Maxwell's Demon: Researchers Create New 'Best-in-Class' Information Engine

The researchers said their information engine achieves power 'comparable to molecular machinery.'
Chris Young
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Researchers from Simon Fraser University (SFU) designed an incredibly fast engine that uses a novel and abundant source of fuel — information. Their study, published in Proceedings of the National Academy of Sciences (PNAS), outlines their engine's particular method for converting the movements of microscopic particles into stored energy. 

An information engine, also known as Maxwell's demon, is a machine that detects and reacts to the motions of individual particles in order to, in theory, achieve perpetual motion. It was originally devised by James Clerk Maxwell as a thought experiment in 1871 in order to illustrate the possibility of violating the second law of thermodynamics.

In Maxwell's original thought experiment, an imaginary demon would open a tiny door between two gas chambers, allowing only fast-moving particles into one chamber, and slow-moving particles into the other — thus decreasing the entropy of both gases without applying any work and violating the second law of thermodynamics.

Testing a real-world information engine

Now the technological advancements of the past 150 or so years mean scientists can actually attempt to build a variation of the machine in a bid to test the principles of Maxwell's thought experiment.

"We wanted to find out how fast an information engine can go and how much energy it can extract, so we made one," Bechhoefer, whose experimental group collaborated with theorists led by SFU physics professor David Sivak, explained in a press statement.

"By systematically studying this engine, and choosing the right system characteristics, we have pushed its capabilities over ten times farther than other similar implementations, thus making it the current best-in-class," Sivak continued.

SFU physics professor and senior author of the study John Bechhoefer says their research into information engines might inform the design of future real-world information engines.

Achieving power 'comparable to molecular machinery'

The information engine designed by the SFU researchers utilizes a microscopic particle attached to a spring and immersed in water. This is fixed to a movable stage, with researchers observing the particle bouncing up and down thanks to thermal motions.

When the researchers see an upward bounce, they move the stage in response, essentially acting as Maxwell's imaginary demon. When they see a downward bounce, they wait. 

"This ends up lifting the entire system using only information about the particle’s position," said lead author and PhD student Tushar Saha. Saha also explained that the researchers used an instrument known as an optical trap, which "uses a laser to create a force on the particle that mimics that of the spring and stage."

The researchers say their machine outperforms previous designs — a previous example was devised by a team from UNIST in 2018.

One of the researchers, postdoctoral fellow Jannik Ehrich, said their information machine achieves power comparable to "molecular machinery in living cells, and speeds comparable to fast-swimming bacteria."

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