Because quantum motion, or noise, is theoretically an intrinsic part of the motion of all objects, Schwab and his colleagues designed a device that would allow them to observe this noise and then manipulate it. The micrometer-scale device consists of a flexible aluminum plate that sits atop a silicon substrate. Credit: Chan Lei and Keith Schwab/Caltech
For the 1st time, Caltech and other researchers have found a way to observe and control quantum motion of an object that is large enough to see. Even large objects obey quantum physics, ie they are never quite at rest.
In classical physics, physical objects indeed can be motionless. Drop a ball into a bowl, and it will roll back and forth a few times, then gravity and friction will cause the ball to come to a stop.
“In the past couple of years, my group and a couple of other groups around the world have learned how to cool the motion of a small micrometer-scale object to produce this state at the bottom, or the quantum ground state,” says Caltech Professor Keith Schwab. “But we know that even at the quantum ground state, at zero-temperature, very small amplitude fluctuations, or noise–remain.”
METHOD: As this quantum motion, or noise, is theoretically an intrinsic part of the motion of all objects, Schwab et al designed a device that would allow them to observe this noise and then manipulate it. The micrometer-scale device consists of a flexible aluminum plate that sits atop a silicon substrate. The plate is coupled to a superconducting electrical circuit as the plate vibrates at a rate of 3.5M times/ second. According to the laws of classical mechanics, the vibrating structures eventually will come to a complete rest if cooled to the ground state.
RESULTS: When they cooled the spring to the ground state in their experiments the residual energy–quantum noise–remained. Because this noise is always present and cannot be removed, it places a fundamental limit on how precisely one can measure the position of an object.
But that limit is not insurmountable. The researchers and collaborators developed a technique to manipulate the inherent quantum noise and found that it is possible to reduce it periodically.
“There are 2 main variables that describe the noise or movement,” Schwab explains. “We showed that we can actually make the fluctuations of one of the variables smaller at the expense of making the quantum fluctuations of the other variable larger. That is what’s called a quantum squeezed state; we squeezed the noise down in one place, but because of the squeezing, the noise has to squirt out in other places. But as long as those more noisy places aren’t where you’re obtaining a measurement, it doesn’t matter.”
APPS: The ability to control quantum noise could improve the precision of very sensitive measurements, eg for LIGO, the Laser Interferometry Gravitational-wave Observatory, searching for signs of gravitational waves, ripples in the fabric of space-time.”We’ve been thinking a lot about using these methods to detect gravitational waves from pulsars–incredibly dense stars that are the mass of our sun compressed into a 10 km radius and spin at 10 to 100 times a second,” Schwab says. In order to do that, the current device would have to be scaled up. http://www.caltech.edu/news/seeing-quantum-motion-47700
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