  The dispersive interaction of atoms and a far-detuned light field allows
nondestructive imaging of the density oscillations in Bose-Einstein
condensates. Starting from a ground state condensate, we investigate how the
measurement back action leads to squeezing and entanglement of the quantized
density oscillations. In particular, we show that properly timed, stroboscopic
imaging and feedback can be used to selectively address specific eigenmodes and
avoid excitation of non-targeted modes of the system.
