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Nematic bits and universal logic gates

Publish Date: 23.12.2022

Category: Outstanding research achievements, Interdisciplinary research, Our contribution to sustainable development goals

Sustainable development goals: 9 Industry, innovation and infrastructure (Indicators)

Assist. Dr Žiga Kos of the Faculty of Mathematics and Physics of the University of Ljubljana shows in the proposed article the functionality of nematic liquid crystals for performing computation operations. The article first introduces a mathematical formulation of nematic computation bits as defect states, and then shows that by controlling the dynamic properties it is possible to implement logical operations on individual nematic bits. In systems of multiple nematic bits, strong correlations lead to universal logic gates, which constitutes an important step towards the use of soft matter for processing information.

The great majority of computers are currently based on digital electronic circuits, where the possible states of individual bits is typically just 0 or 1, while sequences of states such as 0011001 are manipulated through logic gates. Alternative computational mechanisms based on the use of different materials or connective states of bits have been proposed for specific applications. The best known of such approaches is without doubt quantum computing. Other alternative computing approaches include computing based on DNA molecules, in cells, microfluid circuits, active substances and mechanical networks. Another possible example of new computational materials is soft matter, which is characterised by a strong response to external fields. Nematic liquid crystals are an example of soft matter with an orientational order of molecules. Although nematic liquids are a subject of intensive research and modern experimental methods enable the creation and precise control of complex topological states, it was not clear whether they could be used for computing operations.

In the proposed article Dr Kos shows that defects in nematic liquids can be understood as computing bits whose state can be described using associated observables in the analogy of the Poincaré-Bloch sphere. Several such nematic bits are coupled together strongly via elastic interaction. Dr Kos shows that such coupling leads to the implementation of universal logic operations of the NAND and NOR type. In this way he sets up the theoretical basis for the use of soft nematic materials for storing and processing information, and brings up new questions about the interaction and manipulation of complex soft matter. The importance of the results is evidenced by their publication in the prominent journal Science Advances. The achievement was also presented in several lectures given at international conferences (28th International Liquid Crystal Conference, APS March Meeting 2021, 11th Liquid Matter Conference, MIT Physical Mathematics Seminar), and it has also been reported in media such as New Scientist and Physics World. An important part in this scientific achievement has been played by the research of liquid crystals at the University of Ljubljana.

The proposed article came out in the prestigious scholarly journal Science Advances, with Assist. Dr Žiga Kos listed as the first of the two authors.



Figure: Selected defects within the orientation field of a nematic liquid crystal are used as input and output nematic bits (nbits) of the computing operation. The single sphere indicates a deformation that individual nematic bits perform during implementation of the logic operation.


Kos, Ž. and Dunkel, J. (2022). Nematic bits and universal logic gates. Science Advances, 8(33).



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