  Recently, there has been a proposal to test the quantum nature of gravity in
the laboratory by witnessing the growth of entanglement between two masses in
spatial quantum superpositions. The required superpositions can be created via
Stern-Gerlach interferometers, which couple an embedded spin qubit quantum
state to the spatial dynamics of each mass. The masses would entangle only if
gravity is quantum in nature. Here, we generalise the experiment to an
arbitrary spin $j$ or equivalently to an ensemble of uniformly coupled spins.
We first exemplify how to create a generalized Stern-Gerlach interferometer,
which splits the mass into $2j+1$ trajectories. This shows that a controlled
protocol can be formulated to encode the amplitudes of any spin state to a
spatial superposition. Secondly, two masses in spatial superpositions of the
above form are left to interact via gravity, and the entanglement is computed.
Different families of initial spin states are varied to find the optimal spin
state that maximizes the entanglement. We conclude that larger spins can offer
a modest advantage in enhancing gravity-induced entanglement.
