  In this paper, we study the quantum decoherence induced by accumulation of
electron tunnelings during the quantum measurement of a charge qubit. The
charge qubit is a single electron confined in coupled quantum dots. The
measurement of the qubit states is performed using a quantum point contact. A
set of master equations for qubit states is derived within a nonequilibrium
perturbation to the equilibrium reservoir due to the electron accumulation
between the source and drain of the quantum point contact. The quantum
decoherence of the qubit states arose from the electron accumulation during the
measurement is explored in this framework, and several interesting results on
charge qubit decoherence are obtained.
