Grapes improve performance and precision of quantum sensors

Grapes, the simple supermarket staple, have become an unexpected tool in advancing quantum technology. Researchers from Macquarie University have demonstrated that pairing grapes in a microwave oven can create localized magnetic field hotspots.

This phenomenon, previously known for its viral plasma-sparking effect, is now paving the way for more compact and efficient quantum sensing devices.

The sparks observed between two grapes in a microwave are caused by plasma—a glowing state of electrically charged particles. The plasma effect arises from a phenomenon called morphological-dependent resonances (MDRs).

These resonances occur due to the unique shape and high-water content of grapes, enabling them to act as miniature microwave resonators. While earlier studies primarily examined the electric fields that drive this plasma formation, the Macquarie team has shifted focus to explore the magnetic field effects essential for quantum sensing.

The study, published in Physical Review Applied, highlights how grape pairs can enhance magnetic fields. This discovery has far-reaching implications for quantum technologies, where precise control of magnetic fields is critical.

“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 Ali Fawaz, the study’s lead author and a quantum physics PhD candidate at Macquarie University.

The team employed nitrogen-vacancy (NV) centres in nanodiamonds to investigate the magnetic fields around grapes. NV centres are atomic-scale defects within diamonds that act as quantum sensors. These defects, which give diamonds their color, behave like tiny magnets capable of detecting magnetic fields.

“The nitrogen-vacancy centres in the nanodiamonds we used in this study act like tiny magnets that we can use for quantum sensing,” adds Dr. Sarath Raman Nair, a co-author and lecturer in quantum technology at Macquarie University.

The experimental setup involved placing a nanodiamond quantum sensor between two grapes. By shining green laser light through a glass fiber onto the sensor, the researchers could measure the strength of the microwave field around the grapes. The results were remarkable: the magnetic field doubled in intensity when the grapes were added.

Microwave resonators are vital in quantum technologies, enabling precise control of embedded quantum systems like spin qubits or superconducting qubits. Traditionally, materials such as sapphire have been used to confine microwave fields. However, the Macquarie team hypothesized that water, which constitutes the majority of a grape’s interior, could perform this function even better.

“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,” Fawaz notes. Grapes, with their high water content enclosed by a thin skin, provided the perfect test case for this theory.

The size and shape of the grapes played a crucial role in the experiment. Each grape measured approximately 27 millimeters in length, ensuring the microwave energy concentrated at the frequency needed for the diamond quantum sensor.

By combining finite-element modeling and optically detected magnetic resonance (ODMR) measurements, the researchers confirmed that the magnetic hotspots formed between the grapes enhanced the coupling to the quantum sensor by a factor of two.

The team’s breakthrough hinges on understanding how grape dimers create intense microwave hotspots. These hotspots are generated by the interaction of microwave fields with the high permittivity and curvature of the grapes, leading to a strong evanescent field in the gap between them. This localized enhancement provides an efficient means of driving quantum systems, such as the NV centres in nanodiamonds.

NV centres are highly sensitive to magnetic fields and have been widely used for detecting temperature, pressure, and even dark matter. Their intrinsic coherence time—the duration for which quantum information remains intact—can reach millisecond timescales, even at room temperature.

The ability to optically probe these quantum systems with green light makes them ideal for integration into unconventional resonator designs, such as grape dimers.

“Using this technique, we found the magnetic field of the microwave radiation becomes twice as strong when we add the grapes,” Fawaz says. This amplification opens up exciting possibilities for creating compact, cost-effective quantum devices.

The study’s findings not only validate previous work on microwave resonator geometries but also introduce an innovative pathway for designing alternative resonators for quantum applications.

Senior author Professor Thomas Volz, head of the Quantum Materials and Applications Group at Macquarie University, emphasizes the potential impact: “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.”

While grapes provided an accessible and effective medium for this proof-of-concept study, they are not without limitations. The high water content of grapes, while excellent for concentrating microwave energy, also results in higher energy losses compared to more stable materials like sapphire. Addressing these challenges is a critical next step.

“Looking beyond grapes, we are now developing more reliable materials that could harness water’s unique properties,” Fawaz explains. These advancements could bridge the gap between the theoretical benefits of water-based resonators and their practical applications in quantum sensing devices.

The work conducted by the Macquarie team underscores the untapped potential of everyday materials in advancing cutting-edge technology. By leveraging the unique properties of grapes, researchers have uncovered a novel approach to enhancing quantum sensor performance.

This finding not only broadens the scope of quantum technology research but also underscores the creative thinking that drives scientific innovation.

Supported by the Australian Research Council Centre of Excellence for Engineered Quantum Systems, this study exemplifies how interdisciplinary research can transform simple phenomena into groundbreaking technological solutions.

As the quest for more compact and efficient quantum devices continues, the lessons learned from grapes may guide future developments in quantum materials and applications.

Note: Materials provided above by The Brighter Side of News. Content may be edited for style and length.

Like these kind of feel good stories? Get The Brighter Side of News’ newsletter.

The post Grapes improve performance and precision of quantum sensors appeared first on The Brighter Side of News.