It is widely assumed that photons cannot be manipulated using electric or magnetic fields. Even though hybridization of photons with electronic polarization to form exciton-polaritons has paved the way to a number of ground-breaking experiments in semiconductor microcavities, the neutral bosonic nature of these quasiparticles has severely limited their response to external gauge fields. Here, we demonstrate polariton acceleration by external electric and magnetic fields in the presence of nonperturbative coupling between polaritons and itinerant electrons, leading to formation of new quasiparticles termed polaron-polaritons. We identify the generation of electron density gradients by the applied fields to be primarily responsible for inducing a gradient in polariton energy, which in turn leads to acceleration along a direction determined by the applied fields. Remarkably, we also observe that different polarization components of the polaritons can be accelerated in opposite directions when the electrons are in ν = 1 integer quantum Hall state.Controlling photons with external electric or magnetic fields is an outstanding goal. On the one hand, coupling photons to artificial gauge fields holds promises for the realization of topological and strongly correlated phases of light [1][2][3][4]. On the other hand, effecting forces on photons constitutes both a problem of fundamental interest in electromagnetism and an important step in view of technological applications [5][6][7][8]. One promising avenue towards this goal is to hybridize photons with material excitations that are genuinely sensitive to gauge fields [9]. In this non-perturbative regime, exciton-polariton states are formed, ensuring that the forces acting on the material excitations are directly imprinted onto the photon. However, the neutral bosonic nature of polaritons has so far severely limited their response to gauge fields [10][11][12][13].A particularly appealing approach to circumvent this limitation is to leverage on the interaction between excitons and charges. Indeed, early reports on the drift of trions in an electric field [14,15], as well as on the Coulomb drag effect in bilayer systems [16][17][18][19] indicated that it may be possible to manipulate neutral excitations using electric fields in a solid-state setting. Recently, experimental [20] and theoretical studies [21] reported the electrical control of the speed of a polariton superfluid, raising new questions and possibilities regarding the interplay between the normal and condensed fractions of the fluid in the presence of electron-exciton interactions.While interactions between polaritons and electrons have been proposed and analyzed as a mechanism for polariton thermalization [22][23][24][25], early studies reported the modifications to polariton resonances in the presence of a Fermi sea [26][27][28]. These modifications stem form dispersive interactions between the polarizable excitonic component of the polariton with the charge-density fluctuations of the Fermi sea [29][30][31]. ...

When Landau levels (LLs) become degenerate near the Fermi energy in the quantum Hall regime, interaction effects can drastically modify the electronic ground state. We study the quantum Hall ferromagnet formed in a two-dimensional hole gas around the LL filling factor ν ¼ 1 in the vicinity of a LL crossing in the heave-hole valence band. Cavity spectroscopy in the strong-coupling regime allows us to optically extract the spin polarization of the two-dimensional hole gas. By analyzing this polarization as a function of hole density and magnetic field, we observe a spin flip of the ferromagnet. Furthermore, the depolarization away from ν ¼ 1 accelerates close to the LL crossing. This is indicative of an increase in the size of skyrmion excitations as the effective Zeeman energy vanishes at the LL crossing.

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