Elementary quantum-network links and nodes

The paper reports on the experimental demonstration of elementary quantum-network links and nodes with narrowband and transform-limited single-photon pulses that cannot be distinguished from one another. The photon source is realized in form of a strongly coupled atom-cavity system and it employs a controlled energy exchange between the atom and the quantized light field of the cavity. This is accomplished by laser pulses adiabatically driving one branch of a Raman transition in a Λ-type three-level atom, which is located in a high-finesse optical cavity resonant with the other branch of the transition. The transition goes hand-in-hand with a change of the photon number in the cavity.