Fundamental rate-loss tradeoff for optical quantum key distribution

By Masahiro Takeoka, Saikat Guha, Mark M. Wilde. Nature Communications, 2014

460 citations recorded by the source corpus.

Since 1984, various optical quantum key distribution (QKD) protocols have been proposed and examined. In all of them, the rate of secret key generation decays exponentially with distance. A natural and fundamental question is then whether there are yet-to-be discovered optical QKD protocols (without quantum repeaters) that could circumvent this rate-distance tradeoff. This paper provides a major step towards answering this question. Here we show that the secret key agreement capacity of a lossy and noisy optical channel assisted by unlimited two-way public classical communication is limited by an upper bound that is solely a function of the channel loss, regardless of how much optical power the protocol may use. Our result has major implications for understanding the secret key agreement capacity of optical channels—a long-standing open problem in optical quantum information theory—and strongly suggests a real need for quantum repeaters to perform QKD at high rates over long distances. An open question in quantum key distribution (QKD) is whether there exist protocols avoiding the exponential decay of the secret key generation rate with distance. Takeoka et al.show a fundamental tradeoff between the secret-key generation rate and the channel loss for optical repeater-less QKD protocols.

Subfields: Artificial Intelligence, Atomic and Molecular Physics, and Optics

View Paper: https://www.semanticscholar.org/paper/2c76a920d80f0f245b9cb67062b0fe48b4300223

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Citations in the corpus

Phase-Matching Quantum Key Distribution (2018, background): “Therefore, the linear key-rate bound [10,11] was widely believed to hold for practical QKD systems without relays.”
Progress in satellite quantum key distribution (2017, background): “For any pure-loss channel with transmittance η, it has been shown that the secure key rate per mode of any QKD protocol scales linearly with η for small η [5, 6].”
Overcoming the rate–distance limit of quantum key distribution without quantum repeaters (2018, background): “Line d , in particular, is the secret key capacity (SKC) of an optical quantum channel with losses, 9 which quantiﬁes the maximum secret information that can be transmitted in QKD. 8 On the experimental side, the key rates currently achieved are represented by the red symbols.”
Distributing Secret Keys with Quantum Continuous Variables: Principle, Security and Implementations (2015, background): “However, the achievable rates in this case can be very high, within an order of magnitude from the known secret key capacity bounds [45,95].”
Advances in quantum cryptography (2019, unknown): “[575] introduced the Takeoka-Guha-Wilde (TGW) bound by employing the notion of squashed entanglement [576] for a bosonic channel.”
Practical challenges in quantum key distribution (2016, unknown): “48,49 We see that the key rate of DV MDI-QKD is only about 2 orders of magnitude away from the TGW bound at a practical distance, hence this protocol is suitable for high speed communications in metropolitan area networks.”
Optimal architectures for long distance quantum communication (2015, background): “(2) The trapped ions, NV centers, and quantum dots all can implement local quantum operations deterministically34–38, as well as HEG39–42.”