  In this paper, we report a generation of a spin-wave excitation (SWE) with a
near-unity () probability in a given time (~730). Such deterministic generation
relies on a feedback scheme with a millisecond quantum memory. The millisecond
memory is achieved by maximizing the wavelength of the spin wave and storing
the SWE as the magnetic-field-insensitive transition. We then demonstrate
partial retrievals of the spin wave by applying a first read pulse whose area
is smaller than the value of . The remained SWE is fully retrieved by a second
pulse. Anti-correlation function between the detections in the first and second
readouts has been measured, which shows that the partial-retrieval operation on
the SWE is in the quantum regime. The presented experiment represents an
important step towards the realization of the improved DLCZ quantum repeater
protocol proposed in Phys. Rev. A 77, 062301 (2008).
