  We propose an experimentally feasible scheme for generating entangled
terahertz photon pairs in topological insulator quantum dots (TIQDs). We
demonstrate theoretically that in generic TIQDs: 1) the fine structure
splitting, which is the obstacle to produce entangled photons in conventional
semiconductor quantum dots, is inherently absent for one-dimensional massless
excitons due to the time-reversal symmetry; 2) the selection rules obey winding
number conservation instead of the conventional angular momentum conservation
between edge states with a linear dispersion. With these two advantages, the
entanglement of the emitted photons during the cascade in our scheme is robust
against unavoidable disorders and irregular shapes of the TIQDs.
