The crux of using the cascaded emission of a 3-level quantum ladder system to generate indistinguishable photons

TL;DR

This paper studies the indistinguishability of photons emitted from a 3-level quantum ladder system, revealing inherent limitations and proposing structures to improve photon quality for quantum technologies.

Contribution

It demonstrates the fundamental limit on photon indistinguishability in cascaded emissions and offers design strategies to optimize quantum dot structures.

Findings

Indistinguishability is limited by the lifetime ratio of states.

Experimental verification of theoretical predictions.

Simulations align well with experimental data.

Abstract

We investigate the degree of indistinguishability of cascaded photons emitted from a 3-level quantum ladder system; in our case the biexciton-exciton cascade of semiconductor quantum dots. For the 3-level quantum ladder system we theoretically demonstrate that the indistinguishability is inherently limited for both emitted photons and determined by the ratio of the lifetimes of the excited and intermediate states. We experimentally confirm this finding by comparing the quantum interference visibility of non-cascaded emission and cascaded emission from the same semiconductor quantum dot. Quantum optical simulations produce very good agreement with the measurements and allow to explore a large parameter space. Based on our model, we propose photonic structures to optimize the lifetime ratio and overcome the limited indistinguishability of cascaded photon emission from a 3-level quantum ladder system.