Journal of the Optical Society of America B

Continuous-variable quantum key distribution based on a faster-than-Nyquist scheme

Yaxi Pan, Ling Zhang, Ying Guo, Duan Huang

Published Jan 9, 2020• 3 citations

Abstract

In previous continuous-variable quantum key distribution (CV-QKD) systems, the transmission rate is limited by the Nyquist criterion. Since the data symbols transmit without intersymbol interference (ISI) under this limitation, how to improve the secret key rate is still a notoriously hard problem. Faster-than-Nyquist (FTN) technology has been viewed as a potential technique in future communication systems, because of its higher spectrum efficiency and faster symbol rate. In this paper, a CV-QKD system based on FTN is proposed. The transmission of an FTN system is simulated, and then we analyze the Mazo limit and the constrained capacities of the system, and finally compare the secret key rate of FTN signals and Nyquist signals. Our proposed scheme is especially beneficial for the high-speed scenario. Simulation results demonstrate that such a CV-QKD system can increase channel capacity and enhance key rate; it can also improve the safe transmission distance of CV-QKD.

DOI: 10.1364/josab.381689

Related papers

Continuous-variable quantum key distribution based on high-rate phase reference

Jinjing Shi, Fang Zhou, Shuhui Chen +2 more

Abstract We propose a high-rate phase reference scheme for continuous-variable quantum key distribution (CV-QKD). In this scheme, a transmission mode has been employed in which several quantum signal pulses are accompanied by a pair of reference pulses, calibrating the measurement bases of the communicating parties. Within a certain range, and with the ratio between quantum signal pulses and reference pulses increased, the secret key rate approaches that of the traditional CV-QKD scheme (which is a scheme without phase noise). Compared with general CV-QKD schemes, which adopt the transmission mode of a quantum signal pulse plus a pair of reference pulses, this scheme has a higher spectral efficiency, enabling high-rate CV-QKD. In addition, we reduce the interference of strong reference pulses with weak quantum signal pulses by using a pair of polarization beam splitters with a dynamic polarization controller. Simulation results demonstrate that we achieve a higher secret key rate than the self-coherent phase reference scheme. This provides a pathway towards large-scale quantum communication networks.

Laser PhysicsMay 22, 20194 citations

Enhancing the secret key rate of CV-QKD over an optical fiber network by precoding

Yuan Liu, Calvin C. K. Chan

Continuous-variable quantum key distribution (CV-QKD) suffers from significant secret key rate (SKR) limitations in long-haul transmission. Existing hardware-oriented capacity boosting approaches are hindered by prohibitive costs and intricate system architectures. To address these challenges, this paper proposes a time-domain unitary precoding scheme to enhance the SKR by making full use of the non-flat noise frequency spectrum inherent to practical CV-QKD systems. This paper derives an analytical expression for the optimal precoder when only excess or electronic noise is colored and employs the Riemann Conjugate Gradient (RCG) algorithm for iterative optimization when both types of noise are colored. Numerical simulations demonstrate that, for a 40 km transmission link with both colored excess noise and electronic noise, the optimized scheme attains a 1.07 to 5.6 fold SKR improvement compared to conventional CV-QKD systems.

Optics LettersMay 15, 20261 citation

Frequency-Division Multiplexed CV-QKD System

Jaehyeok Han, Donghyeok Lee, Minseok Ryu +3 more

We propose a frequency-division multiplexed (FDM) continuous-variable quantum key distribution (CV-QKD) system with enhanced spectral efficiency through optimized channel spacing of low-symbol-rate signals. A four-channel 10-Mbaud FDM-CV-QKD system was experimentally demonstrated using Gaussian modulation, a transmitted local oscillator, and homodyne detection. Despite the inter-channel interference, under a finite-size scenario (m=1.25x10^6), the system achieved a 3.6-fold back-to-back secret key rate gain and outperformed the single-channel frequency-upconverted signal up to 26.8 km.

quant-pharXiv:2603.20718Mar 24, 20260 citations

High-rate continuous-variable quantum key distribution over 100 km fiber with composable security

Heng Wang, Yang Li, Ting Ye +14 more

Quantum key distribution (QKD), providing a way to generate secret keys with information-theoretic security, is arguably one of the most significant achievements in quantum information. The continuous-variable QKD (CV-QKD) offers the potential advantage of achieving a higher secret key rate (SKR) within a metro area, as well as being compatible with the mature telecom industry. However, the SKR and transmission distance of state-of-the-art CV-QKD systems are currently limited. Here, based on the proposed orthogonal-frequency-division-multiplexing (OFDM) CV-QKD protocol, we demonstrate a high-rate multi-carrier (MC) CV-QKD with a 10 GHz symbol rate that achieves Gbps SKR within 10 km and Mbps SKR over 100 km in the finite-size regime under composable security against collective attacks. The results are achieved by suitable optimization of subcarrier number and modulation variance, well-controlled excess noise induced by both the OFDM mechanism and the efficient DSP scheme, and high-performance post-processing capacity realized by the heterogeneous computing scheme. The composable finite-size SKR reaches 1779.45 Mbps@5 km, 1025.49 Mbps@10 km, 370.50 Mbps@25 km, 99.93 Mbps@50 km, 25.70 Mbps@75 km, and 2.25 Mbps@100 km, which improves the SKR by two orders of magnitude and quintuples the maximal transmission distance compared to the most recently reported CV-QKD results [ Nat. Commun. 13 , 4740 ( 2022 ) NCAOBW 2041-1723 10.1038/s41467-022-32161-y ]. Interestingly, it is experimentally verified that the SKR of the proposed MC CV-QKD can approach five times larger than that of the single-carrier CV-QKD with the same symbol rate without additional hardware costs. Our work constitutes a critical step toward future high-speed quantum metropolitan and access networks.

arXiv:2503.14843OpticaSep 15, 202521 citations

Continuous-mode analysis for practical continuous-variable quantum key distribution

Yanhao Sun, Jiayu Ma, Xiangyu Wang +3 more

Continuous-variable quantum key distribution (CV-QKD) enables two remote parties to establish information-theoretically secure keys and offers high practical feasibility due to its compatibility with mature coherent optical communication technologies. However, as CV-QKD systems progress toward digital implementations, device nonidealities drive the optical field from a single-mode to a continuous-mode region, thereby underscoring the mismatch between theoretical models and practical systems. Here, we introduce temporal modes to construct an entanglement-based scheme that more accurately captures device nonidealities and develop a corresponding secret key rate calculation method applicable to continuous-mode scenarios. We demonstrate that optimizing the pulse-shaping format can significantly improve performance under detector-bandwidth-limited conditions. Experimental results also confirm that the proposed model effectively describes the impact of sampling-time deviations. We further analyze a linear weighted-reconstruction digital signal processing method,which improves the secret key rate by approximately 50% in a 30-km fiber experiment without requiring additional hardware, demonstrating a substantial performance enhancement at metropolitan distances. The proposed theoretical framework accommodates a broader range of experimental conditions and can guide the optimization of digital CV-QKD systems.

quant-pharXiv:2512.15301Dec 18, 20250 citations

Improving the secure transmission distance of continuous-variable quantum key distribution under limited eavesdropping using a quantum scissor

Amene Shafiee, Mojtaba Golshani, Mostafa Motamedifar +1 more

In this paper, we explore the enhancement of secure transmission distance in continuous-variable quantum key distribution (CV-QKD) under limited eavesdropping conditions by employing a quantum scissor (QS). We derive an analytical expression for the output state and demonstrate that QS significantly extends the secure communication range. Additionally, we analyze the impact of limited eavesdropping on the secret key rate, showing that restricted access to intercepted light improves security compared to an unrestricted eavesdropper scenario. To provide a comprehensive assessment, we investigate both direct and reverse reconciliation schemes. Our numerical simulations and analytical comparisons reveal that QS improves the secure transmission distance in both cases, despite reducing the secret key rate at shorter distances. The results show that QS mitigates the detrimental effects of channel loss, allowing for an extended communication range in CV-QKD systems. These findings highlight the potential of QS as a key tool for enhancing long-distance secure quantum communication in practical scenarios. • Study of secure-distance enhancement in CV-QKD with limited eavesdropping using a QS. • QS improves the maximum secure transmission distance of the CV-QKD protocol. • Key rates under limited eavesdropping are analyzed for both reconciliation types. • Limited eavesdropping yields higher key rates than the fully unrestricted case. • Optimal modulation variance and QS gain that extend protocol range are identified.

Results in PhysicsNov 20, 20250 citations