Room-Temperature Quantum Breakthrough Stuns Physicists

Scientists have achieved a breakthrough in quantum research by demonstrating that nanoparticles can exhibit quantum rotational vibrations even at room temperature — and without being cooled close to absolute zero.

Using an elliptical nanoparticle held in an electromagnetic field, they applied carefully tuned lasers and mirrors to drain energy from its rotation until it reached almost pure quantum ground state. Surprisingly, the particle itself remained hundreds of degrees hot, yet its rotation “froze” in quantum terms.

Limits of Quantum Physics Explored

What are the boundaries of quantum physics? Scientists around the world have been exploring this question for decades. To make quantum effects useful in technology, researchers must determine whether quantum behavior is possible not only in atoms and molecules, but also in objects much larger than these tiny building blocks of matter.

One example is microscopic glass spheres about one hundred nanometers in diameter. Although each sphere is more than a thousand times smaller than a grain of sand, it is still considered large in the quantum realm. For years, scientists have tried to find out whether particles of this size can retain quantum properties. A team at ETH Zurich, working with theorists from TU Wien (Vienna), has now made a major discovery. They demonstrated that the rotational vibrations of such spheres follow the rules of quantum physics not only when cooled to near absolute zero with highly complex techniques, but also at ordinary room temperature.

Vibration Quanta: Only Certain Wobbles Are Allowed

“A microscopic particle will always wobble a little,” says Carlos Gonzalez-Ballestero from the Institute of Theoretical Physics at TU Wien. “This oscillation depends on the temperature and on how the particle is influenced by its environment.”

In everyday life, any kind of oscillation seems possible. The pendulum of a clock, for instance, can swing to any angle, and you can make it oscillate more strongly or more gently as you wish. The quantum world works differently. At very low energies, oscillations come in specific, discrete amounts known as “oscillation quanta.”

There is a lowest possible vibration, called the “ground state,” followed by a slightly higher vibration with a bit more energy (the “first excited state”), and so on. No states exist between these levels, but a particle can occupy a quantum combination of multiple vibration states at once, a key principle of quantum mechanics.

“It is very difficult to put a nanoparticle into a state where its quantum properties become apparent,” says Carlos Gonzalez-Ballestero. “You have to let the particle float in order to isolate it from any interference as much as possible. And normally you also have to ensure extremely low temperatures, close to absolute zero, which is minus 273.15 degrees Celsius.”

Isolating Quantum Rotation in Hot Particles

ETH Zurich and TU Wien have now developed a technique that allows a very specific aspect of the nanoparticle to be brought into a quantum physical state, even though the particle itself is in a hot, disordered state.

‘We use a nanoparticle that is not perfectly round, but slightly elliptical,’ explains Carlos Gonzalez-Ballestero. “When you hold such a particle in an electromagnetic field, it starts to rotate. Our question was: Can we see the quantum properties of this rotational vibration? Can we extract energy from this rotational movement until it is mainly in the quantum ground state?‘

Laser beams and mirror systems were used for this purpose. ’The laser can either supply energy to the nanoparticle or take energy away from it,” explains Carlos Gonzalez-Ballestero. ‘By adjusting the mirrors in a suitable way, you can ensure that energy is extracted with a high probability and only added with a low probability. The energy of the rotational movement thus decreases until we approach the quantum ground state.’

To achieve this, however, a number of difficult theoretical problems had to be solved – the quantum noise of the lasers had to be correctly understood and controlled.

Achieving Record-Breaking Quantum Purity

Finally, it was actually possible to demonstrate that the rotation can be brought into a state that corresponds almost exclusively to the quantum mechanical ground state. The amazing thing about this is that the nanoparticle has not cooled down – on the contrary, it is actually several hundred degrees hot.

“You have to consider different degrees of freedom separately,” explains Carlos Gonzalez-Ballestero. “This allows the energy of the rotational movement to be reduced very effectively without having to reduce the internal thermal energy of the nanoparticle at the same time. Amazingly, the rotation can freeze, so to speak, even though the particle itself has a high temperature.”

This made it possible to create a state that is significantly ‘purer’ in terms of quantum physics than was previously possible with similar particles – even though cooling was not required. “This is a technically astonishingly practical way of pushing the boundaries of quantum physics,” says Carlos Gonzalez-Ballestero. “We can now study the quantum properties of objects in a stable and reliable way, which was previously hardly possible.”

Reference: “High-purity quantum optomechanics at room temperature” by Lorenzo Dania, Oscar Schmitt Kremer, Johannes Piotrowski, Davide Candoli, Jayadev Vijayan, Oriol Romero-Isart, Carlos Gonzalez-Ballestero, Lukas Novotny and Martin Frimmer, 6 August 2025, Nature Physics.
DOI: 10.1038/s41567-025-02976-9

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