# A hybrid quantum eraser scheme for characterization of free-space and fiber communication channels

## TL;DR

This paper introduces a quantum eraser-based method using spatial modes, especially orbital angular momentum, to characterize disturbances in free-space and fiber communication channels, enhancing understanding of mode perturbations.

## Contribution

It presents a novel quantum eraser scheme that employs vector modes and orbital angular momentum to analyze channel disturbances, replacing traditional path interferometry with mode-based measurements.

## Key findings

- Effective characterization of fiber perturbations using vector modes.
- Demonstrated applicability to high-order spatial mode encoding.
- Potential for improved ultra-fast fiber communication diagnostics.

## Abstract

We demonstrate a simple projective measurement based on the quantum eraser concept that can be used to characterize the disturbances of any communication channel. Quantum erasers are commonly implemented as spatially separated path interferometric schemes. Here we exploit the advantages of redefining the which-path information in terms of spatial modes, replacing physical paths with abstract paths of orbital angular momentum (OAM). Remarkably, vector modes (natural modes of free-space and fiber) have a non-separable feature of spin-orbit coupled states, equivalent to the description of two independently marked paths. We explore the effects of fiber perturbations by probing a step-index optical fiber channel with a vector mode, relevant to high-order spatial mode encoding of information for ultra-fast fiber communications.