# Coupling microwave photons to a mechanical resonator using quantum interference

## TL;DR

This paper introduces a flux-mediated microwave optomechanical coupling method using a SQUID, enabling tunable, strong single-photon interactions that surpass traditional capacitive approaches, advancing quantum control of mechanical systems.

## Contribution

The authors experimentally demonstrate a novel flux-mediated coupling scheme in microwave optomechanics, achieving in-situ tunability and higher coupling rates than capacitive methods.

## Key findings

- Flux-mediated coupling is tunable via magnetic flux.
- Achieved coupling rates comparable to state-of-the-art.
- Predicted to surpass capacitive coupling limits in the single-photon regime.

## Abstract

In recent years, the field of microwave optomechanics has emerged as leading platform for achieving quantum control of macroscopic mechanical objects. Implementations of microwave optomechanics to date have coupled microwave photons to mechanical resonators using a moving capacitance. While simple and effective, the capacitive scheme suffers from inherent and practical limitations on the maximum achievable coupling strength. Here, we experimentally implement a fundamentally different approach: flux-mediated optomechanical coupling. In this scheme, mechanical displacements modulate the flux in a superconducting quantum interference device (SQUID) that forms the inductor of a microwave resonant circuit. We demonstrate that this flux-mediated coupling can be tuned in-situ by the magnetic flux in the SQUID, enabling nanosecond flux tuning of the optomechanical coupling. Tuning the external in-plane magnetic transduction field, we observe a linear scaling of the single-photon coupling strength, reaching rates comparable to the current state-of-the-art. Finally, this linear scaling is predicted to overcome the limits of single-photon coupling rates in capacitive optomechanics, opening the door for a new generation of groundbreaking optomechanical experiments in the single-photon strong coupling regime.