A tiny nanoparticle has been chilled to the max.

Physicists cooled a nanoparticle to the lowest temperature allowed by quantum mechanics. The particle’s motion reached what’s known as the ground state, or lowest possible energy level.

In a typical material, the amount that its atoms jostle around indicates its temperature. But in the case of the nanoparticle, scientists can define an effective temperature based on the motion of the entire nanoparticle, which is made up of about 100 million atoms. That temperature reached twelve-millionths of a kelvin, scientists report January 30 in Science.