Chiral interaction of light and matter in confined geometries
When light is strongly transversally confined, significant local polarization componentsthat pointin the direction of propagation arise. In contrast to paraxial light fields, the corresponding intrinsic angular momentum of the light field is position-dependent -an effect referred to as spin-orbit interaction of light. Remarkably, the light’s spin can even be perpendicular to the propagation direction. The interaction of emitters with such light fields leads to new and surprising effects. For example, when coupling gold nanoparticles oratomsto the evanescent field surrounding a silica nanophotonic waveguide, the intrinsic mirror symmetry of the particles’ emission is broken. This allowed us to realize chiral nanophotonic interfaces in which the emission direction of light into the waveguide is controlled by the polarization of the excitation light  or by the internal state of the atoms , respectively.Moreover, we employ thischiral interactionto demonstrate nonreciprocal transmission of light at the single-photon level through a silica nanofiber.
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