The observation of single-photon emission from defects in a two-dimensional semiconductor could lead to rapid developments in the pursuit of reliable and low-cost single-photon sources.
A few weeks ago we published two papers reporting the observation of single-photon emission from defects in the plane of a layer of the two-dimensional semiconductor WSe2 (refs 1,2), and two more on the emission of single photons from defects formed at the interface between layers of WSe2 (refs 3,4). All of these papers are included in this issue.
Single-photon generation, which is essential for a range of applications in quantum communication, has been achieved with a variety of systems in the past, most notably with semiconductor quantum dots, atomic defects such as nitrogen–vacancy centres in diamond, and even organic molecules. Each system has its advantages, but also its limitations. It is, for example, still a challenge to find a single-photon source that is stable, can be replicated, and can be easily interfaced with electrical contacts — all desirable, if not essential, features for efficient quantum communication devices.
The results on WSe2 are promising on various fronts. The material is inorganic, and stable. It could be easily used to form heterostructures with other two-dimensional materials, such as graphene or boron nitride, allowing a single-photon emitter or detector to be embedded in a more complex device5. It is also relatively simple to place contacts on a WSe2 layer and apply an electrical voltage. Nick Vamivakas and colleagues show that, for instance, an applied voltage can affect the single-photon emission4.
As Vasili Perebeinos explains in his News and Views article6, the observation of single-photon emission is only the first step towards the realization of quantum communication devices based on a two-dimensional semiconductor. It will be important to understand the origin of the defects and how to create them in a controlled way. Coupling the defects with a photonic cavity may enhance the optical emission and, especially, increase the speed at which photons are emitted. It may be possible to obtain single photons from the recombination of electrons and holes injected through metallic contacts. For use in realistic devices it will be essential to design structures that can provide single-photon emission at room temperature. Clearly there is still a lot to do. The good news is that two-dimensional semiconductors can be isolated relatively easily, at least by mechanical exfoliation, which is perfectly adequate for fundamental studies. This is undoubtedly one of the reasons why a number of research groups were able to observe single-photon emission almost at the same time. Apart from the papers in this issue1,2,3,4, at least another one (to our knowledge) has already been published elsewhere7. There is, therefore, reason to be optimistic and expect that developments will happen rapidly.
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Single photons for all. Nature Nanotech 10, 481 (2015). https://doi.org/10.1038/nnano.2015.127