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Résumé |
Quantum simulation promises to advance materials discovery by accurately simulating complex states of
matter, their microscopic excitations, and macroscopic response functions. The central challenge in
resolving the underlying interacting dynamics is to combine high-fidelity evolution with the sophisticated
control necessary to manipulate individual quasi-particles in quantum many-body states. Here, we report
on high-precision simulation of both linear and non-linear response functions in a 2D XY spin-1/2 magnet
using an analog-digital superconducting processor of up to 97 qubits. By interleaving digital gates with
analog evolution precisely characterized via Hamiltonian learning, we selectively excite magnons at
tunable energy densities. Measuring first the linear magnon response -- a central probe in neutron-
scattering experiments -- we extract temperature-dependent spectra and lifetimes. Our results reveal
stark variations in magnon decay rates across the Brillouin zone, with enhancement near van Hove
singularities and suppression for edge-localized modes. Next, we perform a suite of nonlinear
measurements, including the study of self-scattering mechanisms, as well as pump-probe spectroscopy to
directly characterize the magnon interactions. While matrix-product state simulations capture the
dynamics well in either small systems or at low temperatures, their predictions become inaccurate away
from these limits. This work demonstrates precise simulation of the interacting dynamics in quantum
magnets, and provides key insights into quasi-particles and their microscopic scattering mechanisms.
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