  The diffusion wake accompanying the jet-induced Mach cone provides a unique
probe of the properties of quark-gluon plasma in high-energy heavy-ion
collisions. It can be characterized by a depletion of soft hadrons in the
opposite direction of the propagating jet. We explore the 3D structure of the
diffusion wake induced by $\gamma$-triggered jets in Pb+Pb collisions at the
LHC energy within the coupled linear Boltzmann transport and hydro model. We
identify a valley structure caused by the diffusion wake on top of a ridge from
the initial multiple parton interaction (MPI) in jet-hadron correlation as a
function of rapidity and azimuthal angle. This leads to a double-peak structure
in the rapidity distribution of soft hadrons in the opposite direction of the
jets as an unambiguous signal of the diffusion wake. Using a two-Gaussian fit,
we extract the diffusion wake and MPI contributions to the double peak. The
diffusion wake valley is found to deepen with the jet energy loss as
characterized by the $\gamma$-jet asymmetry. Its sensitivity to the equation of
state and shear viscosity is also studied.
