  Quantum many-body simulation provides a straightforward way to understand
fundamental physics and connect with quantum information applications. However,
suffering from exponentially growing Hilbert space size, characterization in
terms of few-body probes in real space is often insufficient to tackle
challenging problems such as quantum critical behavior and many-body
localization (MBL) in higher dimensions. Here, we experimentally employ a new
paradigm on a superconducting quantum processor, exploring such elusive
questions from a Fock space view: mapping the many-body system onto an
unconventional Anderson model on a complex Fock space network of many-body
states. By observing the wave packet propagating in Fock space and the
emergence of a statistical ergodic ensemble, we reveal a fresh picture for
characterizing representative many-body dynamics: thermalization, localization,
and scarring. In addition, we observe a quantum critical regime of anomalously
enhanced wave packet width and deduce a critical point from the maximum wave
packet fluctuations, which lend support for the two-dimensional MBL transition
in finite-sized systems. Our work unveils a new perspective of exploring
many-body physics in Fock space, demonstrating its practical applications on
contentious MBL aspects such as criticality and dimensionality. Moreover, the
entire protocol is universal and scalable, paving the way to finally solve a
broader range of controversial many-body problems on future larger quantum
devices.
