New Study Shakes A Quantum Bridge

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Back-action can be used to cool quantum objects to extremely low temperatures.

by Staff Writers
UPI Correspondent
Ithaca NY (UPI) Sep 20, 2006
Quantum physicists view what they call "back-action" as a nuisance, but a U.S. study suggests the phenomenon might be put to good use. According to quantum theory, an object cannot be measured without perturbing it; the act of observation delivers a series of "prods" to the object being observed, much like a star deviates from orbit when it passes another object.

That's quantum back-action, and it hinders highly precise measurements. But Keith Schwab and his Cornell University team say back-action can be used to cool quantum objects to extremely low temperatures.

Schwab conducted measurements on a narrow beam of silicon nitride called a nanoresonator. Changes in the position of the beam alter the electrical conductivity of a nearby electronic device called a superconducting single-electron transistor, or SSET. But just making the measurement "shakes" the nanoresonator, because of quantum back-action.

Schwab and colleagues, along with Michael Roukes of the California Institute of Technology, discovered when the SSET voltage corresponds with the quantized energy state of the electrons passing through it, the SSET becomes an absorber, rather than a source, of heat.

That, the scientists say, might be used to produce ultra-cold states of nanoscale mechanical devices.

The study appears in the journal Nature.

Source: United Press International

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