Single polariton nonlinear Faraday rotation

We present the experimental observation of photon-photon interactions at the single-particle level. The linearly polarized signal beam undergoes Faraday rotation by a nonlinear effective magnetic field induced by a very weak circularly polarized control beam due to the giant Kerr-like interactions between exciton-polaritons in our quantum well-based 0D microcavity structures. We measure a phase shift with a slope of 3.5×10^-3 radians per particle for low cavity occupancies between 0.1 and 3 excited by the control beam. These experimental findings are in agreement with theoretical models and pave the way towards the development of scalable photonic quantum gates.