Single-photon blockade in doubly resonant nanocavities with second-order nonlinearity

We propose the use of nanostructured photonic nanocavities made of χ⁽²⁾ nonlinear materials as prospective passive devices to generate strongly sub-Poissonian light via single-photon blockade of an input coherent field. The simplest scheme is based on the requirement that the nanocavity be doubly resonant, i.e., possess cavity modes with good spatial overlap at both the fundamental and second-harmonic frequencies. We discuss the feasibility of this scheme with state-of-the art nanofabrication technology and the possibility to use it as a passive single-photon source on demand.