  Many-body entangled quantum spin systems exhibit emergent phenomena such as
topological quantum spin liquids with distinct excitation spectra accessed in
inelastic neutron scattering (INS) experiments. Here we simulate the dynamics
of a quantum spin dimer, the basic quantum unit of emergent many-body spin
systems. While canonical Trotterization methods require deep circuits
precluding long time-scale simulations, we demonstrate 'direct'
Resource-Efficient Fast-forwarding (REFF) measurements with short-depth
circuits that can be used to capture longer time dynamics on quantum hardware.
The temporal evolution of the 2-spin correlation coefficients enabled the
calculation of the dynamical structure factor $S(\mathbf{Q},\omega)$ - the key
component of the neutron scattering cross-section. We simulate the triplet gap
and the triplet splitting of the quantum dimer with sufficient fidelity to
compare to experimental neutron data. Our results on current circuit hardware
pave an important avenue to benchmark, or even predict, the outputs of the
costly INS experiments.
