Comment on "Entanglement on Demand through Time Reordering"

Abstract

In a recent Letter [Phys. Rev. Lett. {\bf 100}, 120501 (2008)], Avron {\em et al.} discuss a time reordering scheme to achieve efficient "across-generation" of entangled photon pairs in a semiconductor quantum dot with a suppressed biexciton binding energy. They demonstrate that the scheme can be implemented using time delay between the generated photons. In this Comment, we derive an exact expression for the concurrence of the time delayed photons, and show that the predicted values by Avron {\em et al.} are not achievable, which stems from an approximation used in their approximate theoretical analysis.