Complex quantum state generation and coherent control based on integrated frequency combs

The investigation of integrated frequency comb sources characterized by equidistant spectral modes was initially driven by considerations of classical applications, seeking a more practical and miniaturized way to generate stable broadband sources of light. Recently, in the context of scaling the complexity of optical quantum circuits, these on-chip approaches have provided a new framework to address challenges of non-classical state generation and manipulation. For example, multi-photon and high-dimensional states were to date either inaccessible, lacked scalability, or were difficult to manipulate, using elaborate approaches. The emerging field of quantum frequency combs studying spectral multimode sources based on the judicious excitation of (typically) third-order nonlinear optical micro- cavities, has begun to address these issues. Several quantum sources based on this concept have already been demonstrated, among them combs of correlated photons, cross-polarized photon pairs, entangled photon pairs, multi-photon states, and high- dimensional entangled states. While sources have achieved increasing complexity, so have coherent state processing operations, demonstrated in a practical manner using standard telecommunications components. Here, we review our recent work in the development of this framework, with a focus on multi-photon and high-dimensional states. The integrated frequency comb platform thus demonstrates significant potential for the development of meaningful quantum optical technologies.