Photon pair generation and quantum walks in arrays of quadratic nonlinear waveguides

Arrays of coupled optical waveguides provide a flexible platform for manipulation of optical beams and pulses. Recently, the propagation of non-classical light in waveguide arrays has shown a surging attention. It was shown that quantum walks of correlated photon pairs realized through propagation in waveguide arrays can lead to nontrivial quantum correlations at the array output. However, all currently used schemes for quantum walks utilise correlated photon pairs generated externally to the array. Here, we propose and demonstrate numerically a novel scheme enabling simultaneous generation of correlated photon pair through spontaneous parametric downconversion (SPDC) and quantum walks inside a single photonic element an array of quadratic nonlinear waveguides. This scheme avoids entirely the need for complex interfaces between the different photonic elements and enables novel ways for control of the quantum correlations.