Ultracool atoms caught acting strangely

2019-03-07 07:18:12

By Charles Seife IT MAY be degenerate, but scientists are coaxing atoms into doing things that are most unnatural. Deborah Jin, a physicist at the University of Colorado at Boulder, has made a gas of particles behave strangely as a first step towards forming an intriguing new “degenerate” state of matter. When particles get very cold, they act less like billiard balls and more like the waves described by the equations of quantum mechanics. When these waves overlap, the matter is said to become degenerate: the particles stop behaving like separate entities and act like one huge atom, known as a condensate. Unfortunately, this condensation process has only been made to work for bosons, particles that can be crammed into the same place at the same time—something that’s vital for the cooling process. It has been impossible to do the same for fermions, which are forbidden by quantum theory from sitting on top of each other. “Bosons like to go into the exact same quantum state,” says Jin. “Fermions absolutely cannot do that.” But Jin and her colleague Brian DeMarco have got part of the way there using a gas of potassium-40 atoms, which are fermions. By using atoms with two different spin states, they got round the quantum rules by ensuring that the fermions weren’t always in exactly the same quantum state. Sure enough, as they cooled the mix to 0.3 millionths of a kelvin, the atoms became partially degenerate (Science, vol 285, p 1703). In this state, properties such as temperature and kinetic energy don’t relate to each other in the normal way. Randall Hulet, a physicist at Rice University in Texas, hopes to use a similar process to make fermions even colder, perhaps to the point where they form a condensate. They should then pair up in a similar fashion to electrons in superconductors—giving physicists the chance to understand superconductivity better. “In a gas, the interactions are extraordinarily simple,