Direct measurement of Microwave Vacuum Squeezing with a Kinetic Inductance Parametric Amplifier

The uncertainty principle imposes a lower bound on the electromagnetic fluctuations of a vacuum field. Using a phase-sensitive parametric amplifier, it is possible to reduce the noise along one quadrature below the uncertainty limit at the expense of increasing it along the other. This so-called 'vacuum squeezing’ allows for measurements beyond the standard quantum limit, which is widely applicable in quantum information and in the detection of weak signals [1]. Squeezing measurements in the microwave domain have so far been conducted using resonant [1] or travelling wave [2] parametric amplifiers relying upon Josephson junctions, where higher order non-linearities and transmission losses in the microwave components have limited the amount of squeezing.

Here we report on measurements of microwave vacuum squeezing with resonant parametric amplifiers exploiting the non-linear kinetic inductance intrinsic to thin films of NbTiN. In these devices, a DC-current and a pump tone facilitate phase sensitive (de-)amplification through three-wave mixing [3]. With a calibrated thermal noise source, we first confirm that the noise temperatures of the two amplifiers are well below the standard quantum limit. We then make direct measurements of vacuum squeezing by placing two Kinetic Inductance Parametric Amplifiers in series.

[1] M. Malnou et. al. Phys. Rev. X 9, 021023 (2019)

[2] J.Y. Qiu et al. arXiv:2201.11261 (2022)

[3] D. Parker et al. Phys. Rev. Applied 17, 034064 (2022)