Full Bell-basis measurement of an atom-photon 2-qubit state and its application for quantum networks

The efficiency of a Bell-state measurement on photon pairs is bound to 50 % due to the number of Bell states that can be distinguished using linear optics. Here we present the implementation of a protocol that allows us to distinguish all four Bell states by the use of a single-ion quantum memory and heralded absorption as state-selective measurement. The protocol is implemented in two steps. First we demonstrate the state-preserving mapping of a photonic qubit onto the quantum memory, verified by the preservation of entanglement in the process. Then we demonstrate the full Bell state projection between a memory qubit and an incoming photonic qubit, by applying it for atom-to-photon quantum state teleportation.