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Physical Review A

Quantum secured 10-Gbit/s ethernet passive optical access network and its machine-learning-assisted implementation

Jia-Le Kang, Minghui Zhang, Xiaopeng Liu, Chen He

Published Feb 26, 2024• 1 citation
Publisher

Abstract

The extension from point-to-point quantum key distribution (QKD) to multipoint communication is an inevitable trend toward the large-scale development of QKD networks. At present, it is a relatively simple and cost-effective implementation to integrate quantum access networks (QANs) into existing Ethernet passive optical access networks (EPONs). This work proposes a quantum secured 10 Gbit/s EPON (10G-EPON), in which a plug-and-play twin-field QKD (PnP-TF-QKD) architecture is developed, requiring a single untrusted laser and a pair of shared detectors. The PnP-TF-QKD implementation is compatible with standard 10G-EPON and can support up to 64 users. In addition, prior to the deployment of QKD on EPON, it is crucial to predict in advance whether the attainable QAN indicators, such as the secure key rate, the maximum feeder fiber length, etc., meet the requirements of a certain circumstance. However, this task is often complex and time consuming. Therefore, we present a machine-learning-based user-demand-oriented prediction model to facilitate the evaluation of QAN parameters. The plug-and-play twin-field quantum access network (PnP-TF-QAN) and its machine-learning-assisted implementation method provide guidance for further experiments and actual deployments of large-scale QANs.

DOI
10.1103/physreva.109.022617

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The extension from point-to-point quantum key distribution (QKD) to multipoint communication is an inevitable trend toward the large-scale development of QKD networks. At present, it is a relatively simple and cost-effective implementation to integrate quantum access networks (QANs) into existing Ethernet passive optical access networks (EPONs). This work proposes a quantum secured 10 Gbit/s EPON (10G-EPON), in which a plug-and-play twin-field QKD (PnP-TF-QKD) architecture is developed, requiring a single untrusted laser and a pair of shared detectors. The PnP-TF-QKD implementation is compatible with standard 10G-EPON and can support up to 64 users. In addition, prior to the deployment of QKD on EPON, it is crucial to predict in advance whether the attainable QAN indicators, such as the secure key rate, the maximum feeder fiber length, etc., meet the requirements of a certain circumstance. However, this task is often complex and time consuming. Therefore, we present a machine-learning-based user-demand-oriented prediction model to facilitate the evaluation of QAN parameters. The plug-and-play twin-field quantum access network (PnP-TF-QAN) and its machine-learning-assisted implementation method provide guidance for further experiments and actual deployments of large-scale QANs.
Quantum key distribution (QKD) provides an information-theoretically secure method to share keys between legitimate users. To achieve large-scale deployment of QKD, it should be easily scalable and cost-effective. The infrastructure construction of quantum access network (QAN) expands network capacity and the integration between QKD and classical optical communications reduces the cost of channel. Here, we present a practical downstream QAN over a 10 Gbit/s Ethernet passive optical network (10G-EPON), which can support up to 64 users. In the full coexistence scheme using the single feeder fiber structure, the co-propagation of QAN and 10G-EPON signals with 9 dB attenuation is achieved over 21 km fiber, and the secure key rate for each of 16 users reaches 1.5 kbps. In the partial coexistence scheme using the dual feeder fiber structure, the combination of QAN and full-power 10G-EPON signals is achieved over 11 km with a network capacity of 64-user. The practical QAN over the 10G-EPON in our work implements an important step towards the achievement of large-scale QKD infrastructure.
Information-theoretically secure quantum access network (QAN) provides a multiple-user structure for large-scale key distribution. However, active reference-frame compensation and clock synchronization require extra devices and signals, increasing the complexity of the system and time/resource consumption. In this work, a fully passive received QAN comprising both free-space and fiber channels is demonstrated. Based on an improved reference-frame-independent quantum key distribution (RFI-QKD) protocol and qubit-synchronization method, Bob only passively receives quantum signals from all Alices with various wavelengths and laser repetition rates. Extra classical signals for reference frame calibration and clock synchronization are not required, so that the QAN can be asynchronous. Furthermore, RFI-QKD with a 7 km free-space channel in an urban environment is first fully demonstrated with a positive key rate, and the maximal distance over a 250 km fiber channel for four-state RFI-QKD is also achieved. The experimental results show that our fully passive received QAN is robust, cost-effective, and flexible, paving its application in the future quantum network.
Fiber-based quantum key distribution (QKD) systems are mature and commercialized, but their integration into existing optical networks is crucial for their widespread use, in particular in passive optical networks (PONs) if end-to-end quantum-secured communications are to be addressed. While discrete-variable QKD coexistence with classical channels is well-studied in point-to-point links, its performance in point-to-multipoint topologies like PONs has received less attention. We thus developed a numerical tool to estimate quantum-available bandwidth and maximum link lengths for QKD systems in single-fiber PON architectures in coexistence with GPON, XG-PON, NG-PON2, and HS-PON standards. The QKD channel performance is obtained by setting thresholds on the quantum bit error rate and the secret key rate, ultimately limited by spontaneous Raman scattering noise and high optical distribution network losses. We perform a comparison between the performance obtained assuming the asymptotic infinite-key generation rate or taking into account actual implementations in the finite-key regime. We evidence that proper design rules can be obtained as a function of both classical and quantum system parameters to support end-to-end quantum security services in existing optical networks.
Quantum key distribution offers information-theoretic security and is advancing toward real-world quantum secure networks. To meet the growing demand for scalable solutions, we present a high-rate quantum access network (QAN) with 16 user nodes based on a passive optical network, where a highly efficient coherent-state point-to-multipoint (PTMP) protocol is designed for concurrent independent secret key generation between one transmitter and multiple receivers. Such accomplishment is attributed to a subtle shot-noise calibration method, advanced digital signal processing algorithms, and a flexible post-processing strategy. Finally, the experimentally estimated average secret key rate is approximately 2.086 Mbps between the transmitter and each user, two orders of magnitude higher than previous demonstrations. With low cost, excellent compatibility, and wide bandwidth, our work paves the way for practical PTMP QANs, representing a key step toward scalable quantum secure networks.
Quantum key distribution (QKD) is a key application in quantum communication, enabling secure key exchange between parties using quantum states. Twin-field (TF) QKD offers a promising solution that surpasses the repeaterless limits, and its measurement-device-independent nature makes it suitable for star-type network architectures. In this work, we propose a scalable TF-QKD network with adaptable architecture, where users prepare quantum signals and send them to network nodes. These nodes use an optical switch to route the signals to multi-user measurement units, enabling secure key distribution among arbitrary users and adapting to complex connection demands of the network. A proof-of-principle demonstration with three users successfully achieved secure key sharing over simulated link losses of up to 303030 dB, with an average rate of 19.5719.5719.57 bit/s. Additionally, simulations show that the proposed architecture can achieve a total secure key rate of 4.84×1044.84 \times 10^{4}4.84×104 bit/s at 100100100 km in a symmetric 323232-user network. This approach represents a significant advancement in the topology of untrusted-node QKD networks and holds promise for practical, large-scale applications in secure communication.
It is well known that optical access networks are able to provide high data rates over long distances and to a reasonable number of users. Security and privacy are always a challenge for public accessible network infrastructures. Especially in time-division multiplexing passive optical networks (TDM-PONs), in which the downstream signal is broadcasted to all users connected via the same wavelength channel in a shared fiber link, privacy can be a critical concern. Although encryption at the application layer can provide a high level of security, this can be achieved only if the encryption key distribution is perfectly save. On the other hand, encryption on the physical layer such as quantum cryptography or, more precisely, quantum key distribution (QKD) is a very promising approach to achieve secure communication. However, there remain several issues that have to be solved before the quantum cryptography reaches the maturity level needed for a cost effective implementation in practical networks. In this paper, we address quantum key distribution (QKD) over passive optical access networks, which is an enabling technology required to cost efficiently deploy practical quantum encrypted data communication in the access area. We study different methods to integrate QKD systems in conventional optical access networks and quantitatively evaluate their suitability for a potential implementation.