Cool; and at −273.16°C in fact.

Nothing can be chilled below absolute zero, or −273.15°C, because at this temperature all molecular motion stops completely. Per Heisenberg’s uncertainty principle the forces of real particle velocities will always be above zero. It’s a fundamental limit that can’t seem to be broken, and that’s fine, but what bothers scientists, however, are other limits that keep them from cooling things near absolute zero.