New experiment shows that even the heaviest particles experience regular quantum weirdness

One of the most astonishing predictions in physics is entanglement, a phenomenon in which objects remain linked to each other even when they are some distance apart. The best-known example of entanglement involves tiny packets of light (photons) and low energy.

An experiment called ATLAS, conducted at the Large Hadron Collider (LHC) in Geneva, the world’s largest particle accelerator, has just discovered entanglement between a pair of top quarks, the heaviest particles known to science.

The results are described in a new paper by me and my colleagues in the ATLAS collaboration, published today in the journal Nature.

What is entanglement?

In everyday life, we think of objects as either “separate” or “connected.” Two balls one kilometer apart are separate. Two balls connected by a string are connected.

When two objects are “entangled,” there is no physical connection between them, but they are not completely separate either: by measuring the first object, you can know what the second object is doing before you can see it.

The two objects form a single system despite having no connection whatsoever. This has been demonstrated to work with photons on opposite sides of a city.

The idea will be familiar to fans of the recent streaming series “3 Body Problem,” based on Liu Cixin’s sci-fi novel. In the show, aliens send a tiny supercomputer to Earth to disrupt our technology and enable them to communicate with us. The tiny object is entangled with a twin on the aliens’ homeworld, allowing the aliens to communicate with and control it, despite being four light years away.

This part is science fiction. Entanglement doesn’t actually allow you to send signals faster than light. (It seems like entanglement would make this possible, but quantum physics tells us this is not possible. So far, all our experiments are consistent with that prediction.)

But entanglement itself is real: it was first demonstrated for photons in the 1980s in cutting-edge experiments.

Today, you can buy boxes from commercial providers that spit out pairs of entangled photons. Entanglement is one of the properties described in quantum physics, and one that scientists and engineers are trying to harness to create new technologies, such as quantum computing.

Since the 1980s, entanglement has been observed in atoms, some subatomic particles, and even tiny objects undergoing very slight vibrations. All of these examples are at low energies.

The new development from Geneva is that entanglement has been observed in a pair of particles called top quarks, meaning that an enormous amount of energy exists in a very small space.

So what are quarks?

Matter is made up of molecules, which are made up of atoms, and atoms are made up of light particles called electrons that orbit a heavy central nucleus, like the sun at the center of our solar system. We already knew this from experiments by about 1911.

Later, it was discovered that atomic nuclei are made up of protons and neutrons, and in the 1970s it was discovered that protons and neutrons are made up of even smaller particles called quarks.

There are six types of quarks in total: the “up” and “down” quarks that make up protons and neutrons, plus four heavier quarks. The fifth quark, the “beauty” or “bottom” quark, weighs about 4.5 times as much as a proton, which seemed really heavy when it was discovered. But the sixth and final quark, the “top,” is a monster: it’s slightly heavier than a tungsten atom and has 184 times the mass of a proton.

No one knows why the top quark is so heavy, and it’s for this very reason that it’s being intensely studied at the Large Hadron Collider. (In Sydney, where I’m based, most of the research in the ATLAS experiment focuses on the top quark.)

We think that the very large mass may provide a clue. The top quark is so heavy that it may feel new forces beyond the four forces we already know. Or the top quark may have some connection to “new physics.”

We know that our current understanding of the laws of physics is incomplete, and studying the behavior of the top quark may point the way to something new.

So does entanglement mean that the top quark is special?

Probably not. Quantum physics tells us that entanglement is common and that all kinds of things can become entangled.

But entanglement is also fragile: Many quantum physics experiments are performed at extremely low temperatures to avoid perturbing the systems by “colliding” them, so until now entanglement has only been demonstrated in systems where scientists can set up the right conditions to make measurements.

For technical reasons, the top quark’s enormous mass makes it a good laboratory for studying entanglement (the new ATLAS measurements would not have been possible with the other five quarks).

But top quark pairs aren’t the basis for any useful new technology — you can’t carry around the Large Hadron Collider — but they do give us a new kind of tool to do experiments, and entanglement is interesting in itself, so we’ll continue to look for what else we can find.

This article is republished from The Conversation under a Creative Commons license. Read the original article.