Normal thermometers are great for everyday use, but how do you measure the coldest matter in the universe? Well, you’ll probably need a quantum thermometer.
For the record, the coldest thing in the universe is a Bose-Einstein condensate (BEC). This is a state of matter of dilute gas of — or elementary particles — cooled to temperatures as close to absolute zero (the coldest possible temperature) as possible. Because of this condition, a large fraction of the bosons occupy the lowest quantum state, at which point quantum effects appear on a macroscopic scale. When cooled inside a magnetic trap, these millions of atoms act as a single quantum object. BEC is also the coldest thing that can be produced in a scientific lab, as it’s the closest thing to absolute zero. To give you an idea of how cold that is, even deep space is warmer than that.
So obviously, a standard mercury thermometer is not going to be able to measure something that frigid. Instead, physicists count the number of higher-energy particles and compare that to the lower-energy ones. The more high-energy particles there are, the higher the temperature. Previously, in order to measure this, the BEC had to be released from containment, making it impossible to take its temperature.
Scientists at The University of Nottingham in the U.K., though, may have a solution. They have come up with a way to measure the temperature of a BEC without releasing it from containment. In order to do this, they want to trap just a few atoms with lasers and then move these through the BEC. First, however, these atoms must exist in quantum superposition and have two distinct energy states. Each of those states gets modified by a different amount, depending on the BEC’s temperature. The difference between the two states can be used to figure out the temperature of the BEC, which remains contained.
This discovery is significant as the quantum thermometer could be used to test whether black holes emit small amounts of radiation, which is predicted by quantum theory. Obviously, approaching a real black hole isn’t possible, but scientists could test this idea by measuring temperature changes in an artificial black hole created in a lab.
Needless to say, you will probably never need a quantum thermometer in your own home.
Via New Scientist