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Valleytronics Leads the Route to Creating a Reversible Computer

21 December 2017

(a) This is a schematic drawing of the valleytronic logic gate. (b) Operation of the valleytronic logic gate (c-e). Electrical characteristics of the valleytronic logic gate. (f) Traditional reversible logical operation. (g) Valleytronic-based reversible logical operation. Source: Singapore University of Technology and Design (SUTD)(a) This is a schematic drawing of the valleytronic logic gate. (b) Operation of the valleytronic logic gate (c-e). Electrical characteristics of the valleytronic logic gate. (f) Traditional reversible logical operation. (g) Valleytronic-based reversible logical operation. Source: Singapore University of Technology and Design (SUTD)

There are a lot of two-dimensional (2D) materials, and electrons are one of them. Electrons possess charge and spin, but they also display an unusual quantum feature called “valley.” Electrons in 2D materials can live in well-separated energy minima, and the “address” describing which minima the electrons belong to is called a “valley.” Using the “valley address” to encode and process information, the core of a new research called “valleytronics” is created.

Even with the anticipation of valleytronics to be a candidate for ‘beyond CMOS’ technology and continue the legacy of Moore’s law, its progress is hampered by the lack of practical designs for a valleytronic-based information processing unit. One major challenge in developing valleytronics is the construction of a “valley filter.” Valley filters can produce electrical current composed mainly of electronics from only one specific “valley.” This is a fundamental building block in valleytronics.

Through harnessing the unusual electrical properties of 2D materials, like few-layer black phosphorous and topological Weyl/Dirac semimetal thin films, Singapore University Technology and Design (SUTD) researchers have designed a versatile all-electric-controlled valley filter and demonstrated a concrete working design of a valleytronic logic gate. This is capable of performing the full set of two-input Boolean logics.

"A particularly remarkable finding is a previously unexplored approach of achieving logically reversible computation by storing information in the electron's valley state," said first-author Dr. Yee Sin Ang from SUTD.

Conventional digital computer processing method is logically irreversible. This can lead to a major logical issue. Upon receiving a computational output, an end-user can’t unambiguously identify the original input information that produces this output.

Making digital computing logically-reversible is interesting, not only in terms of fundamental information science, but it also has broad applications in areas like cryptography, signal and image processing, quantum computing and is ultimately required to improve the energy efficiency of digital computers beyond the thermodynamic bottleneck that is known as Landauer’s limit. Due to immense potentials, major research efforts have been devoted to the search for a practical reversible computer since the 70s.

The traditional way of making a logically-reversible computer relies on complex circuitries that generate large quantities of wasteful bits. The complex and wasteful methods have prevented reversible computing from gaining widespread industrial and commercial interests.

The key novelty of the valleytronics-based reversible logic gate proposed by SUTD researchers is that the device stores additional bits of input information in the valley state of the computational output to achieve logical-reversibility. The valleytronics approach bypasses a need for complex circuitries. It also significantly reduces the generation of wasteful bits. This simple architecture is more compatible with the ever-growing industrial and commercial demands for compact smart devices that are getting smaller every year.

Professor Ricky Ang, co-author and principal investigator of this research and SUTD professor, said, “The union of valleytronics, digital information processing, and reversible computing may provide a new paradigm towards the future of ultimately energy-efficient computers with novel functionalities."

The paper on this research was published in Physical Review B.

To contact the author of this article, email Siobhan.Treacy@ieeeglobalspec.com


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