报告时间：11月27日 周一 下午3:00
报告题目： Temporal pure single photons generated from a cold atomic cloud
A perfect single photon source is essential for applications in quantum information and quantum metrology. In practice, spontaneous parametric down conversion (SPDC) with nonlinear crystals or spontaneous four wave mixing (SFWM) generates time-frequency entangled biphotons, and thus produces a single photon by heralding the other with a single-photon detector. However, the typical temporal coherence time of the photon source generated from SPDC from nonlinear crystal is of femto-second-scale, which degrade the temporal purity of the heralded single photon source. In contrast, narrow-band biphotons generated from spontaneous four-wave mixing (SFWM) in cold atomic ensembles readily solve this dilemma, since they have the coherence time even exceeding one microsecond with electromagnetically-induced transparency (EIT) effect. In our recent work, by interfering independent heralded single photons from two separate cold atom clouds, we obtain Hong-Ou-Mandel dip with visibility of 80%, over 90% after correcting the multi-photon events. The result demonstrates that the narrow-band heralded single photons still maintain near-perfect purity. The narrow-band single-photon source is a good candidate for exploring the temporal mode of a single photon for quantum information science.