We review recent progress and motivate the need for further developments in nuclear optical potentials that are widely used in the theoretical analysis of nucleon elastic scattering and reaction cross sections. In regions of the nuclear chart away from stability, which represent a frontier in nuclear science over the coming decade and which will be probed at new rare-isotope beam facilities worldwide, there is a targeted need to quantify and reduce theoretical reaction model uncertainties, especially with respect to nuclear optical potentials. We first describe the primary physics motivations for an improved description of nuclear reactions involving short-lived isotopes, focusing on its benefits for fundamental science discoveries and applications to medicine, energy, and security. We then outline the various methods in use today to build optical potentials starting from phenomenological, microscopic, and ab initio methods, highlighting in particular, the strengths and weaknesses of each approach. We then discuss publicly-available tools and resources facilitating the propagation of recent progresses in the field to practitioners. Finally, we provide a set of open challenges and recommendations for the field to advance the fundamental science goals of nuclear reaction studies in the rare-isotope beam era. This paper is the outcome of the Facility for Rare Isotope Beams Theory Alliance (FRIB-TA) topical program ‘Optical Potentials in Nuclear Physics’ held in March 2022 at FRIB. Its content is non-exhaustive, was chosen by the participants and reflects their efforts related to optical potentials.

The interaction of an $E/A=70$-MeV ${}^7\mathrm{Be}$ beam with a Be target was used to populate levels in ${}^6\mathrm{Be}$ following neutron knockout reactions. The three-body decay of the ground and first excited states into the $\alpha +p+p$ exit channel were detected in the High Resolution Array. Precise three-body correlations extracted from the experimental data allowed us to obtain insight into the mechanism of the three-body democratic decay. The correlation data are in good agreement with a three-cluster-model calculation and thus validate this theoretical approach over a broad energy range.

The interactions of an $E/A=70$-MeV ${}^9\mathrm{C}$ beam with a Be target was used to populate levels in Be, B, and C isotopes, which undergo decay into many-particle exit channels. The decay products were detected in the HiRA array and the level energies were identified from their invariant mass. Correlations between the decay products were examined to deduce the nature of the decays, specifically to what extent all the fragments were created in one prompt step or whether the disintegration proceeded in a sequential fashion through long-lived intermediate states. In the latter case, information on the spin of the level was also obtained. Of particular interest is the five-body decay of the ${}^8\mathrm{C}$ ground state, which was found to disintegrate in two steps of two-proton decay passing through the ${}^6\mathrm{Be}$ ${}_{g.s.}$ intermediate state. The isobaric analog of ${}^8\mathrm{C}$ ${}_{g.s.}$ in ${}^8\mathrm{B}$ was also found to undergo two-proton decay to the isobaric analog of ${}^6\mathrm{Be}$ ${}_{g.s.}$ in ${}^6\mathrm{Li}$. A 9.69-MeV state in ${}^{10}\mathrm{C}$ was found to undergo prompt four-body decay to the 2$p$ $+$ 2$\alpha$ exit channel. The two protons were found to have a strong enhancement in the diproton region and the relative energies of all four $p$-$\alpha$ pairs were consistent with the ${}^5\mathrm{Li}$ ${}_{g.s.}$ resonance.

The interaction of an $E/A=57.6\text{−}\mathrm{MeV}$ ${}^{17}\mathrm{Ne}$ beam with a Be target is used to populate levels in ${}^{16}\mathrm{Ne}$ following neutron knockout reactions. The decay of ${}^{16}\mathrm{Ne}$ states into the three-body ${}^{14}\mathrm{O}+p+p$ continuum is observed in the High Resolution Array (HiRA). For the first time for a $2p$ emitter, correlations between the momenta of the three decay products are measured with sufficient resolution and statistics to allow for an unambiguous demonstration of their dependence on the long-range nature of the Coulomb interaction. Contrary to previous measurements, our measured limit $\mathrm{\Gamma }<80\mathrm{keV}$ for the intrinsic decay width of the ground state is not in contradiction to the small values (of the order of keV) predicted theoretically.

The structure of the extremely proton-rich nucleus ${{}_8{}^{11}\mathrm{O}}_3$, the mirror of the two-neutron halo nucleus ${{}_3{}^{11}\mathrm{Li}}_8$, has been studied experimentally for the first time. Following two-neutron knockout reactions with a ${}^{13}\mathrm{O}$ beam, the ${}^{11}\mathrm{O}$ decay products were detected after two-proton emission and used to construct an invariant-mass spectrum. A broad peak of width $\sim 3.4\mathrm{MeV}$ was observed. Within the Gamow coupled-channel approach, it was concluded that this peak is a multiplet with contributions from the four lowest ${}^{11}\mathrm{O}$ resonant states: $J^{\pi }=3/2_1^{-}$, $3/2_2^{-}$, $5/2_1^{+}$, and $5/2_2^{+}$. The widths and configurations of these states show strong, nonmonotonic dependencies on the depth of the $p$-${}^9\mathrm{C}$ potential. This unusual behavior is due to the presence of a broad threshold resonant state in ${}^{10}\mathrm{N}$, which is an analog of the virtual state in ${}^{10}\mathrm{Li}$ in the presence of the Coulomb potential. After optimizing the model to the data, only a moderate isospin asymmetry between ground states of ${}^{11}\mathrm{O}$ and ${}^{11}\mathrm{Li}$ was found.