Vacuum-induced Coherences In Frequency-resolved Correlation And Preparation Of Quantum Sources

Both quantum coherence and quantum source are the cornerstones of implementing quan-tum technologies.A specific coherence,i.e.,vacuum induced coherences(VICs),could be found in the system with nonorthogonal dipole transition moments.While vacuum always causes the destruction of quantum coherence,it is the origin of the VICs.As VICs has poten-tial applications both in overcoming the decoherence caused by environment and the fields of quantum technologies,it is valuable to explore the schemes of probing and controlling VICs.In addition,as the main origin of quantum properties,quantum source is one of the most impor-tant elements in the quantum information and quantum metrology.The security of the quantum key distribution is strongly dependent on the single photon source,and the generation and ma-nipulation of a single-photon source with high quality play an important role in linear optics quantum computation.As another important quantum source,the superbunching light enable to improve the visibility of ghost imaging,probe the weak interaction between the light and matters,and prepare entanglement photon pairs.Therefore,it is our motivation to explore the way to monitor and control the VICs,and to explore the schemes to produce a single-photon source with subnatural or even ultranarrowing linewidth,and superbunching source.Firstly,we investigate theoretically 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.In the cross two-photon correlation of the ? and ?+ 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 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 that the perfect interference effects of time orderings and time symmetry are restored.Recent works verify that the perfect single-photon character is a global property of reso-nance fluorescence including all the spectral components,and then the absence of some compo-nents can spoil the single-photon character,which considerably limits the application of filtering scheme to obtain single-photon source with subnatural linewidth.We note that the linewidth of fluorescent photon is not always limited by the intrinsic linewidth of the emitter,and pro-vide a scheme where the linewidth of the fluorescent single photon can be much smaller than the natural linewidth of emitter by manipulating external coherent fields.By simulating the response of the filter or detection setup with a bandwidth approaching and even much smaller than the natural linewidth of emitter,the realization of ultranarrow single-photon source can be confirmed.Besides,we demonstrate that this scheme of ultranarrow single-photon source can be implemented based on various real physical platforms.Considering a ? three-level system with a coherent electron shelving process as the emitter,we investigated the statistic properties of the resonance fluorescence and the effect of spectral filtering.In weak excitation regime,the emitter can be considered as an equivalent two-level system with an ultranarrow linewidth.The ultranarrow linewidth can be displayed in the realis-tic spontaneous transition channel.This transition channel can not only emit fluorescent single photon with ultranarrow linewidth,but also under ultra-narrow linewidth scale,it can show the Mollow triplet and two-photon spectrum which appear in normal two-level system only under strong excitation regime in a scale of ultranarrow linewidth.The ultranarrow linewidth of the equivalent level system can be reflected in one-and two-photon spectrum.Then,we investi-gated the filtered fluorescence from the transition driven by laser field.We find that value of the zero delay second-order photon correlation can reach to and exceed value of the order of thou-sands,which means the appearance of superbunching effect.And we find the superbunching effect is general in the level system with a coherent electron shelving process.Finally,we give an detailed analysis for the origin of the superbunching effect,and consider that this mechanism of generating superbunching light is different from the ones reported before.Finally,we summarize the research in this article and put forward prospects for related and further research issues.