Phase transitions are an everyday part of life. All around us, there is water in the freezer turning into ice cubes, steam rising off of hot tubs and American teenagers inexplicably going crazy over a young Canadian with ambiguous gender.
Okay, so maybe that last one has nothing to do with physics, but I still hope to God that it’s a phase.
Anyways, outside of the traditional phases of matter that we deal with – solid, liquid and gas – there are also others that you will only find on Earth inside of specialized devices. For example, ionized particles form plasmas and certain materials become superconductors at very low temperatures. Though the properties of most of these phases of matter aren’t all that interesting, how they transition into one from the other is a ripe area of study.
Then, all the way at the end of the spectrum, you have quantum criticality. As materials approach absolute zero – the temperature at which all motion stops, even the orbits of electrons – some weird shit starts to go down. And recently, some really smart people at the University of Chicago figured out a way to observe a handful of atoms as they approach this point of quantum criticality.
In a tabletop experiment, Associate Professor Cheng Chin and graduate student Xibo Zhang trapped 20,000 cesium atoms using lasers in a horizontal plane within an eight-inch cylindrical vacuum chamber. The process transforms the atoms into a superfluid hundreds of degrees below zero.
But then they went further.
The duo managed to chill the atoms all the way down to 5.8 nano-Kelvin, just billions of a degree above absolute zero (minus 459 degrees Farhrenheit). Then they took a CCD camera sensitive enough to image the distribution of atoms and observed how they behaved as the effects of quantum criticality began to take hold. Of course, no camera can actually see an atom, but this one could pick up what amounts to a shadow cast by the atoms.
On its own, this is pretty damn cool. I can’t even begin to think about how you trap a few thousand atoms with lasers and chill them down enough to stop their electrons from moving. But if the picture is any indication, it ain’t easy.
But of course, there’s more to the experiment than simply proving that its possible.
Quantum criticality is a hot topic of research. As atoms move into this realm, they behave extremely strangely and begin to exhibit properties of other physical phenomena, like the gravitational dynamics of black holes and the conditions of the universe moments after the Big Bang. The ability to take this system and observe it as it reaches quantum criticality will allow researchers to make progress towards developing working theories and understanding these exotic phenomena.