title: Quantum state tomography of an itinerant squeezed microwave field.
abstract: We perform state tomography of an itinerant squeezed state of the microwave field prepared by a Josephson parametric amplifier (JPA). We use a second JPA as a preamplifier to improve the quantum efficiency of the field quadrature measurement from 2% to 36%±4%. Without correcting for the detection inefficiency we observe a minimum quadrature variance which is 68(-7)(+9)% of the variance of the vacuum. We reconstruct the state's density matrix by a maximum likelihood method and infer that the squeezed state has a minimum variance less than 40% of the vacuum, with uncertainty mostly caused by calibration systematics.
authors.affiliation: JILA, National Institute of Standards and Technology and the University of Colorado, Boulder, Colorado 80309, USA.
authors.forename: F
authors.initials: F
authors.lastname: Mallet
authors.forename: M A
authors.initials: MA
authors.lastname: Castellanos-Beltran
authors.forename: H S
authors.initials: HS
authors.lastname: Ku
authors.forename: S
authors.initials: S
authors.lastname: Glancy
authors.forename: E
authors.initials: E
authors.lastname: Knill
authors.forename: K D
authors.initials: KD
authors.lastname: Irwin
authors.forename: G C
authors.initials: GC
authors.lastname: Hilton
authors.forename: L R
authors.initials: LR
authors.lastname: Vale
authors.forename: K W
authors.initials: KW
authors.lastname: Lehnert