A high-rate source for single photons in a pure quantum state

We report on the efficient generation of single photons, making use of spontaneous Raman scattering in a single trapped ion. The photons are collected through in-vacuum high-numerical-aperture objectives. Photon frequency, polarization and temporal shape are controlled through appropriate laser parameters, allowing for photons in a pure quantum state. These photons are suitable heralds for single-photon absorption in a single-ion quantum memory. Quantum networks allow for quantum communication between distant locations (nodes) where local quantum information processing is carried out. The key ingredient for this kind of network architecture is to establish entanglement between network nodes (1). Its scalability is facilitated by employing quantum repeaters (2, 3). Different platforms are pursued for implementing quantum networks, and various schemes exist to generate entanglement between their nodes. In the field of trapped single atoms and ions as nodes (4), one approach is to use pairs of entangled photons, split them up and have them absorbed by two separate atoms, thus transferring the photonic entanglement onto