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Scientists and engineers need reliable tools that can calculate the international standards for current, voltage, and resistance.
Typically, this requires laboratories to send equipment to the National Institute of Standards and Technology (NIST), who then use two types of quantum devices to calibrate these standards based on fundamental constants of nature.
But a new technique for measuring ohms, known as the quantum anomalous Hall effect (QAHE), makes the combination of these two devices possible.
Everything from high-flying planes to the smallest of microchips is reliant on accurate electrical standards, measurements based on the fundamental constants of nature that can help calibrate equipment used to power the foundation of our modern world. Typically, laboratories ship equipment to the National Institute of Standards and Technology (NIST) to test for voltage (volt), resistance (ohm), and current (ampere) for calibration. Each device would be tested with a separate cryostat—a device for maintaining the seriously cold temperatures necessary for calibration.
Now, this antiquated system may soon become a relic of the past. In a new paper published in the journal Nature Electronics, scientists at NIST successfully developed an all-in-one, four-square-meter device that can calibrate ohms, amperes, and volts at the same time.
The quantum ampere (amp) standard is “the amount of charge carried by 6.24 billion billion electrons past a given point in one second,” according to NIST, while volts require the programmable Josephson voltage standard, which uses specialized chips that produce hyper-accurate voltages once a microwave signal is applied. And since 1990, the unit of ohms has been based on the quantum Hall effect (QHE), which describes how thin sheets (only an atom wide) take on quantized values based on nature. These sheets are cooled to 4 degrees Kelvin, and a powerful magnetic field flows perpendicular to the flow of current in the sheets.
This strong magnetic field for testing the ohm is why scientists have previously failed to create an all-in-one calibration device. But a new type of quantized resistance technique—known as quantum anomalous Hall effect (QAHE)—requires only one-fifth to one-fortieth of the magnetic field needed for QHE (though, the sheets need to be cooled even further, down to about 0.01 Kelvin). This “Swiss army knife for electrical standards,” as NIST calls it, could finally allow scientists to calibrate instruments in their own laboratories to international standards.
“This early prototype is proof that practical integration is feasible,” Jason Underwood, an NIST researcher and co-author of the study, said in a press statement. “While we always seek to reduce our uncertainties, a deployable calibration instrument doesn’t necessarily have to achieve uncertainties as small as national metrology institute standards.”
However, NIST stresses that laboratories likely won’t see these devices in the near-term, as the equipment used to produce temperatures required for QAHE includes massive refrigeration systems. The hope is that experts will find future materials that display this effect at higher temperatures, which could make NIST’s prototype a more practical, portable cryostat for use in laboratories around the globe. And the good news is that the temperature wouldn’t actually need to be increased by very much.
“As the performance of QAHE materials advances, we can shrink the size of the cryostat substantially, especially if we can achieve a robust QAHE at temperatures above 0.1 Kelvin,” Underwood said in a press statement. “The cryogenic hardware at those higher temperatures is far more compact and transportable.”
So, while missing one of the key features of a Swiss army knife—portability—this QAHE-enabled calibration prototype proves that such a future machine is at least possible.
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