  We introduce a coherence susceptibility method, based on the fact that it
signals quantum fluctuations, for identifying quantum phase transitions, which
are induced by quantum fluctuations. This method requires no prior knowledge of
order parameter, and there is no need for careful considerations concerning the
choice of a bipartition of the system. It can identify different types of
quantum phase transition points exactly. At finite temperatures, where quantum
criticality is influenced by thermal fluctuations, our method can pinpoint the
temperature frame of quantum criticality, which perfectly coincides with recent
experiments.
