Phase noise-immune unconditionally secured classical key distribution using doubly coupled Mach-Zehnder interferometer

TL;DR

This paper introduces a phase noise-immune classical key distribution method using a doubly coupled Mach-Zehnder interferometer, enabling secure free-space optical communication unaffected by environmental phase fluctuations.

Contribution

The work demonstrates an environmental noise-immune USCKD protocol with a two-channel layout that does not require active phase locking, suitable for long-distance free-space links.

Findings

Unconditional security unaffected by environmental phase noise.

Effective for free-space optical links with potentially unlimited distance.

No active phase locking needed for environmental noise immunity.

Abstract

Recently, new physics for unconditional security in a classical key distribution (USCKD) in a frame of a double Mach-Zehnder interferometer has been proposed and demonstrated as a proof of principle, where the unconditional security is unaffected by the no-cloning theorem of quantum key distribution protocols. Due to environmental phase fluctuations caused by temperature variations, atmospheric turbulences, or mechanical vibrations, active phase locking seems to be necessary for the two-channel transmission layout of USCKD. Here, the two-channel layout of USCKD is demonstrated to be an environmental noise-immune protocol especially for free space optical links, where the transmission distance is potentially unlimited if random phase noises are considered.