Benchmarking direct and indirect dipolar spin-exchange interactions between two Rydberg atoms

We report on the experimental characterization of various types of spin-exchange interactions between two individual atoms, where pseudospin degrees of freedom are encoded in different Rydberg states. For the case of the direct dipole-dipole interaction between states of opposite parity, such as between |nS and |nP, we investigate the effects of positional disorder arising from the residual atomic motion on the coherence of spin-exchange oscillations. We then characterize an indirect dipolar spin exchange, i.e., the off-diagonal part of the van der Waals effective Hamiltonian that couples the states |nS and |(n+1)S. Finally, we report on the observation of a new type of dipolar coupling, made resonant using addressable light shifts and involving four different Rydberg levels: this exchange process is akin to electrically induced F\"orster resonance, but featuring local control. It exhibits an angular dependence distinct from the usual 1-3cos²(θ) form of the resonant dipolar spin-exchange.