Feb 6, 2007
Quantum response of carbon nanotube quantum dots to terahertz wave irradiation
Quantum dot (QD) is an artificial atom where electrons are confined in a nano-scale artificial potential. The carbon nanotube (CNT) artificial atom is unique, in that electrons are confined in a one-dimensional hard-wall potential, and energy scales associated with the artificial atom, such as a single electron charging energy and a zero-dimensional level spacing, lie in sub-millimeter to terahertz (THz) ranges. These facts have naturally made us to study the THz response of the CNT artificial atom.
In this work, CNT quantum dots have been fabricated simply by depositing metallic contacts on top of an individual single-wall CNT. A whole CNT between the contacts behaves as a single quantum dot, or single electron transistor with a heavily doped substrate as a back gate. At liquid He temperature, the THz wave was irradiated to the CNT-QD and we have observed, for the first time in QDs, new side peaks that originate from a THz-photon absorption, which indicates a quantum response of the CNT-QD to the THz wave.
The fabrication of an antenna structure, which the present devices do not have, will enhance a coupling efficiency. The present finding may lead to a new type of the THz detector with a spectroscopic mean and an ultra-high sensitivity. Our next step is to modify the present device to coupled QDs, where the THz-photon absorption and emission occur between discrete quantum levels in each dot. Then, the quantum detection may be possible at higher temperature.
About the author
Koji Ishibashi received his PhD in electrical engineering from Osaka University in 1988 and is now the head of the Advanced Device Laboratory, RIKEN in Japan.