How much quantum information survives a single photon's journey through matter?

Sending quantum information on a single photon through an atomic medium degrades the signal — but by exactly how much? This work calculates the quantum channel fidelity for single-photon transmission and finds it drops monotonically with how strongly the photon couples to the atoms, regardless of whether the medium is uniform or random. The result gives a clean performance bound that any quantum communication system using such channels must respect.