We propose a new methodology, namely "quantum Zeno blockade," for managing
light scattering at a few-photon level in general nonlinear-optical media, such
as crystals, fibers, silicon microrings, and atomic vapors. Using this tool,
antibunched emission of photon pairs can be achieved, leading to potent
quantum-optics applications such as deterministic entanglement generation
without the need for heralding. In a practical implementation using an on-chip
toroidal microcavity immersed in rubidium vapor, we estimate that high-fidelity
entangled photons can be produced on-demand at MHz rates or higher,
corresponding to an improvement of ≳107 times from the
state-of-the-art.Comment: to appear in Phys. Rev. Let