  For an open-boundary spin chain with anisotropic Heisenberg (XXZ)
interactions, we present states in which a connected block near the edge is
polarized oppositely to the rest of the chain. We show that such blocks can be
`locked' to the edge of the spin chain, and that there is a hierarchy of
edge-locking effects at various orders of the anisotropy. The phenomenon
enables dramatic control of quantum state transmission: the locked block can be
freed by flipping a single spin or a few spins.
