Photonics Research, Vol. 9, Issue 1, 01000049 (2021)

Second-order interference of true thermal light from a warm atomic ensemble in two independent unbalanced interferometers 

Abstract

We report the demonstration of a second-order interference experiment by use of thermal light emitted from a warm atomic ensemble in two spatially separated unbalanced Michelson interferometers (UMIs). This novel multipath correlation interference with thermal light has been theoretically proposed by Tamma [New J. Phys.18, 032002 (2016)NJOPFM1367-263010.1088/1367-2630/18/3/032002]. In our experiment, the bright thermal light used for second-order interference is superradiantly emitted via collective two-photon coherence in Doppler-broadened cascade-type Rb87 atoms. Owing to the long coherence time of the thermal light from the atomic ensemble, we observe its second-order interference in the two independent UMIs by means of time-resolved coincidence detection. The temporal waveforms of the interfering thermal light in the two spatially separated UMIs exhibit similarities with the temporal two-photon waveform of time–energy entangled photon pairs in Franson interferometry. Our results can contribute toward a better understanding of the relation between first- and second-order interferences that are at the heart of photonics-based quantum information science.