Could you describe the basic idea of your research? 

My group works with ultracold atoms. These are trapped ensembles of neutral atoms, held inside a vacuum system, and cooled to quantum degeneracy. For the non-specialist, this means that we work in a sufficiently cold regime that the quantum nature of the atoms dominates, and we can no longer think of atoms as small billiard balls whizzing along and bumping into each other. Instead, both their wave-like nature and their exchange symmetry matters.

Our broad goals are to understand how to connect the properties of individual particles to the collective behaviour of many particles. For instance, even if you knew everything about H20, you wouldn't understand that an ocean of H20 had waves. Water waves are an emergent phenomenon, that involves the collective, coordinated motion of individual particles. Much of physics addresses these kind of "emergence" questions, so it is a research theme shared between my group and others in the Department.

What unique approaches are you employing in your research? 

While a few hundred ultracold atoms groups exist around the world, our group has a few specialties. One of them is the study of p-wave interactions, which occur when identical fermions scatter with one hbar of relative angular momentum. (For the non-specialist: imagine two particles orbiting around each other, a bit, as they make their closest approach during a collision.) Another focus of the group has been to study non-equilibrium physics, which requires "fast" manipulation and measurement. I am putting fast in quotes because ultracold atoms are actually quite sluggish, evolving on the microsecond time scale... compared to the femtosecond scale inherent in the dynamics of materials. So in this sense, we have it easy: the low densities and temperatures of our samples make them ideal playgrounds for non-equilibrium physics.

What challenges have you encountered during your research, and how have you worked to overcome them? Are there specific strategies or solutions you’ve found particularly effective?

Since you cannot buy an ultracold atoms machine from a company, we face tremendous technical challenges in the lab. My heroic students learn how to work with lasers, optical modulators, high-resolution microscopes, ultrahigh vacuum systems, high-current electromagnets, RF and microwave electronics, digital and analog control systems, and more. One strategy we use to minimize down-time is to have backups of everything already in the lab. When a chilled water unit fails, we can swap in a functional one and not have to wait for repair.

What are your plans for the future of your research? 

A new direction is to study bulk viscosity. This quantifies the dissipative response to a diverging or converging flow pattern. Recent theoretical work has tied this property to breaking of scale invariance in interacting cold fermions. We have worked out some of the tools we need and should be ready to start making measurements soon.

For more information, visit https://www.thywissenlab.ca