December 23, 2025 -- Tiny tubes of carbon that emit single photons from just one point along their length have been made in a deterministic manner by RIKEN researchers. Such carbon nanotubes could form the basis of future quantum technologies based on light.

Light is currently used to freight data over long distances via optical fibers. But harnessing its quantum nature could offer several benefits including unprecedented security since any inception by a third party can be detected.

Such quantum communication technology requires light sources that emit one photon at a time. Several systems are capable of realizing that, but of them carbon nanotubes are the most promising.

“Carbon nanotubes are the only quantum emitters that can emit single photons at room temperature and also at wavelengths used for telecommunications,” explains Yuichiro Kato of the RIKEN Center for Advanced Photonics. “That makes them very attractive for real-world applications.”

However, one problem with nanotubes is that it has been difficult to control the number of points along their length that emit single photons. It has also been challenging to determine the position of light-emitting points along a nanotube.

Now, Kato and co-workers have overcome both issues and produced nanotubes that emit single photons from one point whose position can be controlled.

This demonstration takes fabrication precision to the next level, Kato notes. “We’re already going beyond nanotechnology,” he says. “This is entering the world of atomically defined technology—that’s pretty exciting to me.”

The team realized this by suspending a carbon nanotube across a trench just micrometers wide and exposing it to iodobenzene vapor. They then focused an ultraviolet laser beam on one point on the carbon nanotube. The combination of ultraviolet and iodobenzene generates defects known as color centers on carbon nanotubes (Fig. 1).

To ensure they produced only one color center on the nanotube, the team continuously monitored the light emitted. They immediately stopped the reaction as soon as they noticed a change in the light that indicated the formation of a color center.

The team was able to control the position of the color center to within a micrometer through the position of the focused laser beam on the carbon nanotube.

Kato’s ultimate goal is to create devices that contain single-photon-emitting nanotubes. “We want to integrate them into photonic circuits on chips,” says Kato. “And then once we have a chip, we can probably start talking to photonics manufacturers about real-world applications.”