Practical Limits to Single-Mode Vacuum Squeezing in a SNAIL Parametric Amplifier

TL;DR

This study demonstrates that in practical SNAIL Parametric Amplifiers, internal losses, not Kerr nonlinearity, primarily limit vacuum squeezing, suggesting focus should be on loss reduction for better performance.

Contribution

The paper shows that Kerr nonlinearity is not the main limiting factor in vacuum squeezing for practical SPAs, emphasizing the importance of reducing internal and insertion losses.

Findings

Kerr nonlinearity varies but does not significantly affect squeezing.

Internal resonator loss and microwave chain insertion loss dominate squeezing limitations.

Reducing losses is more effective than suppressing Kerr for improving squeezing.

Abstract

We characterize single-mode vacuum squeezing generated by a SNAIL Parametric Amplifier (SPA) operated under conditions representative of practical sensing and qubit-readout experiments. Motivated by prior expectations that Kerr-induced distortion limits squeezing in degenerate parametric amplifiers, we varied external flux and pump power to explore operating points where Kerr nonlinearity is theoretically minimized. We find that for practical applications where the squeezing frequency is fixed, the Kerr was variable by about a factor of two and the achievable squeezing showed no significant dependence on Kerr. Theoretical modeling supports this observation and indicates that baseline Kerr values in state-of-the-art SPAs are already too small to impose a practical limitation. Instead, squeezing was dominated by internal resonator loss and insertion loss in the microwave chain. These results indicate that, in practical SPAs, reducing loss, rather than suppressing Kerr, is the primary route to improved squeezing performance.