  We propose a quantum computation architecture of double-dot molecules, where
the qubit is encoded in the molecule two-electron spin states. By arranging the
two dots inside each molecule perpendicular to the qubit scaling line, the
interactions between neighboring qubits are largely simplified and the scaling
to multi-qubit system becomes straightforward. As an Ising-model effective
interaction can be expediently switched on and off between any two neighboring
molecules by adjusting the potential offset between the two dots, universal
two-qubit gates can be implemented without requiring time-dependent control of
the tunnel coupling between the dots. A Bell-state measurement scheme for qubit
encoded in double-dot singlet and triplet states is also proposed for quantum
molecules arranged in this way.
