Physicists Finally Observe a Link Between Quantum Criticality And Entanglement

 We know that the realm of natural philosophy is science operating at a mind-bogglingly small scale, thus watching quantum interactions happen is often exciting. Now, physicists have managed to watch billions upon billions of entangled electrons passing through a metal film.

The film may be a mixture of ytterbium, rhodium and silicon, and is what's referred to as a 'strange metal', one that does not act for sure at very low temperatures.

"With strange metals, there's an unusual connection between electrical phenomenon and temperature," explained physicist Silke Bühler-Paschen from Vienna University of Technology in Austria.

"In contrast to simple metals like copper or gold, this doesn't seem to result to the thermal movement of the atoms, but to quantum fluctuations at absolutely the zero temperature."

These fluctuations represent a quantum criticality – that time between quantum states which are the equivalent of transition between liquids, solids and gases in classical physics; the team says this cascade of electrons is that the best evidence yet of a link between quantum criticality and entanglement.

"When we expect about quantum entanglement, we expect about small things," says physicist Qimiao Si, from Rice University. "We don't associate it with macroscopic objects."

"But at a quantum juncture, things are so collective that we've got this opportunity to work out the results of entanglement, even during a metallic film that contains billions of billions of quantum mechanical objects."

The experiments Bühler-Paschen, Si and colleagues ran were incredibly challenging from many levels – from the highly complex materials synthesis required to make the strange metal, to the fragile terahertz spectroscopy required to watch the electrons.

Ultimately, after a painstaking process, the team found what they were looking for: the tell-tale sign of quantum criticality referred to as frequency over temperature scaling.

"Conceptually, it had been really a dream experiment," says Si. "Probe the charge sector at the magnetic quantum crossroads to work out whether it's vital, whether it's dynamical scaling."

The terahertz spectrometer used to measure entanglement. (Jeff Fitlow/Rice University)

"If you do not see anything that's collective, that's scaling, the juncture should belong to some textbook style of description. But, if you see something singular, which after all we did, then it's very direct and new evidence for the quantum entanglement nature of quantum criticality."

What all of this high-level physics means may be a lot of potential: potential quantum advancements in computing, communications and more. Scientists have hypothesised a couple of link between quantum entanglement and quantum criticality before, but now it has been observed.

The study of quantum states remains in its very early stages, but it could hold the key to all or any forms of weird science, like high-temperature superconductivity – which is additionally believed to be underpinned by quantum criticality.

Understanding how these quantum phases switch gives us a far better chance of having the ability to regulate them within the future – and although that's still a protracted way off, it just got a touch closer.

"Our findings suggest that the identical underlying physics – quantum criticality – can cause a platform for both quantum information and high-temperature superconductivity," says Si. "When one contemplates that possibility, one cannot help but marvel at the wonder of nature."