The Efficient Optical Quantum Storage In EIT Cold Atom Medium

In the 21st century, the impact of information on people’s life is growing. Our requirement to information is increasing. The faster, secure and reliable information is needed Quantum computers have a ultrafast computing power, and quantum key is security absolutely. All of these features will have great impact on the national’s security. They have great prospects on both military and civilian, attracting more and more scientist do a deep research on quantum information science.The storage of quantum optical signal is an important tool in quantum repeaters and long-distance quantum communication High quantum storage efficiency has important implications for large-scale linear optical quantum computing and quantum communication over long distances. Using of EIT dynamic process, we can achieve the transfer between optical field and atomic reversible, and completing quantum information storage and release, by adiabatic controling switch coupling light. How to get higher quantum storage efficiency has become a hot topic in the field of quantum information science.This paper mainly introduces the theory of laser cooling and trapping neutral atoms, as well as the equipment of magneto-optical trap system for cooling 87Rb atoms medium in our laboratory. We achieve the storage and release of optical signal in Rb cold atom medium based on EIT dynamic process. We have studied the relationship between storage efficiency and repumping intensity in cold atom EIT medium and compared the optical density of cold atoms and EIT signals, which are achieved by different repumping intensity, show the reason why optical storage efficiency decreases as the increase of repumping intensity. The specific contents are as follows:1.The background of cold atom physics is briefly introduced. Describe the principle of laser cooling and trapping neutral atoms, and equipment of our MOT system, specifically. By expanding the cooling light diameter, improving its power, we get a cold atoms medium, whose diameter is about 5mm, the number is about 109 and the temperature is about 200uK., which provides a good medium, for our experiment of optical signal storage and release2. We achieve optical storage and release by using the 87Rb cold atom medium. We have studied the curve of storage efficiency as a function of the repumping intensity in cooling system. Experimental results showed that:the storage efficiency increases with the repumping intensity, when it lower than a certain intensity, Our highest storage efficiency is up to 18%; if it is larger than this intensity, the storage efficiency begins to decrease. We have compared the optical density of cold atoms and EIT signals, which are achieved by different repumping intensity. When the repumping intensity is increasing, the number of cold atoms trapped in MOT significantly increased. The optical density increases, too. But the transmission peak at resonance frequency in EIT window is decreased. Therefore, when the optical density is increased, the writing light needs a corresponding increase. And then, the storage efficiency will not decrease.3. We have got Cigar-type 87Rb cold atoms by using a rectangular reverse Helmholtz coils in the new MOT as the traping magnetic. The OD of this medium is up to 40, which lays a solid foundation for further improving the optical storage efficiency.