MIT researchers have found that a proposed neutrino laser cannot be built because of basic physical limits. The study shows that both the particles’ strong recoil effects and their fundamental quantum nature prevent the focused beam from forming.
The work was led by Wolfgang Ketterle, the John D. MacArthur Professor of Physics at MIT, along with postdocs Hanzhen Lin and Yu-Kun Lu. Their findings appear in two papers in Physical Review Letters and challenge a neutrino laser idea proposed by MIT physicist Joe Formaggio and Ben Jones.
The original proposal suggested using radioactive atoms cooled to extremely low temperatures. The atoms would form a Bose-Einstein condensate (BEC), a state where atoms behave together as one quantum system, potentially allowing radioactive decay to become synchronized and produce a laser-like neutrino beam.
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The problem is that neutrinos carry far more energy than visible photons. When a radioactive atom releases a neutrino, the atom receives a strong push in the opposite direction. According to the MIT analysis, this recoil happens so quickly that the atom leaves the condensate almost immediately, preventing the quantum effect needed for superradiance.
The researchers also found another fundamental problem. Neutrinos are fermions, while photons are bosons. This difference changes how quantum particles can build correlations. Instead of helping the condensate emit neutrinos in the same direction, the quantum effect would create an “anti-memory” that works against the formation of a focused beam.
The researchers tested these effects using theoretical models of superradiance. Their calculations found that the required amplification could not develop under the conditions they studied, even if radioactive atoms could first be cooled into a Bose-Einstein condensate.
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The finding does not mean neutrinos have become any less interesting to physicists. Instead, it shows how their unusual properties place strict limits on technologies inspired by ordinary lasers. As the original proposal’s researchers noted, further experiments could still test the idea, with nature ultimately deciding the question.
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