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arXiv:1109.1203 · Quantum Information and Computation

Improved Data Post-Processing in Quantum Key Distribution and Application to Loss Thresholds in device independent QKD

Xiongfeng Ma, Norbert Lütkenhaus

Published Mar 1, 2012• 41 citations
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Abstract

Security proofs of quantum key distribution (QKD) often require post-processing schemes to simplify the data structure, and hence the security proof. We show a generic method to improve resulting secure key rates by partially reversing the simplifying post-processing for error correction purposes. We apply our method to the security analysis of device-independent QKD schemes and of detection-device-independent QKD schemes, where in both cases one is typically required to assign binary values even to lost signals. In the device-independent case, the loss tolerance threshold is cut down by our method from 92.4% to 90.9%. The lowest tolerable transmittance of the detection-device-independent scheme can be improved from 78.0% to 65.9%

DOI
10.26421/qic12.3-4-2

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Security proofs of quantum key distribution (QKD) often require post-processing schemes to simplify the data structure, and hence the security proof. We show a generic method to improve resulting secure key rates by partially reversing the simplifying post-processing for error correction purposes. We apply our method to the security analysis of device-independent QKD schemes and of detection-device-independent QKD schemes, where in both cases one is typically required to assign binary values even to lost signals. In the device-independent case, the loss tolerance threshold is cut down by our method from 92.4% to 90.9%. The lowest tolerable transmittance of the detection-device-independent scheme can be improved from 78.0% to 65.9%
Quantum key distribution provides information-theoretically-secure communication. In practice, device imperfections may jeopardise the system security. Device-independent quantum key distribution solves this problem by providing secure keys even when the quantum devices are untrusted and uncharacterized. Following a recent security proof of the device-independent quantum key distribution, we improve the key rate by tightening the parameter choice in the security proof. In practice where the system is lossy, we further improve the key rate by taking into account the loss position information. From our numerical simulation, our method can outperform existing results. Meanwhile, we outline clear experimental requirements for implementing device-independent quantum key distribution. The maximal tolerable error rate is 1.6%, the minimal required transmittance is 97.3%, and the minimal required visibility is 96.896.8%96.8.
Device-independent quantum key distribution (QKD) can permit the superior security even with unknown devices. In practice, however, the realization of device-independent QKD is technically challenging because of its low noise tolerance. In the photonic setup, due to the limited detection efficiency, a large amount of the data generates from no-detection events which contain few correlations but contribute high errors. Here, we propose the device-independent QKD protocol with random postselection, where the secret keys are extracted only from the postselected subset of outcomes. This could not open the detection loophole as long as the entropy of the postselected subset is evaluated from the information of the entire set of data, including both detection and no-detection events. This postselection has the advantage to significantly reduce the error events, thus relaxing the threshold of required detection efficiency. In the model of collective attacks, our protocol can tolerate detector efficiency as low as 68.5%, which goes beyond standard security proofs. The results make a concrete step for the implementation of device-independent QKD in practice.
An efficiency-loophole-free quantum key distribution (QKD) scheme is proposed, which involves no hardware change but a modification in the data post-processing step. The scheme applies to a generic class of detection systems which allow correlations between the detection efficiency and the outcomes. We study the system transmittance and the detection error rate that allow implementing this scheme. We also consider the case that a quantum memory is used to boost the performance and investigate the criteria of the readout probability. The simulation result shows that the lowest tolerable system transmittance (readout probability) is 50%, while the necessary efficiency for an efficiency-loophole-free Bell's inequality test is 82.8%.
Quantum key distribution (QKD) can be proved to be secure by laws of quantum mechanics. In this thesis, we review security proof methods in Renner's framework and discuss numerical methods to calculate asymptotic and finite key rates. These methods are highly versatile and applicable to general device-dependent QKD protocols. We also discuss analytical tools that extend the applicability of these numerical methods. We then present the asymptotic security proof against collective attacks for a variant of the twin-field QKD protocol, which can overcome the repeaterless secret-key capacity bound. Our variant reduces the sifting cost and uses non-phase-randomized coherent states as both signals and test states. We confirm the loss scaling of this protocol. Another important family of protocols that we investigate here are discrete-modulated continuous-variable QKD protocols. They are interesting due to their experimental simplicity and their great potential for massive deployment in the quantum-secured networks. Our security proof method can provide tight asymptotic key rates. We demonstrate that the postselection of data in combination with reverse reconciliation can improve the key rates. We analyze both untrusted and trusted detector noise scenarios. Our results in the trusted detector noise scenario show that we can thus cut out most of the effect of detector noise and obtain asymptotic key rates similar to those had we access to ideal detectors. Finally, we present several simple examples to illustrate our newly developed method for the numerical finite-key analysis against the most general attacks via the entropy accumulation theorem.
Quantum key distribution (QKD) has been researched for almost four decades and is currently making its way to commercial applications. However, deployment of the technology at scale is challenging because of the very particular nature of QKD and its physical limitations. Among other issues, QKD is computationally intensive in the post-processing phase, and devices are therefore complex and power hungry, which leads to problems in certain application scenarios. In this work, we study the possibility to offload computationally intensive parts in the QKD post-processing stack in a secure way to untrusted hardware. We show how error correction can be securely offloaded for discrete-variable QKD to a single untrusted server and that the same method cannot be used for long-distance continuous-variable QKD. Furthermore, we analyze possibilities for multi-server protocols to be used for error correction and privacy amplification. Even in cases where it is not possible to offload to an external server, being able to delegate computation to untrusted hardware components on the device itself could improve the cost and certification effort for device manufacturers.