Biphoton generation in quadratic waveguide arrays: A classical optical simulation

TL;DR

This paper demonstrates that biphoton quantum correlations generated in 1D waveguide arrays can be simulated using classical light in 2D photonic lattices, revealing entanglement and Bell inequality violation.

Contribution

It introduces a classical optical simulation method for biphoton quantum walks in waveguide arrays, linking quantum entanglement to classical beam propagation.

Findings

Classical 2D photonic lattices can simulate biphoton correlations.

Output intensity images reveal Bell inequality violations.

Biphoton degrees of freedom are represented in an additional spatial dimension.

Abstract

Quantum entanglement, the non-separability of a multipartite wave function, became essential in understanding the non-locality of quantum mechanics. In optics, this non-locality can be demonstrated on impressively large length scales, as photons travel with the speed of light and interact only weakly with their environment. With the discovery of spontaneous parametric down-conversion (SPDC) in nonlinear crystals, an efficient source for entangled photon pairs, so-called biphotons, became available. It has recently been shown that SPDC can also be implemented in nonlinear arrays of evanescently coupled waveguides which allows the generation and the investigation of correlated quantum walks of such biphotons in an integrated device. Here, we analytically and experimentally demonstrate that the biphoton degrees of freedom are entailed in an additional spatial dimension, therefore the SPDC and the subsequent quantum random walk in one-dimensional (1D) arrays can be simulated through classical optical beam propagation in a two-dimensional (2D) photonic lattice. Thereby, the output intensity images directly represent the biphoton correlations and exhibit a clear violation of a Bell-type inequality.