An team of physicists has for the first time observed so-called roton quasiparticles in a quantum gas. Empirically introduced by Landau to explain the bizarre properties of superfluid liquid Helium, these quasiparticles reflect an ‘energy softening’ in the system as precursor of a crystallization instability. The new work demonstrates similar phenomena in the quantum-gas phase thanks to magnetic interactions, paving the way for a novel understanding of paradigmatic states of quantum fluids, such as supersolids.
