Accelerating Polaritons with External Electric and Magnetic Fields

Light is the backbone of today’s communication network. While the processing of classical or quantum information, typically stored in a solid-state medium, has witnessed several breakthroughs in recent years, photons have consistently been used as a reliable communication bus. Yet, the possibility of manipulating photons by external electromagnetic fields, as it is done for electrons, holds many promises in the context of all-optical logical operations.

While it is clear that photons in free space cannot be manipulated by electromagnetic fields, the situation is strikingly different when light is confined in a solid. There, photons can hybridize with optical excitations of the medium leading to the formation of exciton-polaritons. [1] The situation is further enriched by immersing exciton-polaritons in a Fermi sea of electrons, which are directly responding to electromagnetic forces: polaritons in such a medium can be considered to be “dressed” by a cloud of material excitations, providing extra knobs to control light.

We have recently found that the close interplay between dressed polaritons, termed polarons, and electrons allow us to effect new electromagnetic forces on light. External fields lead to spatial variation in electron density and consequently a gradient in the polaron energy. In such a medium, polaritons are accelerated towards the high electron density regions. Because polaritons decay back into photons due to their finite lifetime, the electron density profile is directly imprinted to the displacement of photons. Furthermore, when electrons enter the quantum Hall regime where charge and spin densities and intertwined, the direction of the force experienced by polaritons depend on their polarization. [2]