  We present a feasible scheme for performing an optically controlled phase
gate between two conduction electron spin qubits in adjacent self assembled
quantum dots. Interaction between the dots is mediated by the tunneling of the
valence hole state which is activated only by applying a laser pulse of the
right polarization and frequency. Combining the hole tunneling with the Pauli
blocking effect, we obtain conditional dynamics for the two quantum dots, which
is the essence of our gating operations. Our results are of explicit relevance
to the recent generation of vertically stacked self-assembled InAs quantum
dots, and show that by a design which avoids unintended dynamics the gate could
be implemented in theory in the 10 ps range and with a fidelity over 90%. Our
proposal therefore offers an accessible path to the demonstration of ultrafast
quantum logic in quantum dots.
