Path to perfect photon entanglement with a quantum dot

TL;DR

This paper demonstrates that perfect two-photon entanglement from quantum dots is achievable without nuclear spin dephasing, emphasizing the importance of resonant excitation and advanced detection systems.

Contribution

The study shows dephasing-free entanglement from a quantum dot with nuclear spin 9/2 using quasi-resonant excitation, challenging previous assumptions about nuclear spin limitations.

Findings

Achieved dephasing-free two-photon entanglement.

Identified detection system limitations as the reason for past imperfect entanglement.

Highlighted the importance of ultra-low jitter and dark count detection systems.

Abstract

Realizing perfect two-photon entanglement from quantum dots has been a long-standing scientific challenge. It is generally thought that the nuclear spins limit the entanglement fidelity through spin flip dephasing processes. However, this assumption lacks experimental support. Here, we show dephasing-free two-photon entanglement from an Indium rich single quantum dot comprising of nuclear spin 9/2 when excited quasi-resonantly. This remarkable finding is based on a perfect match between our entanglement measurements with our model that assumes no dephasing and takes into account the detection system's timing jitter and dark counts. We discover that neglecting the detection system is responsible for not reaching perfect entanglement in the past and not the nuclear spins. Therefore, the key to unity entanglement from quantum dots comprises of a resonant excitation scheme and a detection system with ultra-low timing jitter and dark counts.