  Jet quenching parameter $\hat{q}$ is essential for characterizing the
interaction strength between jet partons and nuclear matter. Based on the
quark-meson (QM) model, we develop a new framework for calculating $\hat{q}$ at
finite chemical potentials, in which $\hat{q}$ is related to the spectral
function of the chiral order parameter. A perturbative calculation up to the
one-loop order indicates that the momentum broadening of jets is enhanced at
both the high temperature and high chemical potential, and approximately
proportional to the parton number density in the partonic phase. We further
investigate the behavior of $\hat{q}$ in the vicinity of the critical endpoint
(CEP) by coupling our calculation with a recently developed equation of state
that includes a CEP in the universality class of the Ising model, from which we
discover the partonic critical opalescence (PCO) -- a prominent enhancement of
the momentum broadening of jets near CEP, contributed by the scatterings via
the $\sigma$ exchange process. Hence, for the first time, jet quenching is
connected with the search of CEP.
