The problem of measurement in the quantum mechanics refers to how interpret the collapse of wave function. Being unable to observe the process had given rise to various interpretations of the quantum mechanics and has key set of the questions, which each interpretation should answer. The approach to resolving the problem of quantum measurement is provided by Theo Nieuenhuizen and colleagues. They focused on Curie-Weiss model for the quantum measurements whereby joint dynamics of tested system was coupled to measurement apparatus to produce the results explaining measurement postulates.
It indicates that off-diagonal terms like the cat-terms disappear in the physical process because of coupling to apparatus on the selected basis by interaction Hamiltonian.The registration of measurement outcomesby pointer of apparatus takes place. It is because the measurement triggers transitional from initial metastable condition to the stable final conditions with large apparatus, which implies the amplification of signal. Transition of pointer variable from the initial metastable condition to the final stable situations is the process with the classical features like dumping of the excess free energy in bath.