FLEET Seminar: Nina Voronova – Quantum hydrodynamics of cold exciton gases and ultrafast Rabi-oscillating vortices in exciton-polariton condensates

Dr Nina Voronova

National Research Nuclear University, Moscow Engineering Physics Institute

All welcome. Download seminar flyer here.

Abstract:

Excitons and exciton-polaritons are bosonic quasiparticles that can demonstrate high degree of spatial coherence and quantum properties, and at the same time the ability to propagate on macroscopic distances, thus presenting a perfect solid-state platform for studying many-body effects. On top of that, their intrinsic non-equilibrium driven-dissipative nature allows observing unique effects that can be far from reach in ultracold atoms and other conservative systems.

This talk combines several recent research results, including the prediction of the possibility to observe superfluid state and Bose-Einstein condensation in a gas of two-dimensional direct excitons at elevated temperatures, as well as the analysis of the Berezinskii-Kosterlitz-Thouless crossover in this system. To describe the direct and indirect exciton collective kinetic phenomena in single and coupled quantum wells, we develop a formalism based on quantum hydrodynamics approach, extending the description from conservative to driven-dissipative systems.

For geometries with spatially-separated pumping and losses, we demonstrate the existence of the static superfluidity in the system despite the radiative decay of particles. The second part of the talk addresses the striking dynamics of a Rabi-oscillating vortex in an exciton-polariton fluid inside a microcavity that is excited by a sequence of pulses with different topologies. Namely, the motion of a vortex that is observed in the photoluminescence from the system seemingly breaks some basic laws of physics, including the periodically changing angular momentum and going faster than the speed of light.

This apparently counter-intuitive behavior of an otherwise well-studied object (a vortex) is shown to be the consequence of creation of a wave function that realizes simultaneously all the possible quantum states of the system’s Hilbert space, and the measurement being made solely on one of the projections (i.e., photons detected by the CCD camera) results in such a staggering phenomenology.

About the speaker:

Nina S. Voronova graduated from Moscow Physical Engineering Institute (State University) in 2006. During her post-graduate study (2006 to 2009) under supervision of Prof. Dr. Yu. E. Lozovik, started to work on collective excitations in low-dimensional systems.

Received the Ph.D. degree in 2012 in Nanostructures Spectroscopy Lab, Institute of Spectroscopy, Russian Academy of Sciences. Since 2009, works at National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), currently as Associate Professor of the Theoretical physics department. In the end of 2015, joined the theoretical group of Prof. Alexey Kavokin in the group of Quantum Polaritonics at Russian Quantum Center.

She authored papers on vortices in polariton liquids, Rabi-oscillations in microcavities. Predicted the “Polariton Kapitza pendulum”. The area of scientific interests is excitons, exciton-polaritons, multicomponent Bose condensates, topological defects, low-temperature physics, superfluidity and superconductivity, bosonic Josephson phenomena.