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New Means Discovered to Control Light in Photonic Systems


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Photons are poised to become a dominant medium for transmitting information, as they travel very quickly and can carry a lot of information. They can also be placed into quantum states to build quantum networks, but working with light can be difficult as it is emitted in all directions and will go in both directions along photonic channels. Researchers at the Niels Bohr Institute, however, have found a solution to these difficulties with quantum dots.

Quantum dots are nano-sized semiconductor crystals that can have their properties precisely tuned. This tuning makes it possible to pump them with enough energy to emit a single photon of a specific frequency, which is very valuable for photonic and quantum systems. What the researchers discovered with a photonic chip, in which a quantum dot was embedded, was that the quantum spin of the dot determined the direction the emitted photon travelled along, through the photonic channel. This level of control is very useful and can also improve efficiency, as now the light is all going in the same direction.

Another consequence of this discovery is that the photonic channel appears to be different lengths, depending on the end a photon enters. From one end, the photon will just travel directly through the channel, but from the other end, going in the opposite direction the photon will interact with the quantum dot. This interaction causes the photon to slow down, making the length of the channel seem longer, due to the delay. This also opens up new applications, and because the materials involved are already used in the semiconductor industry, they have a head start to becoming reality, though a great deal of work still needs to be done.

Source: University of Copenhagen, Niels Bohr Institute

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