Few-photon all-optical phase rotation in a quantum-well micropillar cavity

Photonic platforms are an excellent setting for quantum technologies as weak photon-environment coupling ensures long coherence times. The second key ingredient for quantum photonics is interactions between photons, which can be provided by optical nonlinearities in the form of cross-phase modulation. This approach underpins many proposed applications in quantum optics(1-7) and information processing(8), but achieving its potential requires strong single-photon-level nonlinear phase shifts as well as scalable nonlinear elements. In this work we show that the required nonlinearity can be provided by exciton-polaritons in micropillars with embedded quantum wells. These combine the strong interactions of excitons(9,10) with the scalability of micrometre-sized emitters(11). We observe cross-phase modulation of up to 3 +/- 1 mrad per polariton using laser beams attenuated to below the average intensity of a single photon. With our work serving as a stepping stone, we lay down a route for quantum information processing in polaritonic lattices.

Automated summary

Photonic platforms are ideal for quantum technologies due to weak photon-environment coupling and interactions between photons. This study demonstrates that the required nonlinearity can be achieved using exciton-polaritons in micropillars with embedded quantum wells, and observes the effect of cross-phase modulation.