Physicists Elevate a Glass Nanosphere Into Quantum Mechanics

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Physicists Elevate a Glass Nanosphere Into Quantum Mechanics

Quantum mechanics is concerned with the behavior of the Universe on an ultra-small scale: with atoms and subatomic particles that behave in ways that classical physics cannot account for. To investigate this tension between quantum and classical mechanics, scientists are seeking to make larger and larger objects act quantum-like.

In this investigation, the object is a tiny glass nanosphere with a diameter of 100 nanometers – roughly a thousand times smaller than the thickness of a human hair. To our brains, that appears to be a very small object, but in terms of quantum mechanics, it is actually quite large, consisting of up to ten million atoms.

Pushing a nanosphere into the domain of quantum mechanics is a significant accomplishment, and yet that is precisely what physicists have done.

The nanosphere was suspended in its lowest quantum mechanical state using precisely calibrated laser light, a state of extremely limited mobility in which quantum behavior can begin to occur.

“This is the first time that such a method has been used to control the quantum state of a macroscopic object in free space,” says Lukas Novotny, a photonics professor at the Swiss Federal Institute of Technology in Zurich.

Quantum states require extreme restraints on movement and energy. Novotny and his colleagues used a vacuum container that had been cooled to -269 degrees Celsius (-452 degrees Fahrenheit) before making further changes via a feedback mechanism.

The researchers estimated the precise position of the nanosphere inside its chamber using the interference patterns made by two laser beams – and from there, the precise changes required to make the object’s movement near to zero using the electrical field created by two electrodes.

It is similar to slowing down a playground swing by pushing and pulling until it reaches a resting position. After reaching the lowest quantum mechanical state, further experiments can commence.

“To clearly see quantum effects the nanosphere needs to be slowed down… all the way to its motional ground state,” explains ETH Zurich electrical expert Felix Tebbenjohanns.

“This means that we freeze the motional energy of the sphere to a minimum that is close to the quantum mechanical zero-​point motion.”

While identical results have been obtained previously, they did it by utilizing what is known as an optical resonator to balance things by light.

The technique taken here safeguards the nanosphere from disruptions and enables viewing of the object in isolation after the laser is turned off – but this will require significant additional investigation.

The researchers intend to utilize their discoveries to further their understanding of how quantum physics drives elementary particles to act like waves. It is likely that ultrasensitive setups like this nanosphere one will aid in the creation of next-generation sensors far superior to anything currently available.

Levitating such a big sphere in a cryogenic environment constitutes a significant step toward the macroscopic scale, where the boundary between classical and quantum mechanics can be explored.

“Together with the fact that the optical trapping potential is highly controllable, our experimental platform offers a route to investigating quantum mechanics at macroscopic scales,” the researchers conclude in their published paper.

The study was published in Nature.

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