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June 24, 2009

Nanoscale Might Allow Fairly Efficient Maxwell Demon: Possible Entropy reduction

A recent study has shown that, on the nanoscale, Maxwell’s demon might be able to do its work with much less energy than previously thought due to tiny thermal fluctuations that occur in small systems.

Dillenschneider and Lutz have accounted for the impact of tiny thermal fluctuations on memory erasure in their nanoparticle-based memory system. Through calculations and simulations, they’ve shown that the nanosystem can be erased with an amount of heat that is less than Landauer’s bound. The finding shows that the macroscopic formulation of Landauer’s principle does not hold on nanoscale systems, and should be generalized to include heat fluctuations in a way similar to the second law.

The result also presents the possibility that Maxwell’s demon might not create as much entropy as it reduces, although the exact difference is still unknown. The scientists noted that large fluctuations are suppressed, even in nanoscale systems, in agreement with the macroscopic formulation of Landauer’s principle.

Wikipedia on Maxwell's Demon

Maxwell's demon is a thought experiment, first formulated in 1867 by the Scottish physicist James Clerk Maxwell, meant to encourage questions about the possibility of violating the second law of thermodynamics.

Maxwell imagines one container divided into two parts, A and B. Both parts are filled with the same gas at equal temperatures and placed next to each other. Observing the molecules on both sides, an imaginary demon guards a trapdoor between the two parts. When a faster-than-average molecule from A flies towards the trapdoor, the demon opens it, and the molecule will fly from A to B. The average speed of the molecules in B will have increased while in A they will have slowed down on average. Since average molecular speed corresponds to temperature, the temperature decreases in A and increases in B, contrary to the second law of thermodynamics.





Abstract: Memory Erasure in Small Systems in the Physical Review Letters.

We consider an overdamped nanoparticle in a driven double-well potential as a generic model of an erasable 1-bit memory. We study in detail the statistics of the heat dissipated during an erasure process and show that full erasure may be achieved by dissipating less heat than the Landauer bound. We quantify the occurrence of such events and propose a single-particle experiment to verify our predictions. Our results show that Landauer's principle has to be generalized at the nanoscale to accommodate heat fluctuations.


FURTHER READING
Wikipedia on Entropy

Wikipedia on the Second law of thermodynamics.


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