Enhancement and state tomography of a squeezed vacuum with circuit quantum electrodynamics

TL;DR

This paper demonstrates how a superconducting cavity-qubit system can generate and characterize highly squeezed vacuum states, with the squeezing enhanced by cavity quality and robust against qubit non-linearity.

Contribution

It introduces a realistic setup for creating and analyzing squeezed vacuum states using circuit QED, including a theoretical framework and practical implications.

Findings

Stationary state approximates a squeezed vacuum.

Squeezing is enhanced by the cavity Q-factor.

Qubit non-linearity minimally affects the squeezed field.

Abstract

We study the dynamics of a general quartic interaction Hamiltonian under the influence of dissipation and non-classical driving. We show that this scenario could be realised with a cascaded superconducting cavity-qubit system in the strong dispersive regime in a setup similar to recent experiments. In the presence of dissipation, we find that an effective Hartree-type decoupling with a Fokker-Planck equation yields a good approximation. We find that the stationary state is approximately a squeezed vacuum, which is enhanced by the $Q$-factor of the cavity but conserved by the interaction. The qubit non-linearity, therefore, does not significantly influence the highly squeezed intracavity microwave field but, for a range of realistic parameters, enables characterisation of itinerant squeezed fields.