Employing long fibre-optical Mach- Zehnder interferometers for quantum cryptography with orthogonal states

TL;DR

This paper demonstrates the practical implementation of a long-distance quantum cryptography protocol using stabilized fibre-optic Mach-Zehnder interferometers with orthogonal states, achieving low error rates over 1 km.

Contribution

It presents an experimental setup for quantum cryptography with orthogonal states over long distances using actively stabilized fibre interferometers, a novel practical approach.

Findings

Successfully implemented a 1 km long fibre quantum cryptography link.

Achieved a quantum bit error rate of 2.2%.

Demonstrated active phase stabilization with classical wavelength multiplexing.

Abstract

We experimentally demonstrate that a long distance actively stabilized Mach-Zehnder fibre optical interferometer can be used to reliably implement the GV95 quantum cryptography protocol employing orthogonal states. A proof-of-principle experiment using an interferometer composed of 1 km of spooled optical fibres connecting Alice and Bob is performed. The active stabilisation against phase drifts is done with a classical channel wavelength-multiplexed with the quantum channel and a high stable visibility implying a QBER of 2.2 % is shown.