The portrait of Mona Lisa is scrutinized with reference to quantum mechanics. The elements of different expressions are first recognized on her face. The contradictory details are then classified in two pictures that, undoubtedly representing distinct moods, confirm the dichotomous character of the original. Consecutive discussion has led to the conclusion that the mysterious state Mona Lisa is in actually is a coherent mixture-superposition of cheerfulness and sadness. The state of the physical system is among the most important concepts of quantum mechanics. Being a primitive concept of the theory, it is usually left undefined. However, by ‘state’ we mean a list of some relevant characteristics of the system in question. More or less exact information about the quantities pertaining to the system are on this list, telling us how it is prepared. For operational reasons, the state of the quantum mechanical system is represented by some vector of the Hilbert space. Precisely, rays represent states, while quantities are represented by the Hermitian operators acting in this Hilbert space of states.
Louvre, Dirac, Pure Quantum States
