Energy Spectrum of Neutron-Rich Helium Isotopes: Complex Made Simple

Open quantum systems that are at or beyond the limit of particle-emission stability exhibit generic features stemming from their coupling to an environment of positive energy states and decay channels. In this talk, I will introduce a practical approach inspired by halo effective field theory for the description of neutron-rich helium isotopes 5-10He within tens of keV uncertainties and discuss the parity inversion in 9He, as well as the possible two-neutron decay of 10He. The possible extension of this strategy to heavier nuclei as an alternative to ab initio methods will be discussed.