  Every Bose-Einstein condensate is in a highly entangled state, as a
consequence of the fact that the particles in a condensate are distributed over
space in a coherent way. It is proved that any two regions within a condensate
of finite particle number are entangled. This entanglement does not depend on
the distance between the two regions. Criteria for the presence of entanglement
are derived in the context of interference experiments. For separable states
there is a trade-off between fluctuations in particle number and interference
visibility.
