Twin-Field Quantum Key Distribution: Protocols, Security, and Open Problems

TL;DR

This survey reviews Twin-Field Quantum Key Distribution, highlighting its protocols, security proofs, variants, experimental progress, and future challenges for scalable quantum networks.

Contribution

It provides a comprehensive overview of TF-QKD, including protocol variants, security analyses, experimental milestones, and open problems for future quantum internet integration.

Findings

TF-QKD achieves long-distance secure communication with square-root rate scaling.

Multiple protocol variants improve performance and security.

Open problems and future directions for quantum network deployment are identified.

Abstract

Twin-Field Quantum Key Distribution (TF-QKD) has emerged as a potential protocol for long distance secure communication, overcoming the rate-distance limitations of conventional quantum key distribution without requiring trusted repeaters. By having two parties transmit phase encoded weak coherent pulses (WCP) to an untrusted central node, the TF-QKD exploits single-photon interference to achieve secret key rates scaling as square-root of channel length, enabling quantum-secured communication over unprecedented distances. This survey provides a comprehensive survey of TF-QKD, covering the original protocol, its fundamental principles, and key-rate derivation. We discuss major TF-QKD variants, including Phase-Matching QKD and Sending-or-Not-Sending QKD, with various improved versions. We compare their performance, implementation trade-offs, protocol-specific vulnerabilities, and countermeasures. The survey summarizes security proofs ranging from asymptotic decoy-state analyses to finite-key composable frameworks, experimental milestones, technological enablers, and practical deployment challenges. Finally, we outline open problems in the field and present a roadmap for integrating TF-QKD into scalable quantum networks, underscoring its central role in the future quantum internet.