Experimental Study Of The Orthogonally Polarized Optical Field Storage In Cold Atoms EIT Medium

Quantum communication is one of the new fields of scientific research.In 2001,Duan et al.proposed the DLCZ protocol which provide an effective method to realize long-distance quantum communication[1].This protocol need the entanglement swapping and requires to transmit quantum states among several atomic ensembles.Long storage lifetime and high-efficiency quantum memory is the basis to establish a network of quantum information,achieve quantum repeaters and exchange information between distant quantum nodes[1,2].Electromagnetically induced transparency is one effective way to achieve quantum memory.Scientists have made great efforts to increase storage efficiency and storage lifetime.However,the magnetic field fluctuations will cause the decoherence of the atomic spin wave and lead to reduce the storage lifetime.By applying a suitable guide magnetic field on the atomic,the Zeeman degeneracy is lifted.By this method,the impact of magnetic-field-sensitive spin waves to storage lifetime can be removed,and storage lifetime will be increased.We further study the relationship between the magnetic field intensity and the storage lifetime.These study results provide foundation for the research of quantum memory of entangled light fields in cold atoms.The main content of this thesis includes:(1)The concept of electromagnetically induced transparency(EIT),laser cooling and trapping cold atoms technology[3]are briefly introduced.This paper specifically elaborated the magneto-optical trap system for trapping 87Rb cold atoms medium.In addition,the magneto-optical trap system has been improved to increase the optical depth of the atomic medium,simplify the experiment setup and stabilize the system.And the magneto-optical trap system also take the advantage of the fibers.These improvements provide better conditions for the experimental study of quantum memory.(2)We studied the storage and retrieval of two orthogonally polarized optical signals in 87Rb cold atoms though electromagnetically induced transparency(EIT)dynamics.We first prepared the cold atoms at special Zeeman sublevels[4],and then achieved the two orthogonal polarization states of light field stored in one atomic ensemble.We further study the relationship between the magnetic field intensity and the atomic storage lifetime.By increasing the intensity of the magnetic field orientation gradually,we measured the lifetime of storage.With the increasing of the intensity of the Guide magnetic field,the Zeeman energy level lifted obviously.It gradually eliminates the influence of the magnetic sensitive spin-wave to the storage lifetime,and the storage lifetime increases gradually.Experimental results show that the impact of magnetic-field-sensitive spin waves to storage lifetime can be removed when the guide magnetic field strength increases to 12.5G,and the storage lifetime attain to 1.5ms.