Quantum nonlinear optics using cold atomic ensembles

Abstract

The fundamental properties of light derive from its constituent particles, photons, which are massless and do no interact with each other. The realization of interactions between photons could enable a wide variety of scientific and engineering applications. In particular, coherent interactions would open the path for the simulation of quantum systems with light. Photon-photon interactions can be mediated by matter, in our case cold atomic ensembles, which provide a nonlinear medium. In conventional nonlinear media, the nonlinearities are negligibly weak at intensities corresponding to single photons and nonlinear optics at the few-photon level is a long-standing goal of optical and quantum science. In this thesis, we report on two different experimental approaches to create optical media with giant nonlinearities. Both approaches rely on Electromagnetically Induced Transparency, in which photons traveling in the medium are best described as part-matter part-light quantum particles, called polaritons. In our first approach, we achieve low-light nonlinearities by loading ensembles of cold atoms in a hollow-core photonic crystal fiber to enhance the polariton-photon interactions. In our second approach, the photons are coupled to strongly interacting Rydberg atoms, which mediate large interactions between single quanta of light. Moreover, the intrinsic nature of these interactions can be tailored to take on a coherent dispersive form.