Universal crossovers between entanglement entropy and thermal entropy

Understand

We postulate the existence of universal crossover functions connecting the universal parts of the entanglement entropy to the low temperature thermal entropy in gapless quantum many-body systems.

• These scaling functions encode the intuition that the same low energy degrees of freedom which control low temperature thermal physics are also responsible for the long range entanglement in the quantum ground state.
• We demonstrate the correctness of the proposed scaling form and determine the scaling function for certain classes of gapless systems whose low energy physics is described by a conformal field theory.
• We also use our crossover formalism to argue that local systems which are "natural" can violate the boundary law at most logarithmically.