New Study Discovers Billions of Entangled Electrons in a Metal

International physicists from Rice University and the Vienna University of Technology collaborated on the project.
Fabienne Lang

A team of physicists from Rice University in the U.S. and the Vienna University of Technology (TU Wien) in Austria has put their heads together for over 15 years to uncover a quantum conundrum.

The study made the incredible discovery of quantum entanglement among "billions and billions" of electrons in a quantum critical matter — or, a "strange metal."

The study was published in the journal Science on Friday.


Fifteen years' worth of research

The research studied the electronic and magnetic behavior of a "strange metal" compound of ytterbium, rhodium, and silicon as it got close to and passed through a critical transition at the boundary between two quantum phases. 

Junichiro Kono (left) and Qimiao Si in Kono’s Rice University laboratory in December 2019, Source: Jeff Fitlow/Rice University

This study offers the strongest and most direct evidence to date of the role of entanglement in bringing about quantum criticality, noted Rice University theoretical physicist and co-author of the study, Qimiao Si.

Si stated "When we think about quantum entanglement, we think about small things."

He continued, "We don’t associate it with macroscopic objects. But at a quantum critical point, things are so collective that we have this chance to see the effects of entanglement, even in a metallic film that contains billions of billions of quantum mechanical objects."

Former Rice University graduate student Xinwei Li (left) and Professor Junichiro Kono in 2016 with the terahertz spectrometer Li used to measure quantum entanglement in YbRh2Si2, Source: Jeff Fitlow/Rice University

Rice University researchers worked alongside scientists from TU Wien to overcome several challenges the study brought about.

TU Wien researchers developed a technique that involved highly complex materials synthesis to create incredibly pure films which contain one part ytterbium for every two parts of rhodium and silicon.

Rice University researchers performed terahertz spectroscopy experiments on these films at the incredibly low temperatures of up to 1.4 Kelvin. That's -271 degrees Celcius (-457 degrees Fahrenheit).

Former Rice University graduate student Xinwei Li in 2016 with the terahertz spectrometer he later used to measure entanglement in the conduction electrons flowing through a “strange metal” compound of ytterbium, rhodium, and silicon, Source: Jeff Fitlow/Rice University

Rice University graduate student and co-author of the paper, Junichiro Kono commented that "Less than 0.1% of the total terahertz radiation was transmitted, and the signal, which was the variation of conductivity as a function of frequency, was a further few percents of that."

Kono continued "It took many hours to take reliable data at each temperature to average over many, many measurements, and it was necessary to take data at many, many temperatures to prove the existence of scaling."

A lot of patience and precision were required for this study, but the outcome is impressive.

Physicist Silke Bühler-Paschen of the Vienna University of Technology, Source: Luisa Puiu/TU Wien

As Si explained "Quantum entanglement is the basis for storage and processing of quantum information."

"At the same time, quantum criticality is believed to drive high-temperature superconductivity. So our findings suggest that the same underlying physics — quantum criticality — can lead to a platform for both quantum information and high-temperature superconductivity. When one contemplates that possibility, one cannot help but marvel at the wonder of nature."

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