Superconducting quantum interference devices (SQUIDs) are among the most sensitive magnetic field detectors ever created by humans. They are used in brain imaging systems, scientific instruments and advanced radio-frequency sensors. But SQUIDs have a long-standing problem: they perform poorly at determining the moment when the magnetic field is exactly zero.
Until now, engineers solved this by assembling complex circuits of hundreds or even thousands of superconducting loops of different sizes. This approach worked but reduced the device's overall sensitivity. A team from the University of Adelaide (Australia) has found a simpler solution.
Instead of making the loops different, the researchers kept them identical but replaced some with "bare loops" - without Josephson junctions, the key component of traditional SQUIDs. Such loops change the path of magnetic signals in the circuit, creating a so-called "synthetic area spread." As a result, the sensor behaves as if it contains many loops of different sizes, even though in reality it does not.
The work was published in the journal Physical Review Applied. The study was led by Giuseppe Tettamanzi, an associate professor at the University of Adelaide's School of Chemical Engineering; the team also included doctoral students Ross Monaghan and Jonathan Marenkovic. The scientists first developed a theory and then confirmed the effect experimentally on fabricated superconducting circuits at very low temperatures. The results matched the predictions.
"For decades, scientists have known how to make these devices detect the absolute magnetic field, but this required design compromises that reduced performance," Tettamanzi is quoted as saying in a press release. "Our work shows that there is another way."
According to the researchers, the approach could in the future be useful in medicine, communications, industry and defense. Possible applications include improved brain monitoring systems, more sensitive radio-frequency receivers, low-noise communication technologies and advanced electromagnetic sensing platforms. In addition, the new design could simplify and reduce the cost of production: there is no need to fabricate large arrays of loops of different sizes.
However, commercialization of the technology is still far off - further testing is required. The concept has already become the subject of an international patent application, and research to improve device performance and find new applications continues.
It is important to understand that this is a laboratory result, not a finished product. The scientists do not claim that the technology is already ready for mass adoption - they only report a new design method that could in the future bring practical quantum sensors closer to the sensitivity limit.