Light is the backbone of today’s communication network. While processing of classical or quantum information is typically realized in the electronic domain and has witnessed several breakthroughs in recent years, photons have consistently been used as a reliable communication medium. However, if we could manipulate photons by external electric and magnetic fields, as we do very successfully with electrons, this would enable the paradigm of all-optical information processing. Here, we leverage the hybridization of photons with electronic excitations in a solid in order to improve our ability to control photons.

We start with excitons, which are hydrogenlike bound states of an electron and a hole in a solid. Excitons can hybridize with photons to form what we call polaritons and at the same time interact with surrounding electrons. This creates the crucial link, which allows us to manipulate photons by exerting forces on electrons.

We tailor the surrounding electrons into regions with higher and lower electron density using electric and magnetic fields. The attraction between excitons and electrons accelerates the polaritons towards the high-density regions. Because polaritons eventually decay back into photons, the electron profile is directly imprinted onto the photons. The situation is further enriched when electrons enter the quantum Hall regime, where electron charge and spin densities are intertwined. There, the direction of the force depends on photon spin.

One question motivated by our work is whether it is possible to realize a Lorentz force on photons using external electric and magnetic fields. Such tunable photonic gauge fields could play a key role in the realization of strongly correlated states of photons.