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Our work has shown the first experimental substantiation of gravitons in condensed matter since the elusive particle was conceptualised in the 1930s, the studys lead author Du Lingjie from Nanjing University told state news agency Xinhua on Thursday.

The graviton is a bridge connecting quantum mechanics and general relativity theory. If confirmed, it will have huge implications for modern physics research, he said.

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The study was highly collaborative, according to the paper. Researchers at Princeton University prepared high-quality semiconductor samples, while the experiment was carried out at a unique facility that took Du and his team three years to build.

In Albert Einsteins theory of general relativity, he described gravity as space-time distortions caused by mass and energy.

Such a theory, which explains gravity beautifully at a large scale, poses challenges in quantum mechanics, which governs the universe at the smallest scale.

As a result, the graviton was proposed as a particle dedicated to carrying gravity. If it existed, a graviton should be massless and travel at the speed of light except that, so far, gravitons have never been observed in space.

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When Du was a postdoctoral researcher at Columbia University in 2019, his team discovered a special excitation phenomenon in quantum materials that led theoretical physicists to think it could point to the detection of gravitons.

However, the requirements for conducting such experiments were high. The system needed to be placed in a powerful refrigerator where temperatures are near absolute zero, and exposed to a magnetic field 100,000 times stronger than the Earths average magnetic field.

Some requirements could even appear contradictory. For instance, we have to install windows on the refrigerator to make optical measurements, but the windows can cause the systems temperature to [easily rise], paper co-author Liang Jiehui, of Nanjing University, told Xinhua.

Du spoke to Xinhua about working in the teams home-developed facility. Working at minus 273.1 degrees Celsius, a special microscope like this can capture particle excitations as weak as 10 gigahertz and determine their spin, he said.

The researchers used a flat sheet of gallium arsenide semiconductor, which when subjected to low temperature and a magnetic field showed a phenomenon called the quantum Hall effect.

Electrons in the semiconductor started to interact with each other and moved in a highly organised fashion, like a liquid.

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The team then shone a finely-tuned laser onto the material to study the potential excitation of the electrons. They found the electrons were doing a so-called type-2 quantum spin, which would only exist in gravitons.

They then measured the momentum and energy of the electrons, and confirmed evidence for them to behave in a graviton-like way.

It took us three years to build the experimental device. It was very challenging and we made it, Du said.

We look forward to using it to continue the hunt for gravitons. Hopefully, it will lead to more cutting-edge discoveries at the quantum frontier, Du said.

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Chinese-led team finds first evidence of particles behaving like gravitons - South China Morning Post