A team at the MIT-Harvard Centre for Ultra-Cold Atoms has devised a thermometer that can potentially measure temperatures as low as tens of trillionths of a degree above absolute zero. The trick is to place the system in a magnetic field, and then measure the atoms’ average magnetization. By determining a handful of easily-measured properties, the physicists extracted the temperature of the system from the magnetization.

While they demonstrated the method on atoms cooled to one billionth of a degree, they also showed that it should work for atoms hundreds of times cooler, meaning the thermometer will be an invaluable tool for physicists pushing the cold frontier.