The experiment reverses the direction of the heat flow

Publicado em 27 junho 2019

Heat flows from hot to cold objects. When a hot and a cold body are in thermal contact, they exchange heat energy until they reach thermal equilibrium, whereby the hot body cools and the cold body heats up. This is a natural phenomenon that we are constantly experiencing.

It is explained by the second law of thermodynamics, which states that the total entropy of an isolated system increases over time until it reaches a maximum. Entropy is a quantitative measure of the disorder in a system. Isolated systems spontaneously develop into increasingly disordered states and lack of differentiation.

An experiment conducted by researchers at the Brazilian Center for Physics Research (CBPF) and the Federal University of ABC (UFABC) and other institutions in Brazil and elsewhere has shown that quantum correlations affect the distribution of entropy to parts in thermal contact and reverse the direction of the so-called "thermodynamic time arrow".

In other words, heat can flow spontaneously from a cold object to a hot object, without having to invest energy in the process, as is required for a household refrigerator. An article describing the experiment with theoretical considerations has just been published inNature Communications.

The first author of the article, Kaonan Micadei, received his doctorate under the supervision of Professor Roberto Serra and is currently doing his doctoral research in Germany. Serra, also one of the authors of the article, was supported by the São Paulo Research Foundation - FAPESP via the Brazilian National Institute of Science and Technology in Quantum Information. FAPESP also awarded two research fellowships related to the project to another co-author, Gabriel Teixeira Landi, a professor at the Physical Institute of the University of São Paulo (IF-USP). In the macroscopic world described by classical physics, the supply of energy from outside can reverse the flow of heat in a system so that it flows from cold to hot. 19659002] "It can be said that in our nanoscopic experiment, the quantum correlations produced an analogous effect to the added energy, and the direction of flow was reversed without violating the second law of thermodynamics, on the contrary, if we include elements in the information theory description of heat transfer we find a generalized form of the second law and demonstrate the role of quantum correlations in this process. "

The experiment was per formed with a sample of chloroform molecules (one hydrogen atom, one carbon atom, and three chlorine atoms) attached to a carbon-13 Isotope are marked. The sample was diluted in solution and examined with a nuclear magnetic resonance spectrometer similar to hospital MRI scanners, but with a much stronger magnetic field.

"We investigated temperature changes in the spins of the nuclei of hydrogen and carbon The chlorine atoms did not play a significant role in the experiment, we used high frequency pulses to bring the spin of each core to a different temperature, one cooler, another warmer Temperature differences were small and on the order of ten billionths of a Kelvin, but we now have techniques that allow us to manipulate and measure quantum systems with extreme precision, in which case we have measured the high-frequency fluctuations produced by the atomic nuclei, "said Serra.

The researchers investigated two situations: First, the hydrogen and carbon nuclei started the process uncorrelated, and second, they were initially quantum correlated.

"In the first case, the cores were uncorrelated We observed how the heat in the usual direction flowed from hot to cold until both cores had the same temperature, and in the second, where the nuclei initially correlated, we observed a heat flux In the opposite direction, from cold to hot, the effect lasted a few thousandths of a second until the initial correlation was used up, "Serra explained.

The most notable aspect of this result is that a process of quantum cooling is proposed in which the addition of external energy (as it is) in refrigerators and air conditioners to cool a given environment.) Can be replaced by correlations ie, an exchange of information between objects The direction of heat flow – in other words, to bring about a local decrease in entropy – originated in classical physics in the mid-19th century, long before information theory was invented.

It was a thought experiment proposed by James in 1867, Maxwell (1831-1879), who among other things set up the famous equations of classical electromagnetism, said the great Scottish physicist in this thought experiment, which at that time triggered a violent controversy that when there would be a being capable of knowing the velocity of each molecule of a gas and manipulating all molecules on a microscopic scale, that entity could divide them into two receptors, placing molecules of above-average velocity in one to make a hot one generate compartment and slower than average molecules in the other to create a cold chamber. In this way, a gas initially in thermal equilibrium due to a mixture of faster and slower molecules would develop into a differentiated state with less entropy.

Maxwell intended to use the thought experiment to prove that the second law of thermodynamics is merely statistical. [19659002] "The being he proposed, capable of intervening in the material world at the molecular or atomic level, became known as 'Maxwell's Demon.' It was a fiction invented by Maxwell In order to present his point of view, we are now actually able to work on an atomic or even smaller scale, so that the usual expectations change, "said Serra.

The experiment carried out by Serra and co-workers and described in the just-published article is proof of this. It did not reproduce Maxwell's thought experiment, of course, but it did produce an analogous result.

"When we talk about information, we're not referring to anything immaterial – information requires a physical substrate, a memory, if you want." "If you want to erase 1-bit of memory from a flash drive, you need to be at least 10,000x Consume energy that consists of the Boltzmann constant and the absolute temperature. This minimum of energy, which is required to erase information, is referred to as the Landauer principle. … 2 / index.html Notebook batteries are more than anything consumed by heat, "says Serra, colder to a hotter object without consuming external energy.

"We can quantify the correlation of two systems with bits, and quantum mechanics and information theory connections create what we call quantum information science." From a practical standpoint, one day the effect we studied could be used to cool part of the processor of a quantum computer. " Serra said.


About the São Paulo Research Foundation (FAPESP)

The São Paulo Research Foundation (FAPESP) is a public body with the mission to carry out scientific research in all areas of knowledge To provide scholarships, scholarships and grants to investigators of higher education and research institutions in the state of São Paulo. Brazil: FAPESP recognizes that the best research results can only be achieved in collaboration with the best researchers at international level, and has therefore partnered with funding organizations, universities, private companies and research organizations in other countries known for their quality Scientists funded by the scholarships were encouraged to further develop their international cooperation. More information about FAPESP can be found at http: // /de and visit the news agency FAPESP at http: // /de To stay up to date on the latest scientific breakthroughs, FAPESP is helping through its numerous programs, awards and research centers. You can also contact the news agency FAPESP at http: // agencia.fapesp.subscribe tosubscribe .

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