# Zero supermode-based multipartite entanglement in $\chi^{(2)}$ nonlinear waveguides arrays

## TL;DR

This paper demonstrates that arrays of $$ nonlinear waveguides can generate scalable, robust multipartite continuous-variable entanglement suitable for optical quantum information processing, using zero-eigenvalue supermodes.

## Contribution

It analytically shows that odd-numbered waveguide arrays produce scalable multipartite entanglement through zero-eigenvalue supermodes, a novel approach for quantum photonics.

## Key findings

- Entanglement grows with propagation length.
- Arrays are scalable and robust to losses.
- Device is compatible with current technology.

## Abstract

We show that arrays of $\chi^{(2)}$ nonlinear waveguides in the second harmonic generation regime are a promising source of continuous-variable entanglement. We indeed demonstrate analytically that optical arrays with odd number of waveguides injected with the zero-eigenvalue fundamental supermode entangle this fundamental supermode with a collective harmonic field. Moreover the fundamental individual modes are multipartite entangled and their entanglement grows with propagation length. The device is scalable, robust to losses, does not rely on specific values of nonlinearity and coupling and is easily realized with current technology. It thus stands as an unprecedented candidate for generation of multipartite continuous-variable entanglement for optical quantum information processing.