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The intriguing rules of quantum physics almost always fail when you move from atoms and molecules to much larger objects at high temperatures.
This is because the bigger an object gets and higher the temperature is, the harder it becomes to stop it from interacting with surroundings, a phenomenon that usually erases the delicate quantum behavior.
However, a new study has managed something that seriously pushes these limits. The research has shown that a tiny glass sphere—still over a thousand times smaller than a grain of sand but huge by quantum standards—can have its rotational motion cooled down to almost the quietest state allowed by quantum physics at about 92% purity, even while the particle itself is burning hot at several hundred degrees.
This is the first time scientists have reached such a pure quantum state without having to chill the entire object to near absolute zero, opening doors to experiments once thought impossible outside of deep-freeze labs.
“The purity reached by our room-temperature experiment exceeds the performance offered by mechanically clamped oscillators in a cryogenic environment, establishing a platform for high-purity quantum optomechanics at room temperature,” the study authors note.
A clever shortcut targeting object’s specific motion
Normally, to see quantum behavior in an object larger than a molecule, researchers have to go to extremes: levitating the particle in a vacuum to shield it from outside interference, and cooling its surroundings to near -273.15°C so its motion becomes as orderly as quantum rules allow.
Even then, it’s tricky. This is because motion in the quantum world is quantized—it can only happen in specific chunks called vibration quanta. There is a lowest-energy mode called the ground state, a first excited state with a little more energy, and so on.
Though the particle can exist in a mix of these states. Reaching the ground state for a large particle has been a milestone goal. Until now, it required cooling everything to frigid extremes.
The study authors took a clever shortcut. Instead of trying to chill the particle’s entire internal energy (which is massive compared to the energy of its motion), they targeted just one specific motion: its rotation.
Controlling laser light, mirror systems to drain rotational energy
The researchers used a nanoparticle shaped not as a perfect sphere, but as a slightly stretched ellipse. When trapped in an electromagnetic field, such a particle naturally rotates around a fixed alignment, like a compass needle wobbling around north.
By precisely controlling laser light and mirror systems, forming a high-finesse optical cavity, the team could influence this wobble. The trick here is that the laser can either feed energy into the rotation or take energy away from it.
By carefully adjusting the mirrors so that energy removal was far more likely than energy addition, scientists drained almost all the rotational energy away. While doing so, they also had to account for and control quantum noise from the lasers, random fluctuations that could otherwise ruin the delicate process.
This resulted in a rotational motion freezing into a state extremely close to the quantum ground state, with just 0.04 quanta of residual energy and about 92% quantum purity, even though the particle’s internal temperature was still hundreds of degrees Celsius.
The key to making quantum systems more practical
This result breaks a long-standing barrier in quantum research. It shows that one does not have to cool an entire object to ultra-low temperatures to study its quantum properties.
Instead, by treating different types of motion, like rotation, separately, one can selectively bring parts of a system into the quantum regime while the rest remains hot and messy.
This approach could make it much easier to explore quantum effects in bigger, more complex systems—from biological structures to engineered devices—without requiring massive cryogenic setups.
However, the work focused on one specific motion in a carefully chosen nanoparticle. Hence, it is not yet an universal recipe for every large object. Future research will likely explore whether the same principles can control other motions or work with different shapes and materials.
The study has been published in the journal Nature Physics.
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