Quantum device detects all units of electricity at once

A single quantum device could define all three units we use to understand electricity.

When you measure electricity, you need to find the flow’s current in amperes, its resistance in ohms and its voltage in volts. But before even getting started, researchers must agree on the size of each of these units. So far, this has required two separate quantum devices, and often, the costly and complicated task of visiting two separate laboratories.

Now, Jason Underwood at the National Institute of Standards and Technology (NIST) in Maryland and his colleagues have shown how we could instead characterise these units using a single device. “The idea of integrating those two quantum standards was always sort of a holy grail,” he says. “It’s been a long time coming. Like Sisyphus, we just kept pushing the rock up the hill.”

This integration was challenging because both devices rely on fragile quantum phenomena that can only be observed at very low temperatures – so low they must be operated in special fridges called cryostats. Traditionally, one device also required a magnetic field that disrupted the operation of the other.

The new “one box” method sidesteps this issue by using a novel material that can perform its quantum tricks without the magnetic field, so two quantum systems that previously had to be kept separate can operate in the same cryostat. The team used it to obtain amperes, ohms and volts with uncertainties as small as a few millionths of each unit.

Before researchers can use the combined device in practice, however, its accuracy must be increased further. For now, it is limited by how the two systems and their wiring heat each other up when they are put side-by-side. Plus, work is ongoing to perfect the still “juvenile” quantum material that enables the two systems to work together, says Linsey Rodenbach at Stanford University in California.

Though he sees the project as an unqualified success, Underwood says another thing that prevented the team from reaching even higher accuracies were poor conditions at NIST, which is funded by the US government. He particularly noted the institution’s “crumbling infrastructure”, as described in a 2023 study that found multiple NIST buildings are deteriorating. NIST declined to comment.

Susmit Kumar at the Norwegian Metrology Service says the new device is an “impressive engineering achievement”, and could make quantum electrical standards more cost-effective and easier to access for scientists and technology developers across the world. He is part of the QuAHMET consortium, which is also using novel materials to develop an easier-to-use device for determining the ohm.

“The international system of units is a common language that all scientists and engineers use. You want to make that as useful as possible,” says Richard Davis, who is retired from the International Bureau of Weights and Measures. He says efforts to unify different devices that are currently in use are bound to accelerate going forward.