  The capability to reliably transmit and store quantum information is an
essential building block for future quantum networks and processors. Gauging
the ability of a communication link or quantum memory to preserve quantum
correlations is therefore vital for their technological application. Here, we
experimentally demonstrate a measurement-device-independent protocol for
certifying that an unknown channel acts as an entanglement-preserving channel.
Our results show that, even under realistic experimental conditions, including
imperfect single-photon sources and the various kinds of noise---in the channel
or in detection---where other verification means would fail or become
inefficient, the present verification protocol is still capable of affirming
the quantum behaviour in a faithful manner without requiring any trust on the
measurement device.
