  We investigate the possibility to have electron-pairs in dephasing-free
subspace (DFS), by means of the quantum-dot cellular automata (QCA) and
single-spin rotations, to carry out a high-fidelity and deterministic universal
quantum computation. We show that our QCA device with electrons tunneling two
dimensionally is very suitable for DFS encoding, and argue that our design
favors a scalable quantum computation robust to collective dephasing errors.
