  We show that quantum computation can be performed in a system at thermal
equilibrium if a spontaneous symmetry breaking occurs. The computing process is
associated to the time evolution of the statistical average of the qubit
coherence operator. This average defines logical states which evolve under the
action of impulsive gate perturbations. Non trivial quantum coherence
properties appear in the ordered phase characterized by a spontaneous symmetry
breaking. Qubits are associated to spins and interaction with the lattice
vibrations is approximated by an effective spin-spin interaction. A finite
decoherence time is obtained only if spin correlations are taken into account
in the framework of the Ising model as corrections to the Mean Field
approximation. Decoherence is slowed down as the order parameter saturates.
