Innovative Quantum Material Could Be Key to Even Faster Quantum Computing

By figuring out a way to let electrons move without using energy, Chinese researchers could have tapped into a new way to speed up quantum computers.

Quantum computing remains one of the most promising sectors for the future of information technologies. Researchers from China recently reported a new quantum material that could help quantum computing systems become even more powerful. 

A team from Tsinghua University and Institute of Physics, Chinese Academy of Sciences in Beijing managed to control the states of matter within semiconductors using a quantum principle. 

By leveraging what's known as the Quantum Anomalous Hall (QAH) effect, teh researchers discovered how to move electrons a few millimeters in distance while maintaining their energy. By being able to store that energy, this effect and the material used to conduct it could help quantum systems become more energy-efficient and, thus, faster.

The Quantum Anomalous Hall (QAH) effect was first observed in 2013 by another team from Tsinghua University, and the school has made considerable strides in quantum research in the years since. 

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Now, in a study published in the journal Chinese Physics Letters, the new Tsinghua team explained how they created an artificial material capable of  being used in developing Topological Quantum Computer using Molecular Beam Epitaxy. This new material allows layers of crystal just one molecule thick to be stacked. 

The ultra-thin material also exploits the QAH effect and a potential evolution in quantum computing systems. Rather than the binary systems found in a normal computer, quantum computers use subatomic particles in multiple states at the same time. This allows the computers to solve complex problems faster than everyday computers. 

Potential for the Topological Quantum Computer

According to the Tsinghua team, the Topological Quantum Computer would be able to use a certain type of quasiparticle called an anyon to encode and send information. 

"We can realise QAH multilayers, or a stack of multiple layers of crystal lattices that are experiencing the QAH effect, with several magnetically doped films spaced by insulating cadmium selenide layers. Since we do it by molecular beam epitaxy, it is easy to control the properties of each layer to drive the sample into different states," said Ke He, a professor at Tsinghua University.

Cadmium selenide is an important molecule consisting of one cadmium atom and one selenium atom used as a semiconductor -- a material whose conductive properties researchers can modify by adding impurities.

Multiple layers of thin crystals serves as a sort of insulation between the conductive layers in a system. This prevents unwanted interacitons of electrons between these thin crystal sheets, forcing electrons into an "edge state." That state allows for a few electrons to go through without resistance. But having more of these layers on top of each other, there are more electrons flowing through without resistance and more electrons can stay in this state.

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The QAH effect and cadmium selenide work together in creating a rare state of matter called the Weyl semimetal.

"By tuning the thicknesses of the QAH layers and cadmium selenide insulating layers; we can drive the system into a magnetic Weyl semimetal, a state of matter that so far has never been convincingly demonstrated in naturally occurring materials," Ke said. 

First observed in 2015, a Weyl semimetal is a rare state of matter. It qualifies as a solid-state crystal that conducts electricity through massless "Weyl Fermions" instead of electrons. The mass difference between these fermions and electrons lets electricity flow through the device faster, thus speeding up a device's performance. 

"Now, what interests me most is to construct independently controllable QAH bilayers," Ke said. "If we could get a pair of counter-propagating edge states, while putting a superconducting contact on the edge of the sample, the two edge states might bind together due to the superconducting contact, leading to Majorana modes which can be used to build a topological quantum computer."

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