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arXiv:0803.1594 · Physical Review A

Decoy states for quantum key distribution based on decoherence-free subspaces

Zhen−Qiang Yin, Yibo Zhao, Zheng-Wei Zhou, Zheng‐Fu Han, Guang‐Can Guo

Published Jun 17, 2008• 21 citations
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Abstract

A quantum key distribution with decoherence-free subspaces has been proposed to overcome collective noise to the polarization modes of photons flying in quantum channels. Prototypes of this scheme have also been achieved with a parametric down-conversion source. However, the photon-number-splitting attack we propose will make practical implementations of this scheme insecure since the parametric down-conversion source may occasionally emit multiphoton pairs. We propose a decoy-state method to make these implementations immune to this attack. With this decoy-state method, both the security distance and key bit rate will be increased.

DOI
10.1103/physreva.77.062326

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A quantum key distribution with decoherence-free subspaces has been proposed to overcome collective noise to the polarization modes of photons flying in quantum channels. Prototypes of this scheme have also been achieved with a parametric down-conversion source. However, the photon-number-splitting attack we propose will make practical implementations of this scheme insecure since the parametric down-conversion source may occasionally emit multiphoton pairs. We propose a decoy-state method to make these implementations immune to this attack. With this decoy-state method, both the security distance and key bit rate will be increased.
We propose an efficient quantum key distribution protocol based on the photon-pair generation from parametric down-conversion (PDC). It uses the same experimental setup as the conventional protocol, but a refined data analysis enables detection of photon-number splitting attacks by utilizing information from a built-in decoy state. Assuming the use of practical detectors, we analyze the unconditional security of the new scheme and show that it improves the secure key generation rate by several orders of magnitude at long distances, using a high intensity PDC source.
The decoy-state method is widely used in practical quantum key distribution systems to replace ideal single photon sources with realistic light sources by varying intensities. Instead of active modulation, the passive decoy-state method employs built-in decoy states in a parametric down-conversion photon source, which can decrease the side channel information leakage in decoy state preparation and hence increase the security. By employing low dark count up-conversion single photon detectors, we have experimentally demonstrated the passive decoy-state method over a 50-km-long optical fiber and have obtained a key rate of about 100 bit/s. Our result suggests that the passive decoy-state source is a practical candidate for future quantum communication implementation.
Subcarrier wave quantum key distribution systems demonstrate promising capabilities for secure quantum networking. However for this class of devices no implementation of secure decoy states protocol was developed. It leaves them potentially vulnerable to photon-number splitting attacks on quantum channel and limiting the key distribution distance. We propose a practical solution to this problem by calculating the required parameters of light source and modulation indices for signal and decoy states in a subcarrier wave system and describing the corresponding experimental scheme.
In this paper, a new decoy state scheme for quantum key distribution with parametric down-conversion source is proposed. We use both three-intensity decoy states and their triggered and nontriggered components to estimate the fraction of single-photon counts and the quantum bit-error rate of single-photon pulses, and then deduce a more accurate value of the key generation rate. The final key rate over transmission distance is simulated, which shows that we can obtain a higher key rate than that of the existing methods, including our own earlier work.
We have experimentally demonstrated a decoy-state quantum key distribution scheme (QKD) with a heralded single-photon source based on parametric down-conversion. We used a one-way Bennett-Brassard 1984 protocol with a four states and one-detector phase-coding scheme, which is immune to recently proposed time-shift attacks, photon-number splitting attacks, and can also be proven to be secure against Trojan horse attacks and any other standard individual or coherent attacks. In principle, the setup can tolerate the highest losses or it can give the highest secure key generation rate under fixed losses compared with other practical schemes. This makes it a quite promising candidate for future quantum key distribution systems.
In this paper, a photon-number-resolving decoy-state quantum key distribution (QKD) scheme is presented based on recent experimental advancements. A new upper bound on the fraction of counts caused by multiphoton pulses is given, which seems inherent as long as weak coherent sources and high lossy channel are used. This implies that our scheme is optimal in long-distance QKD with weak coherent sources. We show that Eve's coherent multiphoton pulse (CMP) attack is more efficient than a symmetric individual attack when the quantum bit error rate is small, so that the CMP attack should be considered to ensure the security of the final key. Our results show that a not-so-weak pulse can be used to transmit the key. Optimal intensity of the laser source is presented which provides a 23.9km23.9\phantom{\rule{0.3em}{0ex}}\mathrm{km}23.9km increase in the transmission distance.