Convexity of the entanglement energy of SU($2N$)-symmetric fermions with attractive interactions

Abstract

The positivity of the probability measure of attractively interacting systems of $2N$-component fermions enables the derivation of an exact convexity property for the ground-state energy of such systems. Using analogous arguments, applied to path-integral expressions for the $n$-th R\'enyi entanglement entropy $S^{}_n$ derived recently, we prove non-perturbative analytic relations for the entanglement energies $\mathcal E^{}_n$ of those systems defined via $\mathcal{E}^{}_n \equiv \frac{n-1}{n}T S^{}_n + F$ where $\beta = 1/T$ is the extent of the imaginary time direction and $-\beta F = \ln \mathcal Z$ where $\mathcal Z$ is the partition sum appropriate to the temperature. These relations are valid for all sub-system sizes, particle numbers and dimensions, and in arbitrary external trapping potentials.