These semiconductors are cooled with laser light

Researchers at the Niels Bohr Institute have managed to successfully combine two worlds: quantum physics and nano physics.

The joining of two very distinct universes has already led to the discovery of a new method for laser cooling semiconductor membranes. 

As you probably already know, semiconductors are vital components in solar cells, LEDs and many other electronic devices. 

As such, the efficient cooling of components is critical for the design of future quantum computers and ultrasensitive sensors. 

So how does the new cooling method work?

Quite paradoxically – by actually heating the material! Indeed, using lasers, researchers cooled membrane fluctuations to minus 269 degrees C. 

“In experiments, we succeeded in achieving a new and efficient cooling of a solid material by using lasers. We have produced a semiconductor membrane with a thickness of 160 nanometers and an unprecedented surface area of 1 by 1 millimeter,” explained Koji Usami, associate professor at Quantop at the Niels Bohr Institute.

“In the experiments, we let the membrane interact with the laser light in such a way that its mechanical movements affected the light that hit it. We carefully examined the physics and discovered that a certain oscillation mode of the membrane cooled from room temperature down to minus 269 degrees C, which was a result of the complex and fascinating interplay between the movement of the membrane, the properties of the semiconductor and the optical resonances.

“The paradox,” continued Usami, “is that even though the membrane as a whole is getting a little bit warmer, the membrane is cooled at a certain oscillation and the cooling can be controlled with laser light. So it is cooling by warming! We managed to cool the membrane fluctuations to minus 269 degrees C.”

According to Usami, laser cooling of atoms has been practiced for several years in experiments in the quantum optical laboratories of the Quantop research group at the Niels Bohr Institute. To be sure, researchers have cooled gas clouds of cesium atoms down to near absolute zero, minus 273 degrees C – using focused lasers – while creating entanglement between two atomic systems. 

The atomic spin becomes entangled and the two gas clouds form a kind of link due to quantum mechanics. Using quantum optical techniques, they measured the quantum fluctuations of the atomic spin.

“For some time we have wanted to examine how far you can extend the limits of quantum mechanics – does it also apply to macroscopic materials?” said Professor Eugene Polzik, head of the Center of Excellence Quantop at the Niels Bohr Institute at the University of Copenhagen.

“It would mean entirely new possibilities for what is called optomechanics, which is the interaction between optical radiation, i.e. light, and a mechanical motion.”

Indeed, the potential of optomechanics could, for example, 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… Such cooling in some cases could replace expensive cryogenic cooling, which is used today and could result in extremely sensitive sensors that are only limited by quantum fluctuations,” added Polzik.