MIT Study Reveals Why a Neutrino Laser May Be Impossible

Physicists proposed a method to focus ghostly neutrinos into a laser-like beam, however brand-new MIT computations reveal that violent atomic recoil and the particles’own quantum nature avoid the impact from taking hold.

Trillions of subatomic particles stream through every square inch of Earth, going through strong rock, enormous stars, and bodies every second without leaving a trace. These particles, called neutrinos, bring near-zero mass and communicate so weakly with regular matter that physicists have actually struggled to find them, much less manage them into a concentrated beam, given that their discovery in 1956.

In 2015, MIT physics teacher Joe Formaggio and Ben Jones, then an associate teacher at the University of Texas at Arlington and now at the University of Manchester, proposed a theoretical method around that physical barrier.

They thought that cooling a cloud of radioactive atoms to nanokelvin temperature levels, one-billionth the temperature level of interstellar area, would bring atomic movement to a standstill governed simply by quantum unpredictability instead of thermal heat. At that severe cold, the atoms form a Bose-Einstein condensate, acting as a single, quantumly associated whole.

If radioactive atoms might be brought into that state, Formaggio and Jones reasoned, their decay may end up being integrated through a quantum result called superradiance. Instead of launching neutrinos separately in random instructions, the atoms might possibly speed up one another’s decay and focus the particles into a laser-like beam. In one proposed circumstance, radioactive rubidium atoms would go from a half-life of 86 days to simply one minute. Nobody has actually yet produced a Bose-Einstein condensate from radioactive atoms.

2 barriers obstruct a neutrino laser

MIT physicists have actually now concluded that the plan can not work. In 2 buddy documents released in Physical Review LettersWolfgang Ketterle, the John D. MacArthur Professor of Physics at MIT, and postdocs Hanzhen Lin and Yu-Kun Lu determined 2 different barriers. One originates from the violent recoil produced when a neutrino leaves an atom. The other originates from neutrinos themselves, which come from a class of particles called fermions.

“These 2 documents are sort of punch one and punch 2,” Ketterle states. “Each paper would have eliminated the proposition.”

Superradiance had actually formerly been shown with photons. When a laser shines into a Bose-Einstein condensate, the ultracold atoms can integrate their scattering so that photons emerge in the exact same instructions. At space temperature level, those photons would rather spread arbitrarily and produce bit more than a scattered radiance.

Each spreading occasion likewise presses an atom backwards through recoil. Inside a condensate, those recoils can stay synchronized, enhancing more scattering and triggering the procedure to grow tremendously. The outcome is a superradiant beam of photons. Formaggio and Jones proposed that radioactive atoms may produce a comparable impact as they launched neutrinos throughout decay.

Neutrino recoil removes quantum memory

Ketterle, who co-discovered Bose-Einstein condensates in 1995 and shared the 2001 Nobel Prize in Physics for associated work, was hesitant that the fragile habits of ultracold atoms might make it through the energy launched in nuclear decay.

“My experience has actually constantly been that the condensate can do wonderful things at low energy– superfluidity, vortices– and if you were to speak in a space filled with condensate, it would take one hour for you to hear my voice. That’s how sluggish the condensate is,” Ketterle states. “And I had actually constantly concerned the conclusion that for anything violent, like nuclear responses, the condensate would refrain from doing anything.”

Noticeable photons bring about 1 electron volt of energy. Neutrinos produced throughout radioactive decay can bring approximately a million times more. That huge distinction suggests an atom launching a neutrino needs to recoil about a million times more highly than an atom engaging with noticeable light.

“As long as the recoil atom remains in the condensate, it can make the condensate superradiant,” Ketterle states. “But when a neutrino is discharged at a million electronvolts, the atom recoils at speeds comparable to Mach 10, faster than a fighter jet. This is so quick that the atom would practically quickly vanish.”

For superradiance to develop, the condensate requires to keep a quantum memory of earlier emissions. The neutrino laser proposition presumed that even after a recoiling atom got away, it would leave an imprint that motivated later on atoms to discharge neutrinos in the exact same instructions.

Ketterle and his coworkers checked that presumption utilizing a theoretical design that explains the conditions required for superradiance. They adjusted it to radioactive atoms and neutrinos while representing the variety of neutrino energies, the recoil of the decomposing atoms, and the altering characteristics of the condensate.

Every circumstance they evaluated stopped working. The recoiling atom left the condensate too rapidly for the needed quantum imprint to establish. Without that memory, radioactive atoms would continue releasing neutrinos typically instead of magnifying one another into a beam.

Fermions reverse the memory result

Even removing that recoil issue would not save the principle. The 2nd paper discovered that neutrinos would produce the incorrect sort of quantum memory for superradiance. Rather of motivating the condensate to produce another neutrino in the exact same instructions, a released neutrino would make subsequent emission because instructions less most likely.

That turnaround originates from the neutrino’s identity as a fermion. Fermions and bosons are the 2 essential classes of particles that comprise matter. Photons are bosons with whole-integer spin, while particles consisting of electrons and neutrinos are fermions with half-integer spin. Those various quantum homes identify how the particles act in relation to one another.

“In superradiance, it has to do with a memory result, or quantum connections in the condensate. And because context, individuals had actually believed that whatever is discharged from the condensate, it does not matter if it is a boson or a fermion,” Ketterle discusses. “But we examined it, and if you explain it properly for released fermions, you get an anti-memory, that makes the condensate not speed up in a superradiant type. It rather has the memory to refrain from doing it.”

An experiment might still check it

Formaggio, who assisted establish the initial proposition, sees the obstacle as part of the regular procedure of evaluating originalities.

“When an originality– such as the one we proposed– is shared, it is the task of the neighborhood to inspect it. Such is the clinical procedure,” Formaggio states. “Indeed, it was excellent to see how our paper produced a great deal of believing beyond our initial principle. We think that will continue.”

Ketterle, Formaggio, and Jones have actually satisfied numerous times to resolve the initial proposition and the objections raised by the brand-new analyses. Formaggio still leaves space for a speculative test.

“I presume that at some point, somebody will do the experiment,” Formaggio states. “Nature, as constantly, is the last arbiter of such things. And here I would be remiss to not mention that every previous forecast about neutrinos has actually been incorrect. The something about neutrinos that never ever surprises physicists is that they never ever stop working to shock.”

“Creative concepts and conversations amongst researchers are required to reveal nature’s surprises,” Ketterle states. “But when it comes to neutrino lasers, the surprise was too great to be real.”

Recommendation:

“Fundamental Impossibility of a Superradiant Neutrino Laser” by Yu-Kun Lu, Hanzhen Lin and Wolfgang Ketterle, 2 September 2026, Physical Review Letters
DOI: 10.1103/ 8x7k-rwx2

“To Lase or Not to Lase: The Question of Neutrino Superradiance” by Ana Maria Rey, James K. Thompson and Haoqing Zhang, 2 September 2026, Physics

This research study is supported, in part, by the National Science Foundation, the Center for Ultracold Atoms, the Vannevar-Bush Faculty Fellowship, the Gordon and Betty Moore Foundation, and the U.S. Army Research Office.

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