Manipulating Light With Quantum Dots

Optical microcavity to measure single-photon nonlinearity (Source: Univ- Leiden)

Optical microcavity to measure single-photon nonlinearity (Source: U. Leiden)

During a presen­tation, when you point a laser pointer at the screen, an immense amount of light particles race through the air at a billion kilo­meters per hour. They don’t travel in a conti­nuous flow, but in packages containing varying numbers of particles. Some­times as much as four so-called photons pass by, and other times none at all. You won’t notice this during your presen­tation, but for light-based quantum techno­logy it is crucial that scientists have control over the number of photons per package.

In theory you can mani­pulate photons with real indi­vidual atoms, but because of their small size it is ex­tremely hard to work with them. Now, Leiden physi­cists have disco­vered that the same principle goes for large arti­ficial atoms or quantum dots that are much easier to handle. In fact, they managed to filter light beams with one photon per package out of a laser. “Another big ad­vantage of quantum dots is that the system already works within nano­seconds,” says Henk Snijders. “With atomic systems you need micro­seconds, so a thousand times longer. This way, we can mani­pulate photons much faster.”

The ultimate goal for the research group led by Dirk Bouw­meester is to entangle many photons using quantum dots. This is essential for example in tech­niques like quantum crypto­graphy. Snijders: “This research shows that we are already able to mani­pulate indi­vidual photons with our system. And the beauty is that in principle we don’t need large expe­rimental setups. We can just integrate our quantum dots in small micro­chips.” (Source: Univ. Leiden)

Reference: H. Snijders et al.: Purification of a single photon nonlinearity, Nat. Comm. 7, 12578 (2016); DOI: 10.1038/ncomms12578

Link: Huygens-Kamerlingh Onnes Laboratory, Leiden University, The Netherlands

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