Entanglement, the phenomena where objects can be somewhat separated but still connected, is one of the most unexpected physics predictions. The most well-known instances of entanglement involve low energy and tiny particles of light called photons.
Entanglement between pairs of top quarks, the heaviest particles known to science, has recently been discovered by the ATLAS experiment at the Large Hadron Collider in Geneva, the largest particle accelerator in the world.
My coworkers and I from the ATLAS project have released a new paper in Nature today that details the findings.
What is entanglement?
We consider items to be either “separate” or “connected” in our daily lives. Two balls are separated by a kilometer. Two balls are connected by a length of string.
Two objects that are “entangled” are not physically connected, yet they are also not completely distinct. You can measure the first object and use that information to determine what the second object is doing without even looking at it.
Despite the lack of a connection between the two objects, they constitute a single system. It has been demonstrated that photons on opposing sides of a city can use this.
Fans of the new streaming series 3 Body Problem, which is based on the science fiction books of Liu Cixin, will recognize the concept.
According to the show, aliens have dispatched a small supercomputer to Earth in order to interfere with human technology and establish communication. Despite being four light-years away, the aliens are able to control and interact with this small device because it is entangled with a twin on their homeworld.
Since entanglement doesn’t actually enable faster-than-light signal transmission, that portion of the novel is science fiction. (This seems to be something that entanglement should enable, but quantum physics says it’s not feasible. All of our experiments to date support that hypothesis.)
However, entanglement is real. It was initially shown for photons in a state-of-the-art experiment in the 1980s.
These days, a commercial vendor sells a contraption that can spit forth entangled pairs of photons. One of the characteristics of quantum physics that researchers and engineers are attempting to use to develop new technologies, including quantum computing, is entanglement.
Entanglement has also been observed with atoms, certain subatomic particles, and even small objects experiencing extremely minute vibrations since the 1980s. All of these instances are at low energies.
Entanglement has been observed in pairs of particles known as top quarks, where there is a great deal of energy in a very small area. This is a recent discovery from Geneva.
So what are quarks?
Like the Sun at the center of the solar system, matter is composed of molecules, which are composed of atoms. Atoms are composed of light particles called electrons that circle a heavy nucleus. By 1911 or so, experiments had already shown us this.
After learning that protons and neutrons make up the nucleus, we realized in the 1970s that even smaller particles known as quarks make up protons and neutrons.
In total, there are six different kinds of quarks: four heavier quarks plus the “up” and “down” quarks that comprise protons and neutrons.
We believed it to be extraordinarily heavy when we discovered the fifth quark, sometimes known as the “beauty” or “bottom” quark, which is around four and a half times heavier than a proton. The “top” quark, the sixth and last one, is a monster, 184 times the mass of a proton and somewhat heavier than a tungsten atom.
Why the top quark is so heavy is unknown. For this reason, the top quark is a subject of considerable research at the Large Hadron Collider. (The top quark is the main focus of our work on the ATLAS project in Sydney, where I am stationed.)
We believe the enormous mass could be a hint. Perhaps the reason the top quark is so large is that it experiences forces other than the four that we currently understand. Or perhaps it’s related to “new physics” in some other way.
We are aware that the existing understanding of the rules of physics is not comprehensive. Investigating the behavior of the top quark could lead to new discoveries.
So does entanglement mean that top quarks are special?
Most likely not. According to quantum physics, entanglement occurs frequently and can involve a wide variety of objects.
However, entanglement is not infallible either.
Ultra-cold temperatures are used for a lot of quantum physics experiments in order to prevent “bumping” and upsetting the system. Thus, entanglement has so far been shown in systems where researchers can provide the ideal environment for the observations.
The top quark is an ideal laboratory for researching entanglement because of its extremely enormous mass. (The remaining five quark kinds would not have been able to undergo the latest ATLAS measurement.)
However, top quark pairs won’t serve as the foundation for a portable new technology because the Large Hadron Collider isn’t portable.
However, top quarks do offer a new type of experimental tool, and entanglement is intriguing in and of itself, so we will continue to search for more.