Reducing number fluctuations of ultracold atomic gases via dispersive interrogation

We have used dispersive laser probing to follow the central density evolution of a trapped atomic cloud during forced evaporative cooling. This was achieved in a heterodyne detection scheme. We propose to use this as a nondestructive precursor measurement for predicting the atom number subsequent to evaporation and provide a simple experimental demonstration of the principle leading to a conditional reduction of classical number fluctuations.