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International Conference on Computing, Communication, Perception and Quantum Technology (CCPQT)

Improving Continuous Variable Quantum Key Distribution Using Heralded Hybrid Linear amplifier and Heralded Noiseless Linear amplifier When source in the Middle

Leixin Wu, Zili Zou, Yanyan Feng, Jian Song Zhou

Published Aug 1, 2022• 0 citations
Publisher

Abstract

We propose a protocol to improve the transmission distance and secure key rate of quantum channels, the NLA-HLA QKD. The untrusted entanglement is sent to users by a quantum channel. It is capable of long transmission distances while maintaining high secure key rates and resisting the higher noise. Using the method of calculating secure key rate with the coherent state, the secure key of the NLA-HLA QKD protocol is derived. The effects of the parameters G and g on the key rate are analyzed through simulation experiments. By regulating the values of G and g, the application range of the protocol can be improved. Optimal parameters are used under specific circumstances to ensure the validity of the protocol.

DOI
10.1109/ccpqt56151.2022.00040

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We propose a protocol to improve the transmission distance and secure key rate of quantum channels, the NLA-HLA QKD. The untrusted entanglement is sent to users by a quantum channel. It is capable of long transmission distances while maintaining high secure key rates and resisting the higher noise. Using the method of calculating secure key rate with the coherent state, the secure key of the NLA-HLA QKD protocol is derived. The effects of the parameters G and g on the key rate are analyzed through simulation experiments. By regulating the values of G and g, the application range of the protocol can be improved. Optimal parameters are used under specific circumstances to ensure the validity of the protocol.
A hybrid linear amplifier is inserted at the output of the source-in-the-middle distribution protocol to overcome the shortcomings of the transmission distance. The modified protocol aims to maintain a high key rate for long-distance transmission under high noise. It has the potential to significantly broaden the application range of the continuous variable quantum key distribution protocol. The effects of amplifier parameters and noise on the modified protocol are analyzed in detail with regard to applying it to a practical system. To make the simulation more realistic, the effect of finite size on the new protocol is taken into account. It will serve as a guideline for the future use of hybrid linear amplifiers. Different parameters can be adjusted to achieve the best performance for key rates of different quantum channels.
Abstract We propose a method to improve transmission distance of continuous-variable quantum key distribution via a heralded hybrid linear amplifier (HLA), involving an ideal deterministic linear amplifier and a probabilistic noiseless linear amplifier. The phase-insensitive amplification of quantum light states may experience a degradation of signal-to-noise ratio (SNR) of 3dB which can be surmounted by the probabilistic amplification process. The new hybrid amplifier allows one to tune between the regimes of high gain or high noise reduction and control the trade-off between the amplification coefficient and a finite heralding probability flexibly. Our equipment could clone unknown coherent states with fidelity surpassing the no-cloning limit by abandoning determinism and using probabilistic methods. The setup has a better compatibility with continuous variable protocols as it only uses Gaussian elements and a post-selection algorithm. The hybrid linear amplifier enhances the SNR and hence the transmission distance of the CVQKD protocol is extended. Both the asymptotic secret key rate and the secret key rate in a finite-size scenario are analyzed in this paper.
In this paper, we introduce a hybrid linear amplifier (HLA) at the interface of the passive state preparation (PSP) continuous-variable quantum key distribution (CVQKD) system to increase the protocol’s transmission performance. Specifically, we find that the noiseless linear amplifier (NLA) component of the HLA increases the maximum transmission distance of the PSP protocol, and the deterministic linear amplifier (DLA) increases the secret key rate within ten kilometres. By appropriately tuning the amplifier parameters, the key rate can be optimized for a given transmission distance. Even with a key length of 1010 and excess noise of 0.1 dB, the protocol achieves secure transmission distances of up to 64 km and 20 km in respective scenarios, which are sufficient to meet the requirements of practical quantum communication systems. Our research provides a new technical way to improve the PSP protocol.
In practical quantum communication networks, the scheme of continuous-variable quantum key distribution (CVQKD) faces a challenge that the entangled source is controlled by a malicious eavesdropper, and although it still can generate a positive key rate and security, its performance needs to be improved, especially in secret key rate and maximum transmission distance. In this paper, we proposed a method based on the four-state discrete modulation and a heralded hybrid linear amplifier to enhance the performance of CVQKD where the entangled source originates from malicious eavesdropper. The four-state CVQKD encodes information by nonorthogonal coherent states in phase space. It has better transmission distance than Gaussian modulation counterpart, especially at low signal-to-noise ratio (SNR). Moreover, the hybrid linear amplifier concatenates a deterministic linear amplifier (DLA) and a noiseless linear amplifier (NLA), which can improve the probability of amplification success and reduce the noise penalty caused by the measurement. Furthermore, the hybrid linear amplifier can raise the SNR of CVQKD and tune between two types of performance for high-gain mode and high noise-reduction mode, therefore it can extend the maximal transmission distance while the entangled source is untrusted.
We show that the successful use of a noiseless linear amplifier (NLA) can help increase the maximum transmission distance and tolerate more excess noise of the plug-and-play dual-phase-modulated continuous-variable quantum key distribution. In particular, an equivalent entanglement-based scheme model is proposed to analyze the security, and the secure bound is derived with the presence of a Gaussian noisy and lossy channel. The analysis shows that the performance of the NLA-based protocol can be further improved by adjusting the effective parameters.
Abstract The current investigation on continuous-variable quantum key distribution (CV-QKD) is mainly based on the optical fibre or the free space atmosphere channel, while the ocean, which covers most of the Earth, has not been well utilized. In this paper, we analyze the influence of depth and wavelength on the attenuation effect of seawater on light by using a model based on the concentration of chlorophyll-a, and propose an improved four-state underwater CV-QKD protocol with a heralded hybrid linear amplifier (HLA). Both homodyne detection with a phase-sensitive amplifier and heterodyne detection with a phase-insensitive amplifier are considered. Simulation results show that the introduction of the heralded HLA can effectively extend the secure transmission distance of the key. Besides, when the transmission distance is relatively long, the secret key rate of the protocol is higher than that of the protocol without HLA.