Quantum spin dynamics and entanglement generation with hundreds of trapped ions

Hundreds of ions simulate magnetism Strongly interacting quantum systems present a challenge to computational methods even at a relatively low particle number of a few dozen. Researchers are looking to tackle such problems by simulating them in a well-understood and controllable system. A linear array of ions is one such system; however, assembling a large enough number of ions is tricky. Bohnet et al. show that a two-dimensional “crystal” of around 200 9Be+ ions held together by magnetic and electric fields in a so-called Penning trap can simulate quantum magnetism. The work sets the stage for simulations with more complicated forms of interaction that classical computers would find intractable. Science, this issue p. 1297 A two-dimensional array of around 200 beryllium ions in a Penning trap simulates the quantum dynamics of the homogeneous Ising model. Quantum simulation of spin models can provide insight into problems that are difficult or impossible to study with classical computers. Trapped ions are an established platform for quantum simulation, but only systems with fewer than 20 ions have demonstrated quantum correlations. We studied quantum spin dynamics arising from an engineered, homogeneous Ising interaction in a two-dimensional array of 9Be+ ions in a Penning trap. We verified entanglement in spin-squeezed states of up to 219 ions, directly observing 4.0 ± 0.9 decibels of spectroscopic enhancement, and observed states with non-Gaussian statistics consistent with oversqueezed states. The good agreement with ab initio theory that includes interactions and decoherence lays the groundwork for simulations of the transverse-field Ising model with variable-range interactions, which are generally intractable with classical methods.