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 Prof. Meschede from the IAP. “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.
An extensive international network
Prof. Mølmer has won various awards for his work. His interest in international dialogue and exchange is reflected in the numerous research trips he has made and visiting professorships he has held over the past few decades. As well as France and Austria, for instance, he has also spent time researching at the Max Planck Institute of Quantum Optics in Garching. In addition, he has enjoyed close links with the Institute of Applied Physics and has been a regular visitor to Bonn over the years.
“As far as I’m concerned, science is something that people do together—with colleagues and students who often become friends for life,” he says. “I first met Professor Meschede when I was a young postdoc in Germany in 1992, and it’s been a great pleasure for me to stay in touch with him and get to know his students and colleagues on my many trips to Bonn over all these years. I’m delighted to have the opportunity to work even more closely together with my friends and colleagues in Bonn thanks to the Humboldt Research Prize.”
He thinks that these are exciting times for both basic research and the development of technologies that draw on quantum interactions between light and matter. “I’m especially looking forward to using the Humboldt Research Prize to support the next generation of students in this field and help them to build their own international networks.”
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.”
Media contacts:
Prof. Dr. Klaus Mølmer
Niels Bohr Institute at the University of Copenhagen
Phone: +45 23382321
Email: klaus.molmer@nbi.ku.dk
Prof. Dr. Dieter Meschede
Institute of Applied Physics at the University of Bonn
Phone: +49 228 73-3471
Email: meschede@uni-bonn.de