Experimental Investigation Of The Stimulated Raman Four-Wave Mixing Gains In Cesium Atoms

Based on the theory of quantum entanglement, American scientists have proposed quantum communication, namely Quantum Teleportation, which uses the quantum state carrying quantum information such as entangled photons to achieve the transmission of big data information at a long distance, completing the quantum secret communication which is not easy to be decoded and eavesdropped. In the field of quantum information, non-classic squeezing and entangled fields are the most important quantum sources which have the incomparable superiority in the guarantee of the relative safety and absolute capacity. Quantum repeater station communication network composed of quantum channels and nodes based on the entanglement exchange and entanglement purification needs the wavelength of non-classic fields near the atomic absorption line. The fields can be generated in the interaction process of laser and atom based on nonlinear effects. Therefore, the continuous variable twin beams have attracted a lot of attention in the field of quantum communication network based on the atomic coherent effects and four-wave mixing process. This paper carried on the experiment and theoretical analysis about the gain characteristic of intensity difference squeezing beams produced in the cesium atomic vapor. The article consists of the following three parts:The first part introduces the basics of the stimulated Raman scattering and four-wave mixing in atomic nonlinearity medium.The second part experimentally investigates the classic gain of injected probe and generated conjugate lights via using stimulated Raman four-wave mixing process in cesium atoms. The dependences of gain on the atomic density and pump detuning are compared when the probe is injected into the atoms as a Stokes or Anti-Stokes field, and the line shape and width of the spectrum are also discussed. The variation of probe gain on the frequency detuning of the pump is theoretical matched. This result provides necessary information for the preparation of quantum correlation via using stimulated Raman four-wave mixing process.In the third part, using the second part of the conclusion, the experiment produces intensity difference squeezing beams below the shot noise level 2.75dB. The dependence of quantum correlation between the probe and conjugate light on pump detuning, the atomic vapor length and density has been investigated experimentally as well as the comparison of the quantum correlation when the probe is injected into the atoms as a Stokes or Anti-Stokes field. The generation of two-mode squeezed state in single four-wave mixing is theoretical calculated and the dependence of quantum correlation on gain, single-photon detuning and the interaction time are compared, which is agreement with the experimental result. In addition, this paper introduces two experimental schemes of cascaded four-wave mixing, and the quantum correlation in the three schemes under the same gain is theoretical fitted. This will improve the degree of the intensity difference squeezing in the next step.