Irish researchers make strides in quantum computing research

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Decoherence issue illuminated by international group



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17 April 2020 | 0

A key issue in the development of practical quantum computers, decoherence, has been illuminated by a research group including AMBER, the SFI Research Centre for Advanced Materials and BioEngineering Research, and the School of Physics and the CRANN Institute, at Trinity College Dublin.

Decoherence is the process by which the information of a quantum system is altered by interaction with its environment. The quantum equivalent of the classic computing bit, the units of 1 and 0s, is the qubit. The qubit can exist in both states simultaneously, a property which is fundamental to quantum computing, known as coherent superposition. When a qubit is measured, it collapses into one state or the other, and that process is a key part of the promise of quantum computing.

The issue of decoherence arose when it was discovered that qubits did not behave as theorised. Therefore, if qubits store information based on being in both states simultaneously then decoherence means data will be lost.




The research teams are now looking at the problem using electronic structure calculations to provide an interpretation of the atom in line with experimental observations.

“So far we don’t fully understand the details of decoherence,” said AMBER Investigator Dr Alessandro Lunghi, from Trinity’s School of Physics, “but one suggested source is that vibrations occur in the material. Through our research we have new insights on the nature of these molecular vibrations and can propose new strategies on how to mitigate their destructive role on spin quantum coherence”.

Working with experimental teams based in the UK and Italy, Dr Lunghi and Professor Stefano Sanvito, Professor in the School of Physics and director of the CRANN Institute, Trinity College Dublin, conducted theoretical and modelling work.

“What makes this research unique,” said Prof Sanvito  “was that the experimental teams were able to observe vibrations of molecular qubits for the first time, and our TCD team made it possible to understand the nature and the details of how the observed vibrations couple to spin”.

Dr Lunghi highlighted the importance of this research, saying “this is at the very forefront of the research field and sheds new light on a fundamental phenomenon such as the interaction between spin and atomic motion. This is a major step for us as it validates the models we have developed and means that we can understand and predict spin coherence in molecular spins starting from simulations. We can now use these models to design new compounds and set the starting point for the design of more efficient molecular qubits”.

The full paper can be read here: Garlatti, E., Tesi, L., Lunghi, A. et al. Unveiling phonons in a molecular qubit with four-dimensional inelastic neutron scattering and density functional theory. Nat Commun 11, 1751 (2020). 

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