Electron Spin Excited States Spectroscopy in a Quantum Dot Probed by QPC Back-action

TL;DR

This study uses quantum point contact back-action as a tool to perform spectroscopy of electron spin excited states in a quantum dot, revealing detailed spin state behaviors under magnetic fields.

Contribution

It demonstrates a novel use of back-action as an excitation source for spin state spectroscopy in quantum dots, including observations of Zeeman and triplet state splittings.

Findings

Zeeman splitting observed for single electron

Triplet state splittings identified for two electrons

Back-action drives singlet to triplet state transitions

Abstract

The quantum point contact (QPC) back-action has been found to cause non-thermal-equilibrium excitations to the electron spin states in a quantum dot (QD). Here we use back-action as an excitation source to probe the spin excited states spectroscopy for both the odd and even electron numbers under a varying parallel magnetic field. For a single electron, we observed the Zeeman splitting. For two electrons, we observed the splitting of the spin triplet states $|T^{+}>$ and $|T^{0}>$ and found that back-action drives the singlet state $|S>$ overwhelmingly to $|T^{+}>$ other than $|T^{0}>$. All these information were revealed through the real-time charge counting statistics.