title: Characterizing entanglement of an artificial atom and a cavity cat state with Bell's inequality.
abstract: The Schrodinger's cat thought experiment highlights the counterintuitive concept of entanglement in macroscopically distinguishable systems. The hallmark of entanglement is the detection of strong correlations between systems, most starkly demonstrated by the violation of a Bell inequality. No violation of a Bell inequality has been observed for a system entangled with a superposition of coherent states, known as a cat state. Here we use the Clauser-Horne-Shimony-Holt formulation of a Bell test to characterize entanglement between an artificial atom and a cat state, or a Bell-cat. Using superconducting circuits with high-fidelity measurements and real-time feedback, we detect correlations that surpass the classical maximum of the Bell inequality. We investigate the influence of decoherence with states up to 16 photons in size and characterize the system by introducing joint Wigner tomography. Such techniques demonstrate that information stored in superpositions of coherent states can be extracted efficiently, a crucial requirement for quantum computing with resonators.
authors.affiliation: Departments of Physics and Applied Physics, Yale University, New Haven, Connecticut 06510, USA.
authors.forename: Brian
authors.initials: B
authors.lastname: Vlastakis
authors.affiliation: Departments of Physics and Applied Physics, Yale University, New Haven, Connecticut 06510, USA.
authors.forename: Andrei
authors.initials: A
authors.lastname: Petrenko
authors.affiliation: Departments of Physics and Applied Physics, Yale University, New Haven, Connecticut 06510, USA.
authors.forename: Nissim
authors.initials: N
authors.lastname: Ofek
authors.affiliation: Departments of Physics and Applied Physics, Yale University, New Haven, Connecticut 06510, USA.
authors.forename: Luyan
authors.initials: L
authors.lastname: Sun
authors.affiliation: Departments of Physics and Applied Physics, Yale University, New Haven, Connecticut 06510, USA.
authors.forename: Zaki
authors.initials: Z
authors.lastname: Leghtas
authors.affiliation: Departments of Physics and Applied Physics, Yale University, New Haven, Connecticut 06510, USA.
authors.forename: Katrina
authors.initials: K
authors.lastname: Sliwa
authors.affiliation: Departments of Physics and Applied Physics, Yale University, New Haven, Connecticut 06510, USA.
authors.forename: Yehan
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Departments of Physics and Applied Physics, Yale University, New Haven, Connecticut 06510, USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Hatridge
authors.affiliation: Departments of Physics and Applied Physics, Yale University, New Haven, Connecticut 06510, USA.
authors.forename: Jacob
authors.initials: J
authors.lastname: Blumoff
authors.affiliation: Departments of Physics and Applied Physics, Yale University, New Haven, Connecticut 06510, USA.
authors.forename: Luigi
authors.identifier: http://orcid.org/0000-0002-0272-5481
authors.initials: L
authors.lastname: Frunzio
authors.affiliation: Departments of Physics and Applied Physics, Yale University, New Haven, Connecticut 06510, USA.|INRIA Paris-Rocquencourt, Domaine de Voluceau, B.P. 105, 78153 Le Chesnay Cedex, France.
authors.forename: Mazyar
authors.initials: M
authors.lastname: Mirrahimi
authors.affiliation: Departments of Physics and Applied Physics, Yale University, New Haven, Connecticut 06510, USA.
authors.forename: Liang
authors.identifier: http://orcid.org/0000-0002-0000-9342
authors.initials: L
authors.lastname: Jiang
authors.affiliation: Departments of Physics and Applied Physics, Yale University, New Haven, Connecticut 06510, USA.
authors.forename: M H
authors.initials: MH
authors.lastname: Devoret
authors.affiliation: Departments of Physics and Applied Physics, Yale University, New Haven, Connecticut 06510, USA.
authors.forename: R J
authors.initials: RJ
authors.lastname: Schoelkopf