Single-wall carbon nanotubes (SWCNTs) are natural choice for building blocks of quantum nanodevices because of their extremely small diameter. I will talk about how they are attractive by giving examples of our experimental demonstrations. The quantum nanodevices we have in mind are spin qubits, single electron devices and novel THz detectors. Quantum dots fabricated with the SWCNT show simple artificial atom behaviors, electrons confined in the one-dimensional hard wall potential. The simple shell structure is advantageous for the spin qubit. Another unique feature of the SWCNT quantum dot is the energy scales associated with the dot, which falls in a millimeter to THz range. I will show two unique THz detection mechanisms as examples. One is the THz photon assisted tunneling (THz-PAT) and the other is the SWCNT single electron transistor on the GaAs/AlGaAs two-dimensional electron gas (2DEG).
The possible chemical modification of the SWCNT is also attractive for fabricating heterostructures with molecules, thereby we could fabricate quantum nanostructures based on the SWCNT/molecule heterostructures. As examples, I will show a chemically connected individual SWCNT ring which is observed in STM, and an individual SWCNT with both sides terminated by molecules in which the DOS is investigated by the STS measurements.
Despite the attractive possibility of the SWCNT for those quantum nanodevices, there are many practical difficulties especially in device fabrication processes, as well as difficulty in the integration of nanodevices. To overcome the problem, our recent effort to characterize an individual SWCNT, which is fabricated in the device, by our original STM combined with simultaneous optical spectroscopy.