  Quantum entanglement is widely recognized as one of the key resources for the
advantages of quantum information processing, including universal quantum
computation, reduction of communication complexity or secret key distribution.
However, computational models have been discovered, which consume very little
or no entanglement and still can efficiently solve certain problems thought to
be classically intractable. The existence of these models suggests that
separable or weakly entangled states could be extremely useful tools for
quantum information processing as they are much easier to prepare and control
even in dissipative environments. It has been proposed that a requirement for
useful quantum states is the generation of so-called quantum discord, a measure
of non-classical correlations that includes entanglement as a subset. Although
a link between quantum discord and few quantum information tasks has been
studied, its role in computation speed-up is still open and its operational
interpretation remains restricted to only few somewhat contrived situations.
Here we show that quantum discord is the optimal resource for the remote
quantum state preparation, a variant of the quantum teleportation protocol.
Using photonic quantum systems, we explicitly show that the geometric measure
of quantum discord is related to the fidelity of this task, which provides an
operational meaning. Moreover, we demonstrate that separable states with
non-zero quantum discord can outperform entangled states. Therefore, the role
of quantum discord might provide fundamental insights for resource-efficient
quantum information processing.
