Ultracold Atoms Simulate Breaking Flux Strings
In quantum chromodynamics and other gauge theories, narrow tubes of field lines called strings connect pairs of charges that cannot exist in isolation—such as the color charges of quarks. When the charge separation exceeds a critical distance, these flux strings can break, ultimately decaying into particle–antiparticle pairs. Determining how flux strings break is fundamental to understanding the dynamics of these field theories, but models of the phenomenon are hard to investigate experimentally. Ying Liu of the University of Science and Technology of China and his colleagues have now demonstrated an ultracold-atom system that serves as an experimental analogue for string breaking [1].
The experimental setup consists of a 1D array of rubidium atoms confined by a set of interfering optical lattices. Each site on the resulting superlattice has a tunable potential, which determines how easily atoms can hop from one site to another. The experiment begins with each lattice site populated by one atom. This initial state represents two charges connected by a flux string. By varying the parameters of the optical superlattice, the researchers cause the atoms to interact with one another and to hop between sites. This evolution represents the dynamics of the flux string as the charges are separated. Whether that string remains intact or breaks is indicated by the atom array’s final configuration, which the team measures using a quantum gas microscope.
So far, Liu and colleagues have used their technique to model string breaking in a simplified gauge theory known as the lattice Schwinger model. They say that their experiment also offers a platform for simulating more complex gauge theories and high-energy physics models and for investigating particle collisions and quantum error-correction schemes.
–Rachel Berkowitz
Rachel Berkowitz is a Corresponding Editor for Physics Magazine based in Vancouver, Canada.
References
- Y. Liu et al., “String-breaking mechanism in a lattice Schwinger model simulator,” Phys. Rev. Lett. 135, 101902 (2025).