# Phonon-induced enhancement of photon entanglement in quantum dot-cavity systems

## TL;DR

This paper demonstrates through simulations that phonons can unexpectedly enhance photon entanglement in quantum dot-cavity systems under certain conditions, challenging the usual view of phonons as solely decoherence sources.

## Contribution

It reveals that phonons can induce a nonmonotonic temperature dependence of entanglement, surpassing phonon-free levels, due to phonon-induced renormalizations of the dot-cavity coupling.

## Key findings

- Phonons can enhance entanglement beyond phonon-free levels.
- Entanglement shows nonmonotonic temperature dependence.
- Specific parameter regimes enable phonon-assisted entanglement enhancement.

## Abstract

We report on simulations of the degree of polarization entanglement of photon pairs simultaneously emitted from a quantum dot-cavity system that demand revisiting the role of phonons. Since coherence is a fundamental precondition for entanglement and phonons are known to be a major source of decoherence, it seems unavoidable that phonons can only degrade entanglement. In contrast, we demonstrate that phonons can cause a degree of entanglement that even surpasses the corresponding value for the phonon-free case. In particular, we consider the situation of comparatively small biexciton binding energies and either finite exciton or cavity mode splitting. In both cases, combinations of the splitting and the dot-cavity coupling strength are found where the entanglement exhibits a nonmonotonic temperature dependence which enables entanglement above the phonon-free level in a finite parameter range. This unusual behavior can be explained by phonon-induced renormalizations of the dot-cavity coupling $g$ in combination with a nonmonotonic dependence of the entanglement on $g$ that is present already without phonons.