  In this work, the definition of the density operator on quantum states in
Hilbert spaces and some of its aspects relevant in thermodynamics and
information-theoretical entropy calculations are given. In this framework, a
physical model describing an electron in a magnetic field is investigated. The
so-called exotic Landau problem in noncommutative plane is also considered.
Then, a model related to the fractional quantum Hall effect is revisited.
Thanks to the completeness relations verified by the coherent states (CS) in
these models, the thermodynamics is discussed by using the diagonal
$P$-representation of thedensity operator. Specifically, the Q-Husimi
distribution and the Wehrl entropy are determined.
