On-Demand Single Photon Emitter

An artist’s impression of single photons emitted from quantum dots in supported layered semiconductors. (Source: P. Latawiec / Harvard U.)

Transi­tion metal dichal­cogenides (TMDs) are layered semi­conductors that can be exfo­liated into layers only a few atoms thick. Recent research has shown that some TMDs can contain quantum light sources that can emit single photons of light. Until now, the occurrence of these quantum light emitters has been random. Now, researchers in the Graphene Flagship working at the Uni­versity of Cambridge, UK, have created large scale arrays of these quantum emitters in different TMD materials. This new approach leads to large quan­tities of on-demand, single photon emitters, paving the way for inte­grating ultra-thin, single photons in electronic devices.

Quantum light emitters, or quantum dots, are of interest for many different appli­cations, including quantum communi­cation and networks. Until now, it has been very difficult to produce large arrays of quantum emitters close together while keeping the high quality of the quantum light sources. “It’s almost a Goldi­locks problem. It seems like one either obtains good single photon sources, or good arrays but not both at the same time. Now, all of a sudden, we can have hundreds of these emitters in one sample,” said Mete Atatüre, a professor at the Cavendish Labora­tory of the Uni­versity of Cambridge.

The random occurrences of quantum dots in TMD made systematic inves­tigation difficult. “The ability to deter­ministi­cally create our sources has made a dramatic change in the way we do our day-to-day research. Previously it was pure luck, and we had to keep our spirits high even if we didn’t succeed. Now, we can do research in a more syste­matic way,” said Atatüre. Not only does this new method make performing research more straight­forward, but it also leads to improve­ments in the emitters them­selves: “The quality of the emitters that we create on purpose seems to be better than the natural quantum dots.”

Dhiren Kara, a researcher at the Cavendish Labora­tory, said: “There is lots of mystery surroun­ding these emitters, in how they ori­ginate and how they work. Now, one can directly create the emitters and not have to worry about waiting for them to appear randomly. In that sense, it speeds up a lot of the science.”

To create the quantum light sources, the researchers cut an array of nano­scale pillars into silica or nanodiamond, and then suspended the few-atom-thick TMD layer on top of the pillars. The quantum emitters are then created in the TMD where it is suppor­ted by the pillars, so it is possible to choose exactly where the single photons should be gene­rated. “The fact that the emitters are generated in a mechanical way is good, because it means that they are quite robust, and material inde­pendent,” said Carmen Palacios-Berra­quero, a researcher at the Cavendish Labora­tory.

The deter­ministic and robust generation of quantum sources means new oppor­tunities for hybrid structures of pho­tonic and elec­tronic functions layered together. The quantum arrays are fully scalable and compa­tible with silicon chip fabri­cation. Andrea Ferrari, Science and Tech­nology Officer and Chair of the Manage­ment Panel of the Graphene Flagship, was also involved in the research. He added: “Quantum techno­logies are recognized as key invest­ment areas for Europe, with a new Quantum Flagship recently announced. It is great to see that layered materials have now a firm place amongst the promising approaches for gene­ration and mani­pulation of quantum light and could be enablers of a future inte­grated tech­nology.” (Source: Graphene Flagship)

Reference: C. Palacios-Berraquero et al.: Large-scale quantum-emitter arrays in atomically thin semiconductors, Nat. Commun. 8, 15093 (2017); DOI: 10.1038/ncomms15093

Link: Quantum Information and Nanoscale Metrology, Cavendish Laboratory, University of Cambridge, UK • Graphene Flagship, EU research project

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