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

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

Published 2019-02-13Version 1

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 special situation of vanishing biexciton binding energy 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 non-monotonic 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 non-monotonic dependence of the entanglement on $g$ that is present already without phonons.