Quantum engine, or how to fool the laws of thermodynamics

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Quantum engine, or how to fool the laws of thermodynamics
Quantum engine, or how to fool the laws of thermodynamics

An article was published in the journal Nature substantiating the feasibility of a special quantum engine. The principles of quantum mechanics in this concept smooths out the constraints that a law, known as the second law of thermodynamics, places on this engine, allowing for maximum efficiency.

Quantum engine

The efficiency of any engine depends on how much energy it loses during operation. Steam engines did not become widespread precisely because too much heat was spent not on conversion into kinetic energy (that is, into motion), but into the surrounding space.

The steampunk world was partly prevented from becoming reality by nature itself, in particular - the second law of thermodynamics, according to which any closed system tends to uniformly dissipate energy and heat. This imposes certain restrictions on almost any engine.

An almost insurmountable obstacle on the way to the most efficient (ideal) engine is also friction when performing mechanical work - against the air, against parts of the mechanism, etc.

Thus, part of the energy released during fuel conversion is irretrievably lost, which leads to a decrease in the efficiency of a particular engine. Avoiding friction and energy loss in macroscopic (that is, large, such as a car's internal combustion engine) systems is difficult.

A natural question arises - is it possible to bypass the limitations of the macrocosm by "descending" into the microcosm?

One atom is enough

As shown by a number of studies devoted to the creation of quantum engines, it is possible. The fact is that on a quantum scale, thermodynamic processes proceed in a completely different way. This even led scientists to the need to create a theory that would combine quantum mechanics and thermodynamics.

As part of the development of such a theory, physicists were attracted by the problem of creating a quantum engine that could perform work absolutely without losing energy, avoiding not only friction, but also heat transfer with the external environment. In other words, such an engine would achieve maximum efficiency.

The last and one of the most impressive works in this direction at the moment is a study published in Scientific Reports by scientists from the USA, Great Britain and Italy, in which the possibility of functioning of such an engine with adiabatic properties (that is, devoid of heat exchange with the external environment) is theoretically substantiated.

In particular, physicists were able to adapt the Otto cycle - a thermodynamic process that describes the action of an ideal internal combustion engine - to the scale of the microworld. The modern achievements of theoretical physics allowed them to do this. For example, scientists used the experimentally proven fluctuation theorem, which neatly corrects the second law of thermodynamics and admits that entropy (energy dissipation) can not only increase over time in some systems, but also decrease.


Using so-called shortcuts to adiabaticity, the scientists showed how an atom-sized Otto cycle engine could work.The "piston" in it would be a quantum harmonic oscillator surrounded by two microscopic chambers for supplying heat to the working fluid (oscillator) and cooling it. The work itself, as in the standard, non-quantum Otto cycle, would be done with the help of compression and expansion of the working fluid.

The absence of friction would be ensured by "superadiabaticity" - a state that simulates the operation of an engine during slow adiabatic processes. Scientists' calculations show that such an engine would function very slowly, but its cycle would be reversible and finite in time, which would still allow it to do some work.

What does all this mean?

The theoretical substantiation of the concept of a working "superadiabatic" quantum engine is a step forward towards the realization of the long-held dream of physicists - to build an engine with maximum efficiency while delivering maximum power. This, of course, is not a perpetual motion machine, but it is also a very impressive and much more realistic perspective.

Also, this work of scientists seems to be useful in the development of quantum thermodynamics - a theory that would reconcile thermodynamic processes and the physics of elementary particles.

“Thermodynamics describes processes involving many particles at once, and its quantum adaptation should also adequately reflect many-particle processes. Implementing such concepts - like what we proposed in our work - will allow us to have much better control over these processes,”says Mauro Paternostro of the University of Queens (UK), one of the authors of the study.

However, the practical implementation of the proposed scheme of a quantum engine is also not something fantastic and distant, the authors of the study believe. Moreover, scientists intend to experimentally implement the engine invented by them in the very near future.

Paternostro and his colleagues are already in talks with representatives of some scientific organizations in Europe to test their theory. In particular, they want to gain access to certain equipment in order to first capture a single atom with a laser, and then subject it to thermal transformations of the Otto cycle.

If physicists succeed in proving their case in practice, this could lead to the ubiquitous proliferation of the most efficient quantum and nanoscale micromotors, the range of applications of which can turn out to be quite impressive.

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