We have to go fringe, zero-point energy coupled with reaction less propulsion turns all of the energy equations inside out- and makes it all possible.
It definitely has to be something well outside the range of current thinking.
Also it doesn’t need to be an overnight trip for the first probes. Something that could get there within a human lifetime would be an excellent start. For that matter sending launch and forget craft that would check in every 20 years or so might be valuable info gathering tools for interstellar space.