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arXiv:2011.03005 · Physical Review Letters

Pathways for Entanglement-Based Quantum Communication in the Face of High Noise

Xiao‐Min Hu, Chao Zhang, Yu Guo, Fang‐Xiang Wang, Wen-Bo Xing, Cen-Xiao Huang, Bi‐Heng Liu, Yun‐Feng Huang, Chuan‐Feng Li, Guang‐Can Guo, Xiaoqin Gao, Matej Pivoluska, Marcus Huber

Published Sep 10, 2021• 64 citations
arXivHTMLPDF

Abstract

Entanglement-based quantum communication offers an increased level of security in practical secret shared key distribution. One of the fundamental principles enabling this security-the fact that interfering with one photon will destroy entanglement and thus be detectable-is also the greatest obstacle. Random encounters of traveling photons, losses, and technical imperfections make noise an inevitable part of any quantum communication scheme, severely limiting distance, key rate, and environmental conditions in which quantum key distribution can be employed. Using photons entangled in their spatial degree of freedom, we show that the increased noise resistance of high-dimensional entanglement can indeed be harnessed for practical key distribution schemes. We perform quantum key distribution in eight entangled paths at various levels of environmental noise and show key rates that, even after error correction and privacy amplification, still exceed 1 bit per photon pair and furthermore certify a secure key at noise levels that would prohibit comparable qubit based schemes from working.

DOI
10.1103/physrevlett.127.110505

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Entanglement-based quantum communication offers an increased level of security in practical secret shared key distribution. One of the fundamental principles enabling this security-the fact that interfering with one photon will destroy entanglement and thus be detectable-is also the greatest obstacle. Random encounters of traveling photons, losses, and technical imperfections make noise an inevitable part of any quantum communication scheme, severely limiting distance, key rate, and environmental conditions in which quantum key distribution can be employed. Using photons entangled in their spatial degree of freedom, we show that the increased noise resistance of high-dimensional entanglement can indeed be harnessed for practical key distribution schemes. We perform quantum key distribution in eight entangled paths at various levels of environmental noise and show key rates that, even after error correction and privacy amplification, still exceed 1 bit per photon pair and furthermore certify a secure key at noise levels that would prohibit comparable qubit based schemes from working.
High-quality, distributed entanglement forms the foundation for the unequaled level of security that can be assured in quantum key distribution (QKD), but its susceptibility to noise hinders practical implementations. This study experimentally demonstrates that enhancing quantum resources with quantum privacy amplification (QPA) increases the noise resilience of QKD beyond classical limits. Leveraging hyperentanglement in different field-tested degrees of freedom of a photon pair increases the efficiency of QPA, thereby unlocking its advantage for QKD. Here is a method to generate secure keys under noisy conditions, which was previously impossible, paving the way for robust QKD.
Quantum correlations or entanglement is a basic ingredient for many applications of quantum information theory.One important application using quantum entanglement exploits the correlation nature of entangled photon states is quantum key distribution, which is proven unbreakable in principle and provides the highest possible security that is impossible in classical information theory. However, generating entangled photon pairs is not a simple task -- only approximately one out of a million pump photons decay into a signal and idler photon pair. This low rate of entangled photon pairs is further reduced by the overhead required in order for the rectification of the inevitable errors due to channel imperfections or caused by potential eavesdroppers. As a consequence, quantum key distribution suffers from a low bit rate, which is in the order of hundreds to thousands bits per second or below. On the other hand, the classical public key distribution does not impose a tight limit on the transmission rate. However, it is subject to the risks of eavesdroppers sitting in the middle of the insecure channel. In this paper, we propose a hybrid key distribution method which uses public key distribution method to generate a raw key, and then uses entanglement assisted communication to modify the raw key by inserting a number of quantum bits in the raw key. Building upon the foundation of the unconditional security of quantum key distribution, we use the privacy amplification to make the affection of inserted bits expand to a whole key. Our quantum entanglement assisted key distribution scheme greatly improves the efficiency of key distribution while without compromising the level of security achievable by quantum cryptography.
Noise can be considered the natural enemy of quantum information.An often implied benefit of highdimensional entanglement is its increased resilience to noise.However, manifesting this potential in an experimentally meaningful fashion is challenging and has never been done before.In infinite dimensional spaces, discretization is inevitable and renders the effective dimension of quantum states a tunable parameter.Owing to advances in experimental techniques and theoretical tools, we demonstrate an increased resistance to noise by identifying two pathways to exploit high-dimensional entangled states.Our study is based on two separate experiments utilizing canonical spatiotemporal properties of entangled photon pairs.Following these different pathways to noise resilience, we are able to certify entanglement in the photonic orbital-angular-momentum and energy-time degrees of freedom up to noise conditions corresponding to a noise fraction of 72% and 92%, respectively.Our work paves the way toward practical quantum communication systems that are able to surpass current noise and distance limitations, while not compromising on potential device independence.
This paper proposes a novel quantum key distribution (QKD) protocol designed to mitigate the vulnerabilities associated with hardware imperfections commonly encountered in existing QKD systems. The core of the approach lies in utilizing entangled photon pairs for key generation, coupled with a sophisticated hardware-level error correction mechanism. This mechanism employs concatenated quantum codes to actively address and correct errors introduced during transmission, thereby bolstering the security and resilience of the key distribution process. We demonstrate a framework where the inherent probabilistic nature of quantum mechanics is directly confronted, rather than relying solely on post-processing techniques. The proposed system offers a significant advancement toward practical, robust QKD implementations, paving the way for more secure communication networks in the quantum era. The effectiveness of the scheme is analyzed through mathematical models, specifically focusing on the error correction performance and key generation rates. The results highlight the potential for achieving high key rates while maintaining strong security against various attack scenarios.
High-quality, distributed quantum entanglement is the distinctive resource for quantum communication and forms the foundation for the unequalled level of security that can be assured in quantum key distribution. While the entanglement provider does not need to be trusted, the secure key rate drops to zero if the entanglement used is too noisy. In this paper, we show experimentally that QPA is able to increase the secure key rate achievable with QKD by improving the quality of distributed entanglement, thus increasing the quantum advantage in QKD. Beyond that, we show that QPA enables key generation at noise levels that previously prevented key generation. These remarkable results were only made possible by the efficient implementation exploiting hyperentanglement in the polarisation and energy-time degrees of freedom. We provide a detailed characterisation of the gain in secure key rate achieved in our proof-of-principle experiment at different noise levels. The results are paramount for the implementation of a global quantum network linking quantum processors and ensuring future-proof data security.
High-dimensional entanglement not only offers a high security level for quantum communication but also promises improved information capacity and noise resistance of the system. However, due to various constraints on different high-dimensional degrees of freedom, whether these advantages can bring improvement to the actual implementation is still not well proven. Here we present a scheme to fully utilize these advantages over long-distance noisy fiber channels. We exploit polarization and time-bin hyperentanglement to achieve high-dimensional coding, and observe significant enhancements in secure key rates and noise tolerance that surpass the capabilities of qubit systems. Moreover, the demonstration achieves a distribution up to 50 km, which is the longest distance for high-dimensional entanglement-based quantum key distribution up to date, to our knowledge. Our demonstration validates the potential of high-dimensional entanglement for quantum communications over long-distance noisy channels, paving the way for a resilient and resource-efficient quantum network.