  We have made a variational analysis on an evolution of superconductivity from
weak to strong coupling regime. In contrast to a crossover without
thermodynamic anomaly found in a dilute system, we show the existence of a
quantum phase transition near half filling. The transition is driven by charge
density waves instabilities. We have found that superconductivity and charge
density waves coexist in the presence of a weak intersite repulsion. The ground
state phase diagram is determined and the quantum phase transition is an
attractive version of the Mott transition.
