Proof-of-Principle Experimental Demonstration of Twin-Field Type Quantum Key Distribution.

Area of Science:

• Quantum Information Science
• Quantum Cryptography
• Experimental Physics

Background:

• Twin-field quantum key distribution (QKD) offers a path beyond the fundamental secret key rate limit for point-to-point QKD without quantum repeaters.
• Practical implementation of TFQKD faces challenges, particularly maintaining quantum state phase stability over long fiber optic distances.

Purpose of the Study:

• To experimentally demonstrate a variant of the twin-field (TF) quantum key distribution (QKD) protocol.
• To achieve a high secret key rate that surpasses the repeaterless bound.
• To address practical implementation challenges in TFQKD, specifically phase stabilization.

Main Methods:

• Experimental demonstration of TFQKD using the protocol by Curty, Azuma, and Lo, which eliminates the need for global phase matching postselection.
• Utilizing a Sagnac loop structure to ensure phase stability of quantum states over kilometer-long optical fibers.
• Collecting experimental data in a high loss region to evaluate secure key rate performance.

Main Results:

• The experimental TFQKD system successfully demonstrated the protocol's feasibility.
• The Sagnac loop structure effectively stabilized quantum state phases over extended fiber lengths.
• The estimated secure key rate in the high loss region surpassed the established repeaterless bound for QKD.

Conclusions:

• The proof-of-principle experiment validates the potential of the Curty, Azuma, and Lo TFQKD protocol.
• The Sagnac loop is a viable solution for overcoming phase stabilization issues in practical TFQKD systems.
• This work shows that TFQKD can achieve secure key rates beyond the repeaterless bound with current technology.