Delayed feedback effects on multiatom correlation measurements in resonance fluorescence

The second-order correlation function of photons emitted from Rb85 atoms into a nanofiber guided mode in the presence of time-delayed feedback is measured and modeled. A laser-cooled atomic cloud is overlapped with the nanofiber and driven from the side. We put a mirror at one fiber end and detectors at the other and measured the intensity-intensity correlation function of guided fluorescence. We observe an antibunching to bunching transition at the null delay as the number of atoms increases. However, at the delay that corresponds to twice the mirror-atomic cloud distance, we always see antibunching independent of number of atoms. This suggests an interplay between delayed interaction of the emitted photon with the atomic cloud and the correlation between oppositely emitted photons, which is known to show antibunching independent of the number of emitters in the system [1]. We model the correlation measurements building upon previous analysis that considered the practical situation of atom-number fluctuation and transit-time effects [2].



[1] Grangier, Roger, Aspect, Heidmann, and Reynaud, Phys. Rev. Lett. 57, 687 (1986).

[2] Kimble, Dagenais, and Mandel, Phys. Rev. A 18, 201 (1978).