Tunable Single-Photon Emitter Could Empower Quantum Info Processing

Carbon nanotube quantum light emitters have been produced that are capable of single-photon emission at room temperature and at telecommunications wavelengths. These emitters could be used for optically based quantum information processing and information security as well as for sensing, metrology and imaging.

Critical to the success of the project was the ability to force the nanotube to emit light from a single point along the tube, specifically at a defect site. The key was to limit defect levels to one per tube so that only one photon could be emitted at a time. To achieve such a high degree of control, researchers used diazonium-based chemistry to bind an organic molecule to the nanotube’s surface to serve as the defect. The diazonium reaction enabled the controlled introduction of benzene-based defects with reduced sensitivity to natural fluctuations in the surrounding environment. The diazonium chemistry also permitted the researchers to access the inherent tunability of nanotube emission wavelengths.

Los Alamos National Laboratory researchers have produced what they believe to be the first known material capable of single-photon emission at room temperature and at telecommunications wavelengths, using chemically functionalized carbon nanotubes. These quantum light emitters could be important for optically based quantum information processing and information security, ultrasensitive sensing, metrology and imaging needs, and as photon sources for quantum optics studies. Courtesy of Los Alamos National Laboratory.

In experiments, exciton localization at covalently introduced defect sites in single-walled carbon nanotubes provided a route to room-temperature single-photon emission with ultrahigh single-photon purity (99 percent) and enhanced emission stability approaching the shot-noise limit.

Researchers further demonstrated that the inherent optical tunability of single-walled carbon nanotubes, present in their structural diversity, facilitated the generation of room-temperature single-photon emission spanning the entire telecommunications band. Single-photon emission deep into the center of the telecom C band (1.55 µm) was achieved at the largest nanotube diameters used in the research (0.936 nm).

The wavelengths produced by most other approaches to quantum emission have been too short for telecommunications applications. By choosing a nanotube of appropriate diameter, the team was able to tune the single-photon emission to the appropriate telecom wavelength region.

“Ideally, a single-photon emitter will provide both room-temperature operation and emission at telecom wavelengths, but this has remained an elusive goal,” said Stephen Doorn, leader of the project at Los Alamos National Laboratory. “Up to now, materials that could act as single-photon emitters in these wavelengths had to be cooled to liquid helium temperatures, rendering them much less useful for ultimate applications or scientific purposes.”

The functionalized carbon nanotubes have significant prospects for further development, including advances in functionalization chemistry; integration into photonic, plasmonic and metamaterials structures for further control of quantum emission properties; and implementation into electrically driven devices and optical circuitry for diverse applications.

The research was published in Nature Photonics (doi:10.1038/nphoton.2017.119).