Probing string-breaking dynamics in a trapped-ion quantum simulator

In quantum chromodynamics, the theory of strong force in nature, color-charged particles do not exist in isolation. They are instead confined together to form color-neutral particles. A simple picture of confinement involves quark-antiquark pairs that are bound by a gluonic flux tube, or string. As the string energy increases (e.g. by separating out the color charges), it becomes energetically favorable to produce a new quark-antiquark pair, hence breaking the string. In this work, we experimentally study string breaking in a long-range Ising Hamiltonian with a trapped-ion quantum simulator. We model the color-charged particles with domain walls in the spin chain, and control the string energy with a longitudinal magnetic field. We characterize the complex dynamics of string breaking as we linearly ramp the string energy through the breaking threshold. With a short spin chain, the string breaks with all the spins flipping, and the probability of string breaking can be modeled via a Landau-Zener process. With a long spin chain, the string breaks by forming domains of flipped spins whose size varies with the ramping speed.