Allowed and forbidden transitions in artificial hydrogen and helium atoms

Toshimasa Fujisawa, David Guy Austing, Yasuhiro Tokura, Yoshiro Hirayama, Seigo Tarucha

Research output: Contribution to journalArticlepeer-review

336 Citations (Scopus)

Abstract

The strength of radiative transitions in atoms is governed by selection rules that depend on the occupation of atomic orbitals with electrons. Experiments have shown similar electron occupation of the quantized energy levels in semiconductor quantum dots-often described as artificial atoms. But unlike real atoms, the confinement potential of quantum dots is anisotropic, and the electrons can easily couple with phonons of the material. Here we report electrical pump-and-probe experiments that probe the allowed and 'forbidden' transitions between energy levels under phonon emission in quantum dots with one or two electrons (artificial hydrogen and helium atoms). The forbidden transitions are in fact allowed by higher-order processes where electrons flip their spin. We find that the relaxation time is about 200 μs for forbidden transitions, 4 to 5 orders of magnitude longer than for allowed transitions. This indicates that the spin degree of freedom is well separated from the orbital degree of freedom, and that the total spin in the quantum dots is an excellent quantum number. This is an encouraging result for potential applications of quantum dots as basic entities for spin-based quantum information storage.

Original languageEnglish
Pages (from-to)278-281
Number of pages4
JournalNature
Volume419
Issue number6904
DOIs
Publication statusPublished - 2002 Sep 19

ASJC Scopus subject areas

  • General

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