Measurement of quantum depletion in a homogeneous Bose-Einstein condensate

Using momentum selective Bragg scattering we measure the condensed fraction of a strongly interacting homogeneous BEC. When adiabatically increasing the scattering length, we see that the condensed fraction decreases linearly with $\sqrt{na^3}$ (where $n$ is the density), in excellent agreement with the Bogoliubov theory of quantum depletion. We also show the reversibility of this process by adiabatically reducing the scattering length.