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Projekt Druckansicht

Exploring the weakest bond: Structure and ionization of the Helium Dimer, Trimer and the search for the Efimov State

Fachliche Zuordnung Optik, Quantenoptik und Physik der Atome, Moleküle und Plasmen
Förderung Förderung von 2009 bis 2016
Projektkennung Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 115609961
 
Erstellungsjahr 2016

Zusammenfassung der Projektergebnisse

The project aimed at exploring helium dimers (He2) and trimers (He3) and their interaction with femtosecond laser pulses, synchrotron radiation, Free Electron Laser (FEL) light. The main goals were to search for the Efimov State of He3, to solve the question of the structure of ground state of He3, to image the wavefunction of the quantum halo He2 and to learn about the ionization dynamics of He2. We have reached all these goals and have in addition made (and published) many interesting (and unexpected) discoveries on the way towards reaching these goals. A total of 31 peer reviewed papers (thereof 1 in Science, 5 in NaturePhysics/Nature Communications and 11 in Phys.Rev.Lett.). We list 4 highlights from our results: 1) In 2015 we have experimentally discovered the Efimov State of He3., almost 40 years after its theoretical prediction. We obtained the first ever image of the square of the wavefunction of an Efimov state. It shows the predicted enormous size (extending to more than 100 times the size of a water molecule) and the shape of an acute triangle. This was the ultimate but also most speculative and risky goal of the project and it was not clear at all if nature would allow us to reach it. The work is published in Science (2015). 2) In a series of experiments at our femtosecond laser and at the free electron laser FLASH we imaged the wavefunction of He2.We found the atoms to about 80 % in the classically forbidden tunneling region, below a potential barrier. In this region, the wavefunction shows a strictly exponential slope, which is a universal feature across all energy scales in physics. From our measured slope we obtain a new value for the long disputed helium dimer binding energy. This result is also of interest for metrology of temperature and the determination of the Boltzmann constant. 3) We performed a coulomb explosion imaging experiment on the 4He3 ground state molecule. From this we obtained the fiercely debated 4He3 geometrical structure to be that of a random cloud while predictions had ranged from this being mainly a linear molecule to it being an equilateral triangle. We could further image also the isotop mixed 3He4He2. We found that due to the tunneling effect the mass change of the one neutron changes the size by a factor of two and also changes the geometry. The results are published in Nature Communications. 4) The discovery and spectroscopy of Interatomic Coulombic Decay in helium dimers and a direct single photon double ionization process in He2. The Interatomic Coulombic Decay turned out spectacular as it shows for the first time the vibrational structure of the wave function of the intermediate excited He2+. We have described the long and rocky road towards the discovery of the Efimov state in a popular scientific article for the DFG magazine “Forschung” which is scheduled for 2016. Physics Today (68 (7), 10 (2015)) has published a long article about our experiment and the German newspaper “Frankfurter Allgemeine Zeitung” (5.Juni 2015) published a long detailed article on our discovery of the Efimov state and the “Neue Züricher Zeitung reported on our results using Coulomb Explosion imaging (NZZ 25.2.2015 article by Uta Neubauer). Furthermore, a 25 min Interview with the PI by Alexander Kluge in the program “10vor11” was aired on RTL, a major german TV channel. Maksim Kunitski, the postdoc behind the discovery of the Efimov state, has been awarded the Michael und Biserka Baum-Award 2015.

Projektbezogene Publikationen (Auswahl)

 
 

Zusatzinformationen

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