  We study the problem of measurement-induced decoherence using the phase-space
approach employing the Gaussian-smoothed Wigner distribution function. Our
investigation is based on the notion that measurement-induced decoherence is
represented by the transition from the Wigner distribution to the
Gaussian-smoothed Wigner distribution with the widths of the smoothing function
identified as measurement errors. We also compare the smoothed Wigner
distribution with the corresponding distribution resulting from the classical
analysis. The distributions we computed are the phase-space distributions for
simple one-dimensional dynamical systems such as a particle in a square-well
potential and a particle moving under the influence of a step potential, and
the time-frequency distributions for high-harmonic radiation emitted from an
atom irradiated by short, intense laser pulses.
