  In this letter, we report the observation of the correlation between two
modes of microwave radiation resulting from the amplification of quantum noise
by the Josephson Parametric Converter. This process, seen from the pump, can be
viewed as parametric down-conversion. The correlation is measured by an
interference experiment displaying a contrast better than 99% with a number of
photons per mode greater than two hundred and fifty thousand. Dispersive
measurements of mesoscopic systems and quantum encryption can benefit from this
development.
