  We discuss the quantum phase transition from a liquid to a gaseous ground
state in a Bose fluid with increasing strength of the zero point motion. It is
shown that in the zero pressure limit, the two different ground states are
separated by a quantum tricritical point whose position is determined by a
vanishing two-body scattering length. In the presence of a finite three-body
scattering amplitude, the superfluid gas at this point exhibits sound modes
whose velocity scales linearly with density while the compressibility diverges
$\sim p^{-1/3}$ in the limit of vanishing pressure $p$. In the liquid regime of
negative scattering lengths, it is shown that $N$-body bound states exist up to
arbitrary $N$, consistent with a theorem by Seiringer. The asymptotic scaling
$a_{-}(N)\sim N^{-1/2}$ of the scattering lengths where they appear from the
continuum is determined from a finite size scaling analysis in the vicinity of
the quantum tricritical point. This also provides a qualitative understanding
of numerical results for the quantum unbinding of small clusters.
