Quantum mechanics deals with the behavior of the universe on a super small scale: atoms and subatomic particles that function in ways that classical physics cannot explain. To explore this tension between the quantum and the classical, scientists are trying to get larger and larger objects to behave in a quantum-like manner.
In the case of this particular study, it is a tiny glass nanospheres with a diameter of 100 nanometers – about a thousand times smaller than the thickness of a human hair. In our opinion this is very, very small, but in terms of quantum physics, it is actually quite large, made up of up to 10 million atoms.
Pushing such a nanosphere into the realm of quantum mechanics is actually a huge achievement, and yet this is exactly what the physicists have now succeeded in doing.
Using carefully calibrated laser lights, the nanosphere was suspended in its lowest quantum mechanical state, a state of extremely limited motion in which quantum behavior can begin.
“This is the first time that such a method is used to control the quantum state of a macroscopic object in free space,” says Lukas Novotny, Professor of Photonics at the ETH Zurich in Switzerland.
In order to reach quantum states, movement and energy have to be chosen all the way down. Novotny and colleagues used a vacuum container that had cooled to -269 degrees Celsius (-452 degrees Fahrenheit) before using a feedback system to make further adjustments.
From the interference patterns of two laser beams, the researchers calculated the exact position of the nanospheres in their chamber – and from there the precise settings required to bring the movement of the object close to zero with the help of the electric field generated by two electrodes.
It’s not much different than slowing down a playground swing by pushing and pulling it until it comes to a rest point. As soon as this lowest quantum mechanical state is reached, further experiments can begin.
“To see quantum effects clearly, the nanosphere has to be slowed down … down to its basic state of motion”, says electrical engineer Felix Tebbenjohanns, from ETH Zurich.
“That means that we freeze the kinetic energy of the ball to a minimum, which is close to the quantum mechanical zero point movement.”
While similar results have been obtained before, they used what is known as An optical resonator to balance objects with light.
The approach used here better protects the nanosphere from interference and allows the object to be viewed in isolation after the laser is switched off – which, however, requires much more research.
The researchers hope that their results can be useful in studying how elementary particles behave like waves through quantum mechanics. It’s possible that super-sensitive setups like this nanosphere could also help develop next-generation sensors that go beyond anything we have today.
To manage to levitate such a large sphere in a cryogenic environment represents a significant leap towards the macroscopic scale, in which the boundary between the classical and the quantum can be examined.
“Coupled with the fact that the optical capture potential is highly controllable, our experimental platform offers a way to study quantum mechanics on macroscopic scales,” the researchers conclude in their published paper.
The study was published in nature.