Exploring the Relaxation Landscape of a 2D Quantum Magnet on a 256-Qubit Processor

T. Mendes-Santos, J. Vovrosh, S. Julià-Farré, D. Claveau, G. Villaret, L. Béguin, L. Leclerc, L. Brunner, W. Krinitsin, M. Hecker, F. Hayes, B. Albrecht, L. Bourachot, C. Briosne-Frejaville, A. Cornillot, J. de Hond, D. Diallo, C. Dupays, R. Dupont, T. Eritzpokhoff, L. Henriet, L. Lassablière, A. Lindberg, Y. Machu, H. Mamann, T. Pansiot, J. Ripoll, B. Ximenez, H. Silvério, J. Tindall, M. Schmitt, M. Heyl, A. Signoles, C. Dalyac, A. Browaeys, and A. Dauphin,

How quantum matter relaxes far from equilibrium is a central open problem in many-body physics, and one for which analog quantum simulators are well positioned to move from confirming theory to discovering new physics. Here, we use a two-dimensional Rydberg atom array of 256 qubits to map the relaxation landscape of the two-dimensional transverse-field Ising model across its phase diagram. Beyond the expected rapid thermalization, we identify two further regimes. The first is a prethermal regime whose dynamics are governed by an effective XY model. The second, and most unexpected, is a crossover regime characterized by a slowdown in relaxation. This slowdown occurs precisely where state-of-the-art classical tensor-network methods lose control at late times, whereas the quantum simulation remains consistent across system sizes. These results establish Rydberg atom arrays as a platform for scientific discovery in nonequilibrium quantum many-body dynamics.