  We modify the time-dependent electric potential of the Paul trap from a
sinusoidal waveform to a square waveform. The exact quantum motion and the
Berry's phase of an electron in the modified Paul trap are found in an
analytically closed form. We consider a scheme to detect the Berry's phase by a
Bohm-Aharonov-type interference experiment and point out a critical property
which renders it practicable.
