Physicists Lift the Nanosphere of Glass, Pushing It into the Realm of Quantum Mechanics

Quantum mechanics deals with the behavior of the Universe on a super -small scale: atoms and subatomic particles operate in ways that classical physics cannot explain. To explore the tension between quantum and classical, scientists seek to get larger and larger objects to behave in a quantum -like way.

In the case of this particular study, the object in question was a small glass nanosphere, 100 nanometers in diameter – about a thousand times smaller than the thickness of a human hair. In our minds it’s very, very small, but in terms of quantum physics, it’s actually quite large, made up of up to 10 million atoms.

Pushing such nanospheres into the world of quantum mechanics is actually a huge achievement, yet that is what physicists have achieved now.

Using a carefully calibrated laser light, the nanosphere is suspended in the lowest quantum mechanical state, one of the very limited motions in which quantum behavior can begin to occur.

“This is the first time such a method has been used to handle the quantum state of macroscopic objects in free space,” said Lukas Novotny, a professor of photonics from ETH Zurich in Switzerland.

To achieve the quantum state, movement and energy must be dialed down. Novotny and his colleagues used a vacuum container cooled to -269 degrees Celsius (-452 degrees Fahrenheit) before using the feedback system to make further adjustments.

Using the interference pattern produced by the two laser beams, the researchers calculated the exact position of the nanosphere in its space – and from there precise adjustments were needed to bring the object’s motion closer to zero, using an electric field created by two electrodes.

Not all that different is slowing down a playground swing by pushing and pulling it all the way to a resting place. Once the lowest quantum mechanical state is reached, further experiments can be started.

“To see the quantum effect clearly, the nanosphere needs to be slowed … to the ground state of its motion,” said electrical engineer Felix Tebbenjohanns, of ETH Zurich.

“This means that we freeze the motion energy of the ball to a minimum level close to the quantum mechanical zero point motion.”

Although similar results have been achieved before, they use what are known as optical resonators to balance objects using light.

The approach used here better protects the nanosphere from interference, and means objects can be seen separately after the laser is turned off – although that requires a lot of further research to be realized.

One way the researchers hope their findings can be useful is by studying how quantum mechanics causes elemental particles to behave like waves. It is possible that highly sensitive preparations such as these nanosphere could also assist in the development of next -generation sensors beyond what we have now.

Managing such a large sphere in a cryogenic environment is a significant leap toward a macroscopic scale where the line between classical and quantum can be learned.

“Along with the fact that the potential of optical traps is highly controllable, our experimental platform offers a way to investigate quantum mechanics at a macroscopic scale,” the researchers concluded in their published paper.

This research was published in Nature.

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