Aug 12 2019
Several phenomena in the natural realm exhibit symmetries in their dynamic evolution, which help scientists to gain better insights into a system’s underlying mechanism.
An expanding cloud of quantum particles violates the scaling symmetry. (Image credit: Tilman Enss)
However, in quantum physics, these symmetries cannot always be realized. Through laboratory experiments with ultracold lithium atoms, for the first time, scientists from the Center for Quantum Dynamics at Heidelberg University have confirmed the theoretically predicted deviation from classical symmetry.
The study outcomes have been reported in the journal Science.
In the world of classical physics, the energy of an ideal gas rises proportionally with the pressure applied. This is a direct consequence of scale symmetry, and the same relation is true in every scale invariant system. In the world of quantum mechanics, however, the interactions between the quantum particles can become so strong that this classical scale symmetry no longer applies.
Dr Tilman Enss, Associate Professor, Institute for Theoretical Physics
His research team partnered with Professor Dr Selim Jochim’s team from the Institute for Physics.
In the experiments, the scientists investigated the behavior of an ultracold, superfluid gas of lithium atoms. When the gas deviates from its equilibrium condition, it begins to repeatedly expand and contract in a “breathing” motion. In contrast to classical particles, these quantum particles can combine into pairs; consequently, the superfluid becomes stiffer as it is compressed more.
The team led by main authors Dr Puneet Murthy and Dr Nicolo Defenu—teammates of Prof. Jochim and Dr Enss—witnessed this deviation from classical scale symmetry and thus directly confirmed the quantum nature of this system.
The scientists state that this effect offers a better understanding of the behavior of systems with comparable properties, like graphene or superconductors, which do not have any electrical resistance upon being cooled below a specific critical temperature.
Source: https://www.uni-heidelberg.de/en/