We demonstrate a coherent and dynamic beam splitter based on light storage incold atoms. An input weak laser pulse is first stored in a cold atom ensemblevia electromagnetically-induced transparency (EIT). A set ofcounter-propagating control fields, applied at a later time, retrieves thestored pulse into two output spatial modes. The high visibility interferencebetween the two output pulses clearly demonstrates that the beam splittingprocess is coherent. Furthermore, by manipulating the control lasers, it ispossible to dynamically control the storage time, the power splitting ratio,the relative phase, and the optical frequencies of the output pulses. Theactive beam splitter demonstrated in this work is expected to significantlyreduce the resource requirement in photonic quantum information and inall-optical information processing as a single cold atom ensemble canfunctionally replace a variety of optical elements, including beam splitters,mirrors, phase shifters, and optical quantum memories.
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