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Field test of quantum key distribution in the Tokyo QKD Network

03/2011;
Source: arXiv

ABSTRACT A novel secure communication network with quantum key distribution in a
metropolitan area is reported. Different QKD schemes are integrated to
demonstrate secure TV conferencing over a distance of 45km, stable long-term
operation, and application to secure mobile phones.

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    • "UANTUM communications is entering a new phase in its development that targets new markets and aims at widespread use and adoption in different scenarios. With the successful demonstration of SECOQC [1] and Tokyo [2] quantum key distribution (QKD) networks, we are now at a stage to develop many-user quantum networks [3]. The reach of conventional QKD links is, nevertheless, limited as they rely on low-power signals, e.g., single photons [4]. "
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    ABSTRACT: We propose orthogonal frequency division multiplexing (OFDM), as a spectrally efficient multiplexing technique, for quantum key distribution (QKD) at the core of trustednode quantum networks. Two main schemes are proposed and analyzed in detail, considering system imperfections, specifically, time misalignment issues. It turns out that while multiple service providers can share the network infrastructure using the proposed multiplexing techniques, no gain in the total secret key generation is obtained if one uses conventional all-optical passive OFDM decoders. To achieve a linear increase in the key rate with the number of channels, an alternative active setup for OFDM decoding is proposed, which employs an optical switch instead of conventional passive circuits. The performance of the latter system will also be analyzed in the presence of system imperfections.
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    • "Quantum key distribution (QKD) [1] [2] is one of the most active and practical areas in quantum information [3] [4], with a number of infield implementations, including the development of metropolitan networks based on point-to-point QKD protocols [5] [6] [7] [8]. A typical QKD protocol involves two parties, usually called Alice and Bob, who aim to generate a secret key by exchanging quantum systems over an insecure communication channel . "
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    ABSTRACT: We extend the field of continuous-variable quantum cryptography to a more robust formulation which can be applied to untrusted networks. We consider two remote parties connected to an untrusted relay by insecure quantum links. To generate correlations, they transmit coherent states to the relay where a continuous-variable Bell detection is performed. Despite the possibility that the working mechanism of the relay could be fully corrupted and the links subject to optimal coherent attacks, the parties are still able to extract a secret key. Furthermore, our analysis shows that very long distances and high rates can be reached when the relay is proximal to one of the parties, configuration typical of a mobile device connecting to a public access point. Thus, using the cheapest possible quantum resources, we show the possibility of long-distance high-rate quantum key distribution in network topologies where direct links are missing between two end-users and intermediate relays cannot be trusted.
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    • "7. Appropriate classical post-processing of the sifted key, i.e. error correction and privacy amplification . Note that while we have not implemented error correction, we have used a realistic estimation of the error correction efficiency [8] to determine the potential secret key rate of our system. Furthermore, we did not consider finite key size effects in our proof-of-principle demonstration (in other words, we assumed that we could run our QKD devices during an infinitely long time and produce an infinite amount of measured data), which, in the case of MDI-QKD, have so far only been investigated using an overly conservative approach [39]. "
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    ABSTRACT: Several vulnerabilities of single-photon detectors have recently been exploited to compromise the security of quantum-key-distribution (QKD) systems. In this Letter, we report the first proof-of-principle implementation of a new quantum-key-distribution protocol that is immune to any such attack. More precisely, we demonstrated this new approach to QKD in the laboratory over more than 80 km of spooled fiber, as well as across different locations within the city of Calgary. The robustness of our fiber-based implementation, together with the enhanced level of security offered by the protocol, confirms QKD as a realistic technology for safeguarding secrets in transmission. Furthermore, our demonstration establishes the feasibility of controlled two-photon interference in a real-world environment and thereby removes a remaining obstacle to realizing future applications of quantum communication, such as quantum repeaters and, more generally, quantum networks.
    Physical Review Letters 09/2013; 111(13):130501. DOI:10.1103/PhysRevLett.111.130501 · 7.51 Impact Factor
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