been an elegant demonstration of Schrödinger's famous cat paradox. Here, we realize a two-mode cat state of electromagnetic fields in two microwave cavities bridged by a superconducting artificial atom, which can also be viewed as an entangled pair of single-cavity cat states. We present full quantum state tomography of this complex cat state over a Hilbert space exceeding 100 dimensions via quantum nondemolition measurements of the joint photon number parity. The ability to manipulate such multicavity quantum states paves the way for logical operations between redundantly encoded qubits for fault-tolerant quantum computation and communication.
authors.affiliation: Department of Applied Physics and Physics, Yale University, New Haven, CT 06511, USA. chen.wang@yale.edu robert.schoelkopf@yale.edu.
authors.forename: Chen
authors.initials: C
authors.lastname: Wang
authors.affiliation: Department of Applied Physics and Physics, Yale University, New Haven, CT 06511, USA.
authors.forename: Yvonne Y
authors.initials: YY
authors.lastname: Gao
authors.affiliation: Department of Applied Physics and Physics, Yale University, New Haven, CT 06511, USA.
authors.forename: Philip
authors.initials: P
authors.lastname: Reinhold
authors.affiliation: Department of Applied Physics and Physics, Yale University, New Haven, CT 06511, USA.
authors.forename: R W
authors.initials: RW
authors.lastname: Heeres
authors.affiliation: Department of Applied Physics and Physics, Yale University, New Haven, CT 06511, USA.
authors.forename: Nissim
authors.initials: N
authors.lastname: Ofek
authors.affiliation: Department of Applied Physics and Physics, Yale University, New Haven, CT 06511, USA.
authors.forename: Kevin
authors.initials: K
authors.lastname: Chou
authors.affiliation: Department of Applied Physics and Physics, Yale University, New Haven, CT 06511, USA.
authors.forename: Christopher
authors.initials: C
authors.lastname: Axline
authors.affiliation: Department of Applied Physics and Physics, Yale University, New Haven, CT 06511, USA.
authors.forename: Matthew
authors.initials: M
authors.lastname: Reagor
authors.affiliation: Department of Applied Physics and Physics, Yale University, New Haven, CT 06511, USA.
authors.forename: Jacob
authors.initials: J
authors.lastname: Blumoff
authors.affiliation: Department of Applied Physics and Physics, Yale University, New Haven, CT 06511, USA.
authors.forename: K M
authors.initials: KM
authors.lastname: Sliwa
authors.affiliation: Department of Applied Physics and Physics, Yale University, New Haven, CT 06511, USA.
authors.forename: L
authors.initials: L
authors.lastname: Frunzio
authors.affiliation: Department of Applied Physics and Physics, Yale University, New Haven, CT 06511, USA.
authors.forename: S M
authors.initials: SM
authors.lastname: Girvin
authors.affiliation: Department of Applied Physics and Physics, Yale University, New Haven, CT 06511, USA.
authors.forename: Liang
authors.initials: L
authors.lastname: Jiang
authors.affiliation: Department of Applied Physics and Physics, Yale University, New Haven, CT 06511, USA. INRIA Paris-Rocquencourt, Domaine de Voluceau, B.P. 105, 78153 Le Chesnay Cedex, France.
authors.forename: M
authors.initials: M
authors.lastname: Mirrahimi
authors.affiliation: Department of Applied Physics and Physics, Yale University, New Haven, CT 06511, USA.
authors.forename: M H
authors.initials: MH
authors.lastname: Devoret
authors.affiliation: Department of Applied Physics and Physics, Yale University, New Haven, CT 06511, USA. chen.wang@yale.edu robert.schoelkopf@yale.edu.
authors.forename: R J
authors.initials: RJ
authors.lastname: Schoelkopf