Polarization rotation of light in a gas of molecular superrotors

We present a detailed theoretical and experimental study of the rotation of the plane of polarization of light traveling through a gas of fast-spinning molecules. This effect is related to the polarization drag phenomenon predicted by Fermi a century ago and is a mechanical analog of the Faraday effect. In our experiments, molecules were spun up by an optical centrifuge and brought to the super-rotor state that retains its rotation for a relatively long time. Polarizability properties of fast-rotating molecules were analyzed considering the rotational Doppler effect and Coriolis forces. We used molecular dynamics simulations to account for intermolecular collisions. We found, both experimentally and theoretically, that the time dependence of the polarization rotation angle is nontrivial and nonmonotonic. This time dependence reflects the transfer of angular momentum from the rotating molecules to the macroscopic gas flow, which may lead to the birth of gas vortices. Moreover, we show that the long-term behavior of the polarization rotation is sensitive to the details of the intermolecular potential. Thus, the polarization drag effect measurement appears as a novel diagnostic tool for the characterization of intermolecular interaction potentials and studies of collisional processes in gases.