Narrow optical linewidths and spin pumping on charge-tunable, close-to-surface self-assembled quantum dots in an ultra-thin diode

TL;DR

This paper reports on a novel ultra-thin diode structure enabling precise charge control, narrow optical linewidths, and optical spin pumping in close-to-surface self-assembled quantum dots, advancing quantum nano-photonics applications.

Contribution

It introduces a new p-i-n-i-n diode design that achieves full charge control and near-transform-limited linewidths in surface-close quantum dots.

Findings

Optical linewidths below 2 μeV, close to the transform limit.

Successful optical spin pumping at 0.5 T magnetic field.

Low-noise current flow enabling high coherence.

Abstract

We demonstrate full charge control, narrow optical linewidths, and optical spin pumping on single self-assembled InGaAs quantum dots embedded in a $162.5\,\text{nm}$ thin diode structure. The quantum dots are just $88\,\text{nm}$ from the top GaAs surface. We design and realize a p-i-n-i-n diode that allows single-electron charging of the quantum dots at close-to-zero applied bias. In operation, the current flow through the device is extremely small resulting in low noise. In resonance fluorescence, we measure optical linewidths below $2\,\mu\text{eV}$, just a factor of two above the transform limit. Clear optical spin pumping is observed in a magnetic field of $0.5\,\text{T}$ in the Faraday geometry. We present this design as ideal for securing the advantages of self-assembled quantum dots -- highly coherent single photon generation, ultra-fast optical spin manipulation -- in the thin diodes required in quantum nano-photonics and nano-phononics applications.