  We demonstrate high-fidelity reversible transfer of quantum information from
the polarisation of photons into the spin-state of an electron-hole pair in a
semiconductor quantum dot. Moreover, spins are electrically manipulated on a
sub-nanosecond timescale, allowing us to coherently control their evolution. By
varying the area of the electrical pulse, we demonstrate phase-shift and
spin-flip gate operations with near-unity fidelities. Our system constitutes a
controllable quantum interface between flying and stationary qubits, an
enabling technology for quantum logic in the solid-state.
