  Entanglement between light and matter combines the advantage of long distance
transmission of photonic qubits with the storage and processing capabilities of
atomic qubits. To distribute photonic states efficiently over long distances
several schemes to encode qubits have been investigated -- time-bin encoding
being particularly promising due to its robustness against decoherence in
optical fibers. Here, we demonstrate the generation of entanglement between a
photonic time-bin qubit and a single collective atomic spin excitation
(spin-wave) in a cold atomic ensemble, followed by the mapping of the atomic
qubit onto another photonic qubit. A magnetic field that induces a periodic
dephasing and rephasing of the atomic excitation ensures the temporal
distinguishability of the two time-bins and plays a central role in the
entanglement generation. To analyse the generated quantum state, we use largely
imbalanced Mach-Zehnder interferometers to perform projective measurements in
different qubit bases and verify the entanglement by violating a CHSH Bell
inequality.
