  Quantum point contact (QPC), one of the typical mesoscopic transport devices,
has been suggested to be an efficient detector for quantum measurement. In the
context of two-state charge qubit, our previous studies showed that the QPC's
measurement back-action cannot be described by the conventional Lindblad
quantum master equation.
  In this work, we study the measurement problem of a multi-state system, say,
an electron in disordered potential, subject to the quantum measurement of the
mesoscopic detector QPC. The effect of measurement back-action and the
detector's readout current are analyzed, where particular attention is focused
on some new features and the underlying physics associated with the
measurement-induced delocalization versus the measurement voltages.
