Macroscopic variables

Pavel Bóna

R. Fukuda

Macroscopic variables of the macroscopic system lose the quantum fluctuations in the macroscopic limit. A separate Hilbert space corresponds to each c-number value of these macroscopic variables. The measuring process in quantum mechanics consists of recording these c-number values and amounts to determination of the Hilbert space to which the system belongs. These observations provide a solution to the problem of measurement and lead to predictions concerning the c-number equations of motion of the macroscopic variables.

Inge Svein Helland

Nikola Burić

It is shown that the conditions for classical behavior, in the sense of zero dispersion of all macroscopic variables, for systems of qubits with different dynamics, depend on whether the interaction is local or global. In the case of local interaction, macroscopic coarse-graining is enough. On the other hand, coarse-grained macroscopic variables of globally interacting large systems of qubits have negligible dispersion only if the system is exposed to some form of the environmental decoherence.

Anupam Garg

The phenomenon of macroscopic quantum coherence is examined within the framework of a two-level system coupled to an Ohmic bath. A bound is obtained for the temperature above which the macroscopic variable cannot display the oscillatory behavior characteristic of quantum coherence. Different approximations for the dynamical behavior of the macroscopic variable in the low-dissipation limit are compared.

Inge Svein Helland