NIST Quantum Refrigerator Offers Extreme Cooling and Convenience

[T]he NIST refrigerator’s cooling elements, consisting of 48 tiny sandwiches of specific materials, chilled a plate of copper, 2.5 centimeters on a side and 3 millimeters thick, from 290 mK to 256 mK. The cooling process took about 18 hours.

One thing not mentioned: this almost certainly does not scale up. It works starting at ~300 mK, but the performance

The cooling power is the equivalent of a window-mounted air conditioner cooling a building the size of the Lincoln Memorial in Washington, D.C

doesn’t mean you are going to be able to build an air-conditioner-sized device and actually cool the Lincoln Memorial, unless you got it down to 300 mK first. (Then we’ll talk)