  Quantum melting of ferroelectric moment in the frustrated hydrogen-bonded
system with "ice rule" is studied theoretically by using the quantum Monte
Carlo simulation. The large number of nearly degenerate configurations are
described as the gauge degrees of freedom, i.e., the model is mapped to a
lattice gauge theory which shows the confinement-deconfinment transition (CDT).
The dipole-dipole interaction $J_2$, on the other hand, explicitly breaks the
gauge symmetry leading to the ferroelectric transition (FT) at finite
temperature $T$. It is found that the crossover from FT to CDT manifests itself
in the reduced correlation length of the polarization $\xi_{\text{FT}} \sim
\Delta (K-K_c)^{-\nu}$ with $\Delta \propto \sqrt{J_2}$ while $K_c$ and $\nu$
remains finite in the limit $J_2 \to 0$. In contrast, the Currie-Weiss-like law
for the susceptibility $\chi$ and the spontaneous polarization behaves smoothly
and the length scale $\xi_{\text{CDT}}$, related to the molecular symmetry and
volume for CDT, does not reduce in this limit.
