Phonon:
At a quantum scale, temperature and motion are one and the same: the more a particle is vibrating, the hotter it is. Those packets of vibration, also called phonons, must be removed to bring an object into its ground state. So far, this has only been achieved with objects with masses of tiny fractions of a gram.
Now, Chris Whittle at the Massachusetts Institute of Technology (MIT) and his colleagues have cooled a system with an effective massof 10 kilograms from room temperature down to 77 nanokelvin, marking a huge leap in the mass of a system that can be brought near its ground state. The full system consists of four mirrors, each weighing 40 kilograms, but together they vibrate as if they were a single 10-kilogram object. [“LIGO mirrors cooled to near absolute zero could probe quantum gravity,” Leah Crane, NewScientist (26 June 2021)]
A nanokelvin is 10-9K. The Kelvin, or K, scale defines absolute zero as 0K, so this is awfully darn close to absolute zero.
And has nothing to do with phonons.
