  We treat heavy quark as an open quantum system in the hot medium and rederive
the Stochastic Schr\"odinger Equation (SSE) from the full Schr\"odinger
equation for both heavy quarks and the medium. We apply the SSE to the
dynamical evolutions of heavy quarks (as a system) in the static hot medium (as
an environment). Heavy quarks interact with the medium via random scatterings,
which exchange the momentum and phase factor randomly between two wave
functions of the system and the environment. The exchange of momentum and phase
factor results in the transition between different eigenstates of the system.
These are included via an external stochastic potential in the Hamiltonian of
SSE. Stochastic wave functions of heavy quarks are evolved with the stochastic
external potential. The mean wave functions and the corresponding momentum
distributions of heavy quarks are obtained after the ensemble average over a
large set of stochastic wave functions. We present the thermalization of heavy
quarks in the static medium with different coupling strength.
