Perturbative approach to the entanglement entropy and the area law in Fock and polymer quantization

Abstract

The area dependence of entanglement entropy of a free scalar field is often understood in terms of coupled harmonic oscillators. In Schrodinger quantization, the Gaussian nature of ground state wave-function for these oscillators is sufficient to provide the exact form of the reduced density matrix and its eigenvalues, thus giving the entanglement entropy. However, in polymer quantization, the ground state is not Gaussian and the formalism which can provide the exact analytical form of the reduced density matrix is not yet known. In order to address this issue, here we treat the interaction between two coupled harmonic oscillators in the perturbative approach and evaluate the entanglement entropy in Schrodinger and polymer quantization. In contrary to Schrodinger quantization, we show that in high frequency regime the entanglement entropy decreases for polymer quantization keeping the ratio of coupling strength to the square of individual oscillator frequency fixed. Furthermore, for a free scalar field, we validate the area dependence of entanglement entropy in Fock quantization and demonstrate that polymer quantization produces a similar area law.