(Press release material)
15th April, 2015
Researchers at Nippon Telegraph and Telephone Corporation (NTT; Head office: Chiyoda-ku, Tokyo, Japan; President and CEO: Hiroo Unoura) and the University of Toronto (Toronto, Ontario, Canada; President: Meric Gertler) have proposed the theory of all-photonic quantum repeaters for long-distance quantum communication, disproving a dogma of the necessity of matter quantum memories*1. This paves a completely new route towards long-distance quantum communication based only on optical devices.
Extending the achievable distance of quantum communication not only expands the market of quantum communication but also realizes the ultimately secure communication network for our social life. Our finding renders such a worldwide quantum communication network or ‘quantum internet’ an ultimate challenge for the future photonic networks.
This work will be made public by the journal Nature Communications on 15th April, 2015.
This research is in part executed under the Project UQCC by the National Institute of Information and Communications Technology (NICT).
Quantum communication holds promise for applications that are intractable by conventional communication—such as quantum cryptography*2 and quantum teleportation*3—by utilizing quantum systems such as atoms and photons*4. Among various applications of quantum communication, the most advanced one is quantum cryptography which is secured by the laws of physics. In fact, field demonstrations of the quantum cryptography over a hundred kilometres have already been performed, for instance, represented by the Tokyo QKD network*5, and even the commercial products are available. So far, such quantum communication has been composed only of optical devices. However, to extend the communication distances from intracity ones (~ 100 km) to international (~ 1000 km) or intercontinental ones (~ 10000 km), we necessitate quantum repeaters, where ‘matter quantum memories’ were believed to be needed in addition to optical devices. As a result, proof-of-principle experiments for matter quantum memories have extensively been performed by lots of research groups in the world. However, unfortunately, the required matter quantum memories are demanding. Hence, as long as matter quantum memories are required, quantum repeaters may be more difficult than a quantum computer without a future experimental breakthrough.
NTT and the University of Toronto theoretically propose ‘all-photonic quantum repeaters’ with optical devices alone and without any matter quantum memory, disproving the dogma of the necessity of matter quantum memories for quantum repeaters. Our all-photonic scheme paves a completely new route towards long-distance quantum communication based only on optical devices, rendering the quantum communication network the ultimate future of the current optical communication. In contrast to conventional quantum repeaters based on matter quantum memories, our scheme has the advantages listed below, opening up the possibility of a worldwide quantum communication network or ‘quantum internet’.
Quantum repeaters are necessary for extending the achievable distances of quantum communication, and the realisation not only expands the market of quantum communication but also realizes the ultimately secure communication network for our social life. On the other hand, in the conventional communications, there has been an approach to the ‘photonic network’ based on optical devices alone towards reducing the power consumption and boosting up the communication speed. Our finding of all-photonic quantum repeaters presents such a conventional research on optical devices with a qualitatively new goal—the quantum internet—as the ultimate future of the photonic network. The all-photonic scheme was just born in the area of the theory, and the realisation still needs to wait further developments of optical devices such as linear optical elements, single-photon sources, photon detectors and an active feedforward technique. However, the step-by-step progress certainly contributes the realisation of not only the all-photon quantum repeaters but also the quantum internet. This may take long time, but it must be fascinating and fantastic journey.
In contrast to conventional theories that need matter quantum memories, all-photonic quantum repeaters without them, of course, have a conceptual jump. This should be called ‘time reversal’.
The goal of quantum repeaters is to supply quantum entanglement*10—which is a resource for quantum communication—to the sender and the receiver, by utilizing repeater nodes between them (Fig. 1 ). To achieve this goal, quantum repeaters perform two operations, ‘entanglement generation’ and ‘entanglement swapping’. Conventional schemes equip each repeater node with matter quantum memories and the quantum interfaces between matter and photons, and start by the entanglement generation, followed by the entanglement swapping (Fig. 2 ). However, our all-photonic quantum repeater scheme is based on taking the time reversal, that is, on a time-reversed protocol where the entanglement generation is performed after the entanglement swapping (Figs. 2 and 3 ). Indeed, the all-photonic quantum repeater protocol is all-optical implementation of the time-reversed protocol (Fig. 4 ). The time-reversed protocol is not only feasible only with photons, but also inherits only the advantages of the conventional quantum repeaters (Table 1 ).
click image to enlarge
Koji Azuma, Kiyoshi Tamaki and Hoi-Kwong Lo,
‘All-photonic quantum repeaters’,
Nature Communications [15th April, 2015 (BST)].
Nippon Telegraph and Telephone Corporation
Science and Core Technology Laboratory Group, Public Relations
NTT Has Instituted a Logo to Represent R&D Activities.
Information is current as of the date of issue of the individual press release.
Please be advised that information may be outdated after that point.