To the best of my knowledge, no atoms of anti-helium or any other antimatter elements have been observed or created in controlled laboratory experiments.
Antimatter is composed of antiparticles, which have the same mass as their corresponding particles but opposite charge. For example, the antiparticle of an electron is called a positron, and the antiparticle of a proton is called an antiproton. When a particle and its corresponding antiparticle collide, they annihilate each other, releasing energy.
Creating and studying antimatter is a complex and challenging task. Antiparticles can be generated in high-energy particle accelerators, such as the Large Hadron Collider (LHC), where particle collisions produce a variety of particles, including antiparticles. However, creating and trapping large numbers of antimatter particles, including anti-helium nuclei, is extremely difficult due to their scarcity and the technical challenges involved.
In nature, it is theoretically possible for antimatter to be created through high-energy processes, such as in cosmic ray interactions or certain types of astrophysical phenomena like gamma-ray bursts. However, the production of significant amounts of antimatter in such processes is believed to be rare.
The study of antimatter and the quest to understand its properties and behavior are ongoing areas of research in physics. Scientists continue to explore new methods and techniques to create, trap, and study antimatter particles, but the production of stable antimatter elements, including anti-helium, remains a significant technological and scientific challenge.