Abstract

For quantum communication, a light pulse is an ideal carrier of quantum information. In quantum communication protocols (quantum cryptography for instance), normally it is required to storage and manipulate quantum information. However, light is very hard to be stored. Very recently, there is the idea to transfer squeezing from light to collective atomic spins [A. Kozhekin et al., quant-ph/9912014 and refs, therein] It. is not clear, however, how to write an arbitrary unknown state of a light pulse with an arbitrary shape onto the atomic internal state, and then after some storage time to read out the state back onto a light pulse with the same or a different chosen shape Here we propose a scheme with the following properties: i) An arbitrary unknown state of the input light pulse with an arbitrary shape (which is only limited by the parameters obtainable in the lab) can be mapped to the collective internal atomic state with tending-to-1 fidelity, and after storage the state can be perfectly transferred back to another light pulse with an arbitrary chosen shape; ii) If the input fight pulse consists of several modes of shapes, the atomic ensemble can selectively store one mode and completely reflect other modes Furthermore, the scheme is shown to be feasible with the current experimental technology

© 2000 IEEE