All-photonic intercity quantum key distribution

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.

Fundamental rate-loss trade-off for the quantum internet

“…Let us first compare the bound (3) with the intercity QKD protocols192021. This class of QKD protocols leads to a square root improvement in the secret key rate over conventional QKD schemes (without quantum repeaters) bounded by the TGW bound.…”

“…For example, the point-to-point quantum communication over 1,000 km needs18 to take almost one century to provide just one secret bit or one ebit for Alice and Bob under the use of a typical standard telecom optical fibre with loss of about 0.2 dB km −1 . Therefore, for the request from far distant Alice and Bob, the quantum internet necessitates long-distance quantum communication schemes utilizing intermediate nodes, such as intercity quantum key distribution (QKD) protocols192021 and quantum repeaters18222324252627282930313233343536. In particular, these schemes would be in greater demand for the quantum internet than the point-to-point quantum communication, analogously to the current Internet, where a client communicates with a far distant client via repeater nodes routinely and even unconsciously.…”

Measurement-device-independent quantum key distribution with nitrogen vacancy centers in diamond

“…We also compare our performance with that of the linear optical elements scheme proposed in [33]. The relevant system parameters are given in the text and in Table I.…”

“…In our simulation, we have assumed N = 1/P A . All put together, the curve labeled linear optical elements scheme shows the performance of the system proposed in [33]. Within the employed assumptions, the NV-center-based system performs better than that of the linear optical scheme.…”

Memory-assisted quantum key distribution resilient against multiple-excitation effects

“…It is, however, shown that once we account for the growing insertion loss with size in optical switches, the rate scaling may not keep up with the desired scaling, and overall the system may perform worse than the MA-MDI-QKD systems [17]. In particular, because, in long distances, the chance of photon arrival decreases, in the scheme of [47], we need to run a larger number of parallel links, hence requiring a larger size for the optical switch resulting in higher insertion losses. Moreover, the fact that we need a large number of parallel links makes the implementation of such systems non-trivial as compared to our schemes, which just require a single physical link.…”