Paul Brumer: quantum coherence and coherent control

By Thomas Farrell on July 24, 2015 • ( 1 )

In JPhysB’s first Featured Author interview, we talk to Professor Paul Brumer. Professor Brumer works in the Chemical Physics Theory Group at the University of Toronto in Canada, where he works on, amongst other things: controlling molecular dynamics with lasers, nanoscale quantum dynamics and other issues in quantum mechanics.

Q: Which research projects are you and your group currently working on?

Our group is currently involved in theoretical and computational studies of quantum coherence, decoherence, and incoherence in molecular systems. Two, somewhat different, examples are (a) the ability to use quantum effects to control the dynamical evolution of molecules, the so-called field of coherent control, and (b) trying to understand the nature of quantum coherences generated in molecules when they are irradiated with natural (e.g. solar) light. In the first category, we continue our efforts to design laser-based scenarios to control the dynamical evolution of molecules. This constitutes a major challenge in molecular physics and one to which we, and several others, have made significant contributions. Indeed, my colleague Moshe Shapiro and I published two books on the subject. The most recent (Quantum Control of Molecular Processes, Wiley-VCH, 2012) describes the principles of quantum control, as well as computational and experimental results in this area up to the time of publication. Applications of this approach include controlling the dissociation of molecules, the collision of molecules, deposition of molecules on surfaces, the chirality of molecules, etc. This work has proven greatly rewarding — when we started, very little was known about the ability to control molecular processes in this way.

The second example, efforts to understand the dynamical evolution of molecules irradiated with natural incoherent light, is motivated by experimental developments in light-harvesting systems, and interest in developing more efficient solar cells. Of particular interest is the extent to which quantum coherence can be seen in atoms and molecules, even when the incident light is essentially incoherent (which is the case with sunlight). I am pleased to note that we have made considerable progress in this area, ranging from studies of atoms in the cosmic microwave background, to models of the first step in vision. We were able to study both large systems, computationally, as well as solve minimal model systems, analytically, gaining deep insight into the nature and extent of quantum coherence in such systems.

Q: What motivated you to pursue this field of research?

This work, as well as all the other work I have done during my career, was motivated by simple curiosity and by the realization that the issues that I addressed were poorly understood. Somehow, the challenges presented in these areas made them all the more interesting.

Q: Where do you think the field is heading?

I anticipate that coherent control will continue to flourish, resolving some of the remaining challenges, such as experimentally implementing the quantum control of bimolecular collision processes, and overcoming deleterious decoherence processes that work to destroy quantum coherence. Within the area of incoherent light excitation, the application of new results to solar cell design promises to be highly rewarding.

Q: What has been the most exciting development in physics during the course of your career?

My career started quite some time ago, at which time fundamental questions in nonrelativistic quantum were ignored. Most interesting and exciting has been the recent focus, formally, computationally and experimentally, on fundamental concepts in quantum mechanics such as non-locality, entanglement, etc. The way is open for a much deeper understanding of quantum mechanics and, hopefully, a resolution to the ever-challenging measurement problem.

Q: What do you find to be the most rewarding aspect of your job?

Although it sounds like “motherhood and apple pie”, the most rewarding thing is to see how young scientists develop, which I observe both in undergraduate teaching and in the growth of members of my own research group. It is highly rewarding to see students turn into quality scientists.

Q: If you were a young physicist just starting out today, what would you study?

This is an extremely difficult question. I chose chemical physics because it provides an opportunity to explore a wide array of research problems, with applications ranging from the biological to the astrophysical. I still think that this multi-disciplinary area offers extraordinarily wide-ranging opportunities for future research endeavors. This said, I would likely attempt to apply these tools to problems in biology which, it seems to me, is an area where numerous challenging issues lie.

On behalf of JPhysB I would like to thank Professor Brumer for answering our questions and for recently publishing “Coherent quantum control of internal conversion: s₂↔ s₁ in pyrazine via s₀→ s₂/s₁ weak field excitation” in our journal. You can read the full paper and more on quantum coherence in our Special Issue on Coherence and Control in the Quantum World.

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