G. B. Lesovik, A. V. Lebedev, I. A. Sadovskyy, M. V. Suslov & V. M. VinokurDOWNLOAD THE FULL RESEARCH
1. Additional Information, Part I
1.1. Argonne researchers posit way to locally circumvent Second Law of Thermodynamics
For more than a century and a half of physics, the Second Law of Thermodynamics, which states that entropy always increases, has been as close to inviolable as any law we know. In this universe, chaos reigns supreme. But researchers with the U.S. Department of Energy’s (DOE’s) Argonne National Laboratory announced recently that they may have discovered a little loophole in this famous maxim. Their research, published in Nature Scientific Reports, lays out a possible avenue to a situation where the Second Law is violated on the microscopic level.
The Second Law is underpinned by what is called the H-theorem, which says that if you open a door between two rooms, one hot and one cold, they will eventually settle into lukewarm equilibrium; the hot room will never end up hotter.
But even in the twentieth century, as our knowledge of quantum mechanics advanced, we didn’t fully understand the fundamental physical origins of the H-theorem.
“What we did was formulate how these beautiful abstract mathematical theories could be connected to our crude reality.”
Recent advancements in a field called quantum information theory offered a mathematical construction in which entropy increases.
“What we did was formulate how these beautiful abstract mathematical theories could be connected to our crude reality,” said Valerii Vinokur, an Argonne Distinguished Fellow and corresponding author on the study.
The scientists took quantum information theory, which is based on abstract mathematical systems, and applied it to condensed matter physics, a well-explored field with many known laws and experiments.
“This allowed us to formulate the quantum H-theorem as it related to things that could be physically observed,” said Ivan Sadovskyy, a joint appointee with Argonne’s Materials Science Division and the Computation Institute and another author on the paper. “It establishes a connection between well-documented quantum physics processes and the theoretical quantum channels that make up quantum information theory.”
The work predicts certain conditions under which the H-theorem might be violated and entropy — in the short term — might actually decrease.
As far back as 1867, physicist James Clerk Maxwell described a hypothetical way to violate the Second Law: if a small theoretical being sat at the door between the hot and cold rooms and only let through particles traveling at a certain speed. This theoretical imp is called “Maxwell’s demon.”
“Although the violation is only on the local scale, the implications are far-reaching,” Vinokur said. “This provides us a platform for the practical realization of a quantum Maxwell’s demon, which could make possible a local quantum perpetual motion machine.”
For example, he said, the principle could be designed into a “refrigerator” which could be cooled remotely — that is, the energy expended to cool it could take place anywhere.
The authors are planning to work closely with a team of experimentalists to design a proof-of-concept system, they said.
The study, “H-theorem in quantum physics,” was published September 12 in Nature Scientific Reports. Other authors on the study were G.B. Lesovik of Russia’s L.D. Landau Institute for Theoretical Physics and Switzerland’s Theoretische Physik; A.V. Lebedev of Theoretische Physik; and M.V. Suslov of the Moscow Institute of Physics and Technology.
The study was supported by the U.S. Department of Energy’s Office of Science, the Swiss National Foundation, the Pauli Center for Theoretical Studies at ETH Zurich and the Russian Foundation for Basic Research.
Argonne National Laboratory seeks solutions to pressing national problems in science and technology. The nation’s first national laboratory, Argonne conducts leading-edge basic and applied scientific research in virtually every scientific discipline. Argonne researchers work closely with researchers from hundreds of companies, universities, and federal, state and municipal agencies to help them solve their specific problems, advance America’s scientific leadership and prepare the nation for a better future. With employees from more than 60 nations, Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy’s Office of Science.
The U.S. Department of Energy’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, visit the Office of Science website.
2. Additional Information, Part II

The second law of thermodynamics states that entropy cannot decrease. In classical physics, this follows from Boltzmann’s H-theorem, which applies to solutions of his kinetic transport equation. There is no quantum analogue of this equation that would allow a quantum H-theorem to be proved. Physicists at Argonne National Laboratory have published in Scientific Reports a quantum version of the H-theorem for systems whose evolution is governed by a unital quantum channel (channels are used in quantum information theory).
There are quantum channels that are not unital. For this reason, these physicists, as well as many media outlets reporting on the finding, suggest that local violations of the second law of thermodynamics may be observable (mediated by quantum Maxwell’s demons). However, the article does not present any concrete example; moreover, the two examples of non-unital channels that it does present comply with the second law. Future studies will have to determine whether such local violations are possible in real physical systems, as well as identify a real example of a quantum Maxwell’s demon.”
The article is G. B. Lesovik, A. V. Lebedev, …, V. M. Vinokur, «H-theorem in quantum physics,» Scientific Reports 6: 32815 (12 Sep 2016), doi: 10.1038/srep32815, arXiv:1407.4437 [quant-ph].

Ludwig Boltzmann’s H-theorem (1872, 1896) is the statistical foundation of the second law of thermodynamics. This theorem states that if is the spatiotemporal distribution of the density of the molecules of an ideal gas at time , at position , and with velocity , then the entropy given by cannot decrease; that is, . To prove this, Boltzmann’s equation for the function f is used under the assumption that the particles colliding in the gas have velocities independent of their positions (the so-called molecular chaos hypothesis). Quantum mechanics, however, relates positions and velocities through Heisenberg’s uncertainty relations.
In 1929, John von Neumann proposed a quantum explanation for the origin of entropy growth. Entropy is defined in terms of the density matrix of quantum mechanics as . It can be shown that this function does not decrease, even without resorting to a kinetic transport equation, by using the measurement procedure of quantum mechanics. Since then, many physicists have attempted to obtain a quantum version of Boltzmann’s H-theorem (a good overview can be found in the book by Jochen Gemmer, Mathias Michel, and Günter Mahler, Quantum Thermodynamics: Emergence of Thermodynamic Behavior Within Composite Quantum Systems, Lecture Notes in Physics, Springer, 2009).

The new article draws on quantum information theory (QIT) and proposes describing the quantum dynamics of a system by means of a quantum channel (QC). In information theory, a (data) channel is the theoretical model of a transmission medium through which information-carrying signals travel from a sender to a receiver. Any quantum system can be interpreted as a (quantum) channel through which information flows. Using quantum channels makes it possible to obtain a quantum formulation of the H-theorem: entropy does not decrease if the evolution of the system is described by a unital quantum channel. The proof presented in the new article applies only to unital channels and makes no claim about non-unital channels.
A quantum channel is a positive, trace-preserving map of the density matrix, denoted ; it is said to be unital if . In general, a quantum channel need not be unital; see, for example, G. G. Amosov, “Estimating the output entropy of a tensor product of two quantum channels,” Theoretical and Mathematical Physics 182: 397–406 (2015), doi: 10.1007/s11232-015-0270-6. The new quantum H-theorem concerns unital channels, but it reaches no conclusion about non-unital ones. The authors of this work suggest that, in a quantum system whose evolution is described by a non-unital quantum channel, entropy might decrease locally and the second law of thermodynamics might therefore fail to hold.
In addition to the mathematical proof of the quantum H-theorem, the article provides three concrete examples of quantum systems modeled by quantum channels. The three figures in this post correspond to each of them. One is unital, while the other two are non-unital. However, in both non-unital systems the second law is still satisfied. As you have read, the article does not present any example of a non-unital channel in which the law is violated, even locally. The authors suggest that such violations may be possible, but they do not provide a demonstration of this claim. This detail appears to have been overlooked by some media outlets reporting on the story.
In short, this is a very interesting article, but one whose interpretation requires great care. Casually claiming that local violations of the second law of thermodynamics may exist in quantum systems is not the same as presenting a concrete example of such a violation. Quantum physics is subtle, and quantum information theory even more so. Claims of this kind should therefore be treated with caution.





