Radioactive atoms in a Bose–Einstein condensate (BEC) may kind a “superradiant neutrino laser” during which the atomic nuclei bear accelerated beta decay. The hypothetical laser has been proposed by two researchers US who say that it could possibly be constructed and examined. Whereas such a neutrino laser has no apparent instant functions, additional developments may probably help within the seek for background neutrinos from the Massive Bang – an essential purpose of neutrino physicists.
Neutrinos – the ghostly particles produced in beta decay – are notoriously troublesome to detect or manipulate due to the weak spot of their interplay with matter. They can’t be used to provide a traditional laser as a result of they’d cross straight via mirrors unimpeded. Extra essentially, neutrinos are fermions reasonably than bosons corresponding to photons. This prevents neutrinos forming a two-level system with a inhabitants inversion as just one neutrino can occupy every quantum state in a system.
Nonetheless, one other quantum phenomenon known as superradiance also can enhance the depth and coherence of the radiation from photons. This happens when the emitters are sufficiently shut collectively to change into indistinguishable. The emission then comes not from any single entity however from the collective ensemble. Because it doesn’t require the emitted particles to be quantum degenerate, this isn’t theoretically forbidden for fermions. “There are units that use superradiance to make gentle sources, and other people name them superradiant lasers – though that’s truly a misnomer” explains neutrino physicist Benjamin Jones of the College of Texas at Arlington and a visiting professor on the College of Manchester. “There’s no stimulated emission.”
Of their new work, Jones and colleague Joseph Formaggio of Massachusetts Institute of Expertise suggest that, in a BEC of radioactive atoms, superradiance may improve the neutrino emission fee and due to this fact velocity up beta decay, with an preliminary burst earlier than the anticipated exponential decay commences. “That has not been seen for nuclear programs to this point – just for digital ones,” says Formaggio. Rubidium was used to provide the primary ever condensate in 1995 by Carl Wiemann and Eric Cornell of College of Colorado Boulder, and conveniently, one among its isotopes decays by beta emission with a half-life of 86 days.
Radioactive vapour
The presence of further hyperfine states would make direct laser cooling of rubidium-83 more difficult than the rubidium-87 isotope utilized by Wiemann and Cornell, however not considerably extra so than the condensation of rubidium-85, which has additionally been achieved. Alternatively, the researchers suggest {that a} twin condensate could possibly be created during which rubidium-83 is cooled by sympathetic cooling with rubidium-87. The larger problem, says Jones, is the Bose–Einstein condensation of a radioactive atom, which has but to be achieved: “It’s troublesome to deal with in a vacuum system,” he explains, “You must watch out to ensure you don’t contaminate your laboratory with radioactive vapour.”
If such a condensate have been produced, the researchers predict that superradiance would enhance with the scale of the BEC. In a BEC of 106 atoms, for instance, greater than half the atoms would decay inside three minutes. The researchers now hope to check this prediction. “That is a kind of experiments that doesn’t require a billion {dollars} to fund,” says Formaggio. “It’s completed in college laboratories. It’s a tough experiment however it’s not out of attain, and I’d like to see it completed and be confirmed proper or mistaken.”
If the prediction have been proved right, the researchers counsel it may ultimately lead in direction of a benchtop neutrino supply. As the identical physics applies to neutrino seize, this might theoretically help the detection of neutrinos that decoupled from the new plasma of the universe simply seconds after the Massive Bang – tons of of 1000’s of years earlier than photons within the cosmic microwave background. The researchers emphasize, nonetheless, that this may not at present be possible.
Sound proposal
Neutrino physicist Patrick Huber of Virginia Tech is impressed by the work. “I feel for a primary, theoretical examine of the issue this is superb,” he says. “The quantum mechanics appears to be sound, so the query is when you attempt to construct an experiment what sort of real-world obstacles are you going to come across?” He predicts that, if the experiment works, different researchers would fairly seemingly discover hitherto unexpected functions.
Atomic, molecular and optical physicist James Thompson of College of Colorado Boulder is sceptical, nonetheless. He says a number of essential points are both glossed over or just ignored. Most notably, he calculates that the de Broglie wavelength of the neutrinos can be under the Bohr radius – which might forestall a BEC from feasibly satisfying the superradiance criterion that the atoms be indistinguishable.
“I feel it’s a extremely cool, artistic thought to consider,” he concludes, “however I feel there are issues we’ve realized in atomic physics that haven’t actually crept into [the neutrino physics] neighborhood but. We realized them the arduous manner by constructing experiments, having them not work after which determining what it takes to make them work.”
The proposal is described in Bodily Overview Letters.
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