Event Details

Physics Colloquium "Ultrafast Control of Particles and Quasiparticles in Superfluid Helium" Speaker: Prof. Valery Milner Department of Physics & Astronomy, University of British Columbia, Canada

Shaped ultrafast laser pulses have become powerful tools for controlling molecular dynamics. By engineering the temporal and polarization properties of femtosecond pulses, one can control the motion of molecules, manipulate their quantum states (e.g. vibration and rotation), and drive them far from equilibrium. My research group uses pulses shaped both as precisely timed pulse trains and as ``optical centrifuges'' -- laser fields with rotating polarization - to control and study molecular rotation in many-body quantum environments.

I will first discuss our studies of optically centrifuged molecules embedded in helium nanodroplets. By doping the droplets with various molecular species (e.g. CS2, OCS), and measuring the degree of their centrifuge-induced spatial alignment as a function of time, we gain a unique insight into the ``microscopic workings'' of superfluidity and the interaction of superfluids with quantum defects at the atomic level.

I will then show how we use shaped laser pulses to study fundamental collective excitations in superfluid helium, such as rotons and maxons, and their interactions with the quantum bath. At equilibrium, these interactions are well described by the existing theory. However, far from equilibrium, e.g. after a sudden localized perturbation of the superfluid by an intense laser field, the dynamics of these quasiparticles remain poorly understood. Our approach to their controlled excitation and time-resolved detection sheds new light on ultrafast nonequilibrium many-body processes in superfluid helium.

About the speaker:

Dr. Valery Milner received his PhD in laser physics at the Weizmann Institute of Science in 1998. After completing his postdoctoral studies on quantum chaos with ultracold atoms at the University of Texas at Austin, Milner has joined Bell Laboratories, where he worked until 2004 on various applications of nonlinear optics in telecommunication technologies. He then moved to the University of British Columbia in Vancouver, Canada, where he is currently an Associate Professor at the Department of Physics and Astronomy. Milner’s current research is in the field of quantum coherent control, where ultrashort laser pulses are used to control the dynamics of atoms, molecules and many-body excitations in a variety of quantum systems.