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Quantum state tomography of an itinerant squeezed microwave field
F Mallet1, M A Castellanos-Beltran, H S Ku
1JILA, National Institute of Standards and Technology and the University of Colorado, Boulder, Colorado 80309, USA.
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.
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