Denmark’s largest research award goes to the ‘voice’ of quantum mechanics

When Professor Klaus Mølmer from Aarhus describes his research in layman’s terms, he says that he “goes cycling in a world of quantum mechanics” – a world that fascinates him with its brain-twisting paradoxes and fundamental importance for physics. This fascination has made him internationally recognised as a researcher in theoretical physics, with quantum optics as one of his special fields.

On 23 January, he is being rewarded for his research efforts when he receives the Villum Kann Rasmussen Annual Award for Technical and Scientific Research.

“It’s really fantastic. It’s possibly hard to understand if you’re not personally involved in getting enough funds to match the expenses related to research projects. This award will give me peace of mind for many years to come, because I can use it a kind of lubricating oil to get my projects to hang together,” says Professor Mølmer about the VILLUM FOUNDATION research prize valued at DKK 2.5 million.

This is the third time in four years that the award has been made to a professor at Aarhus University. In 2011, it went to Professor Christian S. Jensen, Department of Computer Science, while Professor Eva B. Vedel Jensen, Department of Mathematics, won the award in 2009. The award is granted each year to a Danish researcher in recognition of outstanding achievement in science and technology.

Research that builds on Niels Bohr

Professor Mølmer made his first impression on modern physics in the early 1990s, when he developed the so-called Monte Carlo wave-function (MCWF) method in collaboration with two French scientists. At that time, it was generally being recognised that a practical description was necessary of how measurements affect particles in the quantum world. A particle cannot be observed without ‘disturbing’ it, for example.

With the MCWF method, Professor Mølmer and his colleagues contributed with such a description, at the same time as reintroducing Niels Bohr’s famous quantum leap in quantum mechanics.

In 1913, Bohr proposed the quantum leap as a description of how electrons jump between two orbits around the nucleus of an atom and release the surplus energy as light.

“When quantum mechanics emerged in the 1920s, it replaced Bohr’s atomic model and described how the atom emits light steadily and calmly instead of in sudden jumps. In our theory, the electron jumps again, but now it happens because we see the light – the abrupt quantum leap takes place as the result of the measurements. So you suddenly feel that you’re in dialogue with Bohr a century later,” says Professor Mølmer with a smile.

The quantum mechanical cycling trip comes into the picture in applying the theory.

“When you ride a bike, you don’t predict right from the start how you need to move to keep your balance throughout the whole trip. Instead of this, you realise along the way if you’re about to fall and you take action. In much the same way, we try to control a particle’s movement in the quantum world. And this is where it gets very exciting because we disturb the particle simply by measuring it, and that has to be included in the calculation if we take action just as we do on the bike. We’ve even found examples where the disturbances are enough. In other words, we can control one or more microscopic particles simply by measuring them.”

Professor Mølmer’s work is currently used both theoretically and experimentally all over the world, in work that includes developing quantum computers.

Bridal bouquets and violin strings sell quantum physics

It is no coincidence that Professor Mølmer starts off with a bicycle analogy. He has more of these up his sleeve, such as the similarity between bridal bouquets and quantum computers or violin strings and wave functions. These are included in his many lectures at the Danish University Extension in Aarhus, at upper secondary schools, in the book Kvantemekanik: Atomernes vilde verden (Quantum mechanics: the wild world of the atoms), and when journalists call him.

Professor Mølmer is a keen and enthusiastic communicator, who does not allow himself to be hindered by the fact that quantum mechanics is an intellectual marathon project for many people.

“Of course, there’s a danger that when you use these images, you guide people to the completely wrong place. However, the actual mathematical description that I myself use in my research is impossible to relay, so I have to translate,” says Professor Mølmer, and reveals that he does exactly the same for his physics colleagues.

For example, he once used the same PowerPoint presentation for a group of second-year upper secondary school pupils and a lecture at the Niels Bohr Institute.

“I used some different words, but the material was the same,” he says.

“You see, it’s the same tricks that get both colleagues and upper secondary school pupils to remember the lecture. However, it also involves your own personal style. Perhaps I’m like a bee in a bottle, using both my arms and my legs, but I also have important role models who communicate clearly and precisely without resorting to silly analogies.”

Research at the interface between light and atoms

Professor Mølmer’s greatest expertise is now in quantum optics, a science in which the properties of light are studied and used at the quantum level.

“The whole of quantum physics originated back in the days of light research, when Max Planck proposed the theory in 1900 that light is not just electromagnetic radiation, but consists of small packets of energy called quanta or photons. In other words, light is made up of both waves and particles, and the phenomenon is easy to illustrate experimentally. Light can therefore be used as a kind of guinea pig for studying the paradoxes of quantum mechanics,” says Professor Mølmer.

“Detecting light is a fantastic source of information, such as when astronomers learn about space by means of background radiation, or when physicists use laser light for precision measurements. And you know light is actually part of modern technology – from atomic clocks to CD players,” says Professor Mølmer, referring to why precise theories about the behaviour of photons are necessary.

Team player rather than one-man band

Even though the award is being presented to Professor Mølmer as an individual, he regards it as a tribute to his entire team of students and researchers.

“My research results haven’t been one-man accomplishments. If that were the case, I wouldn’t consider it any fun at all being a researcher. My feedback from highly skilled experimental physicists and theoretical colleagues is crucial for the value of my work on pen and paper,” says Professor Mølmer.

“The image of the scientist in his ivory tower looks more and more like a myth,” states the modern scientist Klaus Mølmer.

About Klaus Mølmer

Klaus Mølmer (48) was born in Vejle, and he is married with two daughters. He is a qualified physicist from Aarhus University, where he completed his PhD in 1990. He was appointed associate professor at the university as early as 1991, and has been a professor at the Department of Physics and Astronomy, Aarhus University, since 2000. In 2003, he was appointed honorary professor at the Niels Bohr Institute, University of Copenhagen.

Professor Mølmer’s research career has been characterised by extensive international collaboration, where he has spent several periods of research at universities and research institutions abroad. Throughout the years, he has held a number of positions of trust, including being a member of the editorial committee of the prestigious journal Physical Review Letters. He is a member of both European and American research networks in quantum optics and quantum information. He is also a member of the Royal Danish Academy of Sciences and Letters, and has been awarded a number of Danish research prizes.

With his outstanding and innovative research, Professor Mølmer has contributed to the application of this research in extensive precision measurements using atomic clocks, as well as utilising data communication and processing, including the use of quantum computers. His research has focused particularly on studies of the interaction of atomic systems with light. Professor Mølmer has developed theories for fields such as the disintegration and suppression of microscopic quantum mechanical systems, slowing down atoms with laser light, dynamics for ultracold gases, quantum mechanical computers, and the special significance and application potential of the measuring process in quantum physics.

Contact

• Professor Klaus Mølmer, +45 8715 5641, moelmer@phys.au.dk
• Head of Department Lars Henrik Andersen, +45 8715 5594, lha@phys.au.dk
• VILLUM FOUNDATION, Lennart Rasmussen, +45 3957 0992, LRA@veluxfondene.dk