A new tool for controlling atomic states

Researchers manipulate helium atoms with shaped laser pulses in the extreme energy range / Oldenburg physicists involved in study

12.12.2024

Oldenburg. An international team of scientists led by Dr. Lukas Bruder from the University of Freiburg has succeeded in demonstrating a new method for investigating and controlling processes at the atomic level using extremely short, high-intensity and very high-energy laser pulses. Physicist Prof. Dr. Matthias Wollenhaupt from the University of Oldenburg was also involved in the study, which was published in the journal Nature. As the researchers write, their method could form the basis for investigating or even controlling chemical reactions more precisely than before, for example.

The team used the FERMI free-electron laser in Trieste, Italy, named after the Italian nuclear physicist Enrico Fermi. The machine is capable of generating ultra-short light pulses with enormous energy in the extreme ultraviolet (EUV) region of the spectrum. The researchers have succeeded for the first time in forming shaped light pulses in this wavelength range and using them to manipulate helium atoms. "The technique of pulse shaping has long been established in the visible light range. The fact that this has now also been achieved in the extreme UV range provides us with a new, powerful tool for quantum control," says Wollenhaupt, who heads the "Ultrafast Coherent Dynamics" working group at the University of Oldenburg. By quantum control, experts mean the control of processes at the atomic level that obey the strange laws of quantum physics.

In their experiment, the researchers used special EUV laser pulses whose frequency changes over the course of the signal. Experts refer to these as "chirping" or "chirped" pulses, as comparable acoustic signals resemble the chirping of birds. With these pulses, they put helium atoms into short-lived quantum states in which the light field and the helium atoms form a kind of unit. As the atoms of the noble gas helium are particularly stable, laser pulses of very high-energy light were required to generate these quantum states. "This is referred to as 'dressed states'. They only last as long as the laser pulse lasts," explains Wollenhaupt. In these states, the energy levels of the electrons in the atom shift compared to the undisturbed state and also split into a so-called doublet. As the researchers write, they have succeeded for the first time in specifically controlling the shape of this doublet using differently chirped laser pulses.

The current experiment builds on work by a team led by Wollenhaupt, at that time still at the University of Kassel, which was published back in 2006. At that time, the researchers used laser pulses in the visible and infrared range of light to control the corresponding doublet in potassium atoms with chirped pulses. The Oldenburg physicist is a specialist in quantum control using specifically shaped laser pulses. This expertise was also crucial in the current experiment in order to use chirped laser pulses in the EUV range for quantum control. "The technique we developed opens up a new field of research," says lead author Bruder. "It opens up new possibilities to make experiments with free-electron lasers much more efficient and selective. New insights can be gained into fundamental quantum systems that cannot be reached with visible light."

In addition to Wollenhaupt and the Freiburg team, researchers from the Max Planck Institute for the Physics of Complex Systems in Dresden, the Institute of Photonics and Nanotechnology in Milan (Italy), the University of Innsbruck (Austria), the University of Gothenburg (Sweden), the Institute of Materials Science in Trieste, the National Institute of Nuclear Physics in Rome (Italy), the German Electron Synchrotron in Hamburg, the University of Aarhus (Denmark) and the University of Hamburg were involved in the publication.

Original publication: Fabian Richter et al: "Strong-field quantum control in the extreme ultraviolet using pulse shaping", Nature 636 (2024), DOI: doi.org/10.1038/s41586-024-08209-y

Discovery Days - Spectral colors: From Isaac Newton to ultrafast spectroscopy

31.05.2024/01.06.2024

To celebrate the 50th anniversary of Carl von Ossietzky University, Faculty V opened its doors and presented Oldenburg research to students and anyone interested. We took part with an information stand and hands-on experiment on the decomposition of white light into spectral colors and how this technology is used today to form ultra-short flashes of light. We were delighted with the large number of visitors, from young to old.

Thanks to the organizers and all the visitors for making the event such a success!

Lumos - the perfect light wave - Special lecture

08.12.2023

Organized by the jDPG Oldenburg and the physics student council, the Christmas lecture entitled "Lumos - the perfect light wave" took place yesterday. Matthias Wollenhaupt and Bernd Schwenker delighted the packed lecture hall with numerous experiments.

Thanks to all participants and visitors for this magical evening!

Lumos - the perfect light wave - Special lecture

07.12.2023, 18:00

Soon it will be time again. The "perfect wave" is back! Join us and let Matthias Wollenhaupt and Bernd Schwenker inspire you in a physics show with exciting experiments on the subject of light.

Here you can find more information

The perfect wave - special lecture

06.12.2019

Physics show by Matthias Wollenhaupt, Lea-Christin Feld and Bernd Schwenker about the beauty and diversity of wave functions up to the Schrödinger equation.

Click here for the website of the young DPG