Antibunching and bunching of photons in resonance fluorescence from a few atoms into guided modes of an optical nanofiber

We experimentally investigate the photon correlations in resonance fluorescence from a few atoms into the guided modes of the nanofiber. We show that, when the photons are emitted in the same direction, the photon correlation varies from antibunching to bunching with increasing atom number and, when the photons are emitted in the opposite directions, the photon correlation is always antibunchinglike regardless of the number of atoms. The effect of excitation geometry on the photon correlations is also discussed.