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news digest ♦ Lasers


measures about one by cm, while the nanomembrane itself has a surface area of 1 by 1 millimetere and a thickness of 160 nanometres. Photo: Ola J. Joensen


“We managed to produce a nanomembrane that is only 160 nanometres thick and with an area of more than 1 square millimetre. The size is enormous, which no one thought it was possible to produce,” explains Søren Stobbe, who also works at the Niels Bohr Institute.


Basis for new research


Now a foundation had been created for being able to reconcile quantum mechanics with macroscopic materials to explore the optomechanical effects.


Koji Usami explains that in the experiment they shine the laser light onto the nanomembrane in a vacuum chamber. 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 and releases free electrons. The electrons decay and thereby heat the membrane and this gives a thermal expansion. In this way the distance between the membrane and the mirror is constantly changed in the form of a fluctuation.


you can control the fluctuations of the membrane and the researchers succeeded in cooling a certain oscillation to minus 269 degrees C.


“Changing the distance between the membrane and the mirror leads to a complex and fascinating interplay between the movement of the membrane, the properties of the semiconductor and the optical resonances and you can control the system so as to cool the temperature of the membrane fluctuations. This is a new optomechanical mechanism, which is central to the new discovery. The paradox 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”, Koji Usami explains.


“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,” says Eugene Polzik.


Further details of this research are published in the paper, “Optical cavity cooling of mechanical modes of a semiconductor nanomembrane”, by K. Usami et al, Nature Physics, published online on 22 Jan 2012, DOI:10.1038/ nphys2196.


Seen here are fluctuations of the membrane. With the optical resonance frequency


146 www.compoundsemiconductor.net January / February 2012


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