Klaus Mølmer intensifies collaborations with the Institute of Applied Physics at the University of Bonn


[based on the press release of the University of Bonn]


Prof. Dr. Klaus Mølmer from the Niels Bohr Institute in Copenhagen has been awarded the Humboldt research prize of the Alexander von Humboldt Foundation. The €60,000 award, which is presented in Germany to researchers from abroad, is considered a major honor. Mølmer has been collaborating with the research groups led by ML4Q members, Dieter Meschede and Sebastian Hofferberth, at the University of Bonn’s Institute of Applied Physics (IAP) for many years now. The prize money will now enable them to intensify their cooperation.

Image: Prof. Klaus Mølmer

Klaus Mølmer is regarded as one of Europe’s leading theoreticians in the field of quantum optics. “He’s a truly brilliant mind with an encyclopedic understanding of the interrelationships in physics,” says Meschede. “He’s used to thinking problems through thoroughly and often comes up with unconventional and original solutions.”

Among other things, Mølmer is studying the development of key components for quantum computers of the future, specifically so-called gates. These enable quantum information to be manipulated in a controlled manner, which is vital in order to use it to perform calculations.





Building blocks for future quantum computers

Gates also form the basis for conventional computers. These use “bits,” tiny units of data that can have the value “0” or “1.” A gate can be used to change a bit’s state, for example, thus turning a “0” into a “1” or vice versa. This is what is known as a NOT gate.

By contrast, quantum computers calculate using quantum bits, which can be in a “0” and a “1” state at the same time. If you combine two quantum bits, then four states will be possible simultaneously: 00, 01, 10 and 11. With 10 quantum bits, that figure rises to over 1,000. This property allows certain calculations to be done much, much faster: effectively, a quantum computer tests out thousands of possible outcomes in parallel. Just like in a standard computer, however, this process also requires gates—the only difference being that they need to handle quantum bits.

“Klaus Mølmer invented this kind of gate together with his colleague Anders Sørensen,” Meschede explains. “It’s a conditional NOT gate, meaning that, if you have two quantum bits, it will switch the state of the second depending on the state of the first.” The Mølmer–Sørensen gate scheme, which even has its own Wikipedia page, is already being used in many prototype quantum computers all over the world.


Quantum physics “for the ears”

Mølmer studied physics at Aarhus University, where he also completed his doctorate in 1990. He was appointed Professor of Physics in Aarhus in 2000. In 2022, he moved to the Niels Bohr Institute at the University of Copenhagen. For over 30 years now, he has not only been researching the exotic phenomena of the quantum world with great enthusiasm—he has also been endeavoring to explain them to the general public.

This is something for which he occasionally employs some eccentric methods. For instance, he was involved in a project entitled “Quantum Music” (https://quantummusic.org/), which produced an interactive multimedia show, among other things. This involved creating special snippets of sound that contain formulae and experimental results taken from the world of quantum physics. The show also includes interactive visual elements that introduce the audience to the properties of the quantum world. He has given more than 100 popular science talks in total and has written a book on quantum physics for keen amateurs. “Besides being an outstanding researcher, Klaus Mølmer is also an excellent communicator,” Meschede says, summing up his colleague. “We’re looking forward to being able to work even more closely together in the future.”

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