Physicists Find a Proposed Neutrino Laser Cannot Work

A proposed device that would use an ultracold cloud of radioactive atoms to produce a concentrated beam of neutrinos cannot work, according to a theoretical analysis by physicists at MIT reported by Phys.org. The concept, published in 2025, envisioned cooling radioactive atoms to near absolute zero so they would form a Bose-Einstein condensate—a state in which atoms behave as a coordinated quantum system. Because radioactive decay naturally produces neutrinos, the proposal suggested that the synchronized atoms might amplify their emissions in a process resembling the superradiance used to create laser light. The original proposal described a possible cloud of radioactive rubidium atoms. If cooled into a condensate, the atoms were predicted to decay much faster, potentially shortening a half-life of 86 days to about one minute and producing a directional neutrino beam. No Bose-Einstein condensate made from radioactive atoms has been produced, however. In two papers published in Physical Review Letters, MIT physicists Wolfgang Ketterle, Hanzhen Lin and Yu-Kun Lu examined the idea in detail. Their first objection concerns recoil. A neutrino emitted during radioactive decay carries vastly more energy than a visible photon. The atom left behind would therefore recoil so quickly that it would almost immediately leave the condensate, preventing the quantum “memory” needed to synchronize later emissions. The researchers’ calculations found that superradiance did not occur in any of the scenarios they considered. Instead of building up a coordinated emission, the condensate would continue producing neutrinos without the proposed enhancement. The second paper identified a separate problem linked to neutrinos’ fundamental classification as fermions. Even if the recoiling atom could leave a quantum imprint in the condensate, the researchers found that the effect would work in the wrong direction. Rather than encouraging another neutrino to emerge along the same path, the imprint would create an anti-correlation that discourages emission in that direction. The MIT analysis also concluded that a related proposal involving gamma rays is physically impossible. Joe Formaggio, one of the scientists behind the original neutrino-laser idea, described the new work as a constructive challenge and said scrutiny of new proposals is part of the scientific process. The findings do not change the unusual properties that make neutrinos difficult to detect and study. They do, however, close off this particular route to making a neutrino beam—at least within the physical assumptions examined in the new papers.