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Physical Review Applied

Overcoming noise limitations in quantum key distribution with quantum privacy amplification

Philipp Sohr, Sebastian Ecker, Lukas Bulla, Martin Bohmann, Rupert Ursin

Published Aug 21, 2024• 11 citations
Publisher

Abstract

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.

DOI
10.1103/physrevapplied.22.024059

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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.
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.
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.
This paper presents a novel approach to enhancing the security of Quantum Key Distribution (QKD) protocols by leveraging multi-partite entangled states and dynamic entanglement control. Current QKD protocols, while providing theoretical security guarantees, remain vulnerable to sophisticated attacks that exploit imperfections in quantum hardware and potential eavesdropping strategies. Our work addresses this limitation by introducing a framework where multiple entangled states are employed simultaneously, and their entanglement is dynamically adjusted during the key distribution process. This dynamic control mitigates the impact of noise and reduces the effectiveness of various attack vectors, including those targeting Bell inequality violations and time-dependent attacks. We formally analyze the security of this enhanced protocol, demonstrating its resilience against a broader range of attacks. The key contributions lie in the development of a robust protocol architecture and the implementation of a sophisticated control mechanism that maintains entanglement fidelity and security even under adverse conditions. The proposed method significantly improves the practical security of QKD systems, paving the way for more reliable and secure quantum communication networks.
Quantum key distribution (QKD) offers a theoretically secure method to share secret keys, yet practical implementations face challenges due to noise and loss over long-distance channels. Traditional QKD protocols require extensive noise compensation, hindering their industrial scalability and lowering the achievable key rates. Alternative protocols encode logical qubits in noise-resilient states but at the cost of using many physical qubits, increasing susceptibility to loss and limiting transmission distance. In this work, we introduce a logical-qubit encoding that uses antisymmetric Bell states in the continuous photonic degrees of freedom, frequency and time. By leveraging the continuous space, we overcome this noise-loss robustness trade-off by minimizing the number of photons per logical qubit while optimizing the encoding resilience over noise fluctuations. We analyze the security of our encoding and demonstrate its robustness compared to existing state-of-the-art protocols. This approach provides a path toward scalable, efficient QKD implementations under realistic noise conditions.
This paper investigates the optimization of Quantum Key Distribution (QKD) protocols utilizing entangled states. The core claim is that strategic optimization of entangled state generation and utilization can significantly enhance the security and key rate of QKD. The proposed method leverages principles from quantum information theory and entanglement theory to design a protocol that maximizes key distribution speed while minimizing the risk of key leakage. Current QKD protocols predominantly rely on single photons, often neglecting the full potential of entangled states. This work addresses this limitation, aiming to improve the efficiency and security of quantum key distribution. The presented protocol incorporates techniques for enhanced entanglement distribution, error correction, and privacy amplification, all tailored for maximizing key rate within a secure framework. Mathematical analysis and theoretical considerations are detailed throughout, outlining the protocol's operational parameters and security proofs. The ultimate goal is to demonstrate a more robust and efficient approach to QKD based on the fundamental properties of entanglement. ---
Quantum information protocols are being deployed in increasingly practical scenarios, via optical fibers or free space, alongside classical communications channels. However, entanglement, the most critical resource to deploy to the communicating parties, is also the most fragile to the noise-induced degradations. Here we show that polarization-frequency hyperentanglement of photons can be effectively employed to enable noise-resistant distribution of polarization entanglement through noisy quantum channels. In particular, we demonstrate that our hyperentanglement-based scheme results in an orders-of-magnitude increase in the SNR for distribution of polarization-entangled qubit pairs, enabling quantum communications even in the presence of strong noise that would otherwise preclude quantum operations due to noise-induced entanglement sudden death. While recent years have witnessed tremendous interest and progress in long-distance quantum communications, previous attempts to deal with the noise have mostly been focused on passive noise suppression in quantum channels. Here, via the use of hyperentangled degrees of freedom, we pave the way toward a universally adoptable strategy to enable entanglement-based quantum communications via strongly noisy quantum channels.