Quantum Emitters Generate Single Photons on Demand

Quantum light emitters have been observed previously in atomically thin layers of transition metal dichalcogenides (TMDs). However, they have been found at random locations within the host material and usually in low densities, hindering experiments aiming to investigate this class of emitters.

An artist's impression of single photons emitted from quantum dots in supported layered semiconductors. Courtesy of Pawel Latawiec/Harvard University.

To facilitate investigation, deterministic arrays of hundreds of quantum emitters were created using different TMD materials, emitting across a range of wavelengths in the visible spectrum (610 to 680 nm and 740 to 820 nm), with a greater spectral stability than their randomly occurring counterparts. The controlled creation of quantum emitter arrays could provide a way to produce large quantities of single photon emitters on demand, potentially leading to ultrathin, single photons to be integrated in electronic devices.

Researchers from the University of Cambridge and Harvard University deposited TMD monolayers onto silica substrates nanopatterned with arrays of 150-nm-diameter pillars ranging from 60 to 190 nm in height. The nanopillars created localized deformations in the material resulting in the quantum confinement of excitons.

The quantum emitters were created in the TMD where it was supported by the pillars, making it possible for researchers 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 researcher Carmen Palacios-Berraquero.

The random occurrences of quantum dots (QDs) in TMD have made systematic investigation challenging.

“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 professor Mete Atatüre. “The quality of the emitters that we create on purpose seems to be better than the natural quantum dots.”

This image shows from L-R: Mete Atature, Alejandro Montblanch, Andrea Ferrari, Matteo Barbone, Dhiren Kara, Carmen Palacios-Berraquero. Courtesy of Graphene Flagship.

The researchers believe that their method could enable the placement of emitters in photonic structures such as optical waveguides in a scalable way, where precise and accurate positioning is paramount.

Researcher Dhiren Kara 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.”

The quantum arrays are fully scalable and compatible with silicon chip fabrication. While the approach is compatible with standard silicon processing techniques, it is not restricted to the specific properties of the substrate. The flexibility in the choice of substrate provides an opportunity to create hybrid quantum devices where semiconducting layered material (LM) quantum emitters (QEs) could be coupled to quantum systems in other materials such as spins in diamond and silicon carbide.

Andrea Ferrari, science and technology officer at the Graphene Flagship, said, “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 now have a firm place amongst the promising approaches for generation and manipulation of quantum light and could be enablers of a future integrated technology.”

The research was published in Nature Communications (doi:10.1038/ncomms15093).