Abstract
Quantum cryptography holds the promise to establish an information-theoretically secure global network. All field tests of metropolitan-scale quantum networks to date are based on trusted relays. The security critically relies on the accountability of the trusted relays, which will break down if the relay is dishonest or compromised. Here, we construct a measurement-device-independent quantum key distribution (MDIQKD) network in a star topology over a 200-square-kilometer metropolitan area, which is secure against untrustful relays and against all detection attacks. In the field test, our system continuously runs through one week with a secure key rate 10 times larger than previous results. Our results demonstrate that the MDIQKD network, combining the best of both worlds—security and practicality, constitutes an appealing solution to secure metropolitan communications.
- Received 29 October 2015
DOI:https://doi.org/10.1103/PhysRevX.6.011024
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Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
Quantum cryptography can provide, in theory, secure communication between two remote parties based on the laws of quantum mechanics. All field tests of metropolitan-scale quantum networks to date have been based on trusted relays. The security of such networks relies critically on the accountability of the trusted relays, which will break down if the relay is dishonest or compromised. Here, we construct a measurement-device-independent quantum key distribution network in a star shape over 200 square kilometers of a metropolitan area that is secure against untrustworthy relays and detection attacks.
We demonstrate a network in Hefei, China, that can accommodate three users. The fiber lengths of the network are measured in tens of kilometers, and we adopt a star-shaped network to optimize sharing of expensive single-photon detectors. This kind of network ensures that eavesdroppers are unable to compromise the security of communications even with access to the detection devices. Each user has an infrared (1550.12-nm) laser—we note that one challenge is ensuring that all lasers remain as indistinguishable as possible—and all users share a central relay. We focus on optimizing the parameters of the network to maximize the secure key rate; we extract in the ballpark of 30 bits per second. These results represent an order-of-magnitude improvement over other field tests. Our results demonstrate that a measurement-device-independent quantum key distribution network combines the best of both worlds—security and practicality—and constitutes an appealing solution to secure metropolitan communications.
We expect that our work will motivate other studies to achieve even higher secure key rates in real-world settings.