| Summary: | 碩士 === 國立清華大學 === 物理學系 === 89 === This thesis reports our experimental works on the quantum interference phenomena or coherence-induced effects of electromagnetically induced absorption (EIA), electromagnetically induced absorption (EIT), and interacting dark resonances (IDR) with cold atoms. Cold atoms are produced with a magneto-optical trap (MOT). We measure the spectra of the phenomena without the presence of the MOT fields.
EIA is the phenomenon that absorption of a weak probe field is enhanced by presence of a coupling field. It is due to the spontaneous transfer of coherence among degenerate Zeeman states of the excited level to those of the ground level. We have systematically studied EIA spectra in the two-level system formed by the |5S1/2,F=2 > and |5P3/2,F’=3 > states of 87Rb atoms. Our work shows linewidth of the EIA spectra is as narrow as 100 kHz or 0.017Gamma where Gamma is the natural linewidth of the excited states, and the enhancement of the probe absorption is as high as 1.5 folds.
EIT is the phenomenon that absorption of a weak probe field is suppressed by presence of the coupling field in a three-level system. Constructive interference among different transition pathways results in the transparency. The —type EIT system in our experiment is formed by three Zeeman sublevels of |5S1/2,F=2 > and |5P3/2,F’=2 > states of 87Rb atoms. The measured EIT spectral width is narrower than 40 kHz or 0.007Gamma with a contrast of 80 %. This indicates the relaxation of ground-state coherence has been reduced to 0.002 in our system. Our work also demonstrates that several transparency dips can emerge in the spectra under the presence of a static magnetic field, and that the number of the dips depends on the direction of the field. We have provided a physical picture for the observations.
IDR is the phenomenon in a four-level system. In the system, a coupling and a weak probe fields form a lumbda—type EIT system; a microwave excites the magnetic dipole transition between the fourth level and the ground state that is also driven by the coupling field. Constructive interference between two dark resonances in the system produces the spectrum of a sharp and high-contrast absorption peak emerging inside the narrow EIT transparency window. We report the first experimental observation of the IDR spectra. The measured spectra are in good agreement with the spectra from the theoretical calculation.
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