  We demonstrate experimentally that a cloud of cold atoms with a size
comparable to the wavelength of light can induce large group delays on a laser
pulse when the laser is tightly focused on it and is close to an atomic
resonance. Delays as large as -10 ns are observed, corresponding to
"superluminal" propagation with negative group velocities as low as -300 m/s.
Strikingly, this large delay is associated with a moderate extinction owing to
the very small size of the cloud and to the light-induced interactions between
atoms. It implies that a large phase shift is imprinted on the continuous laser
beam, and opens interesting perspectives for applications to quantum
technologies.
