Allowed and forbidden transitions in artificial hydrogen and helium atoms

TL;DR

This paper investigates allowed and forbidden phonon emission transitions in semiconductor quantum dots, regarded as artificial hydrogen and helium atoms, revealing that total spin remains a good quantum number, which is promising for spin-based quantum information applications.

Contribution

It demonstrates that total spin is an excellent quantum number in quantum dots, providing insights into selection rules and transition mechanisms in artificial atomic systems.

Findings

Total spin is a good quantum number in quantum dots.

Allowed and forbidden transitions are characterized in artificial hydrogen and helium.

Implications for spin-based quantum information storage are discussed.

Abstract

The strength of radiative transitions in atoms is governed by selection rules. Spectroscopic studies of allowed transitions in hydrogen and helium provided crucial evidence for the Bohr's model of an atom. Forbidden transitions, which are actually allowed by higher-order processes or other mechanisms, indicate how well the quantum numbers describe the system. We apply these tests to the quantum states in semiconductor quantum dots (QDs), which are regarded as artificial atoms. Electrons in a QD occupy quantized states in the same manner as electrons in real atoms. However, unlike real atoms, the confinement potential of the QD is anisotropic, and the electrons can easily couple with phonons of the material. Understanding the selection rules for such QDs is an important issue for the manipulation of quantum states. Here we investigate allowed and forbidden transitions for phonon emission in one- and two-electron QDs (artificial hydrogen and helium atoms) by electrical pump-and-probe experiments, and find that the total spin is an excellent quantum number in artificial atoms. This is attractive for potential applications to spin based information storage.