  Spin-exchange collisions in alkali or alkali/noble gas vapors are at the
basis of quantum sensing, nucleon structure studies, tests of fundamental
symmetries, and medical imaging. We here show that spin-exchange collisions in
hot alkali vapors naturally produce strong bipartite entanglement, which we
explicitly quantify using the tools of quantum information science. This
entanglement is shown to have a lifetime at least as long as the spin-exchange
relaxation time, and to directly affect measurable spin noise observables. This
is a formal theoretical demonstration that a hot and dense atomic vapor can
support longlived bipartite and possibly higher-order entanglement.
