Ultimate photon entanglement in biexciton cascade

TL;DR

This paper presents a theoretical approach to generate highly entangled photon pairs from symmetric colloidal quantum dots by mitigating hyperfine interaction effects, surpassing limitations of traditional quantum dot systems.

Contribution

The study introduces a new theory for entangled photon pair generation in symmetric colloidal quantum dots, showing potential for higher entanglement than conventional systems and methods to suppress hyperfine effects.

Findings

Concurrence is higher in symmetric colloidal quantum dots than in self-assembled quantum dots.

Entanglement can be maximized by tuning nanocrystal anisotropy and strain.

Hyperfine interaction effects can be completely suppressed under certain conditions.

Abstract

The polarization entanglement of photons emitted by semiconductor quantum dots is unavoidably limited by the spin fluctuations of the host lattice nuclei. To overcome this limitation, we develop a theory of entangled photon pair generation by a symmetric colloidal quantum dot mediated by a triplet exciton. We derive general analytical expressions for the concurrence as a function of the hyperfine interaction strength and show that it is intrinsically higher than that in conventional doublet-exciton systems such as self-assembled quantum dots. The concurrence sensitively depends on the shape anisotropy and the strain applied to a nanocrystal. In particular, we uncover a possibility of completely suppressing the detrimental effect of the hyperfine interaction due to the interplay between nanocrystal anisotropy and electron-hole exchange interaction. We argue that this represents the ultimate limit for the generation of entangled photon pairs by semiconductor quantum dots.