  We show that two electrons confined in a square semiconductor quantum dot
have two isolated low-lying energy eigenstates, which have the potential to
form the basis of scalable computing elements (qubits). Initialisation,
one-qubit and two-qubit universal gates, and readout are performed using
electrostatic gates and magnetic fields. Two-qubit transformations are
performed via the Coulomb interaction between electrons on adjacent dots.
Choice of initial states and subsequent asymmetric tuning of the tunnelling
energy parameters on adjacent dots control the effect of this interaction.
