Dissipative stabilization of squeezing beyond 3 dB in a microwave mode

TL;DR

This paper demonstrates a reservoir engineering technique in superconducting circuits that stabilizes and enhances intra-resonator squeezing beyond the traditional 3 dB limit, achieving over 8 dB of squeezing.

Contribution

The authors introduce a novel reservoir engineering method using two-tone pumping to surpass the 3 dB squeezing limit in a microwave resonator.

Findings

Achieved up to 8.2 dB of squeezing inside the resonator.

Implemented direct Wigner tomography using an ancillary qubit.

Demonstrated stabilization of highly squeezed states with high purity.

Abstract

While a propagating state of light can be generated with arbitrary squeezing by pumping a parametric resonator, the intra-resonator state is limited to 3 dB of squeezing. Here, we implement a reservoir engineering method to surpass this limit using superconducting circuits. Two-tone pumping of a three-wave-mixing element implements an effective coupling to a squeezed bath which stabilizes a squeezed state inside the resonator. Using an ancillary superconducting qubit as a probe allows us to perform a direct Wigner tomography of the intra-resonator state. The raw measurement provides a lower bound on the squeezing at about $6.7 \pm 0.2$ dB below the zero-point level. Further, we show how to correct for resonator evolution during the Wigner tomography and obtain a squeezing as high as $8.2 \pm 0.8$ dB. Moreover, this level of squeezing is achieved with a purity of $-0.4 \pm 0.4$ dB.