Theoretical Arid Experimental Research On Efficient Light Storage Based On Electromagneticaiiy Induced Transparency In Rubidium Atomic Vapour

Light storage is a key step towards the realization of all-optical communicationnetworks and quantum information processing. Such a process requires coherentlymapping photonic states into and out of an optical memory on demand. Thus, the ratioof retrieved pulse energy to that of the input, namely the storage efficiency, plays animportant role in practical applications. In recent years, light storage based onelectromagnetically induced transparency(EIT) attracts much research interest andresearchers try to use some methods to improve the storage efficiency. However in thehot atoms, the storage efficiency is rather low. This thesis mainly introduces thetheoretical and experimental research on efficient light storage based on EIT inrubidium vapor.The first part: The theoretical research on efficient light storage based on EIT inrubidium vapor. We introduce the effects of a pump field on the EIT transmission andthe suppression in intensity of a four-wave mixing (FWM) signal in a four-levelN-type scheme, which relate to this thesis closely. The EIT signal is dramaticallyenhanced by the applied pump field. When pump field is strong enough, the EIT dipcan be deeper than the background and the probe field is amplified. The swichingeffect of the pump field allows the FWM signal suppression in intensity. In order tounderstand the physical mechanism and to simplify the mathematical calculations, thetheoretical analysis and calculation for storage efficiency indifferent energy levelconfiguration are carried on in cold atoms. Due to the pure atomic status and thesimple interaction between light and atoms in cold atoms, resonance absorption of theprobe field and FWM process produces a small energy loss, so a high storageefficiency is obtained; the storage efficiency is improved by the pump field but it isnot obvious. However, in hot atomic ensemble, the efficiency is rather low because ofthe Doppler broadening. We propose a scheme to improve the storage efficiency byintroducing a pump field beyond three-leve Λ-type configuration. The storage efficiencies are calculated in warm atoms and the numerical results show that thestorage efficiency is improved greatly and were in good agreement with theexperimental results.The second part: The experimental research on efficient light storage based onEIT in rubidium vapor.87%storage efficiency is demonstrated experimentally in afour-level N-type configuration in hot rubidium vapour. The improvement in storageefficiency is mainly dependent on introducing a pump field beyond Λ-typeconfiguration to enhance the EIT signals and to suppress the virtual-level FWMprocess from the probe pulse to FWM pulse. The loss of probe pulse is then reducedto improve storage efficiency. The storage efficiency is measured with and withoutpump field respectively, which agrees well with the theoretical prediction. Thestorage efficiencies are also measured as a function of the storage time and of theoptical depth. With the pump field, the storage time is prolonged a little and thestorage efficiency increases linearly with the optical depth.