Study on quantum interference effects in cold atoms and Bose-Einstein condensates

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We have investigated quantum interference effects such as electromagnetically induced transparency (EIT), coherent population trapping (CPT), and optical information storage in A-type three level atomic systems. In particular, laser-cooled Na atoms and Na atomic vapor have been studied extensively. Under bichromatic radiation that satisfy two-photon resonance condition, the atoms are brought into so-called dark states in which no resonance fluorescence is observed, the phenomenon called CPT. Using this effect, we have studied hyperfine-Zeeman spectra of the Na ground state. The observed spectra agree well with theoretical predictions and reflected properties of two-photon resonance. Quenching of fluorescence can also be useful for mapping of spatially inhomogeneous magnetic field. By imaging the fluorescence distribution by a CCD camera, we have succeeded in two-dimensional mapping of magnetic field produced by anti-Helmholtz coils. This method gives high-resolution, real-time imaging … More of the magnetic field distribution. The EIT linewidth can become extremely narrow, much narrower than Doppler or natural linewidth of the gaseous medium. By careful arrangement of experimental setup and using heterodyne detection technique, we have achieved the observation of subkilohertz (440 Hz) linewidth in Na atoms. Simultaneously obtained dispersion, or refractive index, spectra also showed very slow group velocity of this medium. Finally, we have challenged the possibility of optical information storage by using quantum interference effect. The optical information is stored as sublevel coherence and at later time it is retrieved by converting this sublevel coherence into optical coherence. Proof-of-principle experiment of such idea has been successfully demonstrated. By varying the delay time of the data reading time, we were able to obtain the relaxation time of the sublevel coherence, which was measured to be 72 μs. The evaluation of this constant is quite important since this quantity determines the data-storage time of the futuristic "quantum memory" device that should be applied as a register memory in a quantum computer system. Less