# Genuine time-bin-encoded quantum key distribution over a turbulent depolarizing free-space channel

## TL;DR

This paper demonstrates the feasibility of time-bin-encoded quantum key distribution over turbulent, depolarizing free-space channels, showing stable secure key generation despite wavefront and polarization distortions.

## Contribution

It introduces a novel analyzer apparatus that enables stable quantum key distribution with time-bin states in turbulent free-space conditions, overcoming previous practical limitations.

## Key findings

- Achieved stable quantum bit error ratio of 5.32%
- Demonstrated secure key generation over 1.2 km free-space channel
- Showed viability of time-bin quantum communication in turbulent environments

## Abstract

Despite its widespread use in fiber optics, encoding quantum information in photonic time-bin states is usually considered impractical for free-space quantum communication as turbulence-induced spatial distortion impedes the analysis of time-bin states at the receiver. Here, we demonstrate quantum key distribution using time-bin photonic states distorted by turbulence and depolarization during free-space transmission. Utilizing a novel analyzer apparatus, we observe stable quantum bit error ratios of 5.32 %, suitable for generating secure keys, despite significant wavefront distortions and polarization fluctuations across a 1.2 km channel. This shows the viability of time-bin quantum communication over long-distance free-space channels, which will simplify direct fiber/free-space interfaces and enable new approaches for practical free-space quantum communication over multi-mode, turbulent, or depolarizing channels.