Adrian Chapman and Akimasa Miyake have recently published their paper in Physical Review E, demonstrating that a Maxwell demon can exploit correlations in its memory to enhance its thermodynamic performance over the demon which cannot. In this classic thought experiment, the demon uses information, rather than energy, to perform a thermodynamic task such as refrigeration. One example is realized by a demon who controls the door of a bipartite container filled with gas. Using a microscopic measuring device, the demon allows only faster molecules to one side while allowing only slower molecules to the other, apparently performing cooling for free. Only when one accounts for the inevitable energy cost of erasing the device’s memory does one see that this supposed perpetual motion machine is actually a refrigerator. This fact suggests that information has value in thermodynamics.
In their paper, the authors consider a simple concrete model of physical system, which acts as an autonomous Maxwell demon. In many previous models, the assumption has been that the demon’s information is uncorrelated: its actions at one time do not depend on what it has learned at earlier times. This convenient assumption may neglect some important physics however, especially in a quantum world, where information can be correlated in a “spooky” way. The authors construct a framework for their model in which quantum correlations can be incorporated in full generality and find that correlations can be thermodynamically useful in the same way as energy or uncorrelated information in the original thought experiment. Their framework relies on techniques from condensed matter physics, which are specialized for handling correlations.
Correlated states of knowledge are not the exception, but rather the rule for realistic thermodynamic systems. This research will thus likely cross-fertilize the fields of thermodynamics and condensed matter physics and ignite further such analyses that incorporate correlations.
The full article is available online at http://journals.aps.org/pre/abstract/10.1103/PhysRevE.92.062125.