Machine Design

Uncertainty Principle's "big" test

A well-known quantum-mechanical theory called the Heisenberg Uncertainty Principle limits the precision of simultaneous position and velocity measurements of a particle at ever-smaller scales.

A scanning electron microscope image of an aluminum and silicon nitride resonator coupled to a superconducting single electron transistor (SSET).

Now, a resonator circuit from researchers at Cornell University closely approaches this theoretical limit, but on an unprecedented large scale.

The resonator consists of an 8.7- m long X 200-nm wide sliver of aluminum, equivalent to roughly 10,000 billion atoms, vastly larger than the elementary particles about which Heisenberg theorized. The sliver rigidly mounts at both ends on a silicon-nitride substrate while the middle is free to vibrate. Positioned nearby is a superconducting single-electron transistor (SSET) that detects sliver vibration.

As postulated by Heisenberg, just the act of observing resonator vibration with the SSET charges the vibrational qualities of the resonator, a phenomenon called quantum back action. Further, the application of certain voltages lowers device temperature through a mechanism akin to optical or Doppler cooling, a process by which red laser light cools atomic vapor. This is the first time the phenomenon has been observed in condensed matter, however.

The group is also attempting to quantify the size of the superposition principle envelope. The superposition principle supposes that a particle can simultaneously exist in two places. The goal, say researchers, is to observe superposition in particles, then scale up to larger devices until the theory breaks down. Potential applications for the research include quantum computing and cooling.

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