  The ground-state fidelity has been introduced recently as a tool to
investigate quantum phase transitions. Here, we apply this concept in the
context of a crossover problem. Specifically, we calculate the fidelity
susceptibility for the BCS ground-state wave function, when the intensity of
the fermionic attraction is varied from weak to strong in an interacting Fermi
system, through the BCS-BEC crossover. Results are presented for contact and
finite-range attractive potentials and for both continuum and lattice models.
We conclude that the fidelity susceptibility can be useful also in the context
of crossover problems.
