Dynamic Beam Splitter Based On Electromagnetically Induced Transparency In Atomic Ensemble

In the model of dark state polariton of electromagnetic induced transmission?EIT?,an optical field can be converted into collective atomic excitation and stored in the atomic medium through switching off the strong coupling field adiabatically.By varying the power of the coupling pulse,we can control the ratio between the transmitted optical field and the stored atomic mode.However,the previous model considering infinite long medium gives a wrong prediction of required power for achieving 50:50 splitting ratio.To solve this problem,we theoretically and experimentally study this atom-light hybrid splitter.We use a cloud of cold ⁸⁵Rb atoms prepared in magneto-optical trap as the experimental platform.Based on a model of EIT dark state polariton,we consider the real case where the atomic medium has a finite length.The theoretical calculation gives numerical results which agree well with the experimental data.The results show that the ratio can be changed approximately from 1:99 to 99:1,when the maximum power of the coupling pulse?pulse length is 100 ns?varies from 0 to 20 mW,in the cold atomic ensemble with the optical depth of 40.This process can be used to achieve an atom-light hybrid beam splitter with tunable spitting ratio,and thus find potential application in interferometric measurement and quantum information processing.