If you roll a ball onto a table, it will eventually stop, because friction and gravity will act upon it. That’s classical physics at human scale level. But at an atomic level, where quantum physics acts, nothing is at rest. There are tiny vibrations, or quantum vibrations, sometimes called quantum noise that is caused by atomic scale forces.
This quantum noise was observed and even controlled by a team of researchers from Caltech University and their collaborators. Professor Keith Schwab, head of the research team at Caltech, designed a detector consisting of an aluminum plate on top of a silicone substrate, a few micrometers wide, which is visible with an optical microscope.
This plate is connected to a superconducting electrical circuit which vibrates it at 3.5 million times per second. According to the laws of classical mechanics, this plate should eventually stop, after some vibrating time, especially when the researchers cooled it off to -273.14 degrees Celsius or -459.65 degrees Fahrenheit.
But they discovered that even at that temperature, the plate still manifested extremely tiny vibrations – quantum vibrations, or quantum noise. “This energy is part of the quantum description of nature—you just can’t get it out,” says Schwab. “We all know, quantum mechanics explains precisely why electrons behave weirdly. Here, we’re applying quantum physics to something that is relatively big, a device that you can see under an optical microscope, and we’re seeing the quantum effects in a trillion atoms instead of just one.”
Professor Schwab says quantum noise is a consequence of the Heisenberg Principle, which states that everything behaves like a particle and a wave at the same time. The researchers found that they could also control this quantum noise by applying a controlled microwave field that reduces the vibrations at one end of the plate, but make them larger at the other end.
The ability of controlling quantum vibrations might help physicists detect gravitational waves, a phenomenon caused by the very strong gravitational distortions made by pulsars (fast spinning, super-dense neutron stars). “We’re thinking hard about how to use these techniques on a gram-scale object to reduce quantum noise in detectors, thus increasing the sensitivity to pick up on those gravity waves,” Schwab says. In order to do that, the current device would have to be scaled up.
“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,” added Schwab. The results were published in the online issue of the journal Science.