[Doc] fix typo (#458)

Author: ytdHuang

docs/src/users_guide/time_evolution/mesolve.md

@@ -31,17 +31,16 @@ In `QuantumToolbox`, given a Hamiltonian, we can calculate the unitary (non-diss
 
 ```@example mesolve
 H = 0.5 * sigmax()
-state0 = basis(2, 0)         # state vector
-state0 = ket2dm(basis(2, 0)) # density matrix
+state0 = basis(2, 0) # state vector
 tlist = LinRange(0.0, 10.0, 20)
 
 sol = mesolve(H, state0, tlist, e_ops = [sigmaz()])
 ```
 
-!!! note "Type of initial state"
-    The initial state `state0` here can be given as a state vector ``|\psi(0)\rangle`` (in the type of [`Ket`](@ref)) or a density matrix ``\hat{\rho}(0)`` (in the type of [`Operator`](@ref)). If it is given as a [`Ket`](@ref), it will be transformed to density matrix ``\hat{\rho}(0) = |\psi(0)\rangle\langle\psi(0)|`` internally in [`mesolve`](@ref).
+!!! note "Use sesolve for improved efficiency"
+    Here, if the Hamiltonian `H` is given as an [`Operator`](@ref), and the initial state `state0` is given as a state vector ``|\psi(0)\rangle`` (in the type of [`Ket`](@ref)), it will automatically call [`sesolve`](@ref) for improved efficiency.
 
-The function returns [`TimeEvolutionSol`](@ref), as described in the previous section [Time Evolution Solutions](@ref doc-TE:Time-Evolution-Solutions). The stored `states` will always be in the type of [`Operator`](@ref) (density matrix).
+The function returns [`TimeEvolutionSol`](@ref), as described in the previous section [Time Evolution Solutions](@ref doc-TE:Time-Evolution-Solutions).
 
 ```@example mesolve
 sol.states
@@ -53,6 +52,7 @@ One can also specify `e_ops` and `saveat` separately:
 
 ```@example mesolve
 tlist = [0, 5, 10]
+state0 = ket2dm(basis(2, 0))  # density matrix
 sol = mesolve(H, state0, tlist, e_ops = [sigmay()], saveat = tlist)
 ```
 
@@ -64,6 +64,8 @@ sol.expect
 sol.states
 ```
 
+Note that when the initial state `state0` is given as a density matrix ``|\psi(0)\rangle\langle\psi(0)|`` (in the type of [`Operator`](@ref)), the stored `states` will also be in the type of [`Operator`](@ref) (density matrix).
+
 ## [The Lindblad master equation](@id doc-TE:The-Lindblad-master-equation)
 
 The standard approach for deriving the equations of motion for a system interacting with its environment is to expand the scope of the system to include the environment. The combined quantum system is then closed, and its evolution is also governed by the von Neumann equation