Pumping of nuclear spins by the optical solid effect in a quantum dot

TL;DR

This paper demonstrates efficient nuclear spin polarization in quantum dots through the optical solid effect, achieving record polarization levels by resonant pumping of forbidden transitions, offering a new method for spin initialization.

Contribution

It introduces the optical solid effect as a new mechanism for nuclear spin pumping in quantum dots, enabling higher polarization than traditional allowed transitions.

Findings

Nuclear polarization of 65% achieved, highest in optical studies of QDs.

Pumping via forbidden transitions surpasses allowed transition efficiency.

Demonstrates one-to-one photon-to-nuclear spin conversion.

Abstract

We demonstrate that efficient optical pumping of nuclear spins in semiconductor quantum dots (QDs) can be achieved by resonant pumping of optically "forbidden" transitions. This process corresponds to one-to-one conversion of a photon absorbed by the dot into a polarized nuclear spin, which also has potential for initialization of hole spin in QDs. Pumping via the "forbidden" transition is a manifestation of the "optical solid effect", an optical analogue of the effect previously observed in electron spin resonance experiments in the solid state. We find that by employing this effect, nuclear polarization of 65% can be achieved, the highest reported so far in optical orientation studies in QDs. The efficiency of the spin pumping exceeds that employing the allowed transition, which saturates due to the low probability of electron-nuclear spin flip-flop.