Fast manipulation of spin-wave excitations in an atomic ensemble

We experimentally demonstrated a fast manipulation of two orthogonal spin-wave excitations in an ensemble of cold 87 Rb atoms. The spin-wave manipulation is realized by transferring the excitations between two collective states, and a π rotation between the two spin waves is accomplished on a time scale of ∼100 ns. The multiple π rotations are completed based on the single π rotation. The results show that the retrieval optical signal from the manipulated spin waves gradually decreases along with the increasing of π-rotation numbers. The loss mechanism of spin waves caused by a Raman π rotation is simply analyzed, and the possible methods to mitigate the loss are discussed. Using multiple π rotations, one can implement the dynamical decoupling to protect the qubit memory in an atom ensemble from the influence of environmental noise.