  The key requirement for quantum networking is the distribution of
entanglement between nodes. Surprisingly, entanglement can be generated across
a network without direct transfer - or communication - of entanglement. In
contrast to information gain, which cannot exceed the communicated information,
the entanglement gain is bounded by the communicated quantum discord, a more
general measure of quantum correlation that includes but is not limited to
entanglement. Here, we experimentally entangle two communicating parties
sharing three initially separable photonic qubits by exchange of a carrier
photon that is unentangled with either party at all times. We show that
distributing entanglement with separable carriers is resilient to noise and in
some cases becomes the only way of distributing entanglement through noisy
environments.
