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Optics Express

Enhancing the performance of entanglement-based WDM-QKD

Chen-Peng Hao, Siwei Sun, Bo Liu, Shuang Wang, Hongwei Li

Published May 8, 2025• 4 citations
Publisher

Abstract

Entanglement-based quantum key distribution (EB-QKD) is considered an important implementation method for fully connected quantum networks. Due to practical considerations for conserving fiber resources, the demand for integrating EB-QKD into existing optical networks through wavelength-division multiplexing (WDM) in the same fiber (referred to as EB-WDM-QKD) is increasingly urgent. However, the noise generated from the classical system is an inherent limitation that restricts the performance of EB-WDM-QKD. In this work, we proposed an improved scheme that employs optical amplifiers to enhance the performance of EB-WDM-QKD. Under the fixed classical received power scenario, the transmission distance can be increased by more than 70 km compared to the original EB-WDM-QKD scheme without amplifiers. Moreover, for the scenario where the launch power of data lasers and amplifiers in the classical channel is non-adjustable, we applied the advantage distillation (AD) method to further enhance the performance of EB-WDM-QKD, and the transmission distance can be enhanced by more than 50 km. Our work can significantly enhance the performance of the EB-WDM-QKD system by optimizing the configuration of the classical subsystem and the post-processing of the quantum subsystem. The methods have the potential to be extended to various WDM-QKD systems, providing new perspectives for the advancement of WDM-QKD.

DOI
10.1364/oe.561000

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Entanglement-based quantum key distribution (EB-QKD) is considered an important implementation method for fully connected quantum networks. Due to practical considerations for conserving fiber resources, the demand for integrating EB-QKD into existing optical networks through wavelength-division multiplexing (WDM) in the same fiber (referred to as EB-WDM-QKD) is increasingly urgent. However, the noise generated from the classical system is an inherent limitation that restricts the performance of EB-WDM-QKD. In this work, we proposed an improved scheme that employs optical amplifiers to enhance the performance of EB-WDM-QKD. Under the fixed classical received power scenario, the transmission distance can be increased by more than 70 km compared to the original EB-WDM-QKD scheme without amplifiers. Moreover, for the scenario where the launch power of data lasers and amplifiers in the classical channel is non-adjustable, we applied the advantage distillation (AD) method to further enhance the performance of EB-WDM-QKD, and the transmission distance can be enhanced by more than 50 km. Our work can significantly enhance the performance of the EB-WDM-QKD system by optimizing the configuration of the classical subsystem and the post-processing of the quantum subsystem. The methods have the potential to be extended to various WDM-QKD systems, providing new perspectives for the advancement of WDM-QKD.
Quantum key distribution (QKD) is a promising method for sharing an information-theoretically secure secret key using the properties of quantum mechanics. Although QKD is the most practical field in quantum information science, its widespread adoption is constrained by high implementation costs. Despite the cost-effectiveness of propagating QKD with classical communication using wavelength division multiplexing (WDM), the noise generated by relatively strong classical signals degrades QKD performance. Even though several mitigation strategies exist, they often involve complexity or additional hardware. In this paper, we apply advantage distillation (AD) to enhance the performance of a practical decoy-state BB84 QKD system operating in a WDM environment. We perform finite-key analysis in both co-propagation and counter-propagation scenarios with three classical channels, and furthermore we examine the effects of varying the number of classical channels and the optical power per channel. A comparison of simulation results obtained with and without AD demonstrates that AD is robust to noise originating from classical channels. These results show that AD increases the secure key rate and transmission distance in the WDM-based QKD environment under both co-propagation and counter-propagation without requiring hardware changes. These findings suggest advantage distillation is a promising strategy for the widespread adoption of WDM-based QKD, including in challenging counter-propagation cases.
Background: Quantum Key Distribution (QKD( is a promising technology for secure communication, leveraging the principles of quantum mechanics to provide theoretically unbreakable encryption. With the exponential growth in data traffic and the increasing need for secure communication in backbone fiber networks, integrating high-bit-rate multiplexing techniques into QKD systems can enhance their efficiency and scalability. Problem: Traditional QKD systems face limitations in terms of data rate and network scalability, particularly in high-capacity optical communication networks. As data demands increase, there is a critical need for methods that can support high-bit-rate multiplexing while maintaining the security and performance of QKD. Method: This study proposes a novel QKD approach using high-bit-rate multiplexing in backbone fiber networks. The method involves encoding quantum keys using multiple optical channels simultaneously to increase the data throughput of the QKD system. We employ a combination of time-division multiplexing (TDM( and wavelength-division multiplexing (WDM( to optimize the use of fiber resources and enhance key distribution rates. Results: Simulation results demonstrate that the proposed method achieves a key distribution rate of 10 Mbps over a 200 km fiber link with a quantum bit error rate (QBER( of 1.5%. This represents a 50% improvement in key rate compared to conventional QKD systems without multiplexing. Additionally, the method shows enhanced scalability and network utilization, supporting up to 16 multiplexed channels with minimal impact on security.
Wavelength division multiplexing (WDM) of quantum key distribution (QKD) with classical optical channels has been proven to be feasible experimentally. In this paper, we will analyze the practical security of WDM-QKD theoretically. Specifically, we first establish the noise model of classical signals. Then, the influence of classical noises on the performance of decoy-state WDM-QKD is studied with a finite-key security analysis. For numerical simulations, the effect of classical noise-reduction methods for different experimental settings is given. The secret key rate and maximum transmission distance of WDM-QKD is simulated with various sent number of quantum pulses or transmitted power of classical signals. Furthermore, the performance of two kinds of decoy-state WDM-QKD is compared, which shows that the optimal decoy-state protocol for WDM-QKD is related to the sent number of quantum pulses. Since WDM-QKD is desired to reduce the cost of QKD networks and since experiments have already been carried out, our work can not only close the gap between theory and practice, but also be used to optimize the experimental parameters and improve its performance.
The advantage distillation (AD) method has proven effective in improving the performance of quantum key distribution (QKD). In this paper we introduce the AD method into a recently proposed asynchronous measurement-device-independent (AMDI) QKD protocol, taking finite-key effects into account. Simulation results show that the AD method significantly enhances AMDI QKD, e.g., extending the transmission distance by 16 km with a total pulse count of $N=7.24\ifmmode\times\else\texttimes\fi{}{10}^{13}$, and enables AMDI QKD, previously unable to generate keys, to generate keys with a misalignment error rate of 1010%10. As the AD method can be directly integrated into the current system through refined postprocessing, our results facilitate the practical implementation of AMDI QKD in various applications, particularly in scenarios with high channel losses and misalignment errors.
Abstract Quantum key distribution promises information-theoretically secure communication, with data post-processing playing a vital role in extracting secure keys from raw data. While hardware advancements have significantly improved practical implementations, optimizing post-processing techniques offers a cost-effective avenue to enhance performance. Advantage distillation, which extends beyond standard information reconciliation and privacy amplification, has proven instrumental in various post-processing methods. However, the optimal post-processing remains an open question. Therefore, it is important to develop a comprehensive framework to encapsulate and enhance these existing methods. In this work, we propose an advantage distillation framework for quantum key distribution, generalizing and unifying existing key distillation protocols. Inspired by entanglement distillation, our framework not only integrates current techniques but also improves upon them. Notably, by employing classical linear codes, we achieve higher key rates, particularly in scenarios where one-time pad encryption is not used for post-processing. Our approach provides insights into existing protocols and offers a systematic way for further enhancements in quantum key distribution.
A high-speed quantum key distribution (QKD) system has been developed with the goal of a 1-Mbps final secure key generation rate under 10-dB transmission loss, which corresponds to 50 km of standard single mode fiber. For the purpose of speeding-up all processes in QKD sequence, we apply a wavelength-division-multiplexing (WDM) technique using the colorless interferometric technique and a key distillation hardware (HW) engine. We establish a novel WDM scheme, sharing interferometers and their temperature regulators over multiple channels, which enables us to increase the number of channels with a small impact on system cost and size. To generate a secure key while satisfying both high speed and high security, we develop a key distillation HW engine which enables us to execute key distillation with 1-Mbit code length in real time. We have experimentally evaluated the performance of the developed system through installed fiber. By operating three wavelength channels, a new, world leading key generation rate of greater than 200 kbps over a 14.5-dB transmission loss has been achieved.