  Epitaxially grown quantum dots (QDs) are promising sources of non-classical
states of light such as single photons and entangled photons. However, in order
for them to be used as a resource for long-distance quantum communication,
distributed quantum computation, or linear optics quantum computing, these
photons must be coupled efficiently to long-lived quantum memories as part of a
quantum repeater network. Here, we theoretically examine the prospects for
efficient storage and retrieval of a QD-generated single photon with a 1 ns
lifetime in a multi-level atomic system. We calculate using an experimentally
demonstrated optical depth of 150 that the storage (total) efficiency can
exceed 46% (28%) in a dense, ultracold ensemble of $^{87}$Rb atoms.
Furthermore, we find that the optimal control pulse required for storage and
retrieval can be obtained using a diode laser and an electro-optic modulator
rather than a mode-locked, pulsed laser source. Increasing the optical depth,
for example by using Bose-condensed ensembles or an optical cavity, can
increase the efficiencies to near unity. Aside from enabling a high-speed
quantum network based on QDs, such an efficient optical interface between an
atomic ensemble and a QD can also lead to entanglement between collective
spin-wave excitations of atoms and the spin of an electron or hole confined in
the QD.
