A new experiment conducted at the University of Oxford has created a photonic Maxwell's demon for the first time ever. Maxwell's demon is a hypothetical being that violates the second law of thermodynamics and has been extensively studied since its proposal by James Maxwell in 1867, although these studies were only theoretical. The new study uses a photonic circuit to show that measurements made on two light beams can be used to create an energy imbalance between them, and this imbalance 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.
The original thought experiment proposed that a demon stands between two boxes of gas particles. Although the average energy or speed of gas molecules in each box is the same, the demon has the ability to open a tiny door in the wall between the boxes, measure the energy of each of the gas particles that makes their way toward the door and selectively restrict the passage of particles. As time goes by, one box gains a higher energy than the other, creating a pressure difference - the pushing force created from this difference can be used to do work.
During the course of this experiment, it seems as though the demon has gained work from the system, despite the fact that it was initially in equilibrium at a single temperature, which violates the second law of thermodynamics.
In the new photonic version of the experiment, the team replaced the boxes of gas particles with two light pulses. The demon was created using a photodetector to measure the number of photons from each pulse and a feed-forward operation to open the door and selectively restrict the passage of light beams. Each beam falls onto a different photodiode, which create electric current that makes its way to a capacitor but from opposing directions. With equal pulse energies, the beams would cancel out, but due to the imbalance in the energy of the pulses, a photoelectric charge is created and this leads to the charging of the capacitor.
Although the researchers did not try and gain any significant amount of work from the experiment, Maxwell's demon could be used for practical applications in the 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 findings were published in the Feb. 5 issue of Physical Review Letters.