Laser-Cooling Positronium

Researchers have managed to cool an atom-like system made of an electron and a positron using a technique commonly used in cold-atom experiments.


AEgIS Collaboration's Goal

The AEgIS Collaboration at CERN in Switzerland aims to measure the impact of Earth's gravitational field on antimatter, particularly antihydrogen atoms. Antihydrogen production is dependent on positronium, which consists of an electron and a positron bound together. The faster positronium can be cooled, the higher the antihydrogen production rate. As a result, AEgIS researchers have spent the past four years developing a method to cool positronium. With their successful demonstration of positronium laser cooling, they have achieved their goal.

Laser-cooling positronium is significantly more challenging than laser-cooling regular atoms. Positronium can only survive for 140 nanoseconds before annihilating, even in ultrahigh vacuum. Additionally, the relevant transition frequency for positronium cooling is in the deep ultraviolet range, which is an area where laser technology is not yet highly developed.

Designing a Custom Laser System

The AEgIS Collaboration designed a custom laser system using alexandrite as the lasing medium. Alexandrite-based lasers emit deep-ultraviolet wavelengths, but commercially available devices do not meet the intensity and pulse-length requirements for positronium cooling. Another major obstacle the researchers faced was eliminating the loss of positronium atoms during the cooling process. This required the capability to switch off any external electric and magnetic fields used for manipulating positronium in a matter of nanoseconds.

The researchers had to overcome several challenges in developing this custom laser system. They needed to use alexandrite as the lasing medium to emit deep-ultraviolet wavelengths, which are required for positronium cooling. However, commercially available devices did not meet the intensity and pulse-length requirements for this cooling process. Additionally, the researchers had to find a way to eliminate external electric and magnetic fields that could cause the loss of positronium atoms during the cooling process. This required the electrostatic equipment used for manipulating positronium to be capable of being switched off quickly.

Simultaneous Announcement of Results

The AEgIS researchers were surprised to discover that their achievement was coincidentally shared with another team from the University of Tokyo. These two independent groups announced their results simultaneously, within the same session of the same conference. The University of Tokyo team used a very different laser system for their research. This simultaneous success was a remarkable case of independent and competing research converging at the same time.

The AEgIS Collaboration's success in laser-cooling positronium was a result of years of planning and experiments. Despite the challenges they faced, their breakthrough coincided with the achievements of another research group. This convergence of independent research demonstrates the excitement and competition within the field.