The drop that makes helium overflow
© Alain Herzog
Helium droplets measuring just a few nanometers that have been associated with a highly excited atom have recently been observed for the first time. These nanodroplets, the theoretical existence of which was predicted around fifteen years ago, are the object of a new field of study and experimentation for basic research. Marcel Drabbels and his colleagues are taking part in this research by associating the drops with sodium, which they excite with a laser to form a stable system.
Nanodroplets associated to a highly excited atom, which had been theoretically predicted, are revealing themselves to scientists who recently succeeded in producing them for the first time in a stable state. When injected into a vacuum and submitted to pressure, helium disintegrates into thousands of droplets. Their size depends essentially on the temperature of the injected helium, close to absolute zero. At these temperatures, helium is super fluid, and flows without friction. But what are the characteristics of nanodroplets? Marcel Drabbels and Evgeniy Loginov of the Laboratory of Molecular Physical Chemistry have begun to answer this question in a recent publication.
Drops that burst
Drops of this size consist of just a few thousand atoms. Because of quantum effects, the properties of these droplets are difficult to calculate. The scientists make them burst by associating them with complex molecules and then exciting them with a laser. This enables the scientists to study the dynamics of these helium agglomerations and the way in which they interact with other elements.
By linking a sodium atom to helium, the researchers were also able to demonstrate two cases: one in which an electron of the sodium atom enters the droplet, an unstable configuration, and the other – at higher energy – in which the drop is surrounded by an electron in a stable configuration known as the Rydberg state. In the latter case, the sodium ion is in the helium which is then surrounded by an electron cloud at the “great distance” of a few micrometers.
Upcoming research activities will focus on adding elements other than sodium, to enable the researchers to refine their understanding of the mechanisms that control these phenomena. “The interesting thing is that we don’t know exactly where we are going with this,” adds Marcel Drabbels. As well as advancing our basic knowledge, these discoveries offer new ideas to stimulate the imagination of those who dream of quantum computers. Yet before taking the lead, the theory will still need to follow up the progress being made through experimentation.
Links:
http://lcpm.epfl.ch/
http://infoscience.epfl.ch/record/162383/files/PRL106.pdf