  Quantum metrology promises improved sensitivity in parameter estimation over
classical procedures. However, there is an extensive debate over the question
how the sensitivity scales with the resources (such as the average photon
number) and number of queries that are used in estimation procedures. Here, we
reconcile the physical definition of the relevant resources used in parameter
estimation with the information-theoretical scaling in terms of the query
complexity of a quantum network. This leads to a completely general optimality
proof of the Heisenberg limit for quantum metrology. We give an example how our
proof resolves paradoxes that suggest sensitivities beyond the Heisenberg
limit, and we show that the Heisenberg limit is an information-theoretic
interpretation of the Margolus-Levitin bound, rather than Heisenberg's
uncertainty relation.
