Cavity-Less Brillouin Strong Coupling in a Solid-State Continuous System

A strongly coupled system can coherently transfer energy between two states before it decoheres. This is a prerequisite to have quantum coherent control over a system. In the context of optomechanics, light has success-fully been strongly coupled to discrete mechanical resonances of an optomechanical cavity [1]. In this work, we present the first experimental realization of cavity-free strong coupling between groups of photons and phonons in a continuous optoacoustic system. This work can path the way to optical-fiber-based and chip-integrated quantum optoacoustic control for application to photon-phonon entanglement and quantum memory.