  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 pre-amplifier to improve the quantum efficiency of the field quadrature
measurement (QM) from 2% to 36 +/- 4%. Without correcting for the detection
inefficiency we observe a minimum quadrature variance which is 69 +/- 8% 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.
