  We introduce a one-dimensional (1D) extended quantum breakdown model
comprising a fermionic and a spin degree of freedom per site, and featuring a
spatially asymmetric breakdown-type interaction between the fermions and spins.
We analytically show that, in the absence of any magnetic field for the spins,
the model exhibits Hilbert space fragmentation within each symmetry sector into
exponentially many Krylov subspaces and hence displays non-thermal dynamics.
Here, we demonstrate that the fragmentation naturally occurs in an entangled
basis and thus provides an example of "quantum fragmentation." Besides
establishing the nature of fragmentation analytically, we also study the
long-time behavior of the entanglement entropy and its deviation from the
expected Page value as a probe of ergodicity in the system. Upon introducing a
non-trivial magnetic field for the spins, most of the Krylov subspaces merge
and the model becomes chaotic. Finally, we study the effects of strong
randomness on the system and observe behavior similar to that of many-body
localized systems.
