Quantum interference of concurrent nonlinear processes in a single silicon waveguide.

Optical nonlinearity provides a key resource for quantum information processing and the interference of quanta lies at the heart of quantum physics as well. As an interesting combination, the nonlinear interference can extend the scalability and flexibility of quantum manipulations as well as what we believe to be novel applications. In this manuscript, we propose and experimentally demonstrate what we believe to be a new nonlinear interferometer on a silicon chip between a degenerate and a non-degenerate spontaneous four-wave mixing process in the same waveguide. We observed the interference in the pairs generation rate and obtained broadband interference visibility up to 96%. Furthermore, we also provide a feasible scheme for observing four-photon nonlinear interference in a single waveguide. This work provides a novel method for realizing and controlling optical nonlinear interference, and enriches the toolbox of quantum state preparation and quantum manipulation by nonlinear processes.