  Quantum tunneling dominates coherent transport at low temperatures in many
systems of great interest. In this work we report a many--body tunneling (MBT),
by nonperturbatively solving the Anderson multi-impurity model, and identify it
a fundamental tunneling process on top of the well--acknowledged sequential
tunneling and cotunneling. We show that the MBT involves the dynamics of
doublons in strongly correlated systems. Proportional to the numbers of
dynamical doublons, the MBT can dominate the off--resonant transport in the
strongly correlated regime. A $T^{3/2}$--dependence of the MBT current on
temperature is uncovered and can be identified as a fingerprint of the MBT in
experiments. We also prove that the MBT can support the coherent long--range
tunneling of doublons, which is well consistent with recent experiments on
ultracold atoms. As a fundamental physical process, the MBT is expected to play
important roles in general quantum systems.

Mesoscale and Nanoscale Physics