Completely characterizing multimode nonlinear-optical quantum processes

TL;DR

This paper introduces a comprehensive experimental method for fully characterizing multimode nonlinear-optical quantum processes, enabling better understanding and development of advanced photonic technologies.

Contribution

It presents a novel technique to determine the amplification and noise matrices of multimode nonlinear processes, extending characterization beyond linear optics.

Findings

Successfully characterized a second-order nonlinear process of parametric downconversion.

Demonstrated the method's applicability to various processes including cluster state generation and mode-dependent loss.

Provided full information to identify eigenquadratures and their properties.

Abstract

Complete characterization of a multimode optical process has paved the way for understanding complex optical phenomena, leading to the development of novel optical technologies. Until now, however, characterizations have mainly focused on a linear-optical process, despite the plethora of multimode nonlinear-optical processes crucial for photonic technologies. Here we report the experimental characterization of multimode nonlinear-optical quantum processes by obtaining the full information needed to describe them while satisfying the necessary physical condition. Specifically, to characterize a second-order nonlinear-optical process of parametric downconversion, we determine the amplification and noise matrices of multimode field quadratures. The full information allows us to factorize the multimode process, leading to the identification of eigenquadratures and their associated amplification and noise properties. Moreover, we demonstrate the broad applicability of our method by characterizing various nonlinear-optical quantum processes, including cluster state generation, mode-dependent loss with nonlinear interaction, and a quantum noise channel. Our method, by providing a versatile technique for characterizing a nonlinear-optical process, will be beneficial for developing scalable photonic technologies.