Signature of Quantum Depletion in the Dynamic Structure Factor of Atomic Gases

We study the linear response and the dynamic structure factor of weakly interacting Bose gases at low temperatures. Going beyond lowest order in the weak coupling expansion allows us to determine the contribution of the thermal and quantum depletion of the condensate to the dynamic structure factor. We find that the quantum depletion produces a pronounced peak in the dynamic structure factor, which allows for its detection via a spectroscopic analysis.