# Real-time shaping of entangled photons by classical control and feedback

## TL;DR

This paper demonstrates real-time control of entangled photons through classical beam shaping, significantly enhancing free-space quantum communication links by leveraging classical signals for quantum optimization.

## Contribution

It introduces a novel method to shape entangled photons in real-time by controlling the classical laser beam, enabling practical quantum communication over turbulent channels.

## Key findings

- Increased quantum link length by up to two orders of magnitude.
- Classical beam shaping effectively optimizes quantum signals.
- Method applicable to real-world quantum communication scenarios.

## Abstract

Quantum technologies hold great promise for revolutionizing photonic applications such as cryptography. Yet their implementation in real-world scenarios is held back, mostly due to sensitivity of quantum light to scattering. Recent developments in optimizing the shape of single photons introduce new ways to control quantum light. Nevertheless, shaping single photons in real-time remains a challenge due to the weak associated signals, which are too noisy for optimization processes. Here, we overcome this challenge and control scattering of entangled photons by shaping the classical laser beam that stimulates their creation. We discover that since the classical beam and the entangled photons follow the same path, the strong classical signal can be used for optimizing the weak quantum signal. We show that this approach can increase the length of free-space turbulent quantum links by up to two orders of magnitude, opening the door for employing wavefront shaping for quantum communications.