  We present a scheme for coherently manipulating quantum states of photons by
incorporating multiple photonic modes in a system with long-range interactions.
The presence of nonlocal photon-photon interactions destroys the energy or
momentum matching conditions between distinct propagating polaritons, and
consequently gives rise to blockaded effective coupling between the
corresponding polaritons. Such a blockade mechanism protects the system from
interaction-induced dissipations and enables highly tunable few-photon
nonlinearities. Taking Rydberg atomic ensemble as an example, we illustrate
several intriguing phenomena based on the proposed scheme, e.g., the
deterministic generation of entangled photon pairs, the nonlinear beam
splitting, as well as the establishment of a tunable dressed interaction
between individual photons.
