  Generation of nonclassical light is an essential tool for quantum optics
research and applications in quantum information technology. We present
realization of the source of nonclassically correlated photon pairs based on
the process of spontaneous four-wave-mixing in warm atomic vapor. Atoms are
excited only by a single laser beam in retro-reflected configuration and
narrowband frequency filtering is employed for selection of correlated photon
pairs. Nonclassicality of generated light fields is proved by analysis of their
statistical properties. Measured parameters of the presented source promise
further applicability for efficient interaction with atomic ensembles.
