Physicists design zero-friction quantum engine

super-adiabatic quantum engines
Scientists have devised a way to run a quantum cycle based on the use of quantum shortcuts to adiabaticity, where friction-like effects are quenched. Shown are the four steps of a quantum Otto cycle, where heat enters (exits) the working medium and those where work is performed by (done onto). Credit: A. del Campo, et al. ©2014 Nature Scientific Reports

(Phys.org) —In real physical processes, some energy is always lost any time work is produced. The lost energy almost always occurs due to friction, especially in processes that involve mechanical motion. But in a new study, physicists have designed an engine that operates with zero friction while still generating power by taking advantage of some quantum shortcuts.

The laws of successfully describe the concepts of work and heat in a wide variety of systems, ranging from refrigerators to black holes, as long as the systems are macroscopic. But for on the micro- and nano-scale, that are insignificant on large scales start to become prominent. As previous research as shown, the large quantum effects call for a complete reformulation of the thermodynamics laws.

What a quantum version of thermodynamics might look like is not yet known, and neither are the limitations or possible advantages of the quantum devices that would be described by such laws. However, one intriguing question is whether it may be possible to build a reversible quantum engine—one in which the engine's operation can be reversed without energy dissipation (an "adiabatic" process).

In the new paper, the physicists have shown one example of a quantum engine that is "super-adiabatic." That is, the engine uses quantum shortcuts to achieve a state that is usually achieved only by slow adiabatic processes. This engine can achieve a state that is fully frictionless; in other words, the engine reaches its , while still generating some power.

"Shortcuts allow us to 'mimic' what would be achieved by running a cycle quasi-statically, i.e., very slowly, while performing transformations at finite time," coauthor Mauro Paternostro at Queen's University in Belfast, UK, told Phys.org. "Now, consider for instance a compression or expansion stage of a cycle run using a piston. When doing it at finite time, i.e., non-zero velocity, friction might affect the performance of the transformation. Yet, by using a shortcut to adiabaticity, friction-like effects would get quenched, the cycle performance being the same as that of a quasistatic motor."

The work marks a step toward the key engineering goal in this context, which is to find the maximum efficiency allowed at the maximum possible power. As the scientists note, this pursuit is complicated by the existence of a trade-off between the running time of the super-adiabatic process and the corresponding amount of work dissipated.

"This work is one of the first steps into the merging of quantum control and thermodynamics," Paternostro said. "We have shown that it is possible to use techniques that, to date, have only been used for other goals (population transfer, for instance) for thermodynamic tasks and the engineering of efficient cycles."

Overall, the results suggest the possibility of a frictionless quantum engine operating at maximum efficiency, which has implications in designing micro- and nano-scale motors operating at the verge of the quantum scale. In the meantime, there are still several hurdles to overcome.

"I think that the real challenge is the use of such techniques in interacting quantum many body systems, whose inherent complexity and rich phenomenology could be 'tamed' by the use of this sort of quantum control," Paternostro said. "At the end of the day, thermodynamics is a theory of many particles, and its quantum formulation should be able to cope with many-body effects, whose control could hugely benefit from the implementation of schemes similar to the one proposed in our paper. We have new and exciting results, in this context, that will come up soon and that will hopefully have an impact in the community interested in many-body physics and quantum thermodynamics."


Explore further

Quantum engines must break down

More information: A. del Campo, et al. "More bang for your buck: Super-adiabatic quantum engines." Scientific Reports. DOI: 10.1038/srep06208
Journal information: Scientific Reports

© 2014 Phys.org

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Sep 16, 2014
Sooo...is friction just a 'lag' issue?

(Not sure where I'm going with this comment, but it seems to me that if you can have frictionless quantum systems (i.e. friction is not an inherent quantumechanical property). And if everything macroscopic is a collection of quantum systems (which seems plausible) ...Then friction is an emergent property. And the only thing that really comes into the picture with macroscopic objects is lag of information transmission over distances.

Sep 16, 2014
And, of course, the next question....
Can a quantum perpetual motion machine be far behind?

Sep 16, 2014
The assumed reversibility (quasi-stationarity) of an engine cycle, 'which implies an infinitely long cycle-time, determines its inevitable zero-power nature.' - this is practically a quantum mechanical definition of entropy!

"In fact, far from equilibrium, quantum fluctuations become dominant and cannot be neglected. In turn, thermodynamic quantities such as work and heat become inherently stochastic and should be reformulated accordingly." - this would do Ilya Prigogine proud!

Sep 16, 2014
@antialias
I think it's not a lag issue - it's more an issue of quantizing the allowed lattice vibration states in a material. In other words, friction produces heat by sending vibrations into a material, which quickly randomize. If you can operate a motor so that each individual process has an energy transition that is smaller than the first excited state of the atomic lattice, the thermal vibrations are effectively "frozen out" of the system - the motor can't cause heat vibrations.

Just for people's reference, an example of the phenomena I just described is the Mossbauer effect (which I have used experimentally). In this case, radioactive atoms (gamma emitters) are bound in a large, flaw-free atomic lattice. In a normal atomic decay, the nucleus recoils, stealing some of the energy from the emitted gamma. However in the MB effect, the nucleus is restrained by the lattice vibrational energy - the entire lattice recoils as a unit - meaning the gamma comes out full force.

Sep 16, 2014
And, of course, the next question....
Can a quantum perpetual motion machine be far behind?


machines that can operate with lower drag ( at the nano scale of course) can presumably be designed to exploit sources of power that are not now feasible to be exploited.

power must come from motion of mass or of radiation. it cannot come from a static field, but only a dynamic one.

perpetual motion machines cleverly use static fields to lengthen the period of motion resulting from an initial input energy. thus giving us the illusion that the input energy was NOT the source of work energy, but that the static field is.

however----there ARE DYNAMIC FIELDS AROUND US THAT ARE INVISIBLE.

the earth's tides of water are a result of the dynamic interaction between the moons gravitational field, the mass of the water in the oceans, and the earths gravitational field. It is possible to make a tidal like machine directly exploiting the dynamic gravity fields. a friction-less machine.?

Sep 17, 2014
And, of course, the next question....
Can a quantum perpetual motion machine be far behind?
Atoms are quantum perpetual motion machines.

Sep 17, 2014
This is an inevitable consequence of the Fluctuation Theorem. The Second Law of Thermodynamics does not apply to quantum level systems; they're too small and too fast.

Sep 18, 2014
I am not physicist. But i feel absolute energy efficient engines is impossible. But we can develop near absolute efficient engines. The key is to look at life. This can lead us not only to develop such technologies but help us understand universe as living as ancient east understood it. This however calls for dramatic change in our fundamental thinking - http://www.scribd...nologies

Sep 18, 2014
Further proof needed.
Check out the Fluctuation Theorem. Note that this is a theorem, not a theory.

Sep 19, 2014
And, of course, the next question....
Can a quantum perpetual motion machine be far behind?
Atoms are quantum perpetual motion machines.

Until we split it...:-)

Sep 19, 2014
Actually that makes two perpetual motion machines out of one.

Sep 19, 2014
This comment has been removed by a moderator.

Sep 19, 2014
Can quantum physics compete with https://www.jstag...article? Measured frictional coefficient was only about 0.07.
Sure. That's why electrons in their base orbitals keep going forever without slowing down. Quantum interactions have no friction; friction is a macroscopic effect. Zero beats 0.07.

Sep 19, 2014
Actually that makes two perpetual motion machines out of one.

Which means - they were 2 BEFORE it combined to make one...

Sep 19, 2014
Actually that makes two perpetual motion machines out of one.
Which means - they were 2 BEFORE it combined to make one...
No, not really. How do you figure?

Sep 20, 2014
Actually that makes two perpetual motion machines out of one.
Which means - they were 2 BEFORE it combined to make one...
No, not really. How do you figure?

Aww... you first...:-) How does it make two out of one?

Sep 20, 2014
Don't you get two halves when you split something?

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