  We develop a scheme of generating highly indistinguishable single photons
from an active quantum Su-Schrieffer-Heeger chain made from a collection of
noisy quantum emitters. Surprisingly, the single photon emission spectrum of
the active quantum chain is extremely narrow compared to that of a single
emitter or topologically trivial chain. Moreover, this effect becomes
dramatically strong close to the non-trivial-to-trivial phase transition point.
Using this effect, we show that the single photon linewidth of a long
topological quantum chain can become arbitrarily narrow, constituting an ideal
source of indistinguishable single photons. Finally, taking specific examples
of actual quantum emitters, we provide a microscopic and quantitative analysis
of our model and analyze the most important parameters in view of the
experimental realization.
