  We propose a new physical implementation of spin qubits for quantum
information processing, namely defect states in antidot lattices defined in the
two-dimensional electron gas at a semiconductor heterostructure. Calculations
of the band structure of a periodic antidot lattice are presented. A point
defect is created by removing a single antidot, and calculations show that
localized states form within the defect, with an energy structure which is
robust against thermal dephasing. The exchange coupling between two electrons
residing in two tunnel-coupled defect states is calculated numerically. We find
results reminiscent of double quantum dot structures, indicating that the
suggested structure is a feasible physical implementation of spin qubits.
