# From strong to weak temperature dependence of the two-photon entanglement resulting from the biexciton cascade inside a cavity

## TL;DR

This paper studies how the entanglement of photon pairs emitted from a quantum dot in a cavity varies with temperature, cavity configuration, and energy splitting, revealing conditions for optimal entanglement.

## Contribution

It compares four different quantum dot-cavity configurations to understand their impact on photon entanglement under various conditions, highlighting the influence of phonons and temperature.

## Key findings

- Maximum entanglement occurs when cavity modes resonate with the two-photon transition.
- Entanglement is highly sensitive to temperature and cavity detuning.
- Certain configurations become more favorable at higher temperatures due to phonon effects.

## Abstract

We investigate the degree of entanglement quantified by the concurrence of photon pairs that are simultaneously emitted in the biexciton-exciton cascade from a quantum dot in a cavity. Four dot-cavity configurations are compared that differ with respect to the detuning between the cavity modes and the quantum dot transitions, corresponding to different relative weights of direct two-photon and sequential single-photon processes. The dependence of the entanglement on the exciton fine-structure splitting $\delta$ is found to be significantly different for each of the four configurations. For a finite splitting and low temperatures, the highest entanglement is found when the cavity modes are in resonance with the two-photon transition between the biexciton and the ground state and, in addition, the biexciton has a finite binding energy of a few meV. However, this widely used configuration is rather strongly affected by phonons such that other dot-cavity configurations, that are commonly regarded as less suited for obtaining high degrees of entanglement, become more favorable already at temperatures on the order of 10 K and above. If the cavity modes are kept in resonance with one of the exciton-to-ground-state transitions and the biexciton binding energy is finite, the entanglement drastically drops for positive $\delta$ with rising temperatures when $T$ is below $\simeq$ 4 K, but is virtually independent of the temperature for higher $T$.