  The exact quantum decay of a one-dimensional Bose gas with inverse-square
interactions is presented. The system is equivalent to a gas of particles
obeying generalized exclusion statistics. We consider the expansion dynamics of
a cloud initially confined in a harmonic trap that is suddenly switched off.
The decay is characterized by analyzing the fidelity between the initial and
the time-evolving states, also known as the survival probability. It exhibits
early on a quadratic dependence on time that turns into a power-law decay,
during the course of the evolution. It is shown that the particle number and
the strength of interactions determine the power-law exponent in the latter
regime, as recently conjectured. The nonexponential character of the decay is
linked to the many-particle reconstruction of the initial state from the
decaying products.
