Full-Bloch beams and ultrafast Rabi-rotating vortices

Abstract

Strongly coupled quantum fields, such as multicomponent atomic condensates, optical fields, and polaritons, are remarkable systems where the simple dynamics of coupled oscillators can meet the intricate phenomenology of quantum fluids. When the coupling between the components is coherent, not only the particles' number, but also their phase texture that maps the linear and angular momentum, can be exchanged. Here, on a system of exciton polaritons, we have realized a so-called full-Bloch beam: a configuration in which all superpositions of the upper and the lower polaritons—all quantum states of the associated Hilbert space—are simultaneously present at different points of the physical space, evolving in time according to Rabi-oscillatory dynamics. As a result, the light emitted by the cavity displays a peculiar dynamics of spiraling vortices endowed with oscillating linear and angular momenta and exhibiting ultrafast motion of their cores with striking accelerations to arbitrary speeds. This remarkable vortex motion is shown to result from distortions of the trajectories by a homeomorphic mapping between the Rabi rotation of the full wave function on the Bloch sphere and Apollonian circles in the real space where the observation is made. Such full-Bloch beams offer prospects at a fundamental level regarding their topological properties or in the interpretation of quantum mechanics, and the Rabi-rotating vortices they yield should lead to interesting applications such as ultrafast optical tweezers.