| Optical quantum entanglement refers to the quantum state at the photon or optical field of two components with quantum correlation.The atom-photo entangled state can be obtained by storing a component of the entangled state in the atomic medium.The atom-photo entanglement is the core resource to realize quantum relay and construct quantum communication network.Atom-photo system is relatively pure quantum mechanics systems,which can provides a direct and easy-to-observe method for studying the basic principles of quantum physics.They are considered as important physical systems for studying quantum information science.Since Duan,Lukin,Cirac,Zoller proposed the DLCZ quantum information long-distance transmission scheme in 2001,the quantum relay based on atomic ensemble has attracted much attention.The entanglement of atom-photo has also become a research hotspot.In recent years,these studies have made rapid progress.Different schemes have been demonstrated in experiments,such as the entanglement of photons and spin-wave spatial modes,and light.Experiments on entanglement of spin-wave internal states,photon orbital angular momentum and spin-wave angular momentum are carried out.The research content of this paper is based on 87 Rb cold atoms.The influence of writing light field on quantum signal under excitation background noise is studied.By changing the power of writing light and adjusting the excitation rate,high fidelity atom-photo entanglement source can be prepared under suitable conditions.By improving the experimental operation mode and using the feedback mechanism,the entanglement generation rate of atomphoto is enhanced.The main contents of this paper are as follows:(1)Firstly,the related concepts of optical quantum information technology and optical quantum storage are introduced,and EIT(Electromagnetically Induced Transparency)storage and Raman storage schemes are compared.Finally,some experimental schemes for the generation of atom-photo entanglement in recent years are reviewed.(2)The physical properties of rubidium atom as storage medium,the method of trapping cold atoms by magneto-optical trap,the influence of light field and magnetic field on cold atoms are introduced.The influence of writing excitation rate on the entanglement source of light and atoms and the influence of magnetic field on the storage life of atomic spin wave are studied.(3)Experiments on the generation of atom-photo entanglement in cold atomic medium are carried out.The experimental device for the generation of atom-photo entanglement is introduced.The influence of background noise excited by writing light field on the quantum signal of light field is analyzed.The influence of writing excitation rate on the preparation of entanglement between light and atom is measured.The high excitation rate will affect the quality of the entanglement source.When the writing power is controlled at 120 ?W and the writing excitation rate is about 1%,the Bell parameter S is measured to be 2.6,and the fidelity of the entanglement source is measured to be 87.9%,and the storage life is 80 ?s.The generation of spin wave depends on Raman scattering process.In order to suppress the occurrence of higherorder cases,the probability of entanglement generation is controlled very low.Therefore,the efficiency of the experimental device is improved and the efficiency of entanglement generation can be improved by using efficient feedback mechanism.The operation principle of DLCZ schemes in the experiment is introduced.The entanglement generation rate of atom-photo is different under normal and feedback timing modes.The entanglement generation rate of atom-photo is improved by feedback regulation. |
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