| Quantum coherence and interference can change optical properties of the me-dia greatly, and can be used to manipulate and control absorption, dispersion, spon-taneous emission and nonlinear optical effect efficiently, as well as have manyapplications in laser physics, quantum optics, nonlinear optics and quantum infor-mation. In this thesis, we study mainly the quantum manipulation of spontaneousemission and the realization of optical bistability (OB) in coherent media. Themain content is as follows:1. we have theoretically investigated the spontaneous emission spectra of afive-level atom embedded in the photonic crystals (PCs). The influence of the rel-ative position between the transition frequency and the photonic-band-gap (PBG)edge, the detunings and Rabi frequencies of two external driving fields and initialstates of the atomic system on the spontaneous emission spectra are discussed. Itis shown that the spontaneous emission spectra are sensitively dependent on therelative position of the transition frequency to the PBG, and the spontaneous emis-sion can be controlled effectively by appropriately adjusting the external pump andcontrol fields. A few interesting phenomena can be observed in the spontaneousemission spectra, such as spectral-line narrowing, spectral-line enhancement andspectra-line suppression, as well as the appearance of dark lines and multi-peakstructures under certain conditions. This gives us a helpful clue to control thespontaneous emission of an atom in PCs.2. The spontaneous emission properties of a microwave-field-driven four-level atom embedded in anisotropic double-band PCs are investigated. The influ-ences of the band-edge positions, Rabi frequency and detuning of the microwavefield on the emission spectrum are discussed. 3. We have theoretically investigated the spontaneous emission spectra ofa cold double tripod-type five-level atom controlled by an elliptically polarizedfield and an external magnetic field in free space. A wave function approach isused to derive explicit and analytical expressions of atomic spontaneous emissionspectra. The results clearly show that, by choosing appropriate parameters of thecoupled system, such as the intensity of external magnetic field, Rabi frequencyof elliptically polarized control field and the initial probability amplitudes, we canmanipulate the spontaneous emission effectively. These investigations may providemore degrees of freedom to manipulate the atomic spontaneous emission.4. We investigate spontaneous emission properties and control of the zerophonon line (ZPL) from a diamond nitrogen-vacancy (NV) center coherentlydriven by a single elliptically polarized control field. The numerical results showthat a few interesting phenomena such as enhancement, narrowing, suppression,and quenching of the ZPL spontaneous emission can be realized by modulatingthe polarization-dependent phase, the Zeeman shift and the intensity of the controlfield in our system. In the dressed-state picture of the control field, we qualitativelyexplain these results from viewpoint of physics5. We have theoretically investigated the OB behaviors in a tripod-type four-level atomic system driven by an elliptically polarized control field and a linearlypolarized probe field inside the unidirectional ring cavity. We discuss the effectsof the frequency detuning of the probe field, the control field intensity, the relativephase between two electric field components of the control field and the coopera-tion parameter on the behavior of OB.6. We explore laser-polarization-dependent and magnetically controlled OBin an optical ring cavity filled with diamond nitrogen-vacancy (NV) defect centersunder optical excitation. The shape of the OB curve can be significantly modifiedin a new operating regime from the previously studied OB case, i.e., by adjusting the intensity of the external magnetic field and the polarization of the control beam.The influences of the intensity of the control beam, the frequency detuning, andthe cooperation parameter on the OB behavior are also discussed in details. Theseresults are useful in real experiments for realizing an all-optical bistate switchingor coding element.In conclusion, this thesis not only deepens our awareness and understandingof spontaneous emission in quantum coherent media, but also provides thetheoretical foundation for investigating OB in experiment. These investigationsmay have some reference value for optical communications and the fabrication ofnovel optoelectronic devices, as well as all-optical switching and quantum coding. |
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