Thermal pure state path integral and emergent symmetry

Abstract

We investigate a thermally isolated quantum many-body system with an external control represented by a time-dependent parameter. We formulate a path integral in terms of thermal pure states and derive an effective action for trajectories in a thermodynamic state space, where the entropy appears with its conjugate variable. In particular, for quasi-static operations, the symmetry for the uniform translation of the conjugate variable emerges in the path integral. This leads to the entropy as a Noether invariant.

12 pages. Explanations have been added in ver.2, Introduction has been substantially revised in ver.3, Withdrawal because our new paper arXiv:1812.06375 provides a better formulation for the result of this paper