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Single-Photon Non-Locality

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Quantum networks hold key to future communication

Could quantum mechanics hold the key to the development of superfast, next-generation communication? A Marie Curie-funded project has made important steps towards answering this question.

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The EU-funded SIPHON project successfully created on-demand single photons and demonstrated that these particles can outperform natural atoms in experiments related to a specific quantum phenomenon. This achievement could have important implications in the pioneering world of quantum communication. “Today’s society is based on fast access to information,” says SIPHON project coordinator Klaus Jöns from the KTH Royal Institute of Technology in Sweden. “Getting a head-start on information is vital in business, finance, politics and security. Most of our information exchange is now done via the internet of course, but even this medium has capacity limits. Furthermore, data transfer is not secure.” Future networks Jöns’ EU-funded project tapped into the fascinating and mysterious world of quantum mechanics to further determine the feasibility of a future network that can handle massive amounts data flow. “The idea is that at the quantum level, we can encode information on the smallest quanta of energy, a single light particle called a photon,” he explains. “This would not only reduce the amount of energy needed to transfer information, but also allow for totally secure communication due to the principles of quantum mechanics.” The project focused specifically on a quantum phenomenon known as non-locality. This quantum mechanical effect is already well understood, and several experiments have been performed, usually involving two entangled photons. A projective measurement on one photon instantly collapses the state of the other entangled photon at a distant location. However non-locality of a single particle, in particular of a single-photon, raises some a fundamental question: can a single-photon be simultaneously at different locations? “Non-locality, which Albert Einstein described as ‘spooky actions at a distance’, occurs when particles separated in space are instantaneously influenced by an action that takes place in one part of the system and at one location,” explains Jöns. “In this project we wanted to see if modern nano-scale semiconductor quantum light sources could demonstrate non-locality in photons.” Artificial atoms Jöns and his team used nano-scale devices, also called artificial atoms, in their experiments and demonstrated that these are indeed excellent single photon sources. These artificial atoms also outperformed natural atoms in many cases. “These nano-scale semiconductor quantum light sources exhibited the lowest unwanted multi-photon emissions,” says Jöns. “They can also be used to generate deterministic entangled photon pairs.” This new method of generating pairs of entangled photons, on-demand, could help speed up research. The project also discovered that these quantum emitters “blink”, which means that they sometimes do not emit light. This, says, Jöns, should be taken into account when developing future applications in quantum communications. While it is clear that single and entangled photons are important blocks to building up quantum networks, Jöns stresses that a great deal more fundamental research is needed in order to identify the best quantum light sources that meet the most stringent requirements. “This Marie Curie project enabled me to build up my own network of collaborators,” he says. “This was an important step in helping me to become more independent and to build up my own research portfolio. It also offered me a unique research environment with excellent supervision and mentoring, which in my case was Prof Val Zwiller at KTH Stockholm.”


SIPHON, quantum, Marie Curie, networks, communication, photons, atoms

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