A new paper on the arXiv today. In this one we describe how to implement entangling gates between two quantum dots, mediated by a third optically excited quantum dot. Suppose you have three quantum dots in a row. The central one is of a different species and does not ordinarily interact with the neighboring two. However, when optically excited an interaction is 'switched on'. We show that by suitably timing the switching of the central qubit, the system can mediate a maximally entangling gate between the neighboring two qubits. Having such an entangling gate has many different uses in quantum information processing.