  The most important ability of a quantum channel is to preserve the quantum
properties of transmitted quantum states. We experimentally demonstrate a
continuous-variable system for efficient benchmarking of quantum channels. We
probe the tested quantum channels for a wide range of experimental parameters
such as amplitude, phase noise and channel lengths up to 40 km. The data is
analyzed using the framework of effective entanglement. We subsequently are
able to deduce an optimal point of operation for each quantum channel with
respect to the rate of distributed entanglement. This procedure is a promising
candidate for benchmarking quantum nodes and individual links in large quantum
networks of different physical implementations.
