  We show, for the first time, that continuous dynamical decoupling can
preserve the coherence of a two-qubit state as it evolves during a SWAP quantum
operation. Hence, because the Heisenberg exchange interaction alone can be used
for achieving universal quantum computation, its combination with continuous
dynamical decoupling can also make the computation robust against general
environmental perturbations. Furthermore, since the exchange-interaction
Hamiltonian is invariant under rotations, the same control-field arrangement
used to protect a stationary quantum-memory state can also preserve the
coherence of the driven qubits. The simplicity of the required control fields
greatly improves prospects for an experimental realization.
