Positively and negatively charged versions of the
same particle have been entangled for the first time, allowing us to map the
hearts of atoms more precisely and opening the doors to more powerful
communication tools.
The neutrons and protons that make up the nuclei of
atoms are, in turn, composed of quarks. However, quarks alone would be
unstable; they need gluons, the carriers of the strong force, to hold them
together. Gluons are orders of magnitude too small to see, even with the most
powerful microscopes – but they can still interact with photons to produce
exceptionally short-lived rho particles that decay to charged two-quark
particles called pions.
By measuring the angles and speed at which the
positive and negative pions (π+ and π-) emerge, scientists at the Brookhaven
National Laboratory have created a map of gluon distribution within the nuclei
of gold and uranium atoms. They report this map to be the most precise
description of the inner workings of an atomic nucleus.
“This technique is similar to the way doctors use
positron emission tomography (PET scans) to see what’s happening inside the
brain and other body parts,” said former Brookhaven physicist Dr Daniel
Brandenburg in a statement. “But in this case, we’re talking about mapping out
features on the scale of femtometers—quadrillionths of a meter—the size of an
individual proton.”
The map provides particle physicists with a better
understanding of the nature of reality, but the method by which it was made
could prove more important still.
Quantum entanglement maintains a connection between
separated particles such that a change to one affects the other. Although major
advances in entanglement now happen frequently and even win Nobel Prizes, these
have previously involved increasing the number of entangled particles or the distances
over which entanglement occurs.
The entangled particles have usually been electrons,
identical to each other, or photons. “This is the first-ever experimental
observation of entanglement between dissimilar particles,” Brandenburg said.
The entangled particles may both be pions, but their
opposite charges make them easy to distinguish from each other.
Most exploration of the inner workings of atomic
nuclei is conducted in particle accelerators that smash nuclei together at
close to the speed of light. Although watching the debris from these collisions
tells us a lot about particle behavior under extreme conditions, such as
shortly after the Big Bang, it is a little like observing the actions of
animals in a zoo and extrapolating to how they behave in the wild. Brandenburg
and co-authors are seeking to get closer to nuclei in their natural habitat.
To do this they had gold and uranium nuclei slip
past each other at extreme speeds without colliding, just a few nucleus-widths
apart. Each nucleus was surrounded by a cloud of photons produced by its
acceleration in a magnetic field. The photons of one nucleus interacted with
gluons in the other.
Having previously demonstrated these surrounding
photons are polarized, the authors could produce a two-dimensional map of gluon
distribution, with the direction of polarization providing one axis. Previous
efforts that lacked knowledge of the polarization only revealed how far each
gluon was from the center of the nucleus. Physicists had misinterpreted these results
in ways that made the nucleus bigger than experiments conducted in other ways,
and theoretical models, suggested.
“With this 2D imaging technique, we were able to
solve the 20-year mystery of why this happens,” Brandenburg said.
The authors conclude previous measurements confused
the photon’s own momentum and energy with that of the gluons. Disentangling the
two allows for maps so clear Brandenburg claimed; “The images are so precise that we can even
start to see the difference between where the protons are and where the
neutrons are laid out inside these big nuclei.” They also fit much better with
theoretical models.
How and why the pions entangle remains a mystery,
although the paper offers several possible explanations.
.webp)
0 Comments