Photonics has the potential to advance modern quantum technologies and high-speed applications such as communications and the processing of large amounts of data. However, to replace or improve the well-established systems with photonic solutions, there is still a way to go. A new promising approach to manipulate light all-optically is to use the link of optical waves with acoustic vibrations. Our research experimentally investigates how traveling sound waves can be used to process states of light in the classical and quantum regime.

Via the nonlinear effect of stimulated Brillouin scattering (SBS), acoustic waves can be created all-optically by counter-propagating optical signals. With help of acoustic waves, we implement several building blocks for photonic machine learning, such as an optoacoustic recurrent operator, optical memory and a photonic activation function for all-optical neural networks. We experimentally demonstrate a temporary storage for light information and show how to extend the performance in terms of bandwidth and storage time. SBS is also a versatile tool for processing polarization states and orbital angular momentum (OAM), where we demonstrate a non-reciprocal device for OAM modes, a vortex laser and frequency conversion of OAM information. In order to enter the regime of quantum signal processing, cooling of traveling acoustic phonons is an essential precondition and we show experimental results of optomechanical cooling by 220K starting from room temperature. As a milestone towards quantum interactions of photons and traveling phonons, 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.