Quantum dots help manipulate light

They don't travel in a continuous flow, but in packages containing varying numbers of particles. Sometimes as many 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—so-called 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 first author 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 Prof. 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."