antibunching in passive photonic devices\
    based on coupled nonlinear resonators 
---

Introduction
============

Emerging quantum photonic technologies mostly rely on the ability to generate, manipulate, and detect quantum states of light, with the challenging goal of bringing quantum information and communication devices to large scale applications (see [@qp_review; @focus_iqo] for recent overviews). Single-photon sources (SPS) and linear optical operations are necessary ingredients for prospective developments in quantum information processing [@klm_protocols; @mete2004], and remarkable progress toward a fully integrated and CMOS-compatible technology has been achieved in the last few years [@politi08sci]. However, the ability to generate pure single-photon Fock states on demand in a fully integrated quantum photonic platform is still lacking. Commonly employed SPS in quantum optical experiments rely on attenuated laser beams and parametric down-conversion. Typically, a coherent source of radiation is sent through a nonlinear medium possessing an intrinsic $\chi^{(2)}$ nonlinear susceptibility [@hong86prl], which is able to produce entangled photon pairs and hence heralded single-photon states upon projective measurement of one of the two channels [@Fasel2004]. Even if such sources inevitably suffer from low efficiencies [@focus_sps], this is currently the preferred way to inject single-photon wave packets as input for integrated quantum circuits through external fibre coupling [@politi08sci], 