# Characterization of Depolarizing Channels Using Two-Photon Intereference

## TL;DR

This paper presents a method using Hong-Ou-Mandel interference to distinguish true depolarization from rapid polarization rotations in quantum channels, overcoming limitations of detector timing resolutions.

## Contribution

The authors introduce a novel technique leveraging two-photon interference to accurately characterize depolarizing channels in quantum communication.

## Key findings

- Method effectively separates depolarization from polarization rotations.
- Results are independent of photodetector timing resolution.
- Provides a practical approach for quantum channel characterization.

## Abstract

Depolarization is one of the most important sources of error in a quantum communication link that can be introduced by the quantum channel. Even though standard quantum process tomography can, in theory, be applied to characterize this effect, in most real-world implementations depolarization cannot be distinguished from time-varying unitary transformations, especially when the time scales are much shorter than the detectors response time. In this paper, we introduce a method for distinguishing true depolarization from fast polarization rotations by employing Hong-Ou-Mandel interference. It is shown that the results are independent of the timing resolutions of the photodetectors.