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Entanglement, its generation, manipulation and fundamental understanding is at the very heart of quantum mechanics. The phrase entanglement was coined by Erwin Schrödinger in 1935 for particles that are described by a common wave function where individual particles are not independent of each other but where their quantum properties are inextricably interwoven 1 . Entanglement properties of two and three particles have been studied extensively and are very well understood. Entanglement of four 2 and five 3 particles was demonstrated experimentally. However, both creation and characterization of entanglement become exceedingly difficult for multi-particle systems. Thus the availability of such multiparticle entangled states together with the full information on these states in form of their 1

The key to explaining a wide range of quantum phenomena is understanding how entanglement propagates around many-body systems. Furthermore, the controlled distribution of entanglement is of fundamental importance for quantum communication and computation. In many situations, quasiparticles are the carriers of information around a quantum system and are expected to distribute entanglement in a fashion determined by the system interactions [1]. Here we report on the observation of magnon quasiparticle dynamics in a one-dimensional many-body quantum system of trapped ions representing an Ising spin model [2,3]. Using the ability to tune the effective interaction range [4][5][6], and to prepare and measure the quantum state at the individual particle level, we observe new quasiparticle phenomena. For the first time, we reveal the entanglement distributed by quasiparticles around a many-body system. Second, for long-range interactions we observe the divergence of quasiparticle velocity and breakdown of the light-cone picture [7][8][9][10] that is valid for short-range interactions. Our results will allow experimental studies of a wide range of phenomena, such as quantum transport [11,12], thermalisation [13], localisation [14] and entanglement growth [15], and represent a first step towards a new quantum-optical regime with on-demand quasiparticles with tunable non-linear interactions.Quasiparticles, such as magnons, phonons, and anyons, are elementary excitations in the collective behaviour of an underlying many-body quantum system. While precise control is already possible in the laboratory for systems of individual atoms, ions, or photons, it remains a challenge to extend this to quasiparticles. In systems with nearest-neighbour interactions, quasiparticles are expected to distribute entanglement within light-like-cones defined by a strict quantum information speed limit, enforced not by relativity but by the finite interaction range itself [7,16,17]. These results, known as Lieb-Robinson bounds, have allowed various important theorems to be proven about systems with nearest-neighbour interactions, including restrictions on ground-state correlations [18,19] and the time to create states for topological quantum computation [16]. Recently, wavefronts of correlations have been observed in bosonic atoms in optical lattices with nearest-neighbour interactions [20,21], and an outstanding challenge is to observe the entanglement dynamics.Extending these results to systems with long-range interactions is of great interest: the interactions in many natural systems fall into this class, exhibiting a power-law dependence (1/r α ), such as van-der-Waals (α=6), dipole-dipole (α=3), or Coulomb interactions (α=1). In each case, a new set of quasiparticles are predicted with unique properties. If the interactions fall off sufficiently fast, one can still formulate generalized Lieb-Robinson bounds [8][9][10]. However, the notion of a speed of information propagation becomes invalid. For even longer-range interactions, these bounds...