[Paper Review] Homodyne Detection Quadrature Phase Shift Keying Continuous-Variable Quantum Key Distribution with High Excess Noise Tolerance

Wen‐Bo Liu, Chen-Long Li+8 more|arXiv (Cornell University)|Apr 22, 2021

Quantum Information and Cryptography81 references103 citations

TL;DR

This paper proposes a homodyne detection-based continuous-variable quantum key distribution protocol using quadrature phase shift keying (QPSK) with four-phase coherent states. By leveraging reverse reconciliation and optimizing signal mapping, the protocol achieves high tolerance to excess noise and outperforms previous homodyne schemes, enabling secure key distribution over nearly intercity distances with improved robustness against detector noise.

ABSTRACT

Discrete-modulated continuous-variable quantum key distribution with homodyne detection is widely recognized for its ease of implementation, efficiency with respect to error correction, and its compatibility with modern optical communication devices. However, recent studies report that the application of homodyne detection obtains poor tolerance to excess noise and insufficient transmission distance, hence seriously restricting the large-scale deployment of quantum secure communication networks. In this paper, we propose a homodyne detection protocol using the quadrature phase shift keying technique. By limiting information leakage, our proposed protocol enhances excess noise tolerance to a high level. Furthermore, we demonstrate that homodyne detection performs better than heterodyne detection in quaternary-modulated continuous-variable quantum key distribution under the untrusted detector noise scenario. The security is analyzed using the tight numerical method against collective attacks in the asymptotic regime. Our results imply that the current protocol is able to distribute keys in nearly intercity area and thus paves the way for constructing low-cost quantum secure communication networks.

Motivation & Objective

• Address the poor excess noise tolerance and limited transmission distance of existing homodyne detection protocols in discrete-modulated CV-QKD.
• Improve the practicality of continuous-variable quantum key distribution for large-scale quantum secure communication networks.
• Demonstrate that homodyne detection can outperform heterodyne detection under untrusted detector noise conditions.
• Enhance security and key rate performance using a quaternary-modulated protocol with optimized signal mapping.

Proposed method

• Uses four-phase coherent states at π/4, 3π/4, 5π/4, and 7π/4 for discrete modulation.
• Employs homodyne detection with random choice of quadrature (q or p) per round.
• Applies reverse reconciliation: Alice's raw key is derived from the phase label based on Bob's measured quadrature.
• Introduces post-selection via threshold ∆ to filter measurement outcomes and reduce information leakage.
• Uses tight numerical security analysis against collective attacks in the asymptotic regime.
• Optimizes key rate calculation through parameter tuning and noise resilience in the presence of excess noise.

Experimental results

Research questions

• RQ1 Can homodyne detection with discrete modulation achieve high excess noise tolerance in CV-QKD?
• RQ2 Does a QPSK-modulated protocol with phase-based key mapping outperform existing homodyne schemes in key rate and transmission distance?
• RQ3 Can homodyne detection surpass heterodyne detection in performance under untrusted detector noise?
• RQ4 What is the maximum transmission distance achievable with high excess noise tolerance using this protocol?

Key findings

• The proposed protocol achieves significantly higher excess noise tolerance compared to prior homodyne detection protocols with discrete modulation.
• Transmission distance is extended to nearly intercity scale, enabling practical deployment in metropolitan networks.
• The secret key rate is comparable to that of heterodyne detection protocols, with improved performance under untrusted detector noise.
• Homodyne detection outperforms heterodyne detection in scenarios with detector imperfections, particularly under excess noise.
• The protocol maintains high security under collective attacks, verified via tight numerical analysis in the asymptotic regime.
• Post-selection with ∆ > 0 enhances key rate and noise resilience, demonstrating the effectiveness of signal mapping optimization.