Microscopic origin of thermodynamic entropy in isolated systems
J. M. Deutsch, Haibin Li, and Auditya Sharma
Accepted
The quantum entropy is usually defined using Von Neumann's formula which measures lack of information and vanishes for pure states. In contrast, we obtain a formula for the entropy of a pure state as is measured from thermodynamic experiments, solely from the self-entanglement of the wavefunction, and find strong numerical evidence that the two are in agreement for non-integrable systems, both for energy eigenstates and for states that are obtained at long times under evolution of more general initial conditions. This is an extension of Boltzmann's hypothesis for classical systems, relating microscopic motion to thermodynamics.