Physics
Quantum mechanics predicts a strange dual identity for particles, and now we have seen it in action
ATOMS have been clearly imaged behaving like waves, as predicted by quantum mechanics. Such images could be used to study this exotic and poorly understood quantum behaviour.
The fact that particles like atoms can behave like waves is a key insight of quantum theory. One specific shape of wave that an atom can adopt is known as a “wave packet”, which is like a series of ripples on water, but more bunched up and compressed.
Physicists can predict how a wave packet will change over time by using an equation developed by physicist Erwin Schrödinger. This makes analysing wave packets a great test for how well an atom can be controlled and imaged in the quantum realm, says Tarik Yefsah at the French National Centre for Scientific Research and the École Normale Supérieure in Paris.
He and his colleagues have chilled lithium atoms to close to absolute zero so they display quantum properties. To do this, the team placed the atoms in a small, airless chamber, then hit them with lasers and magnetic fields, which lowered their energy and made them cooler.
The team used the same tools to control the atoms’ quantum states and their shape as waves. Consequently, the researchers arranged the atoms so as not to be too close to each other, made sure each atom’s quantum state corresponded to a wave packet and then loosened some of the forces that were keeping the atoms pinned in place so they could watch the wave packets change.
In images, each atom started as a tight dot. The Schrödinger equation predicts that a wave packet that is free to move rather than being held still will spread as
