  The superfluid transition in liquid 4He filled in Gelsil glass observed in
recent experiments is discussed in the framework of quantum critical phenomena.
We show that quantum fluctuations of phase are indeed important at the
experimentally studied temperature range owing to the small pore size of
Gelsil, in contrast to 4He filled in previously studied porous media such as
Vycor glass. As a consequence of an effective particle-hole symmetry, the
quantum critical phenomena of the system are described by the 4D XY
universality class, except at very low temperatures. The simple scaling agrees
with the experimental data remarkably well.
