Three-Basis Loop-Back QKD: A Passive Architecture for Secure and Scalable Quantum Mobile Networks.

Area of Science:

• Quantum Information Science
• Quantum Cryptography
• Optical Communication

Background:

• Conventional Quantum Key Distribution (QKD) protocols often require complex setups with detectors on both ends.
• Existing one-way schemes like BB84 have limitations in noise tolerance and hardware requirements.
• There is a need for compact, low-power, and robust QKD solutions for emerging quantum-mobile and IoT applications.

Purpose of the Study:

• To introduce and analyze the Loop-Back Quantum Key Distribution (LB-QKD) protocol.
• To demonstrate the advantages of a bidirectional architecture with a single photon traveling through the same channel.
• To enhance noise tolerance and security features for practical QKD implementations.

Main Methods:

• Development of a bidirectional LB-QKD protocol where Alice handles both state preparation and measurement.
• Implementation of an extended three-basis {X,Y,Z} configuration for improved noise filtering.
• Analytical modeling to evaluate protocol error, information gain, and Quantum Bit Error Rate (QBER) tolerance.

Main Results:

• The three-basis configuration reduces effective protocol error from e/2 to e/3, a 33% improvement in noise resilience.
• LB-QKD doubles the tolerable QBER, supporting secure operation up to 22% (two bases) and 47.58% (three bases).
• Despite lower sifting efficiency, post-sifting throughput remains comparable to BB84, with a total information gain of 0.26 bits per pulse.

Conclusions:

• LB-QKD provides a scalable, energy-efficient framework for secure key distribution and authentication.
• The passive, self-verifying architecture offers enhanced resistance against common quantum attacks.
• LB-QKD is well-suited for next-generation quantum-mobile and distributed quantum networks due to its simplified hardware and improved performance.