  We study the non-Markovian effect on a two-photon polarization entangled
state in which one photon from the pair is stored in a fiber delay-line buffer.
We propose a model of a photonic qubit coupled to fiber birefringence and a
fiber reservoir representing the environment. We analytically derive a
non-Markovian probability function for the buffered photon and its paired
photon. To verify the probability function, we perform the full quantum state
tomography of the photon pairs. We further exploit the measures of quantum
mutual information for studying the quantumness of the buffered photon and its
paired photon. We find that Werner's well-known separability criterion occurs
at the buffer time of about 0.9$\,$ms. Furthermore, our result implies that the
non-zero quantum discord can surpass Werner's criterion, and hence the quantum
bi-partite correlation can exist for a buffer time greater than 0.9$\,$ms.
