Magnetizing quantum communication

Kyoto, Japan -- As the demand for more secure data transmission increases, conventional communication technologies are facing limitations imposed by classical physics, and are therefore approaching their limits in terms of security. Fortunately, quantum communication may help us overcome these restrictions.

Quantum communication harnesses the quantum nature of light by utilizing single photons as information carriers. This is a fundamentally different approach from conventional communication technologies and has the potential to lead to the development of secure, high-performance communication systems.

These future quantum technologies will require new single-photon emission sources. Recently, extremely thin two-dimensional semiconductors with a thickness of only a few atomic layers have shown great potential due to their excellent electrical and optical properties. Although increasing the efficiency of such single-photon generation is extremely important, the capacity of these materials and its strategy had not been thoroughly explored.

This inspired a team of researchers at Kyoto University to investigate what they predicted may be a functional single-photon emission source. They hypothesized that a semiconductor in single-layer tungsten diselenide, in which they introduced a single defect, would bind excitons -- electron-hole pairs -- to the defect and emit only a single photon.

To realize this idea, the team prepared a sample of monolayer tungsten diselenide, heating it to introduce a small number of defects and to artificially break the crystal symmetry, which resulted in two distinct luminescence peaks representing bright excitons and dark excitons.

The researchers then measured the luminescence and photon correlation at a temperature of about -265°C, applying an external magnetic field to control the emission, revealing that the emission intensity significantly increased even when they applied a relatively weak magnetic field.

Using photon correlation measurements, the team also observed that emitted light demonstrated photon antibunching, indicating that photons are emitted one by one. This suggests that, even under a magnetic field, it can function as a single-photon source, and that the magnetic field can enhance the efficiency of single-photon generation.

"This is significant because it shows that single-photon emissions can be generated and manipulated with an external magnetic field in a two-dimensional semiconductor, revealing it to be a promising platform for the development of secure, efficient, and compact quantum information devices," says team leader Kazunari Matsuda.