  We have measured transport through mesoscopic Aharonov-Bohm (AB) rings with
two different four-terminal configurations. While the amplitude and the phase
of the AB oscillations are well explained within the framework of the
Landaur-B\"uttiker formalism, it is found that the probe configuration strongly
affects the coherence time of the electrons, i.e., the decoherence is much
reduced in the configuration of so-called nonlocal resistance. This result
should provide an important clue in clarifying the mechanism of quantum
decoherence in solids.
