On-chip generation of spatial entanglement

Combining the generation and manipulation of complex quantum states of light on a single chip is a crucial step toward practical quantum information technologies. This work addresses this challenge by merging two fundamental concepts—nonlinear optics and quantum walks—to realize a compact and versatile source of photon pairs exhibiting strong spatial correlations, that cannot be produced by classical means.

Traditional photonic devices generate and manipulate photons in a step-by-step fashion, using a sequence of discrete optical components. By contrast, nonlinear waveguide systems offer a promising alternative where photons can be generated and interfere in a continuous manner, unveiling novel capabilities within a reduced footprint. In this work, photon pairs produced by parametric generation in an AlGaAs waveguide array hop randomly from one waveguide to the other during their propagation—they experience quantum walks, a non-classical analogue of the famous Galton board. By tailoring the pump beam, the output state can be reconfigured, enabling the creation of a wide variety of spatially entangled states of light. Combined with the ability to engineer at will the device geometry, this novel approach opens exciting prospects for simulating with photons physical problems that are otherwise difficult to access in condensed matter.

Reference :

Tunable generation of spatial entanglement in nonlinear waveguide arrays

A. Raymond, A. Zecchetto, J. Palomo, M. Morassi, A. Lemaître, F. Raineri, M. Amanti, S. Ducci, F. Baboux

Phys. Rev. Lett. 133, 233602 (2024)