  Precise parameter estimation plays a central role in science and technology.
The statistical error in estimation can be decreased by repeating measurement,
leading to that the resultant uncertainty of the estimated parameter is
proportional to the square root of the number of repetitions in accordance with
the central limit theorem. Quantum parameter estimation, an emerging field of
quantum technology, aims to use quantum resources to yield higher statistical
precision than classical approaches. Here, we report the first room-temperature
implementation of entanglement-enhanced phase estimation in a solid-state
system: the nitrogen-vacancy centre in pure diamond. We demonstrate a
super-resolving phase measurement with two entangled qubits of different
physical realizations: an nitrogen-vacancy centre electron spin and a proximal
${}^{13}$C nuclear spin. The experimental data shows clearly the uncertainty
reduction when entanglement resource is used, confirming the theoretical
expectation. Our results represent an elemental demonstration of enhancement of
quantum metrology against classical procedure.
