Reviewed by Lexie CornerDec 5 2024
In a recent study published in the journal Nature Electronics, researchers from the University of Würzburg and the German National Metrology Institute (PTB) developed a new type of quantum standard of resistance based on the Quantum Anomalous Hall Effect.
This device can be used to measure the resistance standard based on the Quantum Anomalous Hall Effect. Image Credit: Fijalkowski, University of Würzburg
Accurate electrical resistance measurement is essential in electronics and industrial production, including the manufacturing of advanced sensors, microchips, and flight controls.
Very precise measurements are essential here, as even the smallest deviations can significantly affect these complex systems.
Charles Gould, Physicist and Professor, Institute for Topological Insulators, University of Würzburg
The so-called quantum resistance standard, which does not require an external magnetic field to function, has now been experimentally implemented for the first time by scientists.
In physics, standards are used as fixed reference points for the precise measurement of physical quantities and the calibration of measuring instruments. A quantum standard operates based on invariant principles of quantum mechanics, which makes it extraordinarily stable.
Charles Gould, Physicist and Professor, Institute for Topological Insulators, University of Würzburg
How the Standard Works
The classic Hall effect is familiar to many from physics classes: The Hall voltage is generated when a current passes through a conductor exposed to a magnetic field.
The Hall resistance is calculated by dividing this voltage by the current. As the magnetic field strength increases, the resistance rises. However, in very thin conductors, less than a few nanometers thick (for comparison, a human hair is roughly 100,000 nm thick), and in strong magnetic fields, the resistance no longer increases steadily. Instead, it reaches fixed values in discrete steps, which are universal and independent of device properties.
This phenomenon is known as the Quantum Hall Effect (QHE), which is essential for establishing a resistance standard, as the resistance takes on universal values in this state.
A unique feature of the Quantum Anomalous Hall Effect (QAHE) is that it can occur without the need for a magnetic field.
The operation in the absence of any external magnetic field not only simplifies the experiment but also gives an advantage when it comes to determining another physical quantity: the kilogram. To define a kilogram, one has to measure the electrical resistance and the voltage standards at the same time, but measuring the voltage standard only works without a magnetic field, so the QAHE is ideal for this.
Charles Gould, Physicist and Professor, Institute for Topological Insulators, University of Würzburg
Until now, the QAHE measurements at zero external magnetic field lacked the accuracy needed for contemporary quantum metrology applications. The new measurements reach the required precision thresholds and put the magnetic field-free QAHE standard on par with early conventional QHE-based resistance standards for the first time.
Further Plans
The quantum resistance standard can only operate at very low temperatures and currents, and it requires the absence of an external magnetic field. For the standard to become commercially viable in the future, particularly for industrial use, further refinement of the experiment is needed.
To advance this, Gould's team in Würzburg continues collaborating with the Physikalisch-Technische Bundesanstalt (PTB) in Braunschweig, Germany, and with global researchers involved in the QuAHMET European metrology consortium.
The study received support from the European Commission, the Free State of Bavaria, and the German Research Foundation (DFG).
Journal Reference:
Patel, D. K., et al. (2024) A zero external magnetic field quantum standard of resistance at the 10−9 level. Nature Electronics. doi.org/10.1038/s41928-024-01295-w.