  With a recent rising interest of single photon superradiance due to its
potential usefulness for efficient collection of single photon from an atomic
ensemble, bright and narrow photon pair source is a key component in
realization of quantum communication and quantum computer based on coherent
interaction between light and atomic ensemble. We report the superradiant
emission of ultra-bright photon pairs with a coincidence counting rate per
input power of 64,600 cps/mW via spontaneous four-wave mixing in a thermal
vapour cell. The photon-pair generation rate is enhanced by the contribution of
two-photon coherence of almost atomic velocity groups in the Doppler-broadened
ladder-type atomic system. The quadratic proportionality of the probability of
detecting a heralded single photon as a function of the optical depth clarifies
that the ultra-brightness results from the superradiance. In addition, a single
photon superradiant beating at a high optical depth of the atomic ensemble is
observed for the first time.
