How Tiny Quantum Twists Could Power Tomorrow’s Tech

Researchers at Penn State are developing advanced quantum electronics using kink states, which are unique electron pathways in semiconducting materials.

These states could potentially form the backbone of a quantum interconnect network, crucial for transmitting quantum information efficiently. The team has made significant advancements in controlling these states through innovative material combinations and device designs, enhancing the potential for scalable quantum electronics.

The key to developing quantum electronics may have a few kinks. According to a team led by researchers at Penn State, that’s not a bad thing when it comes to the precise control needed to fabricate and operate such devices, including advanced sensors and lasers. The researchers fabricated a switch to turn on and off the presence of kink states, which are electrical conduction pathways at the edge of semiconducting materials. By controlling the formation of the kink states, researchers can regulate the flow of electrons in a quantum system.

Exploring Kink States for Quantum Information

“We envision the construction of a quantum interconnect network using the kink states as the backbone,” said team leader Jun Zhu, professor of physics at Penn State. Zhu is also affiliated with Penn State’s Center for 2-Dimensional Layered Materials. “Such a network may be used to carry quantum information on-chip over a long distance, for which a classical copper wire won’t work because it has resistance and therefore cannot maintain quantum coherence.”

The work, published recently in the journal Science, potentially provides a foundation for researchers to continue investigating kink states and their application in electron quantum optics devices and quantum computers.

Switch Mechanics and Quantum Valley Hall Effect

“This switch operates differently from a conventional switch, where the electrical current is regulated through a gate, similarly to traffic through a toll plaza,” Zhu said. “Here, we are removing and rebuilding the road itself”.

Kink states exist in a quantum device built with a material known as Bernal bilayer published on the kink states before, they only achieved the quantization of the quantum valley Hall effect in the current work after improving the electronic cleanness of the devices, meaning they removed sources that could allow electrons moving in opposite directions to collide. They did this by incorporating a clean graphite/hexagonal boron nitride stack as a global gate — or a mechanism that can allow the flow of electrons — into the devices.

Both graphite and hexagonal boron nitride are compounds commonly used as lubricant for paints, cosmetics and more. Graphite conducts electricity well while hexagonal boron nitride is an insulator. The researchers used this combination to contain electrons to the kink states and control their flow.

Future Directions in Quantum Electronics

“The incorporation of a graphite/hexagonal boron nitride stack as a global gate is critically important to the elimination of electron backscattering,” Huang said, noting that this material use was the key technical advancement of the current study.

The researchers also found that the quantization of the kink states remains even when the temperature is raised to several tens of Kelvin, the scientific unit of temperature. Zero Kelvin corresponds to -460 degrees arsenal of kink state-based quantum electronics widgets that help control and direct electrons — valve, waveguide, beam splitter — previously built by the Zhu lab.

“We have developed a quantum highway system that could carry electrons without collision, be programmed to direct current flow and is potentially scalable — all of which lays a strong foundation for future studies exploring the fundamental science and application potentials of this system,” Zhu said. “Of course, to realize a quantum interconnect system, we still have a long way to go.”

Zhu noted that her lab’s next goal is demonstrate how electrons behave like coherent waves when traveling on the kink state highways.

Reference: “High-temperature quantum valley Hall effect with quantized resistance and a topological switch” by Ke Huang, Hailong Fu, Kenji Watanabe, Takashi Taniguchi and Jun Zhu, 18 July 2024, Science.
DOI: 10.1126/science.adj3742

Other authors include Hailong Fu, a former postdoctoral scholar and Eberly Fellow in physics at Penn State, and a current assistant professor at Zhejiang University, China; and Kenji Watanabe and Takashi Taniguchi, both with the National Institute for Materials Science in Japan.

The U.S. National Science Foundation, the U.S. Department of Energy, the Penn State Eberly Research Fellowship, the Kaufman New Initiative of the Pittsburgh Foundation, the Japan Society for the Promotion of Science and the World Premier International Research Initiative of Japan’s Ministry of Education, Culture, Sports, Science and Technology funded this research.