Physicists reaches milestone towards optical computing

Physicists at Aarhus University, Denmark have proven that the methods for slow light can be used for creating optical transistors, an important milestone they say.

The scientists use a method known as electromagnetically induced transparency, which is the same that Danish physicist Lene Vestergaard Hau from Harvard University uses in her experiments concerning slow light.

A crystal of cold calcium ions can be utilized as an optical transistor, where the photons (light) can check and control the amount of other photons that can escape the crystal - the same way that the voltage of a gate-electrode in a transistor can control the current running through the transistor, writes physicists at Aarhus University in a new article in Nature Photonics.

Professor Michael Drewsen and two of his coworkers from Aarhus University have taken this research a step further by controlling the transmission of photons through a Coulomb crystal. A Coulomb crystal is a collection of ions, in this case calcium ions that are cooled down to only a thousands of a degree above absolute zero.

The typical distance between these ions is 10 micrometers, which is 100.000 times longer than the distance between atoms in a normal solid. That means that the Coulomb crystal is both a solid and a collection of free particles at the same time, which gives the crystal a bunch of special properties.
  One of which is that the transmission of photons through the crystal can be adjusted with the principle of electromagnetically induced transparency by tuning the properties of photons and ions in the crystal in relation to each other.

Through an experiment, the scientists have shown that they can turn on and off for a passage of light with a wavelength of 866 nano meters through the crystal by sending a switching signal consisting of photons with a wavelength of 850 nano meters.

In a purely optical quantum computer they would have to be able to control the passage of a single photon by using another single photon. Currently they use 150.000 controlled photons for their experiment, but they say that they are already working on ideas to decrease the amount of photons needed by a factor of 100.