Quantum process tomography of linear and quadratically nonlinear optical systems

TL;DR

This paper introduces a modified interferometric method to characterize both linear and quadratically nonlinear optical quantum processes, using coherent states and single photons respectively, advancing quantum process tomography techniques.

Contribution

It presents a novel interferometric approach capable of characterizing a broad class of optical quantum processes, including nonlinear transformations.

Findings

The method effectively characterizes linear optical transformations.

Single photons are necessary for nonlinear process characterization.

The approach simplifies quantum process tomography in optical systems.

Abstract

A central task in quantum information processing is to characterize quantum processes. In the realm of optical quantum information processing, this amounts to characterizing the transformations of the mode creation and annihilation operators. This transformation is unitary for linear optical systems, whereas these yield the well-known Bogoliubov transformations for systems with Hamiltonians that are quadratic in the mode operators. In this paper, we show that a modified Mach-Zehnder interferometer can characterize both these kinds of evolutions for multimode systems. While it suffices to use coherent states for the characterization of linear optical systems, we additionally require single photons to characterize quadratically nonlinear optical systems.