= Quantum metrology
<Quantum metrology> studies estimation of physical parameters using <quantum states>, evolution and <measurements>. A parameter changes the probe state; the <measurement> outcome distribution carries information about that change.
For $N$ independent comparable probes, uncertainty often scales as $N^{-1/2}$. <Entangled states> can improve scaling under suitable ideal resource assumptions, but losses, decoherence and the allowed preparation and <measurement> operations matter. Quoting an enhanced sensitivity requires identifying what counts as a resource and which noise model is being compared. <Quantum Fisher information> bounds the attainable local precision under specified estimation assumptions.
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