Observation of string-breaking and charge confinement in a trapped-ion quantum simulator

Within the theory of the strong force, or quantum chromodynamics, quarks, carrying `color' charges, can only be found confined in color-neutral mesons and baryons, which are bound together by a gluon flux tube, or string. For a mesonic string, when it becomes energetically favorable to produce two mesons instead, a new quark and anti-quark pair is generated and the string `breaks'. In this work, we adopt an analog of this phenomenon in an Ising spin chain with long-range interactions, which exhibit confinement of domain walls of spin [1,2]. We report on the observation and characterization of string breaking in such systems using a programmable analog trapped-ion quantum simulator. Our experiment features two \textit{static} charges imposed at the two ends of a string of L=13 spins. The static charges are simulated via inhomogeneous spatial profiles of longitudinal magnetic field, which demonstrates the capability of 3D spatial control of the local magnetic fields in a trapped-ion quantum simulator. Implementing quantum quenches across the string-breaking point, we elucidate the patterns of dynamical string breaking, monitoring non-equilibrium charge evolution with spatio-temporal resolution. Furthermore, by initializing the charges away from the string boundary, we create isolated charges and observe localization effects arising as a competition of confinement and lattice effects.

[1] Wen Lin Tan et al. Nature Physics, 17(6):742–747, 2021

[2] Fangli Liu, et al.  Physical review letters, 122(15):150601, 2019.