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

Tim Seidelmann, Florian Ungar, Moritz Cygorek, Alexei Vagov, Andreas M. Barth, Tilmann Kuhn, Vollrath Martin Axt

Published 2019-02-05Version 1

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 configuration is rather strongly affected by phonons such that other dot-cavity configurations become more favorable 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 positve $\delta$ with rising temperatures when $T$ is below $\simeq$ 4$\,$K, but is virtually independent of the temperature for higher $T$.