Monitoring and manipulation of vacuum-induced coherences in frequency-resolved correlation

Abstract

The frequency-resolved correlations of the fluorescence emitted by a four-level system in the $J=1/2$ to $J=1/2$ transition driven by a linearly polarized laser field are theoretically investigated. In the cross two-photon correlation of the $\ensuremath{\pi}$ and ${\ensuremath{\sigma}}^{+}$ transitions, we show that VICs can induce the interference of time orderings between the two-photon paths with different dipole moments, which can serve as a good scheme to exhibit the effects of vacuum-induced coherences (VICs). An external magnetic field can cause frequency differences between two-photon paths with different time orderings. When the differences can be distinguished by detectors, the effects of VICs are destroyed and time asymmetry of the two-photon correlations appears due to the reveal of ``which path'' information. However, the which path information can be erased by tuning the filtering frequencies so the perfect interference effects of time orderings and time symmetry are restored.