  We show how realistic charge manipulation and measurement techniques,
combined with the exchange interaction, allow for the robust generation and
purification of four-particle spin entangled states in electrically controlled
semiconductor quantum dots. The generated states are immunized to the dominant
sources of noise via a dynamical decoherence-free subspace; all additional
errors are corrected by a purification protocol. This approach may find
application in quantum computation, communication, and metrology.
