Tuesday, November 16, 2010

Converting information to energy

From Demonic device converts information to energy:
"A paradox put into practice

To create a real-life version of the demon experiment, Sano and his colleagues placed an elongated nanoscale polystyrene bead, which could rotate either clockwise or anticlockwise, into a bath of buffer solution. The team applied a varying voltage around the bead, making it progressively harder for the bead to rotate a full 360 degrees in the anticlockwise direction. This effectively created a "spiral staircase" that was harder to "climb up" in the anticlockwise direction than to "fall down" in the clockwise direction, says Sano.

“This is a beautiful experimental demonstration that information has a thermodynamic content.”
When left alone, the bead was randomly jostled by the surrounding molecules, sometimes being given enough of a push to turn anticlockwise against the voltage — or jump up the stairs — but more often turning clockwise — or going "downstairs". But then the team introduced their version of Maxwell's demon.

They watched the motion of the bead, and when it randomly turned anticlockwise they quickly adjusted the voltage — the equivalent of Maxwell's demon slamming the door shut on a gas molecule — making it tougher for the bead to turn back clockwise. The bead is thus encouraged to keep climbing "upstairs", without any energy being directly imparted to the bead, says Sano.

The experiment does not actually violate the second law of thermodynamics, because in the system as a whole, energy must be consumed by the equipment — and the experimenters — to monitor the bead and switch the voltage as needed. But it does show that information can be used as a medium to transfer energy, says Sano. The bead is driven as a mini-rotor, with a information-to-energy conversion efficiency of 28%."
Preprint Information heat engine: converting information to energy by feedback control and the abstract in Nature Physics Experimental demonstration of information-to-energy conversion and validation of the generalized Jarzynski equality.
P.S. See Using Information to Extract Energy:
"It’s a great result, worth making a fuss about. But some commentators spun it as “converting information into energy.” That’s not quite right — it’s more like “using information to extract energy from a heat bath.”"

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