Entanglement-preserving absorption of single SPDC photons by a single atom

The emission and absorption of single photons by single atomic particles is a fundamental limit of light-matter interaction. As a controlled process, it is a tool for quantum optical information technology. A key task in quantum networks is to establish entanglement between distant atomic qubits that serve as nodes. We show that besides the time and frequency correlation that the photon pairs share, also their polarization entanglement is preserved during the absorption of one of the photons by a single atom.