Quantum simulating thermalization dynamics of a U(1) lattice gauge theory

Gauge theories are fundamental to our understanding of modern physics. The highly constrained gauge theory dynamics couples fermionic matter through dynamical gauge fields, which find its applications ranging from early universe cosmology to heavy-ion collisions. However, computing real-time quantum many-body dynamics in these problems is in general beyond the capability of classical computers. Using a 71-site Bose–Hubbard quantum simulator, we study emergent thermal equilibrium in the wake of quenches from out-of-equilibrium initial states and demonstrate the irreversible behavior within unitary dynamics of a U(1) lattice gauge theory. While the unitary quantum evolution admits no loss of information, we find the system relax towards a common steady-state well approximated by a thermal ensemble. Our work paves the way for investigating real-time many-body dynamics of gauge theories, and opens up the possibility of studying more complex generic gauge theories in synthetic quantum matter devices.