Observation of Two-Mode Squeezing in the Microwave Frequency Domain
Christopher Eichler, Deniz Bozyigit, Christian B. Lang, Matthias Baur, L. Steffen, J. M. Fink, Stefan Filipp, Andreas J. Wallraff · Physical Review Letters · 2011
Continuous variable entanglement between two modes of a radiation field is usually studied at optical frequencies. Here we demonstrate experiments that show the entanglement between microwave photons of different energy in a broadband squeezed beam. We use a Josephson parametric amplifier to generate the two-mode correlated state and detect all four quadrature components simultaneously in a two-channel heterodyne setup using amplitude detectors. Analyzing two-dimensional phase space histograms for all possible pairs of quadratures allows us to determine the full covariance matrix, which is in good agreement with the one expected for a two-mode squeezed state.