  In their Letter, Zhou, Kato, Kawashima, and Trivedi claim that
finite-temperature critical points of strongly correlated quantum models
emulated by optical lattice experiments can generically be deduced from kinks
in the derivative of the density profile of atoms in the trap with respect to
the external potential, $\kappa = -dn(r)/dV(r)$. In this comment we demonstrate
that the authors failed to achieve their goal: to show that under realistic
experimental conditions critical densities $n_c(T,U)$ can be extracted from
density profiles with controllable accuracy.
