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Mechanical systems we use daily often require expensive maintenance or replacement because friction caused by physical contact — gears grinding or wheels rubbing against another material — can wear these systems down, causing them to malfunction or work inefficiently.

Maglev, or magnetic levitation train system, e.g. Shanghai Maglev Train and the Chuo Shinkansen in Japan currently under construction, use magnetic force to levitate the whole train in the air from the track which enables a nearly “frictionless” condition for the train to operate. They are much faster than conventional trains which run on a track. The system, however, is costly to build and is energy-intensive in operation.

UC Berkeley researchers led by HKU President Professor Xiang Zhang when he was professor in Berkeley have developed a novel approach to eliminate friction in mechanical systems by harnessing a phenomenon of theoretical quantum physics, known as the Casimir effect.

The Casimir effect is based on the fact that in quantum physics, a vacuum in space isn’t empty. It is filled with fluctuating electromagnetic waves that can’t be completely eliminated.

“Until recently, people thought of the Casimir effect as an attractive force. But for the first time, our work proposed theoretically and demonstrated experimentally a repulsive Casimir force that eventually leads to a stable Casimir trap, without input of extra energy,” said Professor Zhang.

The team successfully trapped a tiny gold flake between gold and Teflon surfaces with no energy input, using tuneable combinations of attractive and repulsive Casimir forces. Measuring the tiny forces involved in the trapping process was a triumph of optical metrology and provides a better understanding of how Casimir forces affect the operation of micromechanical devices.

The discovery paves the way for exploring new forms of non-friction mechanics and quantum mechanical applications, and could result in practical applications such as contact-free nanomachines and ultrasensitive force sensors.

The achievement was selected as one of the top 10 Breakthrough of the Year 2019 research by Physics World, a membership publication of the Institute of Physics (IOP), for being the first to trap tiny objects using the Casimir effect. Other breakthrough research named include the first direct image of a supermassive black hole and Google’s quantum computer outperforms conventional supercomputer.

The discovery was earlier published in leading academic journal Science. (Please click here for UC Berkeley’s full press release of the research in English.)

Based in the UK, IOP is one of the largest physical societies in the world. The Breakthrough of the Year finalists are picked by a highly specilised team of five Physics World editors. They need to meet the criteria of having significant advance in knowledge or understanding and show importance for scientific progress or development of real-world applications.


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Casimir effect creates “quantum trap” for tiny objects

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