Adjusting the Chern number for the nitrogen-vacancy center in diamond

Adjusting the Chern number for the nitrogen-vacancy center in diamond

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Credit: npj Quantum Information (2023). DOI: 10.1038/s41534-023-00732-6

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Credit: npj Quantum Information (2023). DOI: 10.1038/s41534-023-00732-6

The Chern number, a constant that characterizes topological phases in physical systems, has recently been modified in a controlled manner by researchers from Tokyo Tech. They achieved this in the electronic-nuclear spin system, which is the center of the nitrogen-vacancy in diamond, to check the Chern numbers from zero to three. This work opens the door to explore the unusual topology and its application to topological quantum information.

The Chern number is a constant (or “invariant”) property that characterizes different states called “topological phases” in different physical systems. In short, Chern numbers provide information about the behavior of electrons and their associated properties within a material.

Scientists try to investigate the transition between different topological phases by adjusting the Chern number to shed more light on the properties of matter. However, the robustness of the system topology to external disturbances makes it a challenging experiment. Despite an established theoretical basis, high Chern numbers are rarely observed experimentally in condensed matter systems. However, recent advances in materials science and experimental techniques have opened up new possibilities.

Recently, a group of international researchers, including Professor Walsworth from the Department of Physics at the University of Maryland in the US and Professor Keigo Arai from the Department of Electrical and Electronic Engineering at the Tokyo Institute of Technology (Tokyo Tech) in Japan, conducted an investigation. changes in the Chern number in the electron-nuclear spin system associated with the nitrogen-vacancy (NV) center in diamond. Their work is published in npj Quantum Information journal.

“The NV center, a defect in the diamond lattice, contains a nitrogen atom connected to a vacant lattice site. This system provides a unique platform to investigate topological phases due to its controlled electronic and nuclear spin degrees of freedom,” explained Dr. Arai.

The researchers vary the control parameters of the Hamiltonian (a function used to solve the problem of the correct control of a dynamic system) by using spin-control microwaves to drive the Chern number, which represents the number of degeneracies included in the control Hamiltonian parameter sphere. Consequently, transitions between different topological phases can be made by adjusting the radius and offset of this sphere.

The team then used a combination of experimental techniques and numerical simulations to characterize the resulting behavior of the system, looking at Chern numbers from zero to three. In addition, the measured topological phase diagram was in agreement with numerical simulations and could be mapped to a system of three qubits. Finally, the researchers showed that the NV process can enable high Chern numbers to be reached, paving the way for the exploration of complex topological phases.

The novelty of this work, however, lies not only in observing the change of the Chern number but also in demonstrating its control. The ability to sing a Chern number within a single program opens up possibilities for practical use. “For example, high Chern phases in quantum anomalous Hall insulators hold the promise of low power consumption. As the Chern number increases, the contact resistance between conventional metal electrodes and chiral edge channels decreases, making it an attractive area for upcoming electronics,” Dr. Arai points out.

Indeed, the validity of the Chern number within the NV center system provides interesting opportunities for exploring unusual topologies and their application to topological quantum information. This has the potential to advance the fields of quantum metrology, next-generation electronics, spintronics, and quantum computation.

More information:
Junghyun Lee et al, Controllable controllability of the Chern number within the electron-nuclear spin system in diamond, npj Quantum Information (2023). DOI: 10.1038/s41534-023-00732-6

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