  For matrix model and QFT, we discuss how dual gravitational geometry emerges
from matrix degrees of freedom (specifically, adjoint scalars in super
Yang-Mills theory) and how operator algebra that describes an arbitrary region
of the bulk geometry can be constructed. We pay attention to the subtle
difference between the notions of wave packets that describe low-energy
excitations: QFT wave packet associated with the spatial dimensions of QFT,
matrix wave packet associated with the emergent dimensions from matrix degrees
of freedom, and bulk wave packet which is a combination of QFT and matrix wave
packets. In QFT, there is an intriguing interplay between QFT wave packet and
matrix wave packet that connects quantum entanglement and emergent geometry. We
propose that the bulk wave packet is the physical object in QFT that describes
the emergent geometry from entanglement. This proposal sets a unified view on
two seemingly different mechanisms of holographic emergent geometry: one based
on matrix eigenvalues and the other based on quantum entanglement. Further
intuition comes from the similarity to a traversable wormhole discussed as the
dual description of the coupled SYK model by Maldacena and Qi: the bulk can be
seen as an eternal traversable wormhole connecting boundary regions.
