What is quantum in quantum thermodynamics?

quantum thermodynamics
Physicists have shown that the three main types of engines (four-stroke, two-stroke, and continuous) are thermodynamically equivalent in a certain quantum regime, but not at the classical level. Credit: Uzdin, et al. Published by the American Physical Society under CC-BY-3.0

(Phys.org)—A lot of attention has been given to the differences between the quantum and classical worlds. For example, quantum entanglement, superposition, and teleportation are purely quantum phenomena with no classical counterparts. However, when it comes to certain areas of thermodynamics—specifically, thermal engines and refrigerators—quantum and classical systems so far appear to be nearly identical. It seems that the same thermodynamic laws that govern the engines in our vehicles may also accurately describe the tiniest quantum engines consisting of just a single particle.

In a new study, physicists Raam Uzdin, Amikam Levy, and Ronnie Kosloff at the Hebrew University of Jerusalem have investigated whether there is anything distinctly quantum about thermodynamics at the , or if "quantum" thermodynamics is really the same as classical thermodynamics.

For the first time, they have shown a difference in the thermodynamics of heat machines on the quantum scale: in part of the quantum regime, the three main engine types (two-stroke, four-stroke, and continuous) are thermodynamically equivalent. This means that, despite operating in different ways, all three types of engines exhibit all of the same thermodynamic properties, including generating the same amounts of power and heat, and doing so at the same efficiency. This new "thermodynamical equivalence principle" is purely quantum, as it depends on quantum effects, and does not occur at the classical level.

The scientists also showed that, in this where all engines are thermodynamically equivalent, it's possible to extract a quantum-thermodynamic signature that further confirms the presence of quantum effects. They did this by calculating an upper limit on the work output of a classical engine, so that any engine that surpasses this bound must be using a quantum effect—namely, quantum coherence—to generate the additional work. In this study, , which accounts for the wave-like properties of quantum particles, is shown to be critical for power generation at very fast engine cycles.

"To the best of my knowledge, this is the first time [that a difference between quantum and classical thermodynamics has been shown] in heat machines," Uzdin told Phys.org. "What has been surprising [in the past] is that the classical description has still held at the quantum level, as many authors have shown. The reasons are now understood, and in the face of this classicality, people have started to stray to other types of research, as it was believed that nothing quantum can pop up. Thus, it was very difficult to isolate a generic effect, not just a numerical simulation of a specific case, with a complementing theory that manages to avoid the classicality and demonstrate quantum effects in thermodynamic quantities, such as work and heat."

quantum thermodynamics 2
(Left) (a) In the quantum regime where the engine action is relatively small, all three engines generate the same amount of work after the completion of each cycle (the vertical lines indicate a complete cycle). (b) When the engine action is increased, the engines perform differently and the equivalence no longer holds. (Right) Quantum heat engines exhibit a quantum-thermodynamic signature, which occurs in the shaded region above the upper bounds on the power of two-stroke (dashed blue line) and four-stroke (dashed red line) engines. Credit: Uzdin, et al. Published by the American Physical Society under CC-BY-3.0

One important implication of the new results is that quantum effects may significantly increase the performance of engines at the level. While the current work deals with single-particle engines, the researchers expect that may also emerge in multi-particle engines, where between particles may play a role similar to that of coherence.

Explore further

Maxwell's demon can use quantum information to generate work

More information: Raam Uzdin, et al. "Equivalence of Quantum Heat Machines, and Quantum-Thermodynamic Signatures." Physical Review X. DOI: 10.1103/PhysRevX.5.031044
Journal information: Physical Review X

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Oct 12, 2015
Not sure if this makes any sense without a better definition of "Heat" and "Cold". Boltzmann only states the possibilities of the number of states, or the available states. All states do not necessarily exist at the same time. Therefore QM cannot agree with classical, it's an approximation tool that loses precision as we decrease the volume. Classical physics is an exact science. This paper is without merit! Try a classical 4D space! Use QM sparingly.

Oct 12, 2015
Now all that needs to be quantized is Time. Because if Time is forward entropy, and entropy turns out to be quantic, so therefore must be time as well.

Oct 13, 2015
For example, quantum entanglement, superposition, and teleportation are purely quantum phenomena with no classical counterparts.
This is WRONG, These effects can be derived directly from Maxwell's equations. Coherent superposition of EM waves is a everyday experience that do not require "quanta". A photon is also a single coherent wave, and two photons can superpose to form another SINGLE coherent wave with a higher energy. The latter wave is then "entangled" since it is not two separate waves. Teleportation is not a purely quantum phenomenon. It can be generated by laser light, which is a SINGLE coherent macro-wave.

Time cannot be quantised just like time cannot dilate.

Oct 13, 2015
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Oct 14, 2015
Planck's quantum theory was based on classical analysis. It would seem that the first place to look would be to go back and examine his theory, as today's physicists appear to be totally void in that knowledge.
Exactly correct! The light-waves within a black-body cavity are not "particles" but stationary waves that fill the whole cavity. Furthermore, since there is NO aether these waves cannot have kinetic=energy. Their energies are all rest-mass.

Oct 14, 2015
swordsman: better yet, lets go back and examine (better yet, start with) Aristotle's theories, should be even more useful than Planck's mere century old thinking.

One must go back to Pythagoras. Minkowski did not understand the theorem of Pythagoras and thus assumed that one of the sides of a right-triangle can be the hypotenuse. All 20th century theoretical physics is based on this impossible mathematics and must thus be flawed: Physics that is modelled in terms of impossible mathematics can obviously not be correct..

Oct 14, 2015
Very fundamenal paper to read and understand very carefully.
It opens the possibility to obtain a "quantum signature" similar to Bell inequalities of perfect quantum coherent machines with reduced dissipation, like macroscopic superfluidity or superconductivity.

Oct 14, 2015
An obvious system where these effects may be at work would be cellular chemical engines, such as chaperons. They are isolated, and sometimes rare, ATP (energy) driven mechanic work molecules. [ https://en.wikipe...protein) ]

@ It is known that classical physics is a useful approximation, is all. So are heat and cold sinks.

@Hav3000: Time is not entropy, as seen by their different units. Is a pear a chair?

@inkosana: References, please! Minkowski didn't assume anything about triangles that wasn't implicit in the geometry of his spacetime, say. And that spacetime is simple and sound.

Oct 14, 2015
@docile: Thermodynamics is also time reversible in essence, it is just the constraint of entropy that makes it directed. Quantum mechanics is also time irreversible, as a state is formed from the collapse mechanism.

Nit: Quantum mechanics and general relativity is consistent in the core theory (GR + SM). it is GR that breaks down at large energies/small scales. "It's often said that it is difficult to reconcile quantum mechanics (quantum field theory) and general relativity. That is wrong. We have what is, for many purposes, a perfectly good effective field theory description of quantum gravity. ... In other words, as an effective field theory, gravity is no worse, nor better, than any other of the effective field theories we know and love. The trouble is that all hell breaks loose for ε ~ 1. " [ https://golem.ph....639.html ]

Oct 14, 2015
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Oct 14, 2015
@inkosana: References, please! Minkowski didn't assume anything about triangles that wasn't implicit in the geometry of his spacetime, say. And that spacetime is simple and sound.
The hypotenuse which always also acts as the position-vector of a point, when using Cartesian coordinates, MUST always be the POSITIVE-SUM of the squares of the coordinates.

To keep the discussion simple let us consider a 2 dimensional plane: If the coordinates are x and y, the square of the position vector is given by x^2+y^2 (NOTE THE PLUS). Minkowski claimed that when one of the coordinates is (ct) one can write that the position vector (hypotenuse) is given by (ct)^2 MINUS x^2.. This violates the theorem of Pythagoras which demands that the hypotenuse MUST ALWAYS be the POSITIVE SUM of the coordinates. Not even grade 8 pupil would be so stupid as Minkowski was.


Oct 14, 2015
It is correct that the template equation for the derivation of the Lorentz equations must be (ct')^2-x^2=(ct)^2-x^2; Einstein stupidly claimed that this equation follows from (ct)^2-x^2-y^2-z^2=0=(ct')^2-x'^2-y'^2-z'^2: And that since y=y' and z=z', they cancel so that (ct)^2-x^2=0=(ct')^2-x'^2 is the template equation. This cannot be a template equation for a coordinate transformation fro x',y' into unique corresponding coordinates x, y. Since when choosing specific values for x' and y', there are an infinite number of sets x,y which do not violate the template equation. To camouflage this stupidity, Einstein invoked an imaginary time coordinate; which is even more stupid, since the components of a complex number in the Argand plane cannot be coordinates of positions in space EVER!!!!!


Oct 14, 2015
The template equation comes from the fact the a single wavefront, emitted by a light source within K', can never be coincident with itself within K. Thus within K' such a wavefront reaches the position x',y' z' within K', BEFORE the wavefront within K reaches these same coordinates x',y',z' within K'. Within K the wavefront reaches the same position within K' at a LATER time. But since Einstein and Minkowski was too stupid to realise this, they concluded that the same wavefront observed within K' and K does coincide, so that it reaches the position x',y', z' within K' "simultaneously" at two different times t' and t. Only a retard will believe that "simultaneous" means different times. It is obviously absurd. One does not need imaginary time to derive the Lorentz equations when one does not use the latter impossible and absurd concept.

The correct derivations are given in my books: Why Galileo TRUMPS Einstein and in Why does E=mc2. They are available in Kindle format on Amazon.

Oct 15, 2015
Note that the symmetry of the Lorentz transformation is cylindrical around the direction of relative motion so that one has that x'^2+y'^2=x^2+y^2=(rho)^2: The template equation is thus given by (rho)^2=(ct')^2-x'^2=(ct)^2-x^2. Minkowski stupidly claimed that the radial coordinate (rho) is a position-vector in "space-time". It is amazing that he could have claimed that he understood mathematics; and even taught this subject. What is more amazing Is that the hundreds of thousands of mainstream theoretical physicists like Einstein, Dirac, Feynman, Penrose, Hawking, etc. etc. etc. could not pick it up that there is something wrong with the concept of "space-time". What is even more worrying is that those scientists like Herbert Dingle who did argue that something is wrong were vilified in the same manner that Galileo were vilified by his peers! We are truly back in the dark ages!

Oct 17, 2015
Torbjorn?...... Torbjorn?
Must have gone to hunt bear in the far North.

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