  We propose a scheme for trapped atom interferometry using an interacting
Bose-Einstein condensate. The condensate is controlled and spatially split in
two confined external momentum modes through a series Bragg pulses. The
proposed scheme (i) allows the generation of large entanglement in a
trapped-interferometer configuration via one-axis twisting dynamic induced by
interatomic interaction, and (ii) avoids the suppression of interactions during
the interferometer sequence by a careful manipulation of the state before and
after phase encoding. The interferometer can be used for the measurement of
gravity with a sensitivity beyond the standard quantum limit.
