  Quantum metrology is an auspicious discipline of quantum information which is
currently witnessing a surge of experimental breakthroughs and theoretical
developments. The main goal of quantum metrology is to estimate unknown
parameters as accurately as possible. By using quantum resources as probes, it
is possible to attain a measurement precision that would be otherwise
impossible using the best classical strategies. For example, with respect to
the task of phase estimation, the maximum precision (the Heisenberg limit) is a
quadratic gain in precision with respect to the best classical strategies. Of
course, quantum metrology is not the sole quantum technology currently
undergoing advances. The theme of this thesis is exploring how quantum
metrology can be enhanced with other quantum techniques when appropriate,
namely: graph states, error correction and cryptography.
