Belle Dumas, PhysicsWeb (translation: Dikla Oren)
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A new experiment in the United States has come close to discovering quantum effects in macroscopic bone. Keith Schwab and his colleagues from the National Security Agency (National Security Agency), working at the University of Maryland, measured the vibrations of a tiny nanoelectromechanical arm. They did this with the aim of exploring the limits where quantum behavior disappears and classical physics takes the reins. Although the experiment was not sensitive enough to test the uncertainty principle, it came closer than previous attempts.
The uncertainty principle states that we cannot know the position and speed of a particle at the same time with absolute certainty. The principle is used to describe the movement of particles at the atomic level, but its action has not been seen so far in macroscopic objects. The behavior of these is described by classical physics.
To find out whether the effects of the uncertainty principle are felt in the macroscopic world, Schwab and his colleagues studied the movement of a vibrating mechanical arm made of silicon nitride. The arm, whose size amounts to eight microns (eight millionths of a meter), is considered tiny on an everyday scale, but it is still a macroscopic object (its mass is about 12/10 the mass of hydrogen atoms).
The researchers positioned the arm at a distance of about six hundred microns from a single electron transistor - used as a motion detector - and connected the two through a capacitor. Then they applied voltage, which caused the arm to oscillate, and cooled the experimental system to a temperature of a few milli degrees Kelvin. Cooling the system to such low temperatures has reduced the thermal vibrations to near the point where only quantum "zero point" oscillations remain. The movement of the zero point results from the uncertainty principle, which prevents the arm from being completely at rest.
As the arm moved toward the detector and back the other way, the current flowing through the transistor changed. Measuring the current allowed the physicists to measure the arm's spin with a sensitivity that is only 4.3 times greater than the amplitude of the quantum zero-point oscillations.
The physicists from the National Security Agency intend to increase the sensitivity of the detector and continue to reduce the thermal fluctuations of the arm. They also hope to expand their research to larger objects. "These experiments address a great mystery in physics: where does the quantum world end and the classical world begin?" Schwab told Physics Web. "Success in manipulating the quantum state of a mechanical device will raise the possibility, because there is no limit, and it will encourage us to pursue even greater goals."
Schwab said that his team would be interested in utilizing the described system for uses in quantum computing.
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