A millisecond quantum memory for scalable quantum networks

Scalable quantum-information processing requires the capability of storing quantum states(1,2). In particular, a long-lived storable and retrievable quantum memory for single excitations is of key importance to long-distance quantum communication with atomic ensembles and linear optics(3-7). Although atomic memories for classical light(8) and continuous variables(9) have been demonstrated with millisecond storage time, lifetimes of only around 10 mu s have been reported for quantum memories storing single excitations(10-13). Here we present an experimental investigation into extending the storage time of quantum memory for single excitations. We identify and isolate distinct mechanisms responsible for the decoherence of spinwaves in atomic-ensemble-based quantum memories. By exploiting magnetic-field-insensitive states so- called clock states-and generating a long-wavelength spin wave to suppress dephasing, we succeed in extending the storage time of the quantum memory to 1 ms. Our result represents an important advance towards long-distance quantum communication and should provide a realistic approach to large-scale quantum information processing.