Squeezed states of light have been used extensively to increase the precision
of measurements, from the detection of gravitational waves to the search for
dark matter. In the optical domain, high levels of vacuum noise squeezing are
possible due to the availability of low loss optical components and
high-performance squeezers. At microwave frequencies, however, limitations of
the squeezing devices and the high insertion loss of microwave components makes
squeezing vacuum noise an exceptionally difficult task. Here we demonstrate a
new record for the direct measurement of microwave squeezing. We use an ultra
low loss setup and weakly-nonlinear kinetic inductance parametric amplifiers to
squeeze microwave noise 7.8(2) dB below the vacuum level. The amplifiers
exhibit a resilience to magnetic fields and permit the demonstration of record
squeezing levels inside fields of up to 2 T. Finally, we exploit the high
critical temperature of our amplifiers to squeeze a warm thermal environment,
achieving vacuum level noise at a temperature of 1.8 K. These results enable
experiments that combine squeezing with magnetic fields and permit
quantum-limited microwave measurements at elevated temperatures, significantly
reducing the complexity and cost of the cryogenic systems required for such
experiments.Comment: Main text: 9 pages, 4 figures. Supplementary information: 21 pages,
17 figure