  Spin-orbit coupling is a source of strong spin dephasing in two- and
three-dimensional semiconducting systems. We report that spin dephasing in a
two-dimensional electron gas can be suppressed by introducing a quantum point
contact. Surprisingly, this suppression was not limited to the vicinity of the
contact but extended to the entire two-dimensional electron gas. This
facilitates the electrical control of the spin degree of freedom in a
two-dimensional electron gas through spin-orbit coupling.
