At optical frequencies the radiation produced by a source, such as a laser, ablack body or a single photon source, is frequently characterized by analyzingthe temporal correlations of emitted photons using single photon counters. Atmicrowave frequencies, however, there are no efficient single photon countersyet. Instead, well developed linear amplifiers allow for efficient measurementof the amplitude of an electromagnetic field. Here, we demonstrate how theproperties of a microwave single photon source can be characterized usingcorrelation measurements of the emitted radiation with such detectors. We alsodemonstrate the cooling of a thermal field stored in a cavity, an effect whichwe detect using a cross-correlation measurement of the radiation emitted at thetwo ends of the cavity.
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