The Elements of Innovation Discovered

Quantum computing quest lands on rare earth

Metal Tech News - March 18, 2024

Materials scientists identified europium as an ideal element for a new material that is a strong candidate for use in quantum memory.

Pioneering into the frontiers of technology has scientists venturing deeper into the periodic table to discover elements with properties required for tomorrow's innovations. This is especially true for quantum computers and networks, which demand very specific and unique attributes that require a scientific expedition into unexplored chemical realms to discover the materials needed to build components capable of transmitting and storing quantum information.

"Normally in materials engineering, you can go to a database and find what known material should work for a particular application," said Daniel Shoemaker, materials science and engineering professor at the University of Illinois Urbana-Champaign. "For example, people have worked for over 200 years to find proper lightweight, high-strength materials for different vehicles. But in quantum information, we have only been working at this for a decade or two, so the population of materials is actually very small, and you quickly find yourself in unknown chemical territory."

The quest for new materials to build a quantum computing future often sends scientists to the row of 15 lanthanides known as rare earth elements at the bottom of the periodic table.

Shoemaker and University of Illinois Urbana-Champaign graduate student Zachary Riedel found themselves exploring this enigmatic group of technology metals as they sought materials ideally suited to serve as a new quantum memory platform.

"The problem that we are trying to tackle here is finding a material that can store that quantum information for a long time. One way to do this is to use ions of rare earth metals," said Shoemaker.

Specifically, the materials scientists identified europium as an ideal element for a brand new, air-stable material that is a strong candidate for use in quantum memory, a system for storing quantum states of photons or other entangled particles without destroying the information held by that particle.

Mapping the quantum quest

While the sometimes seemingly magical qualities of rare earths like europium have not been as thoroughly studied as mainstay metals like iron or copper, these elements have shown promise for quantum information devices due to their unique atomic structures.

One property that makes rare earth ions particularly well suited for quantum computing is they have many electrons densely clustered close to the nucleus of the atom.

The excitation of these electrons from resting state can "live for a long time" – seconds or possibly even hours – which is an eternity in the world of quantum computing.

The University of Illinois researchers say that such long-lived states are vital to avoiding the loss of quantum information. This quality alone positions rare earth ions as top candidates for qubits, the fundamental units of quantum information.

Based on what is known about rare earth elements, Shoemaker and Riedel imposed a few rules to map their expedition to formulating a new quantum storage compound.

First, the researchers narrowed the rare earths field down to a specific ion configuration of europium known as EU3+ because it operates at the right optical wavelength. To be "written" optically, the materials should be transparent.

Second, they wanted a material made of other elements that have only one stable isotope. Elements with more than one isotope yield a mixture of different nuclear masses that vibrate at slightly different frequencies, scrambling the information being stored.

Third, they wanted a large separation between individual europium ions to limit unintended interactions. Without separation, the large clouds of europium electrons would act like a canopy of leaves in a forest rather than well-spaced-out trees in a suburban neighborhood, where the rustling of leaves from one tree would gently interact with leaves from another.

Compound synthesized; candidates discovered

Grainger College of Engineering at University of Illinois Urbana-Champaign

The double perovskite crystal structure of Cs2NaEuF6 synthesized in the research carried out by Professor Daniel Shoemaker and graduate student Zachary Riedel.

With this set of rules to guide their quest for a quantum storage compound, Riedel completed a computational screening to predict which materials would work.

The graduate student narrowed the top candidates from this screening down to a special mineral compound known as a double perovskite halide made up of cesium, sodium, europium, and fluorine (Cs2NaEuF6).

This new compound is stable in the air, which means it can be integrated with other components, a critical property in scalable quantum computing.

The computer screening carried out by Riedel, now a postdoctoral researcher at Los Alamos National Laboratory, also predicted several other potential quantum computing compounds that have yet to be created.

"We have shown that there are a lot of unknown materials left to be made that are good candidates for quantum information storage," Shoemaker says. "And we have shown that we can make them efficiently and predict which ones are going to be stable."

The quantum materials research by Shoemaker and Riedel was supported by the U.S. Department of Energy, Office of Science, National Quantum Information Science Research Center Q-NEXT. The National Science Foundation, through the University of Illinois Materials Research Science and Engineering Center, supported the use of facilities and instrumentation.

The paper detailing Riedel and Shoemaker's research, Design Rules, Accurate Enthalpy Prediction, and Synthesis of Stoichiometric Eu3+ Quantum Memory Candidates, was published in the Journal of the American Chemical Society (2024).

Author Bio

Shane Lasley, Metal Tech News

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With more than 16 years of covering mining, Shane is renowned for his insights and and in-depth analysis of mining, mineral exploration and technology metals.


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