Experimental polarization encoded quantum key distribution over optical fibres with real-time continuous birefringence compensation

TL;DR

This paper demonstrates an active, real-time polarization compensation method for optical fibers in quantum key distribution, enabling continuous secure communication despite polarization fluctuations.

Contribution

The study introduces a novel active polarization drift compensation scheme that operates continuously during quantum key distribution over optical fibers.

Findings

Effective compensation of fast polarization rotations (~40*pi rad/s)

Continuous quantum key distribution maintained under random polarization fluctuations

Potential for long-distance Bell-state measurements with linear optics

Abstract

In this paper we demonstrate an active polarization drift compensation scheme for optical fibres employed in a quantum key distribution experiment with polarization encoded qubits. The quantum signals are wavelength multiplexed in one fibre along with two classical optical side channels that provide the control information for the polarization compensation scheme. This set-up allows us to continuously track any polarization change without the need to interrupt the key exchange. The results obtained show that fast polarization rotations of the order of 40*pi rad/s are effectively compensated for. We demonstrate that our set-up allows continuous quantum key distribution even in a fibre stressed by random polarization fluctuations. Our results pave the way for Bell-state measurements using only linear optics with parties separated by long-distance optical fibres.