  Using the process of cavity-enhanced spontaneous parametric down-conversion
(SPDC), we generate a narrow-band polarization-entangled photon pair resonant
on the rubidium (Rb) D1 line (795 nm). The degenerate single-mode photon pair
is selected by multiple temperature controlled etalons. The linewidth of
generated polarization-entangled photon pairs is 15 MHz which matches the
typical atomic memory bandwidth. The measured Bell parameter for the
polarization-entangled photons S=2.73+-0.04 which violates the Bell-CHSH
inequality by ~18 standard deviations. The presented entangled photon pair
source could be utilized in quantum communication and quantum computing based
on quantum memories in atomic ensemble.
