Beyond the four-level model: Dark and hot states in quantum dots degrade photonic entanglement

TL;DR

This study investigates how increasing temperature affects polarization entanglement in GaAs quantum dots, revealing that hot and dark states degrade entanglement and providing insights for optimizing quantum dot sources at higher temperatures.

Contribution

It introduces an extended four-level model including hot and dark states to explain entanglement degradation at elevated temperatures in quantum dots.

Findings

Entanglement degrades with temperature increase up to 65 K.

Decay dynamics change due to thermal population of additional states.

The extended model explains the observed entanglement degradation.

Abstract

Entangled photon pairs are essential for a multitude of photonic quantum applications. To date, the best performing solid-state quantum emitters of entangled photons are semiconductor quantum dots operated around liquid-helium temperatures. To favor the widespread deployment of these sources, it is important to explore and understand their behavior at temperatures accessible with compact Stirling coolers. Here we study the polarization entanglement among photon pairs from the biexciton-exciton cascade in GaAs quantum dots at temperatures up to 65 K. We observe entanglement degradation accompanied by changes in decay dynamics, which we ascribe to thermal population and depopulation of hot and dark states in addition to the four levels relevant for photon pair generation. Detailed calculations considering the presence and characteristics of the additional states and phonon-assisted transitions support the interpretation. We expect these results to guide the optimization of quantum dots as sources of highly entangled photons at elevated temperatures.