  We develop a model of a strongly correlated Bose fluid model in a confined
potential for the purpose of analyzing the localization of Bose-Einstein
condensation and the disappearance of superfluidity. This work is motivated by
the recent observation of a quantum phase transition in liquid $^4$He in porous
glass at high pressures. By introducing a pressure-dependent localization
length of the localized condensates, we could make a new analytical criterion
for the localization of the condensate. Without introducing any free
parameters, the resulting critical pressure of the transition from superfluid
to localization is shown to be quantitatively consistent with observations.
