  In recent years, Arenz et al. proposed the idea of reachable set
characterization based on the quantum speed limit (QSL); that is, the reachable
set of the target unitary gate in a closed qubit system can be characterized by
considering the QSL as the necessary condition that the control setup must
satisfy in order to achieve the goal. Inspired by this idea, in this paper we
characterize a general Markovian open quantum system based on the QSL derived
in \cite{Kohei2}. Note that this bound is not only explicitly computable with
respect to system parameters, but also tighter than the other bounds. Some
examples for demonstrating this analysis will be given.
