# Ultrastrong parametric coupling between a superconducting cavity and a mechanical resonator

## TL;DR

This paper reports the development of an optomechanical device with ultrastrong parametric coupling between a superconducting microwave cavity and a mechanical resonator, enabling advanced quantum control applications.

## Contribution

It demonstrates a novel architecture achieving ultrastrong coupling where the interaction surpasses dissipation and approaches the mechanical frequency.

## Key findings

- Achieved 88% frequency splitting of hybrid modes
- Coupling exceeds mechanical thermal decoherence rate
- Enabled potential for ultrafast quantum state transfer

## Abstract

We present a new optomechanical device where the motion of a micromechanical membrane couples to a microwave resonance of a three-dimensional superconducting cavity. With this architecture, we realize ultrastrong parametric coupling, where the coupling rate not only exceeds the dissipation rates in the system but also rivals the mechanical frequency itself. In this regime, the optomechanical interaction induces a frequency splitting between the hybridized normal modes that reaches 88% of the bare mechanical frequency, limited by the fundamental parametric instability. The coupling also exceeds the mechanical thermal decoherence rate, enabling new applications in ultrafast quantum state transfer and entanglement generation.