  Many-body localization (MBL) describes a quantum phase where an isolated
interacting system subject to sufficient disorder displays non-ergodic
behavior, evading thermal equilibrium that occurs under its own dynamics.
Previously, the thermalization-MBL transition has been largely characterized
with the growth of disorder. Here, we explore a new axis, reporting on an
energy resolved MBL transition using a 19-qubit programmable superconducting
processor, which enables precise control and flexibility of both disorder
strength and initial state preparations. We observe that the onset of
localization occurs at different disorder strengths, with distinguishable
energy scales, by measuring time-evolved observables and many-body
wavefunctions related quantities. Our results open avenues for the experimental
exploration of many-body mobility edges in MBL systems, whose existence is
widely debated due to system size finiteness, and where exact simulations in
classical computers become unfeasible.
