IEEE Globecom Workshops (GC Wkshps)

Inter-Symbol-Interference Reduction in Continuous Variable QKD Using Equalization

Xinke Tang, Rupesh Kumar, D. G. Cunningham, A. Wonfor, Richard V. Penty, Ian H. White

Published Dec 1, 2018• 2 citations

Abstract

Inter-symbol-interference (ISI) noise in Continuous Variable Quantum Key Distribution (CVQKD) is caused by the overlap between the consecutive detected signals. In practice, this problem limits the repetition rate of the quantum signals for a given bandwidth detector and hence reduces the rate of secure key generation. We propose a method of using equalization to mitigate ISI noise in CVQKD systems. Its feasibility is studied using an analytical model with practical parameters. The improved performance of CVQKD detection is investigated using secure key analysis. The simulation results show an increase of 12.8 Mbits/s in secure key rate for a 1GHz bandwidth CVQKD system operating over a 20 km link.

DOI: 10.1109/glocomw.2018.8644125

Related papers

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

Yaxi Pan, Ling Zhang, Ying Guo +1 more

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.

Journal of the Optical Society of America BJan 9, 20203 citations

Impact of homodyne receiver bandwidth and signal modulation patterns on the continuous-variable quantum key distribution

Jianqiang Liu, Yanxia Cao, Pu Perry Wang +4 more

In continuous-variable quantum key distribution (CV-QKD), the key information are encoded on quadratures of the optical field, which are measured via balanced homodyne detector (BHD). The bandwidth of the BHD is one of key parameters for precise characterization of quantum states. We establish a theoretical model to analyze the impact of the BHD bandwidth and signal modulation patterns on the channel parameters estimation of CV-QKD systems. Based on the proposed model, the secure key rate of a practical CV-QKD system under different BHD bandwidths and signal modulation patterns are investigated. Our results show that insufficient BHD bandwidth will result in wrong estimate of the transmission loss and excess noise, which significantly affects the performance of CV-QKD systems. Given the BHD bandwidth, there exists an optimal signal repetition rate that maximizes the secure key rate. The BHD bandwidth requirement of the QKD system increases with the transmission distance for large duty cycle pulse. Furthermore, the root raised-cosine pulse signal modulation performs better than the square pulse signal modulation in general.

Optics ExpressJul 8, 202210 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

Experimental Demonstration of Free-Space Unidimensional Continuous-Variable Quantum Key Distribution Under High Detector Noise

Rachita Nandan, Jayanth Ramakrishnan, Shashi Prabhakar +1 more

Continuous-variable quantum key distribution (CV-QKD), which uses quadratures of the electromagnetic field, enables practical quantum communication using standard telecommunication technologies. Unidimensional CV-QKD (UD-CVQKD) simplifies the implementation by restricting modulation to a single quadrature. In this work, we experimentally demonstrate a free-space Gaussian-modulated UD-CVQKD system operating under a high detector electronic-noise regime (1.4 shot-noise units). The system employs polarized coherent states with signal and local oscillator co-propagating in the same spatial mode in orthogonal polarizations, ensuring stable interference. System security is analyzed under both untrusted (UTD) and trusted (TD) detector noise models. While no positive secret key rate is obtained under the UTD model, the TD model enables secure key generation over a finite range of modulation variances, highlighting the critical role of detector trust in high-noise conditions. A maximum secret key rate of 270 kbps is achieved at an optimal modulation variance of 11.57. Furthermore, secure operation requires high-transmittance (low-loss) channels under such noise conditions. This study demonstrates the practical feasibility of free-space UD-CVQKD in realistic high electronic-noise detection constraints and highlights detector electronic noise as a key limiting factor in practical systems.

quant-pharXiv:2606.07206Jun 8, 20260 citations

Phase Noise Reduction in Continuous-Variable Quantum Key Distribution Using Digital Filtering

Samael Sarmiento, E. Llanos, Pol Adillon +3 more

Quantum key distribution (QKD) enables information-theoretic-secure secret key exchange thanks to the laws of quantum mechanics. Since it can easily be incorporated into existing telecom networks, continuous-variable QKD (CV QKD) using coherent states and coherent detection has recently emerged as a promising candidate. However, the secret key rate and link distance in CV QKD systems are still limited by the imperfections of used components. In this work, through simulations, we study the use of different digital filtering techniques for optical phase recovery, aided by pilot symbols, to mitigate the phase noise induced by the coherent mixing of two free-running lasers in a CV QKD system. Moving average, Butterworth and unscented Kalman filters are evaluated for different phase drift conditions. Results show that phase recovery from small amplitude pilot symbols, along with further digital filtering, can considerably reduce phase noise and measurement error, while increasing the secret key rate and link distance of the CV QKD system.

International Conference on Transparent Optical NetworksJul 14, 20242 citations

Spectral Attack on Continuous-Variable Quantum Key Distribution Systems

Chen Gong, Mingxuan Guo, Peng Huang +2 more

Continuous-variable quantum key distribution (CVQKD) has attracted extensive attention due to its compatibility and low costs. However, bandwidth mismatch exists to varying degrees between the transmitter and receiver. This may prevent frequency components carrying modulation information from being fully perceived by the legitimate party. In this paper, we identify a practical security loophole caused by bandwidth mismatch and propose a corresponding spectral attack scheme. Different from previous approaches that exploit security loopholes to conceal the excess noise introduced by intercept-resend attacks, this scheme can directly obtain raw-key information without introducing additional disturbances. A proof-of-principle attack on a CVQKD system with filtering operation is constructed to verify the feasibility. Experimental results indicate that Eve can obtain enough information to render the system insecure if this practical security loophole is ignored. Based on the identified security loophole, corresponding defense strategies are proposed. This work helps bridge the gap between theoretical models and practical implementations, providing a reference for defense design in practical quantum communication systems.

quant-pharXiv:2607.15668Jul 20, 20260 citations