Squeezing Thermal Microwave Radiation.

We have demonstrated squeezing of 4.2K thermal noise using a Josephson-parametric amplifier operated at 19.4 GHz. A 42% reduction in the equilibrium noise was observed. When operated at 0.1K, the amplifier exhibited an excess noises of 0.28K referred to the amplifier's input. This excess noise is less than the vacuum fluctuation noise at the input. The device can be operated in a nonchaotic mode with a signal gain of 9 dB.