Tiny quantum breakthrough with big implications for medicine and technology

Adelaide University quantum engineers have found a new way to improve some of the world's most sensitive sensors of electromagnetic fields, a breakthrough that could help advance brain imaging, medical diagnostics, communications technology and next-generation quantum devices.

The research, published today in Physical Review Applied, is led by the University's Quantum and Nano Technology Group (QuaNTeG) and solves a long-standing problem that has limited the performance of superconducting quantum interference devices, known as SQUIDs.

SQUIDs are among the most sensitive magnetic field detectors ever created. They are used in specialised applications including brain imaging systems, scientific instruments and advanced radio-frequency sensors. However, while they can detect incredibly small changes in magnetic fields, they have struggled to accurately identify when a magnetic field is exactly zero.

Until now, engineers have addressed this problem by building complex circuits containing hundreds or even thousands of differently sized superconducting loops. While effective, that approach reduces the overall sensitivity of the device.

The Adelaide team, which includes PhD students Ross Monaghan and Jonathan Marenkovic, discovered a simpler solution. Instead of making loops different sizes, the researchers kept them the same size but strategically replaced some with "bare loops" that contain no Josephson junctions, a key component of traditional SQUID devices.

These bare loops change how magnetic signals move through the circuit, creating what the researchers call a "synthetic area spread". The result is that the sensor behaves as though it contains many differently sized loops, without needing them.

Lead researcher Associate Professor Giuseppe Tettamanzi, from Adelaide University’s School of Chemical Engineering, said the discovery could help unlock the full potential of quantum sensing technologies.

"For decades, scientists have known how to make these devices identify an absolute magnetic field but doing so required design compromises that reduced their performance," Associate Professor Tettamanzi said.

"Our work shows there is another way. By introducing carefully positioned bare loops, we can achieve the same result while preserving the conditions needed for maximum sensitivity."

The researchers developed the theory behind the approach and then confirmed the effect experimentally using fabricated superconducting circuits operating at very low temperatures. The results showed the new design behaved exactly as predicted.

Associate Professor Tettamanzi said the advance could eventually benefit a wide range of applications.

"Highly sensitive superconducting quantum sensors have enormous potential in medicine, communications, industry and defence," he said. "The closer we get to the fundamental quantum limit of detection, the more information we can extract from very weak signals.”

Potential future applications include improved brain monitoring systems, more sensitive radio-frequency receivers, low-noise communication technologies and advanced electromagnetic sensing platforms.

The discovery could also make future devices easier and less costly to manufacture because the new approach removes the need to fabricate large arrays containing many different loop sizes.

While further testing is required before the technology can be commercialised, the researchers believe the breakthrough brings practical quantum-limited sensors a significant step closer to reality.

The concept is the subject of an international patent application, and further studies are already underway to improve device performance and explore new applications.

‘Synthetic areas spread in two-dimensional Superconducting Quantum Interference Filter Arrays’ is published in Physical Review Applied. DOI: https://doi.org/10.1103/wc1k-wxtc.