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New candidate emerges for a universal quantum electrical standard
- German physicists have created a way to define the standard unit of electrical resistance, using the quantum anomalous Hall effect rather than the ordinary quantum Hall effect. This technique avoids the need for applied magnetic fields, and the advancement could allow quantum-based voltage and resistance standards to be integrated into a universal quantum electrical reference.
- Since 2019, all base units in the International System of Units (SI) have been defined with reference to fundamental constants of nature, necessitating new ways of measuring and defining elements.
- Currently, to determine the value of Planck's constant, physicists use quantum-based electrical resistance and voltage measurements. It requires the large external magnetic fields essential to the quantum Hall effect, which renders Josephson devices inoperable.
- Researchers from the Institute for Topological Insulators at the University of Würzburg have created a new method that does not require the use of external magnetic fields. They used the quantum anomalous Hall effect (QAHE) instead of the QHE, which arises from electron transport phenomena in a family of materials called ferromagnetic topological insulators.
- The team found that resistance can be quantized even at weak and zero magnetic fields, making it possible to determine Planck's constant value with previously unachievable precision.
- Although the present form of this measurement requires very low temperatures and low electrical currents, an improved version could make a universal quantum electrical reference simple, compact and possible.
- The possible applications of this technique have attracted attention from the European Union, with the creation of a metrology consortium called QuAHMET, which aims to further exploit operating the new standard at more relaxed experimental conditions.
- The study was made possible by two teams from the Institute for Topological Insulators and the Physikalisch-Technische Bundesanstalt respectively, who combined their expertise and methods to make the measurement possible.
- The international System of Units (SI) now requires measurement based on fundamental constants of nature, necessitating innovative methods of measuring and defining units. The latest method uses the quantum anomalous Hall effect, which avoids the use of magnetic fields to determine Planck’s constant with greater precision than before.
- While it currently requires low temperature and current levels, the method may be used to create an all-in-one compact quantum electrical reference that could be used universally.
- The quantum anomalous Hall effect may even provide a quantum standard of voltage, resistance, and current in one experiment.
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