Supermarket Grapes Spark a Quantum Technology Revolution

Scientists at Macquarie University have discovered a novel way to enhance quantum sensor performance using ordinary grapes.

By utilizing the water content and specific size of grapes, they created strong magnetic field hotspots that improve the efficiency of microwave-based quantum sensing.

Supermarket Grapes and Quantum Sensors

Researchers at Macquarie University have discovered that ordinary supermarket grapes can boost the performance of quantum sensors, paving the way for more efficient quantum technologies.

Published on December 20, 2024, in Physical Review Applied, the study reveals that pairs of grapes generate concentrated magnetic field hotspots when exposed to microwaves. These hotspots are critical for quantum sensing, a breakthrough that could lead to the creation of smaller, more affordable quantum devices.

“While previous studies looked at the electrical fields causing the plasma effect, we showed that grape pairs can also enhance magnetic fields, which are crucial for quantum sensing applications,” explains lead author Ali Fawaz, a quantum physics PhD candidate at Macquarie University.

From Viral Plasma to Quantum Innovation

The research builds on viral social media videos showing grapes creating plasma — glowing balls of electrically charged particles — in microwave ovens.

While previous studies focused on electric fields, the Macquarie team examined magnetic field effects crucial for quantum applications.

The team used specialized nano-diamonds containing nitrogen-vacancy centers — atomic-scale defects that act as quantum sensors. These defects (one of the many defects giving diamonds their color), behave like tiny magnets and can detect magnetic fields.

“Pure diamonds are colorless, but when certain atoms replace the carbon atoms, they can form so-called ‘defect’ centers with optical properties,” says study co-author Dr Sarath Raman Nair, who is a lecturer in quantum technology at Macquarie University.

“The nitrogen-vacancy centers in the nanodiamonds we used in this study act like tiny magnets that we can use for quantum sensing,” he says.

Grapes as Quantum Tools

The team placed their quantum sensor — a diamond containing special atoms — on the tip of a thin glass fiber and positioned it between two grapes. By shining green laser light through the fiber, they could make these atoms glow red. The brightness of this red glow revealed the strength of the microwave field around the grapes.

“Using this technique, we found the magnetic field of the microwave radiation becomes twice as strong when we add the grapes,” says Fawaz.

Implications for Quantum Technology Miniaturization

Senior author Professor Thomas Volz, who heads the Quantum Materials and Applications Group at Macquarie’s School of Mathematical and Physical Sciences, says the findings unlock exciting possibilities for quantum technology miniaturization.

“This research opens up another avenue for exploring alternative microwave resonator designs for quantum technologies, potentially leading to more compact and efficient quantum sensing devices,” he says.

Why Grapes Work: The Role of Water and Size

The size and shape of the grapes proved crucial to the experiment’s success. The team’s experiments relied on precisely sized grapes — each approximately 27 millimeters long — to concentrate microwave energy at approximately the right frequency of the diamond quantum sensor.

Quantum sensing devices traditionally use sapphire for this purpose. However, the Macquarie team theorized that water might work even better. This made grapes, which are mostly water enclosed in a thin skin, perfect for testing their theory.

“Water is actually better than sapphire at concentrating microwave energy, but it’s also less stable and loses more energy in the process. That’s our key challenge to solve,” says Fawaz.

Future Innovations Inspired by Grapes

Looking beyond grapes, the researchers are now developing more reliable materials that could harness water’s unique properties, bringing us closer to more efficient sensing devices.

Reference: “Coupling nitrogen-vacancy center spins in diamond to a grape dimer” by Ali Fawaz, Sarath Raman Nair and Thomas Volz, 19 December 2024, Physical Review Applied.
DOI: 10.1103/PhysRevApplied.22.064078

The work was supported by the Australian Research Council Centre of Excellence for Engineered Quantum Systems.

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