  We study weak ergodicity breaking in a one-dimensional, nonintegrable spin-1
XY model. We construct for it an exact, highly excited eigenstate, which
despite its large energy density, can be represented analytically by a finite
bond-dimension matrix product state (MPS) with area-law entanglement. Upon a
quench to a finite Zeeman field, the state undergoes periodic dynamics with
perfect many-body revivals, in stark contrast to other generic initial states
which instead rapidly thermalize. This dynamics can be completely understood in
terms of the evolution of entangled virtual spin-1/2 degrees of freedom, which
in turn underpin the presence of an extensive tower of strong-eigenstate
thermalization hypothesis (ETH)-violating many-body eigenstates. The resulting
quantum many-body scars are therefore of novel origin. Our results provide
important analytical insights into the nature and entanglement structure of
quantum many-body scars.
