Quantum theory of Kerr nonlinearity with Rydberg slow light polaritons

We study the propagation of Rydberg slow light polaritons through an atomic medium in the regime where the dispersion relation for the polaritons is well described by the slow light velocity alone. In this regime, the quantum many-body problem can be solved analytically for arbitrary shape of the atomic cloud. We demonstrate the connection of Rydberg polaritons to the behavior of a conventional Kerr nonlinearity for weak interactions and determine the leading quantum corrections for increasing interactions. We propose an experimental setup which allows one to measure the effective two-body interaction potential between Rydberg polaritons as well as higher-body interactions. Our work shows that the locality and causality based no-go theorems for quantum gates do not apply to setups based on Rydberg polaritons.