Thermodynamic entropy of a many body energy eigenstate

Understand

It is argued that a typical many body energy eigenstate has a well defined thermodynamic entropy and that individual eigenstates possess thermodynamic characteristics analogous to those of generic isolated systems.

• We examine large systems with eigenstate energies equivalent to finite temperatures.
• When quasi-static evolution of a system is adiabatic (in the quantum mechanical sense), two coupled subsystems can transfer heat from one subsystem to another yet remain in an energy eigenstate.
• To explicitly construct the entropy from the wave function, degrees of freedom are divided into two unequal parts.