Laser-Cooled Ions Reveal More about the Origin of the Universe

How was our universe created 14 billion years ago? That's a good question. Scientists believe that the same conditions prevailed everywhere shortly after the Big Bang in an originally symmetrical universe. Yet this raises the question: how could a breaking of symmetry occur to form stars and galaxies? That's what researchers set to find out. Using laser-cooled ions, researchers discovered how symmetry breaking can be generated in a controlled manner and how the occurrence of defects can then be observed.

Using so-called ion Culomb crystals, the researchers demonstrated topological defects in an atomic-optical experiment. Topological defects are errors in the spatial structure which are caused by the breaking of the symmetry when particles of a system cannot communicate with each other. They form during a phase transition and present themselves as non-matching areas.

Within the experiment, the scientists controlled a complex multi-particle system and induced an intentional change in the external conditions to obtain the breaking symmetry. In this case, they used ytterbium ions trapped in radio-frequency ion traps in ultra-high vacuum. The trapped, positively charged particles repel each other inside the trap and take on a crystalline structure. This particular structure was due to the ultra-low temperatures that the scientist used during their experiment. They found that if the parameters of the trap enclosure were varied faster than the speed of sound in the crystal, the topological defects occur while the ions are seeking a new equilibrium conditions in the crystal.

The work is closely related to the Kibble-Zurek mechanism, which is a theory based on special topological defects in the early universe. A fraction of seconds after the Big Bang, a symmetry breaking took place and the young universe "decided" to adopt a certain state. With this new study, the researchers reveal that the Kibble-Zurek mechanism can be transferred to a relatively simple experiment. The findings could have implications for further experiments on phase transitions in classical systems and in the quantum universe.

The findings are published in the journal Nature Communications.