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International Conference on Transparent Optical Networks

Precise Noise Calibration for CV-QKD

Hans H. Brunner, Stefano Bettelli, Chi‐Hang Fred Fung, Momtchil Peev

Published Jul 1, 2020• 7 citations
Publisher

Abstract

Continuous-variable quantum-key-distribution (CV-QKD) devices, conveniently based on standard components from the domain of coherent optical communication, can guarantee an information-theoretic secure-key expansion. Their security analysis assumes that all power lost in the channel, as well as channel noise in excess with respect to the shot noise, is due to an eavesdropper limited only by quantum mechanics. Quantifying the excess noise, which typically has significantly less power than the shot noise, is essential for secure-key generation. In this article a heterodyne-receiver setup capable of measuring optical power with an extremely high sensitivity (approximately -130 dBm within a 12.5 MHz bandwidth at 1550 nm, corresponding to a power 40 dB below the shot noise) is analysed and demonstrated in a CV -QKD prototype device. Such accuracy is achieved by means of continuous calibration and long-time averages.

DOI
10.1109/icton51198.2020.9203405

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Continuous-variable quantum-key-distribution (CV-QKD) devices, conveniently based on standard components from the domain of coherent optical communication, can guarantee an information-theoretic secure-key expansion. Their security analysis assumes that all power lost in the channel, as well as channel noise in excess with respect to the shot noise, is due to an eavesdropper limited only by quantum mechanics. Quantifying the excess noise, which typically has significantly less power than the shot noise, is essential for secure-key generation. In this article a heterodyne-receiver setup capable of measuring optical power with an extremely high sensitivity (approximately -130 dBm within a 12.5 MHz bandwidth at 1550 nm, corresponding to a power 40 dB below the shot noise) is analysed and demonstrated in a CV -QKD prototype device. Such accuracy is achieved by means of continuous calibration and long-time averages.
Continuous variable-quantum key distribution (CV-QKD) based on coherent detection has potential to be a cost-effective solution to deploy secure keys over optical networks. This is due to its compatibility with mature optical communication technologies, such as homodyne and heterodyne detection schemes. Nevertheless, realistic implementations of CV-QKD systems suffer from imperfections in the practical devices used to generate and detect the coherent states. Those imperfections deteriorate the performance of the CV-QKD system and can be exploited by an eavesdropper to steal key information without being detected. In this work, we discuss the impact of practical device imperfections on the excess noise of the CV-QKD and on the achievable transmission distance. We also analyze the impact of detection imperfections on the measurement of the shot noise, and its impact on CV-QKD system security.
In this paper, using the full security framework for continuous-variable quantum key distribution (CV-QKD), we provide a composable security proof for the CV-QKD system in a realistic implementation.We take into account equipment losses and contributions from various components of excess noise and evaluate performance against collective and coherent attacks assuming trusted hardware noise.The calculation showed that the system remains operable at channel losses up to 10.2 dB in the presence of collective attacks and up to 7.5 dB in the presence of coherent ones.
Secure communication protocols based on quantum physics compel worldwide attention. Continuous-variable quantum key distribution (CV-QKD) uses a cost-effective detection technique instead of dedicated single-photon-counting technology, and can provide high key rates over metropolitan distances. Traditional coherent-state CV-QKD protocols, however, suffer from low tolerance of channel excess noise. The authors succeed in distributing Einstein-Podolsky-Rosen entangled states over a 50-km standard fiber with negligible excess noise, and further demonstrate CV-QKD in a high-noise environment with performance superior to that of the optimized coherent-state protocol.
Continuous-Variable Quantum Key Distribution (CV-QKD) relies on accurate noise calibration at the receiver to ensure the security of quantum communication. Traditional calibration methods often oversimplify noise characteristics, neglecting the impact of local oscillator (LO) noise and the critical role of noise spectral properties, which can lead to imprecise Shot Noise Calibration (SNC). Our contributions are threefold: 1) we propose an operational framework for calibration, relying on the notion of stationarity 2) in this framework, we give a method allowing us to derive the optimal calibration duration for a given experiment 3) leveraging our knowledge of noise spectral properties, we introduce a novel SNC method. This work also formalizes the calibration procedures, addressing implicit assumptions and providing a better foundation for the certification of CV-QKD protocols, of which calibration is a fundamental part. We demonstrate that our improved calibration technique offers higher performance and higher tolerance to receiver imperfections, which can enhance the performance and cost-effectiveness of CV-QKD systems.
Continuous-variable quantum key distribution (CV-QKD) enables information-theoretically secure key generation between legitimate parties. To further enhance system performance, an improved two-way CV-QKD protocol has been proposed, which is accessible in practice and exhibits increased robustness against excess noise. However, in practical implementations, device nonidealities inevitably drive the optical field from the single-mode regime into the continuous-mode regime. In this work, we introduce temporal modes to characterize the evolution of optical fields in the improved two-way protocol and establish a security analysis framework for the continuous-mode scenario based on adaptive normalization with calibrated shot-noise unit. In addition, finite-size effects are taken into account in the analysis. Our results demonstrate that the improved two-way protocol retains a performance advantage over one-way counterpart. The analysis provides useful guidance for the practical implementation and performance optimization of improved two-way CV-QKD systems.