System Bits: Sept. 17

Quantum computing; graphene in astronomy; lithium-ion batteries.


Quantum computing R&D in Germany
IBM is teaming with the Fraunhofer Society for research and development of quantum computing technology, backed by the German government, which is providing €650 million (about $715.4 million) in funding over two years for the program.

IBM has agreed to install a Q System One system at one of its facilities in Germany for the program. The system has 20 quantum bits, or qubits.

“This effort is poised to be a major catalyst for Europe’s innovation landscape and research capabilities,” said Martin Jetter, senior vice president and chairman of IBM Europe.

The Q System One was introduced in January. The shipment to Germany represents the first such shipment outside of the United States.

Meanwhile, the U.S. Department of Energy seeks experts in quantum information science to advise the White House and federal agencies. The Energy Department will appoint experts to the National Quantum Initiative Advisory Committee. The National Quantum Initiative Act was signed into law last year provides $1.2 billion over five years to support quantum computing R&D. The German government last year budgeted €3 billion (around $3.3 billion) for research into artificial intelligence by 2025.

Graphene devices for terahertz detection in astronomy
Researchers from Sweden’s Chalmers University of Technology have demonstrated a detector made from graphene that could revolutionize the sensors used in next-generation space telescopes. The findings were recently published in the scientific journal Nature Astronomy.

Beyond superconductors, there are few materials that can fulfill the requirements needed for making ultra-sensitive and fast terahertz (THz) detectors for astronomy. Chalmers researchers have shown that engineered graphene adds a new material paradigm for THz heterodyne detection.

“Graphene might be the only known material that remains an excellent conductor of electricity/heat even when having, effectively, no electrons. We have reached a near zero-electron scenario in graphene, also called Dirac point, by assembling electron-accepting molecules on its surface. Our results show that graphene is an exceptionally good material for THz heterodyne detection when doped to the Dirac point,” says Samuel Lara-Avila, assistant professor at the Quantum Device Physics Laboratory and lead author of the paper.

In detail, the experimental demonstration involves heterodyne detection, in which two signals are combined, or mixed, using graphene. One signal is a high intensity wave at a known THz frequency, generated by a local source (i.e., a local oscillator). The second is a faint THz signal that mimics the waves coming from space. Graphene mixes these signals and then produces an output wave at a much lower gigahertz (GHz) frequency, called the intermediate frequency, that can be analyzed with standard low noise gigahertz electronics. The higher the intermediate frequency can be, the higher bandwidth the detector is said to have, required to accurately identify motions inside the celestial objects.

“According to our theoretical model, this graphene THz detector has a potential to reach quantum-limited operation for the important 1-5 THz spectral range. Moreover, the bandwidth can exceed 20 GHz, larger than 5 GHz that the state-of-the-art technology has to offer.”

Another crucial aspect for the graphene THz detector is the extremely low power needed for the local oscillator to achieve a trustable detection of faint THz signals, few orders of magnitude lower than superconductors require. This could enable quantum-limited THz coherent detector arrays, hence opening the door to 3D imaging of the universe.

Image credit: Hans He.

Elvire De Beck, astronomer at the Department of Space, Earth and Environment, who did not take part in the research, explains the possible implications for practical astronomy: “This graphene-based technology has enormous potential for future space missions that aim at, e.g., unveiling how water, carbon, oxygen, and life itself came to earth. A lightweight, power-effective 3D imager that is quantum-limited at terahertz frequencies is crucial for such ambitious tasks. But, at the moment, THz 3D imagers are simply not available.”

Sergey Kubatkin, professor at the Quantum Device Physics Laboratory and co-author of the paper, explains: “The core of the THz detector is the system of graphene and molecular assemblies. This is in itself a novel composite 2D material that deserves deeper investigation from a fundamental point of view, as it displays a whole new regime of charge/heat transport governed by quantum-mechanical effects.”

The research was supported by the Swedish Foundation for Strategic Research, Knut and Alice Wallenberg Foundation, Chalmers Excellence Initiative Nano, the Swedish Research Council, the Korea-Sweden Research Cooperation of the NRF, and the European Union’s Horizon 2020 research and innovation program.

A new design in lithium-ion batteries
The growing popularity of lithium-ion batteries in recent years has put a strain on the world’s supply of cobalt and nickel – two metals integral to current battery designs – and sent prices surging.

In a bid to develop alternative designs for lithium-based batteries with less reliance on those scarce metals, researchers at the Georgia Institute of Technology have developed a promising new cathode and electrolyte system that replaces expensive metals and traditional liquid electrolyte with lower cost transition metal fluorides and a solid polymer electrolyte.

“Electrodes made from transition metal fluorides have long shown stability problems and rapid failure, leading to significant skepticism about their ability to be used in next generation batteries,” said Gleb Yushin, a professor in Georgia Tech’s School of Materials Science and Engineering. “But we’ve shown that when used with a solid polymer electrolyte, the metal fluorides show remarkable stability – even at higher temperatures – which could eventually lead to safer, lighter and cheaper lithium-ion batteries.”

In a typical lithium-ion battery, energy is released during the transfer of lithium ions between two electrodes – an anode and a cathode, with a cathode typically comprising lithium and transition metals such as cobalt, nickel and manganese. The ions flow between the electrodes through a liquid electrolyte.

For the study, which was published Sept. 9 in the journal Nature Materials and sponsored by the Army Research Office, the research team fabricated a new type of cathode from iron fluoride active material and a solid polymer electrolyte nanocomposite. Iron fluorides have more than double the lithium capacity of traditional cobalt- or nickel-based cathodes. In addition, iron is 300 times cheaper than cobalt and 150 times cheaper than nickel.

To produce such a cathode, the researchers developed a process to infiltrate a solid polymer electrolyte into the prefabricated iron fluoride electrode. They then hot pressed the entire structure to increase density and reduce any voids.

Two central features of the polymer-based electrolyte are its ability to flex and accommodate the swelling of the iron fluoride while cycling and its ability to form a very stable and flexible interphase with iron fluoride. Traditionally, that swelling and massive side reactions have been key problems with using iron fluoride in previous battery designs.

“Cathodes made from iron fluoride have enormous potential because of their high capacity, low material costs and very broad availability of iron,” Yushin said. “But the volume changes during cycling as well as parasitic side reactions with liquid electrolytes and other degradation issues have limited their use previously. Using a solid electrolyte with elastic properties solves many of these problems.”

The researchers then tested several variations of the new solid-state batteries to analyze their performance over more than 300 cycles of charging and discharging at elevated temperature of 122 degrees Fahrenheit, noting that they outperformed previous designs using metal fluoride even when these were kept cool at room temperatures.

The researchers found that the key to the enhanced battery performance was the solid polymer electrolyte. In previous attempts to use metal fluorides, it was believed that metallic ions migrated to the surface of the cathode and eventually dissolved into the liquid electrolyte, causing a capacity loss, particularly at elevated temperatures. In addition, metal fluorides catalyzed massive decomposition of liquid electrolytes when cells were operating above 100 degrees Fahrenheit. However, at the connection between the solid electrolyte and the cathode, such dissolving doesn’t take place and the solid electrolyte remains remarkably stable, preventing such degradations, the researchers wrote.

“The polymer electrolyte we used was very common, but many other solid electrolytes and other battery or electrode architectures – such as core-shell particle morphologies – should be able to similarly dramatically mitigate or even fully prevent parasitic side reactions and attain stable performance characteristics,” said Kostiantyn Turcheniuk, research scientist in Yushin’s lab and a co-author of the manuscript.

In the future, the researchers aim to develop new and improved solid electrolytes to enable fast charging and also to combine solid and liquid electrolytes in new designs that are fully compatible with conventional cell manufacturing technologies employed in large battery factories.

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