Probing spin relaxation in an individual InGaAs quantum dot using a single electron optical spin memory device

TL;DR

This paper demonstrates all-optical control and long-term storage of a single electron spin in an InGaAs quantum dot, enabling detailed probing of spin relaxation and coherence for quantum information applications.

Contribution

It introduces a novel all-optical method for initializing, storing, and reading out a single electron spin in a quantum dot with long storage times and high polarization.

Findings

Electron spin can be stored for over 40 microseconds.

Spin polarization up to 65% achieved via voltage control.

Effective spin to charge conversion enables optical readout.

Abstract

We demonstrate all optical electron spin initialization, storage and readout in a single self-assembled InGaAs quantum dot. Using a single dot charge storage device we monitor the relaxation of a single electron over long timescales exceeding 40{\mu}s. The selective generation of a single electron in the quantum dot is performed by resonant optical excitation and subsequent partial exciton ionization; the hole is removed from the quantum dot whilst the electron remains stored. When subject to a magnetic field applied in Faraday geometry, we show how the spin of the electron can be prepared with a polarization up to 65% simply by controlling the voltage applied to the gate electrode. After generation, the electron spin is stored in the quantum dot before being read out using an all optical implementation of spin to charge conversion technique, whereby the spin projection of the electron is mapped onto the more robust charge state of the quantum dot. After spin to charge conversion, the charge state of the dot is repeatedly tested by pumping a luminescence recycling transition to obtain strong readout signals. In combination with spin manipulation using fast optical pulses or microwave pulses, this provides an ideal basis for probing spin coherence in single self-assembled quantum dots over long timescales and developing optimal methods for coherent spin control.