MULTIPROB

Marie Sklodowska-Curie Individual Fellowship No. 798397

Photon-based quantum technologies are a promising platform for processing quantum information, because it combines the resilience of the photon with simple and powerful tools for its manipulation. A key requirement towards this goal is building and understanding deterministic light-matter quantum interfaces, where photons and quantum emitters can interact strongly at the level of few quanta. This enables the engineering of strong photon-photon interactions mediated by the emitters and the construction of two- or multi-photon quantum photonic devices for creating quantum superpositions and entanglement between propagating photons.

Modern nanophotonic and nanofabrication techniques allow for the control of these quantum light-matter interactions in many labs around the world, for instance, with quantum dot or atomic emitters coupled to nanophotonic waveguides or ---in the microwave regime---with superconducting qubits coupled to transmission lines. Nevertheless, the characterization of those interactions is typically limited to measure single-photon transmission, second order correlations, or pump-probe experiments, which give only partial information about the generated photon-photon quantum correlations and the effect of the nanophotonic environment.

The overall objective of this project was to develop more sophisticated multi-photon probing protocols to enable a complete characterization of photon-photon correlations induced by complex quantum emitters, including realistic conditions of noise and dissipation due to the nanophotonic environment. In addition, these techniques should be simple enough to be implemented with standard optical control and measurement tools, such as monochromatic coherent input states and homodyne or intensity detection methods. The action concluded with the theoretical development of such a protocol and with its experimental testing it in collaboration with the group of Prof. Peter Lodahl at the Niels Bohr Institute, Copenhagen.

The method can be further applied to characterize photon-photon correlations in diverse and realistic situations of nanophotonic devices and to study strongly correlated many-body quantum simulators coupled to light.