  We present a deterministic scheme for generating large-scale atomic W states
in cavity QED system via a simple expansion mechanism, which is realized only
by a detuned interaction between two identical atoms and a vacuum cavity mode.
With the presented scheme, a W-type Bell pair can be created and an n-atom W
state can be expanded to a 2n-atom W state with a unit probability of success
in principle. No multi-atom gates, quantum memories or quantum non-demolition
measurements are required, greatly simplifying the experimental realization of
the scheme. The feasibility analysis shows that our expansion scheme can be
implemented with state-of-the-art technologies. Our scheme enables advances not
only in quantum information and communication but also in quantum
thermodynamics, where atomic W states plays a crucial role.
