RESEARCHERS at the Niels Bohr Institute have found a new way of laser cooling semiconductor membranes.
Paradoxically, the new method of cooling involves heating the semiconductor material, but the researcher managed to cool the membrane to -269 degrees Celsius.
The results are published in the scientific journal, Nature Physics.
The specific type of membrane the researchers worked with is a photonic crystal membrane made of gallium arsenide (GaAs). However, they had to fabricate one with specific dimensions to work with the experiement.
The researchers produced a membrane with a thickness of 160nm and a surface area of 1 x 1mm. They then allowed the membrane to interact with the laser light within a vacuum chamber in such a way that its mechanical movements affected the light that hit it.
When the laser light hits the semiconductor membrane, some of the light is reflected and the light is reflected back again via a mirror in the experiment so that the light flies back and forth in this space and forms an optical resonator. Some of the light is absorbed by the membrane, which heats up the membrane, causing expansion. In this way the distance between the membrane and the mirror is constantly changed in the form of a fluctuation.
The scientists examined the physics and discovered that a certain oscillation mode of the membrane cooled from room temperature down to -269 degrees C. This was due to a interplay between the movement of the membrane, the properties of the semiconductor and the optical resonances.
Researchers at the Niels Bohr Institute have experimented with laser cooling of atoms for some time now. They have cooled gas clouds of cesium atoms down to near absolute zero, using focused lasers and have created quantum entanglement between two atomic systems.
This latest development is an examination of how far the limits of quantum mechanics can be applied to macroscopic materials. For the researchers, this could open up new possibilities in optomechanics, which is the interaction between light and a mechanical motion.
The potential of optomechanics could pave the way for cooling components in quantum computers. Efficient cooling of mechanical fluctuations of semiconducting nanomembranes by means of light could also lead to the development of new sensors for electric current and mechanical forces.