  We propose a method to produce entangled states of several particles starting
from a Bose-Einstein condensate. In the proposal, a single fast $\pi/2$ pulse
is applied to the atoms and due to the collisional interaction, the subsequent
free time evolution creates an entangled state involving all atoms in the
condensate. The created entangled state is a spin-squeezed state which could be
used to improve the sensitivity of atomic clocks.
