Preparation Of Long-life Atom-photon Entanglement Sources

With the development of quantum research,quantum communication network has attracted much attention.However,the decoherence caused by the long-distance transmission of quantum information seriously hinders the realization of quantum communication and quantum network.Quantum repeater provides the possibility for long-distance quantum communications,followed by DLCZ?Duan,theory,Cirac,Zoller?scheme based on atomic ensemble and the advent of the quantum of the linear optical relay has become a hot research in the field of quantum,the core of the DLCZ is entangled atoms and light,light and atomic entanglement is the key to building a quantum repeater,the life of a source for long life entanglement is a crucial research in the field of quantum repeater.The analysis of magnetic field effect is very important to understand the decoherence mechanism.We know that magnetic field is an important factor affecting the decoherence of spin wave.The methods to suppress the magnetic field interference are: compensating coil magnetic field,using torsion-free coil,feedback compensating magnetic field,using magnetic shielding material and so on.So the analysis of magnetic field effect is very important to understand the decoherence mechanism.The main research of this paper is to realize the entanglement source of light and atoms on the basis of ⁸⁷Rb cold atomic assemblage.We conduct experiments and measure the change of storage efficiency under different axial magnetic fields,and then carry out quasi-merging of the data to analyze the results.The experimental results show that the storage life can be significantly increased by applying the axial magnetic field.The advantage of this scheme is that it provides the experimental basis for obtaining the long-life storage entanglement source in the future,and helps us to understand and control the decoherence of quantum storage.This paper mainly includes the following parts:?1?We introduce the background of quantum repeater,with emphasis on DLCZ scheme,and reviewed the Raman scattering process based on atomic ensemble,we also listed the domestic and foreign research achievements in this field.?2?This paper introduces the physical background of laser trapping atoms and the principle of laser cooling atoms,and describe in detail the magnetooptical trap technology for trapping cold atoms experimentally,including the experimental optical path of constructing magneto-optical trap,experimental device and experimental operation of increasing optical depth.?3?In the cold atom ensemble of ⁸⁷Rb,the experimental study on the generation of atom-photons entanglement was carried out.And we introduced the experimental device and program.By applying different axial magnetic field,we measured the corresponding retrieval efficiency under different magnetic field,and theoretically fitted the data results,analyzed the relationship between the storage life and the axial magnetic field.The results show that the experimental environment is affected by the three-dimensional magnetic field noise,at zero magnetic field the three-dimensional magnetic field has a great influence on the phase noise of spin wave signal,lead to restore the signal direction was damaged.And the application of the axial magnetic field suppresses the effect of magnetic field noise on the phase of spin wave,so that the retrieval signal can be obtained after a long storage time.Finally,we carried out a theoretical analysis on the influence of magnetic field on the storage life,and we measured the value of Bell parameter S under the magnetic field strength of 100 m G.It was found that the storage time was around 400 and the Bell parameter S value was greater than 2.1,indicating that our experimental system obtained the storage life of 400 .?4?Finally,the research content of this paper is summarized.Based on the research content of this paper,we carry out follow-up work in order to further realize the entanglement source of long-lived atom-photon in cold atomic ensemble.