Dipolar Dephasing of Rydberg D-State Polaritons.

We experimentally study the effects of the anisotropic Rydberg interaction on D-state Rydberg polaritons slowly propagating through a cold atomic sample. We observe the interaction-induced dephasing of Rydberg polaritons at very low photon input rates into the medium. We develop a model combining the propagation of the two-photon wave function through our system with nonperturbative calculations of the anisotropic Rydberg interaction to show that the observed effect can be attributed to pairwise interaction of individual Rydberg polaritons at distances larger than the Rydberg blockade.