Abstract
Recent field demonstrations of quantum key distribution (QKD) networks hold promise for unconditionally secure communication. However, owing to loss in optical fibres, the length of point-to-point links is limited to a hundred kilometers, restricting the QKD networks to intracity. A natural way to expand the QKD network in a secure manner is to connect it to another one in a different city with quantum repeaters. But, this solution is overengineered unless such a backbone connection is intercontinental. Here we present a QKD protocol that could supersede even quantum repeaters for connecting QKD networks in different cities below 800 km distant. Nonetheless, in contrast to quantum repeaters, this protocol uses only a single intermediate node with optical devices, requiring neither quantum memories nor quantum error correction. Our all-photonic ‘intercity' QKD protocol bridges large gaps between the conventional intracity QKD networks and the future intercontinental quantum repeaters, conceptually and technologically.
Highlights
Recent field demonstrations of quantum key distribution (QKD) networks hold promise for unconditionally secure communication
Otherwise, quantum repeaters are overengineered from the following reasons: Major cities to be equipped with an intracity QKD network may be within a radius o1,000 km, and the polynomial scaling of quantum repeaters usually necessitates quantum memories[5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20] or quantum error correction5,7,11,13,17–21—which is extremely challenging as it requires a huge number of qubits as well as many repeater nodes
Note that it is impossible for our protocol alone to serve as quantum repeaters blessing an exponential improvement
Summary
Recent field demonstrations of quantum key distribution (QKD) networks hold promise for unconditionally secure communication. In contrast to quantum repeaters, this protocol uses only a single intermediate node with optical devices, requiring neither quantum memories nor quantum error correction. Recent field demonstrations for intracity quantum key distribution (QKD) networks hold promise for unconditionally secure communication with point-to-point links up to a 100 km (refs 1,2), such intracity networks will be connected by a backbone quantum link to build a worldwide QKD network in the future. An intercity backbone quantum link—which would be more effective in connecting intracity QKD networks in different major cities than quantum repeaters—may be in greater demand than an intercontinental one based on quantum repeaters, to compose the future worldwide QKD network. All known QKD prepare-and-measure QKD schemes[1,2] whose final key rates G per pulse are limited[27] by the Takeoka–Guha–Wilde because of the lack of i(nTtGerWme) dbiaotue nndod2elso—g2s1⁄2hð1arþe1Z,2L
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