Observation of magnon bound states in the long-range, anisotropic Heisenberg model

Over the recent years coherent, time-periodic modulation has been established as a versatile tool for realizing novel Hamiltonians. Using this approach, known as Floquet engineering, we experimentally realize a long-ranged, anisotropic Heisenberg model with tunable interactions in a trapped ion quantum simulator. We demonstrate that the spectrum of the model contains not only single magnon excitations but also composite magnon bound states. For the experimentally realized long-range interactions, the group velocity of magnons is unbounded. Nonetheless, for sufficiently strong interactions we observe bound states of these unconventional magnons which possess a non-diverging group velocity. By measuring the configurational mutual information between two disjoint intervals, we demonstrate the implications of the bound state formation on the entanglement dynamics of the system. Our observations provide key insights into the peculiar role of composite excitations in the non-equilibrium dynamics of quantum many-body systems.

We acknowledge support from the Deutsche Forschungsgemeinschaft under Germany's Excellence Strategy-EXC-2111-390814868 and DFG Grants No. KN1254/1-2, KN1254/2-1, and from the Austrian Science Fund through the SFB BeyondC (F7110). Furthermore, The project leading to this application has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (Grant agreements No. 741541 and No. 851161), from the Munich Quantum Valley, which is supported by the Bavarian state government with funds from the Hightech Agenda Bayern Plus, and from the Institut für Quanteninformation GmbH.