  Low-frequency quadrupole vibrations in deformed ${}^{36,38,40}$Mg are studied
by means of the deformed Quasiparticle-RPA based on the coordinate-space
Hartree-Fock-Bogoliubov formalism. Strongly collective $K^{\pi}=0^{+}$ and
$2^{+}$ excitation modes (carrying 10-20 W.u.) are obtained at about 3 MeV. It
is found that dynamical pairing effects play an essential role in generating
these modes. It implies that the lowest $K^{\pi}=0^{+}$ excitation modes are
particularly sensitive indicators of dynamical pairing correlations in deformed
nuclei near the neutron drip line.
