“Infrared-microwave radiation ice condition sensor for cars”
timespan would have otherwise travelled almost a kilometre. He still feels passionate about this field today. In 2005 he returned to Germany and took over as head of an independent research group at the Max Planck Institute in Garching. There he rubbed shoulders with Theodor Hänsch, winner of the Nobel Prize for Physics, and took his habilitation at the Ludwig Maximilian University of Munich. In 2008 he was awarded a post at the EPFL, first as an assistant professor, then in 2013 as a full professor. Today he is studying a minute oscillator made of glass, shaped like a bicycle wheel but with a diameter of just 12 micrometres. It was this that won him the Latsis Prize for 2014. This resonator is both mechanical and optical. It allows light to circulate in the toric part of its structure (the tyre of the bicycle wheel, as it were). The walls reflect the light, thereby producing “radiation pressure”. In an experiment reported in Nature in 2012, the regulator was cooled to half a degree above absolute zero. Kippenberg and his team showed for the first time that it is possible to reduce its temperature even further, by injecting photons into the resonator and creating well-controlled radiation pressure. During this process, a particularly strong coupling is produced between the light and the mechanical movement, so strong in fact that the optical and mechanical properties of the structure become inseparable. Let's put it to work! At this point, the oscillator becomes so cold that it starts to become almost entirely submerged in what is known as its fundamental state. This state of minimal vibration is something that can only be described by quantum mechanics. The theory predicts, amongst other things, that an object can never be perfectly still, even at absolute zero, and that there is always a slight movement. “We managed to cool an object composed of billions of atoms to temperatures so low that we could observe quantum phenomena”, says Kippenberg. “This really is
fundamental science, and we aim to continue our work in this direction. But that doesn’t mean that we are not interested in possible applications for our research. Quite to the contrary, my passion for science has always included both”. Indeed, this was the goal that he was pursuing whilst at the Max Planck Institute when he managed to discover another remarkable property of microresonators. Light in a laser beam connected to a microresonator using a small fibre-optic cable can produce so-called “frequency combs”. These are essential, for example, in calibrating high-precision spectrometers used in astronomy and atomic clocks. Generators of frequency combs have always been cumbersome; they are the size of tables, very expensive and very complex. Kippenberg’s, however, is tiny and is built using the same methods as for electronic chips. A first patent was filed in 2007, followed by a second in 2013 at the EPFL. This invention won Kippenberg the Helmholtz Prize for Metrology in 2009 and is very close to being put on the market, a step that Kippenberg hopes to take by launching a start-up. Anton Vos is a science journalist, working chiefly at the University of Geneva.
Tobias Kippenberg Tobias Kippenberg was born in 1976 in Berlin. He spent his childhood in G roningen in Holland and then went to Bremen in Germany. He graduated in physics at Aachen before going on to take his Master (2000), his Ph.D. (2004) and a postdoc at Caltech in Pasadena, California. After a few years as an independent researcher at the Max Planck Institute in Germany, he landed a job at the EPFL, where he became a full professor in 2013.
Swiss National Science Foundation – Swiss Academies: Horizons No. 103
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