  The R\'enyi entanglement entropy is calculated exactly for mode-partitioned
isolated systems such as the two-mode squeezed state and the multi-mode
Silbey-Harris polaron ansatz state. Effective thermodynamic descriptions of the
correlated partitions are constructed to present quantum information theory
concepts in the language of thermodynamics. Boltzmann weights are obtained from
the entanglement spectrum by deriving the exact relationship between an
effective temperature and the physical entanglement parameters. The partition
function of the resulting effective thermal theory can be obtained directly
from the single-copy entanglement.
