In physics we do things and afterwards worry about whether they worked
According to Wikipedia, quantum metrology is the study of making high-resolution and highly sensitive measurements of physical parameters using quantum theory to describe the physical systems, in particular exploiting quantum entanglement.
If you are interested, you might want to take a look at this. It is a paper entitled Ensemble based quantum metrology. Quoting the abstract:
We consider measurement of magnetic field strength using an ensemble of spins, and we identify a third essential resource: the initial system polarisation, i.e. the low entropy of the original state. We find that performance depends crucially on the form of decoherence present; for a plausible dephasing model, we describe a quantum strategy which can indeed beat the standard quantum limit.