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For The First Time Physicists Create Maxwell's Demon In Photonic Circuit

Update Date: Feb 15, 2016 02:15 AM EST
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A photonic Maxwell's demon has been created for the first time ever, through a new experiment at the University of Oxford.

Maxwell's demon is a hypothetical being violating the second law of thermodynamics. It was proposed by James Maxwell in 1867, but the study since then on the concept was just theoretical.

The new study has been conducted with a photonic circuit, showing that measurements on a couple of light beams can construct an energy imbalance, which can be used to extract work.

"Our work shows how photonics can be used as a platform to investigate the relation between energy and information," Oscar Dahlsten, co-author of the study, said in a press release.

In the original thought experiment, it was proposed that there was a demon between two boxes of gas particles. Even though the average energy or speed of gas molecules in either box is the same, the demon can open a tiny door in the wall in between, assess the energy of the gas particles and restrain the particles. With time, one box gets higher energy and makes for a pressure difference, even as the pushing force created due to the difference can be harnessed to perform the work.

In the experiment, it looked like the demon gained work, although it was in equilibrium at a single temperature, violating the second law of thermodynamics.

The novel photonic version had the boxes of gas particles replaced with a couple of light pulses. With a photodetector, the team created the demon to measure the photons from either pulse and use a feed-forward operation in order to open the door and limit the passage of light beams falling onto a different photodiode. It created an electric current making its way to a capacitor, though from opposing directions.

The beams would cancel out with equal pulse energies. With the imbalance in the energy, there is the creation of a photoelectric charge, leading to the charging of the capacitor.

It is exciting to think of using Maxwell's demon for practical energy applications, sometime in future.

"Often we have more information available than thermodynamics supposes," Dahlsten said. "We can then use demon setups such as this one to extract work, making use of that information. Similarly, we can use extra information to reduce work costs of, for example, cooling systems. Personally, I think that sort of technology will have a real impact on meeting the energy challenge facing the world."

The study was published in Feb. 5,2016 issue of Physical Review Letters.

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