# Probing free-space quantum channels with laboratory-based experiments

## TL;DR

This paper introduces a laboratory method to simulate and analyze atmospheric free-space quantum channels affected by turbulence, enabling controlled characterization of turbulent quantum communication links.

## Contribution

The authors develop a novel technique to emulate arbitrary atmospheric turbulence effects on quantum channels in the lab, facilitating detailed study and testing of turbulent quantum communication.

## Key findings

- Successfully modeled turbulence-induced losses in the lab
- Characterized nonclassical states under simulated atmospheric conditions
- Analyzed the effectiveness of post-selection protocols in turbulent channels

## Abstract

Atmospheric channels are a promising candidate to establish secure quantum communication on a global scale. However, due to their turbulent nature, it is crucial to understand the impact of the atmosphere on the quantum properties of light and examine it experimentally. In this paper, we introduce a method to probe atmospheric free-space links with quantum light on a laboratory scale. In contrast to previous works, our method models arbitrary intensity losses caused by turbulence to emulate general atmospheric conditions. This allows us to characterize turbulent quantum channels in a well-controlled manner. To implement this technique, we perform a series of measurements with different constant attenuations and simulate the fluctuating losses by combining the obtained data. We directly test the proposed method with an on-chip source of nonclassical light and a time-bin-multiplexed detection system. With the obtained data, we characterize the nonclassicality of the generated states for different atmospheric noise models and analyze a post-selection protocol. This general technique in atmospheric quantum optics allows for studying turbulent quantum channels and predicting their properties for future applications.