Single-photon strong cooperativity in microwave magneto-mechanics

The possibility to operate massive mechanical resonators in the quantum regime has become central in fundamental sciences, in particular to test the boundaries of quantum mechanics. Optomechanics, where photons (e.g. optical, microwave) are coupled to mechanical motion, provide the tools to control mechanical motion near the fundamental quantum limits. Reaching single-photon strong coupling would allow to prepare the mechanical resonator in non-Gaussian quantum states. Yet, this regime remains challenging to achieve with massive resonators due to the small optomechanical couplings. Here we demonstrate a novel approach where a massive mechanical resonator is magnetically coupled to a microwave cavity. By improving the coupling by one order of magnitude over current microwave optomechanical systems, we achieve single-photon strong cooperativity, an important intermediate step to reach single-photon strong coupling. Such strong interaction allows for cooling the mechanical resonator with on average a single photon in the microwave cavity. Beyond tests for quantum foundations, our approach is also well suited as a quantum sensor or a microwave to optical transducer.