Imagine a diamond.
You probably thought of a clear and flawless gemstone used in jewellery. But to a physicist, a perfect diamond might actually be quite boring. Something magical happens when the diamond is just a little broken.
For decades, scientists have been fascinated by a specific type of defect in the diamond crystal lattice called the nitrogen-vacancy (NV) centre. All diamonds are made of a rigid grid of carbon atoms. An NV centre occurs when one carbon atom is replaced by a nitrogen atom, and the spot next to it is left empty.
This seeming blemish turns the diamond into a powerhouse for quantum technologies.
Magnetic arrows
The NV centre is often called a ‘perfect defect’ because it behaves like a single atom trapped in a solid cage. This structure gives it some remarkable abilities that hold great potential to transform how we think about computers and sensors.
The NV centre has a property called spin. Think of it as a small magnetic arrow. Because the NV centre is trapped inside the diamond structure, it’s shielded from much of the noise that would otherwise scramble its spin. This helps the spin stay coherent, or quantummy, for longer.
This is useful because scientists can then measure how the spin’s internal energy levels respond to the environment, including very weak magnetic or electric fields.
This is why NV centres are some of the world’s smallest and most precise sensors. And scientists have been using them to map the magnetic fields associated with brain activity and to detect microscopic cracks in metals.
Most quantum experiments require large, heavy, and expensive refrigerators to cool atoms down to near absolute zero (-273 ºC). If an environment becomes too warm, the quantum effects disappear in a chaotic mess because they’re sensitive to stray amounts of energy.
But NV centres are special because their rigid diamond cage protects them. They can hold onto their quantum state even at room temperature. This makes them much more practical for real-world devices, like portable medical scanners and navigation systems that don’t need GPS.
Trillions of centres
One of the most useful traits of the NV centre is the way it interacts with light.
If you shine a green laser on it, the centre will glow red. The brightness of the red glow will change depending on the state of its spin. This allows scientists to ‘read’ the quantum information stored in the diamond just by looking at how much light it emits. It’s a bridge between the invisible world of quantum mechanics and the visible world we live in.
While NV centres are amazing on their own, matters become complicated when you pack millions of them together. Usually, when these quantum spins are too close to one another, they start interacting in messy ways. They push and pull on each other, creating noise that destroys the quantum signal. This is generally seen as a problem to be fixed.
However, a study published in Nature Physics on January 2 has turned this problem on its head. A team of researchers from Austria and Japan has reported a way to use these messy interactions to create a powerful and continuous beam of microwave light.
A diamond maser
The researchers took a diamond packed with about 9 trillion NV centres and placed it inside a superconducting microwave cavity — a device that traps microwaves so they can bounce back and forth and build up, like sound echoing in a room.
Then they used a microwave pulse to energise, or invert, the spins of the NV centres. In a standard experiment, the NV centers would release this energy as a quick, bright burst of microwave light called superradiance and then stop.
After the initial burst, however, the system didn’t stop in the experiment. Instead, it started pulsing again, eventually settling into a continuous, steady emission of microwave light for up to one millisecond. In the world of quantum physics, a millisecond is a very long time.
The team had effectively created a maser. You’ve probably heard of a laser, an acronym for ‘light amplification by stimulated emission of radiation’. A maser is the same thing but for microwave radiation instead of visible light.
Bucket brigade
The researchers discovered that the very thing usually considered a nuisance, the interaction between the spins, was actually powering this maser.
“This discovery changes how we think about the quantum world,” Okinawa Institute’s director of the Center for Quantum Technologies and study coauthor Kae Nemoto said in a statement. “We’ve shown that the very interactions once thought to disrupt quantum behavior can instead be harnessed to create it. That shift opens entirely new directions for quantum technologies.”
When the first group of NV centers released their energy into the cavity, they became de-excited, or tired. Usually, that would be the end of the show. But because the diamond was so dense, these tired spins were surrounded by other energetic spins that weren’t quite tuned to the cavity’s frequency.
Through magnetic dipole-dipole interactions, essentially magnets pushing on magnets, the energetic spins passed their energy to the tired spins. This process re-filled the energy hole left behind by the first burst.
It was like the bucket brigade firefighting technique, where neighbouring spins handed off their energy to the spins that could release it as light.
Potential benefits
The finding could lead to the development of highly stable superradiant masers with a very narrow linewidth, meaning the frequency of the light is extremely pure.
“The principles we observe here could also enhance quantum sensors capable of detecting minute changes in magnetic or electric fields,” Jörg Schmiedmayer of the Vienna Center for Quantum Science and Technology, TU Wien, and study coauthor said in the release.
“Such advances could benefit medical imaging, materials science, and environmental monitoring.”
mukunth.v@thehindu.co.in
Published – January 07, 2026 09:00 am IST
