Generation Of Correlated Photons And Quantum Noise In An Active Raman Gain Medium

An active Raman gain phenomenon is one of the nonlinear effects of optical field interacting with atoms. Generation of correlated photon pairs using this nonlinear effect is one of the research frontiers on crossover region of quantum optics and quantum information. In this thesis, we present the quantum optics models of double A -type four-level and A -type three-level atoms interaction with laser fields, respectively, which are based on the quantum mechanics, the experiment and theory of active Raman gain processes. Then through solving Langevin-Heisenberg equations of motion, we study the generation of correlated (2+1) photons and properties of quantum noise of active Raman gain system. We get some valuable results of theoretical research.In the first chapter, we simply reviewed Raman gain system, non-classical two photons source and quantum noise, and recommend the basic knowledge and properties of active Raman system, and recent experimental and theoretical schemes of non-classical two photons source research, and the origin, classify, solving methods and properties of quantum noise. In the second chapter, we present a scheme of generating (2+1) photons based on active Raman system and four wave mixing in a double (?)-type four-level atomic system (so called (2+1) photons, that is we can obtain a correlated or entangled photon pair (i.e., '2') as the photon '1' acts as a trigger). In this scheme, once a single probe photon is introduced to the four-level atomic system, a photon exactly as the inject-seeding quantum probe photon is generated in the direction of the probe field due to low Raman gain (here two photons exist and one of them use as a trigger), and a FWM process also occurs with a new photon being created, i.e., the one photon of '2'. Then, we have two photons in the probe mode and one photon in the FWM mode. This correlated (2+1) photons is better than the spontaneous parametric down-conversion (SPDC) and electro-magnetically induced transparency (EIT) based schemes, such as the direction of photons. We can always use one photon as a trigger and we still have a pair of photons for other experiments.The other important content of this thesis is the quantum noise properties of quantum probe field. In the third chapter, we study a three-level atom assemble interacting with a pump field and a quantum probe field. We study about the response function, response time and the quantum noise properties of quantum probe field. We calculate the output noise spectrum of active Raman scattering field through the medium when introducing one non-classical squeezed field. We find that the noise is low when the Rabi frequency is low. We can adjust parameters to control the noise. In the second chapter we do not consider noise as in the third chapter, so in the fourth chapter we consider the noise of a double (?)-type four level active Raman system. We give out the quantum noise affect the quantum laser field, and then we perfect the theory of the second chapter.The research in this thesis attributes to the crossover of quantum optics, atom optics, and quantum information. The results of this thesis have significant meanings on application research of active Raman gain system in quantum information science.