Enhancement of microwave squeezing via parametric down-conversion in a superconducting quantum circuit

TL;DR

This paper proposes a superconducting circuit design that significantly enhances microwave squeezing through parametric down-conversion, enabling stronger and more stable quantum states for potential quantum information applications.

Contribution

The authors introduce a novel superconducting circuit with nonlinear coupling that increases PDC efficiency and stability, surpassing traditional Josephson parametric amplifiers.

Findings

PDC coefficient can reach tens of megahertz.

Enhanced microwave squeezing demonstrated numerically.

System remains stable near the critical point, allowing stronger transient squeezing.

Abstract

We propose an experimentally accessible superconducting quantum circuit, consisting of two coplanar waveguide resonators (CWRs), to enhance the microwave squeezing via parametric down-conversion (PDC). In our scheme, the two CWRs are nonlinearly coupled through a superconducting quantum interference device embedded in one of the CWRs. This is equivalent to replacing the transmission line in a flux-driven Josephson parametric amplifier (JPA) by a CWR, which makes it possible to drive the JPA by a quantized microwave field. Owing to this design, the PDC coefficient can be considerably increased to be about tens of megahertz, satisfying the strong-coupling condition. Using the Heisenberg-Langevin approach, we numerically show the enhancement of the microwave squeezing in our scheme. In contrast to the JPA, our proposed system becomes stable around the critical point and can generate stronger transient squeezing. In addition, the strong-coupling PDC can be used to engineer the photon blockade.