  Single photons produced by fundamentally dissimilar physical processes will
in general not be indistinguishable. We show how photons produced from a
quantum dot and by parametric down-conversion in a nonlinear crystal can be
manipulated to be indistinguishable. The measured two-photon coalescence
probability is 16%, and is limited by quantum-dot decoherence. Temporal
filtering to the quantum dot coherence time and accounting for detector time
response increases this to 61% while retaining 25% of the events. This
technique can connect different elements in a scalable quantum network.
