  We investigate the fundamental viability of cooling ultracold atomic gases
with quantum feedback control. Our study shows that the trade-off between the
resolution and destructiveness of optical imaging techniques imposes
constraints on the efficacy of feedback cooling, and that rapid
rethermalization is necessary for cooling thermal gases. We construct a simple
model to determine the limits to feedback cooling set by the visibility of
density fluctuations, measurement-induced heating, and three-body atomic
recombination. We demonstrate that feedback control can rapidly cool
high-temperature thermal clouds in quasi-2D geometries to degenerate
temperatures with minimal atom loss compared to traditional evaporation. Our
analysis confirms the feasibility of feedback cooling ultracold atomic gases,
providing a pathway to new regimes of cooling not achievable with current
approaches.
