Pushing Photons with Electrons: Observation of the Polariton Drag Effect*

Exciton-polaritons are quasiparticles that are a superpositions of excitons and photons. In a microcavity, exciton-polaritons have an effective mass and can form a Bose-Einstein condensate (BEC). Experimentally, this condensate can be generated by pumping light into a microcavity structure with quantum wells at the antinodes of the light field, and then we can measure the the energy, real-space and momentum-space distributions of the polaritons using the light they emit, using conventional optical methods.
In our experiment, we observed a change in the angle of emission of the photons when injecting electrons to the system, which indicates that the interaction of electrons with the polaritons changes the momentum of the polariton condensate. The condensate flow was accelerated when electrons flow with the same direction, while the condensate was slowed down when electrons flow in the opposite direction. Because the experiment is a photon-in, photon-out system, this is equivalent to steering photons using a DC electrical current.