A remarkable experiment has successfully seen the effects of “quantum motion” at a relatively large scale. These are essentially tiny vibrations caused on an atomic level when an object otherwise appears to be stationary. Among its many implications, the research – which was also able to temporarily stop the effect – could aid the hunt for elusive ripples in space-time called gravitational waves.
The study, published in the journal Science, was carried out by a team of researchers from the California Institute of Technology (Caltech) and collaborators. In classical physics, an object – such as a ball in a bowl – will eventually come to rest as the forces of gravity and friction act upon it. But in quantum mechanics, which governs the behavior of matter and light at an atomic scale, nothing is ever truly at rest.
This means that everything has an extremely small quantum noise, or motion; tiny vibrations at an atomic scale. In this experiment, the researchers were able to observe the effect not just at an atomic level, but at a larger micrometer-scale and, for the first time, control the effect.
To detect it, they placed a flexible aluminum plate on top of a silicon substrate. A superconducting electrical circuit was then used to vibrate the plate at 3.5 million times per second. Subsequently cooling the plate to 0.01 Kelvin (-273.14°C, -459.65°F) reduced the vibrations in a classical sense to zero, but probing it with microwave fields showed a small quantum motion – roughly the diameter of a proton, or 10,000 times smaller than a hydrogen atom.
“What we have found is that the motion of a micron scale object requires a quantum description,” co-author Keith Schwab from Caltech told IFLScience. “Classical physics just can’t capture the quantum noise we see.”
The technique could detect gravitational waves from powerful events like merging stars, illustrated. GSFC/D. Berry
According to Schwab, the noise is an “unavoidable consequence of the Heisenberg Uncertainty Principle,” which essentially states that everything behaves like a particle and a wave at the same time. However, the team found that by carefully applying a controlled microwave field, they could reduce the motion in certain places, at the cost of making it much larger elsewhere. This technique is known as quantum squeezing.
One of the most intriguing areas that this research might be useful is in detecting gravitational waves. These ripples in space-time are thought to be caused by intense gravitational events, such as spinning neutron stars called pulsars, with a nearly perfect regularity. But they are yet to be detected, with instruments such as the Laser Interferometer Gravitational-Wave Observatory (LIGO) unsuccessful so far.
If the device in this research can be scaled up, though, it could be used to detect these ripples in space-time coming from across the universe. “Our work aims to detect quantum mechanics at bigger and bigger scales, and one day, our hope is that this will eventually start touching on something as big as gravitational waves,” Schwab said in a statement.