  We numerically investigate the minimum number of interacting particles, which
is required for the onset of strong chaos in quantum systems on a
one-dimensional lattice with short-range and long-range interactions. We
consider multiple system sizes which are at least three times larger than the
number of particles and find that robust signatures of quantum chaos emerge for
as few as 4 particles in the case of short-range interactions and as few as 3
particles for long-range interactions, and without any apparent dependence on
the size of the system.
