Analysis Of Polariton And Manipulation Of Light In The Quantum Gradient-Echo Memory

The storage of optical quantum states is one of important task in the development of quantum network and quantum computing in the future. With the development of quantum technology, the optical quantum memory have gotten a running start. Several protocols that store optical quantum states in the atomic ensemble had been proposed. And they have their own advantages and disadvantages. As a variant ofthe controlled reversible inhomogeneous broadening(CRIB)protocol, the gradient echo memory(GEM) is a promising candidate for quantum memory because of its multimode storage and high recovery efficiency not achieved yet with other techniques. GEM had gotten a lot of attention since it was proposed in 2006. Description of polariton in the quantum gradient-echo memory is a new research method, which has gotten a series of outstanding achievement. This paper based on this, working at the polariton a step farer away and optimizing the storage procedure of GEM.Start from the interaction between light and atomic ensemble, we deduce the storage in CRIB protocol, then we analyzed the storage of light in GEM in detail. It can be seen by comparing to CRIB that The gradient echo memoryis purely electro-optic andπpulses are notrequired. What is more, GEM is predicted to be 100% efficient inthe limit of large optical depths. The three-level GEM system is controlled by the combination of coupling field and frequency gradient, which let us store and manipulation of light using it.In the last half of this paper we deduce the polaritonic description of the GEM in the spatialfrequency( k) domain space and its differential equation in order to research polariton and information manipulation. Solving the differential equation, we get the wave solution of evolution of thedecoherence-freepolaritonicmode inside the GEM system. It helps to illustrate the result of experiment and numericalsimulation that had been done. We also propose the principle of conservation of polariton as a connection with the loss of storage. In the same way, we take decoherence into account, and solved the differential equation with the parameter of decoherence rate. We find the contribution that the decohence made to the distortion within echo-pulse. Based on our analysis, we optimized the storage procedure of GEM. It not only improve the fidelity of echo pulse, but also reduce duration between manipulation of gradientfield and output of echo-pulse, which will make sense in practical application of GEM in the future.