It is shown that, besides the previously predicted photon antibunching effect, photon bunching may occur in resonance fluorescence. This effect can be observed by measuring the time-delayed coincidences of photons from the side components of resonance fluorescence in a strong driving field.
We study the correlation between photons in the fluorescence light scattered from an atom driven by an intense bichromatic field having one strong and one weak component, with or without the use of frequency filters in front of the photodetectors. Depending on the filters used and on the spectral components selected, we predict signals corresponding either to bunching or to antibunching, and modulations at the driving field Rabi frequencies as well as at their sum and difference. In contrast with the case of monochromatic driving, the antibunching can occur between photons emitted into different (as well as the same) lines of the fluorescence spectrum.
Photon antibunching in resonance fluorescence - the emission from a single, resonantly driven two-level quantum emitter - is a paradigmatic signature of nonclassical light. Photon entanglement, by contrast, manifests as correlations that can defy any classical description and is typically regarded as a distinct quantum effect. Here, we experimentally extract pairs of narrowband, time-bin-entangled photons from the antibunched resonance fluorescence of a single trapped atom. We verify entanglement via violation of the CHSH Bell inequality and by reconstructing the two-photon density matrix. The observed correlations vanish when the coincidence time window exceeds the antibunching timescale, revealing underlying multimode entanglement in the emitted field. Our results establish a direct link between photon antibunching and photon-photon entanglement, unifying two canonical signatures of nonclassical light.
The moments of the fluorescent radiation of a J2-invariant, cooperative fluorescent group of atoms are calculated exactly. Both photon bunching and antibunching can occur in the fluorescent radiation. All finite-order moments have a critical-point behavior at ${\ensuremath{\Omega}}_{c}=J\ensuremath{\gamma}$ in the cooperative limit of $J\ensuremath{\rightarrow}\ensuremath{\infty}$. The maximum normalized intensity correlation is 6/5 which shows greatly reduced intensity fluctuations compared to noncooperative resonance fluorescence. Enhanced antibunching in all the fluorescent correlation functions occurs in the threshold region.