Since February 2021 Tijs Karman is Assistant Professor in the Theoretical and Computational Chemistry group within the Institute for Molecules andtijs_karman Materials (IMM) at Radboud University. This group aims to explain and predict properties of molecules, clusters and molecular solids. Part of the research is to study quantum phenomena in ultracold molecular collisions. Karman focusses on understanding losses in these collisions, and to control interactions between molecules. Ultracold molecules are promising for quantum computing and simulation, but these applications requires cooling molecules further to achieve higher phase-space densities. Karman lives in Kranenburg in Germany, together with his wife.
Where exactly did your curiosity for science start?
“Actually, I have a very broad interest and many things fascinate me. I have always found natural sciences very interesting. Science is very important in our daily life and it is everywhere, from the air we breathe to the products we consume. During my chemistry studies, it fascinated me what complex processes we can understand and describe. At the same time, the microscopic details of many seemingly simpler processes elude us, and I found that studying molecules in detail is what I enjoy the most.”
What did you study and what was your PhD study about?
“I studied chemistry and I also did my PhD at Radboud University, in the Theoretical Chemistry group of Professor Gerrit Groenenboom. I like doing research on the cutting edge of physics and chemistry, IMM is the place to be for that! In my PhD I focused on atmospheric chemistry; I studied the absorption of light by oxygen molecules in the air. Absorption by collisions with other oxygen molecules has a qualitatively different, broader spectrum than by collisions with nitrogen. I wanted to know what causes this. My theoretical models have since been used to analyze experiments. This collision-induced absorption by oxygen enables accurate calibration of satellites. Astronomers would also like to measure oxygen absorption in the atmospheres of exoplanets, as it could be interpreted as a sign of life outside our Earth.”
What did you do after your PhD?
“I have worked as postdoctoral researcher at University of Durham (UK) for one year, in Professor Jeremy Hutson's group. His group studies molecules at ultracold temperatures, so very different conditions from the atmosphere that I studied before. The aim is to cool these molecules down to near absolute zero such that all molecules are in the same quantum state and we can control them coherently. This fundamental knowledge is useful for applications in all kinds of quantum technologies, e.g. the quantum simulations or the quantum computers. After this I moved to ITAMP (Institute for Theoretical Atomic, Molecular and Optical Physics) at Harvard University (USA). I had been granted both a Rubicon Grant and an ITAMP fellowship, which enabled me to work in this inspirational working environment for two years. At ITAMP I was exposed to all branches of atomic and molecular physics, which was great and broadened my horizon scientifically. I continued to work on cold molecules research and I was able to collaborate with leading experimental groups at both Harvard and MIT.”
You did Covid19 research as well. Tell us about it.
“In April 2020, there was an explosion of research related to Covid-19 from many disciplines. I was contacted by a colleague researcher who studied the spread of moisture droplets. The droplets were tracked using light at a wavelength where the air should not absorb, but nevertheless this caused turbulence which affected the movement of the droplets. The reason why? Collision-induced absorption, again, the subject of my PhD thesis. This is a prime example of how quickly research motivated by academic interest can find applications and contribute to society.”
What is your research focus now?
“My focus is theoretical research into collisions between ultracold molecules. The challenge we need to overcome in order to realize new quantum technologies using ultracold molecules is that we can not cool molecules as efficiently as atoms. The reason for this is that we need collisions for thermalization, but ultracold molecules tend to “break” whenever they collide. At first we thought it was a chemical reaction. However, it turns out this also happens for non-reactive molecules, and no one really knows why. It is absurd when you think about it, but we have no idea what is going on in these simple molecular collisions. We want to get to the bottom of this because when we know what causes these losses, perhaps we can prevent them. Then we could cool these molecules further and make a simulator just like with atoms.”
What makes you happy going to work every day?
“Working in an academic environment is awesome as I have the opportunity to perform research in a field that really fascinates me. I get answers to fundamental questions that seem rather simple but are actually very complex. These mysterious collisional losses are a good example of such a paradox; On the one hand, we have excellent control over these individual molecules, but as soon as two molecules collide we have no idea what happens, or how they are destroyed. I also enjoy working together with students and collaborating with colleagues, especially across the traditional boundaries of disciplines.”
What are your future plans in terms of research?
“I am starting to build my group, with the first PhD student starting after the summer, and I am looking to hire more. There are also many projects for bachelor and master students. We will focus on how ultracold molecules are destroyed when they collide and to develop ways to prevent these losses. We also want to develop ways and methods to do the reverse and actually use these losses, for example to create certain exotic quantum states and to simulate dissipative models. I am continuing to work with my international collaborators, but also within the IMM. For example, I am actively collaborating with Professor Bas van de Meerakker’s group to control molecular collisions using external fields.”