Physicists set a limit on the uncertainty of the subatomic particle's position. cientists used a superconducting sensor chip (shown) to detect the energy of atoms recoiling after they decayed within a layer of tantalum on the sensor. That measurement helped set a limit on a quantum property of neutrinos, which are also emitted in the decay.
Neutrinos are known for funny business. Now scientists have set a new limit on a quantum trait responsible for the subatomic particles’ quirkiness: uncertainty. The lightweight particles morph from one variety of neutrino to another as they travel, a strange phenomenon called neutrino oscillation (SN: 10/6/15). That ability rests on quantum uncertainty, a sort of fuzziness intrinsic to the properties of quantum objects, such as their location or momentum. But despite the importance of quantum uncertainty, the uncertainty in the neutrino’s position has never been directly measured.
“The ‘quantum properties of the neutrino’ stuff is a little bit of the Wild West at the moment,” says nuclear physicist Kyle Leach of Colorado School of Mines in Golden. “We’re still trying to figure it out.” It’s impossible to know everything about a quantum particle. Heisenberg’s uncertainty principle famously states that it’s futile to attempt to precisely determine both the momentum of a quantum object and its position (SN: 1/12/22). Now, Leach and colleagues report new details about the size of the neutrino’s wave packet, which indicates the uncertainty in the particle’s position.
Quantum particles travel as waves, with ripples that are related to the probability of finding a particle at a given location. A wave packet is the set of ripples corresponding to a single particle. The new experiment sets a limit on the size of the wave packet for neutrinos produced in a particular type of radioactive decay, Leach’s team reports in a paper submitted April 3 to arXiv.org. The particles have a wave packet size of at least 6.2 trillionths of a meter. The researchers studied neutrinos produced in the decay of beryllium-7, via a process called electron capture. In this process, a beryllium-7 nucleus absorbs an electron, and the atom transforms into lithium-7 and spits out a neutrino. The team implanted beryllium-7 atoms in a highly sensitive device made from five layers of material, including superconducting tantalum, which can transmit electricity without resistance. In the decay, the newly produced lithium-7 recoils away from the neutrino. When cooled to 0.1 degrees above absolute zero (–273.05° Celsius), the device allowed the researchers to detect the energy of that recoil. The spread in the energy of the lithium atoms revealed the neutrino wave packet’s minimum size. Neutrinos are special in that they interact so rarely with matter that they maintain their quantum properties over long distances. Most quantum effects take place on very small scales, but neutrino oscillations occur over thousands of kilometers.
International Research Conference on High Energy Physics and Computational Science
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