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 [1]. 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 [2, 3]. 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 [3] and enables novel ways for control of the quantum correlations.