Thermodynamics is a losing game. No matter what you do, no system will be able to run without losing energy. One of its most famous paradoxes, “Maxwell’s demon”, has become a symbol of this fight against the tyrannical rules of physics. And now it appears that the demon is also going to be a problem for the future of computing.
Back in 1867, physicist James Clerk Maxwell was trying to think of how the second law of thermodynamics could be violated. His thought experiment starred a being (which became known as a “demon”) in charge of two vessels full of air at different temperatures. If the two are put in contact with each other and isolated from the rest of the universe, they would eventually reach equilibrium and have the same temperature. Here enters the demon.
The connection between the two vessels can be opened and closed. This hypothetical demon has an incredibly sharp sense and can spot both the higher and lower energy molecules. By closing and opening a little door, the demon can keep the system from reaching equilibrium, violating the laws of thermodynamics.
The paradox breaks down the more we question the nature of the demon. Over the years, the essence of this demon has become more like a machine rather than a mystical creature. In particular, there has been a distinct focus on how the information is obtained by the demon and how it is manipulated. In the 20th century, this brought about an important realization. Information must obey the laws of thermodynamics. And this is where computers come in as they do nothing but manipulate information.
Information is not purely abstract, it has a physical connotation. Manipulation of information has a thermodynamic effect. In particular, erasing information releases heat. Our demon doesn’t have to remember all the particles in the system, just those of a certain energy that get close to the door. Once they have passed, he can forget about those. And this simple act of forgetting releases heat. The demon's work in trying to violate the second law is balanced by the demon's memory itself.
This heat release for deleting information is known as Landauer’s limit. Our computers, smartphones, and tablets are still too imperfect to be affected by it, but that doesn’t mean that this isn't going to be a problem in the future.
The limit is tiny but it can be measured, and at the current rate of computer advancement it will be a big problem in 2050. The limitations of regular computing are expected to be solved by quantum computing, but a new paper published in Physical Review Letters shows that the demon’s reach is far greater than expected.
In the work, researchers from Trinity College Dublin have shown that due to the quirks of quantum mechanics, it is perfectly possible that even when an ideal quantum computer is created, the heat released by erasing information is a lot greater than Landauer’s limit.
“We asked: ‘what difference does this distinctly quantum feature make for the erasure protocol?’ And the answer was something we did not expect. We found that even in an ideal erasure protocol – due to quantum superposition – you get very rare events which dissipate heat far greater than the Landauer limit,” senior author Professor John Goold said in a statement.
“In the paper we prove mathematically that these events exist and are a uniquely quantum feature. This is a highly unusual finding that could be really important for heat management on future quantum chips – although there is much more work to be done, in particular in analyzing faster operations and the thermodynamics of other gate implementations.”
The question now is can we swindle the demon long enough to solve this looming issue? Only time will tell.