Graphs on chip: a silicon photonics platform
We present a versatile photonic waveguide network platform implementing quantum (wave) graphs, proposed by Kottos \& Smilansky [Phys. Rev. Lett. \textbf{79}, 4794 (1997)] to investigate ray-wave correspondence and quantum chaos. Realized on a silicon-on-insulator chip at telecom wavelengths, it enables a unique capability: the direct, non-invasive imaging of individual optical wave functions with unprecedented resolution via third-harmonic generation in silicon, which we use to study the localization of intensity distributions. Furthermore, by investigating two graphs with contrasting classical dynamics -- one strongly chaotic, the other one ergodic, but non-mixing -- we reveal strikingly different spectral statistics, in quantitative agreement with random matrix theory and a minimal unitary quantum-map model. This establishes silicon photonics networks as a versatile and scalable platform for investigating quantum chaos and non-linear graphs, and paves the way for optical quantum computing in complex networks.