The Quantum Noise Properties Of Light Field In Electromagnetically Induced Transparency Media

Over the past two decades, the interaction between the light field and atomic ensembles has attracted much attention as a basic unit of quantum information processing and quantum state engineering, which starts with the realization of the interface between atomic ensembles and quantum optical field. Atomic coherence effect of electromagnetically induced transparency (EIT) is one of the effective ways to achieve quantum interface. In the EIT medium, almost all atoms are in a coherent superposition state induced by probe and coupling light field, and therefore absorption of the probe field at the resonant frequency decreases, accompanied by a strong normal dispersion, which can be used to reduce group velocity, and furthermore it could enable the realization of quantum memory for light, in which the quantum state of the input probe field should be retained at the output, this realization is an important part of the quantum interface. However, during the process of interaction of light with atoms, there are various factors that affect the quality of the output state, and a lot of extra noise will inevitably be introduced into the probe field. So that the study of quantum noise characteristics of probe in the EIT process is very important and imperative.This dissertation mainly analyzes the quantum noise property of the probe field throughout the EIT medium and resonant medium with the velocity selective optical pumping, and it contains five parts:In the first chapter, the atomic coherent processes in the interaction between light and atoms are presented, such as Rabi oscillation, ac-Stark effect and coherent population trap; and then EIT effect is introduced and briefly explained by two methods; finally the development and application of EIT are elaborated.In the second chapter, the absorption and dispersion property of the two-level system and A-type EIT system are analyzed by semi-classical theory; the influence of optical pumping on the absorption property of the A-type EIT system is also analyzed. In the third chapter, the amplitude noise spectrum of outgoing coherent probe field through cesium vapor under the condition of A-type EIT is analyzed experimentally and theoretically. The amplitude noise of the probe field is largely influenced by the phase noise of probe field and coupling field, because the phase noise of probe and coupling can be converted to the amplitude noise of probe in EIT. The results are very useful for quantum memory. Their phase-to-amplitude conversion noise spectra are analogous and composed of four peaks, and two of them in the middle are higher than the other two. The conversion noise changes with the two-photon detuning, and at some two-photon detuning the conversion noise is the maximum value, where almost all phase noise is converted to amplitude noise. On the other hand, though phase noise is an important index to reflect laser quality and a significant factor in quantum optics and quantum communications, it can not be measured directly. The substitute way to measure it is by using conversion of phase noise to amplitude noise. So EIT can be used as a new device to measure laser phase noise.In the fourth chapter, the quantum noise property of a squeezed probe passing through an EIT medium is analyzed theoretically. In a A-type EIT medium, the squeezing of probe can be preserved well at some two-photon detuning with non-zero detection frequency. In a four-level system, with the dynamic Stark splitting the transparency window and the noise spectrum splits into two parts. At every two-photon resonance, the noise of output probe is the minimum value, and the squeezing can be preserved well. The noise spectrum and transparency window are also related to the detuning of fileds, however, the minimum noise value is invariable. When the detection frequency is equal to the Rabi frequency of the control field, the resonant probe filed always comes out with the minimum noise. So the dynamic Stark splitting can be as a method for process and control the quantum state with more degree of freedom, and has a potential application to many channel quantum communication and quantum information.In the fifth chapter, the effect of velocity selective optical pumping on the laser phase noise to amplitude noise conversion in a resonant medium is analyzed. When the diode laser with large phase noise is absorbed by a resonant medium, the phase noise will convert to its amplitude noise. With the optical pumping, much more phase noise can be converted. Then the power of the amplitude noise spectrum is enhanced and the linewidth of that is narrowed, so the high-resolution noise spectrum of cesium is observed experimentally. The effect of optical pumping on the probe absorption and dispersion is analyzed theoretically, which can give a qualitative explanation for the noise spectrum. So the high-resolution noise spectroscopy can provide a useful handle to research atomic energy-level structure and the absorption and dispersion of the atom, especially it would be useful for phase noise detection with high sensitivity.The characterized works among the above are as follows:Ⅰ. We have comparatively analyzed the phase to amplitude noise conversion for probe and coupling fields throughout a cesium vapor in the full EIT window. It is found that the same amount of conversion for probe and coupling fields is obtained. Our analysis is based on a theoretical quantum treatment for the probe field which propagates through the EIT media and detection using self-homodyne system. The experimental observations are in good agreement with the numerical calculations, which shows that EIT can be used as a new device to measure laser phase noise, and the result might be a useful reference for quantum memory.Ⅱ. We theoretically analyzed that the output quantum noise property of the squeezed probe field through EIT medium under the condition of dynamic Stark splitting. The squeezing of probe can be preserved well at two channels simultaneously; the resonant probe can keep the property of the maximum squeezing with the detection frequency equal to the Rabi frequency of the control field, avoiding the low frequency noise.Ⅲ. We experimentally study the laser phase noise to amplitude noise conversion in the resonant medium under the condition of velocity selective optical pumping, also give a qualitative explanation, and observe the high-resolution noise spectrum related to Cs D1and D2line. So the noise spectrum of the laser passing through atoms can be used as a kind of high resolution spectrum to measure the atomic energy-level structure precisely.