Quantum mechanics trumps the second law of thermodynamics at the atomic scale

Amazing stuff!

"Two physicists at the University of Stuttgart have proven that the Carnot principle, a central law of thermodynamics, does not apply to objects on the atomic scale whose physical properties are linked (so-called correlated objects). This discovery could, for example, advance the development of tiny, energy-efficient quantum motors.  ..."

"... In recent years, quantum mechanical experiments have succeeded in reducing the size of heat engines to the microscopic range. “Tiny motors, no larger than a single atom, could become a reality in the future,” ..."

From the abstract:

"The laws of thermodynamics strongly restrict the performance of thermal machines.

Standard thermodynamics, initially developed for uncorrelated macroscopic systems, does not hold for microscopic systems correlated with their environments.

We here derive an exact formula for the efficiency of any cyclically driven quantum engine by using generalized laws of quantum thermodynamics that account for all possible correlations between all involved parties, including initial correlations.

Furthermore, we demonstrate the existence of two basic modes of engine operation: the usual thermal case, where heat is converted into work, and an athermal regime, where work is extracted from entropic resources, such as system-bath correlations.

In the latter regime, the efficiency is not bounded by the usual Carnot formula. Our results provide a unified formalism to determine the efficiency of correlated microscopic quantum machines."

Quantum mechanics trumps the second law of thermodynamics at the atomic scale

More efficient than Carnot: Quantum mechanics trumps the second law of thermodynamics (original news release) "Two physicists at the University of Stuttgart have proven that the Carnot principle, a central law of thermodynamics, does not apply to objects on the atomic scale whose physical properties are linked (so-called correlated objects). This discovery could, for example, advance the development of tiny, energy-efficient quantum motors."

Correlated quantum machines beyond the standard second law (open access)

Fig. 1. Operation regimes of correlated engines.

Fig. 2. Two-oscillator quantum engine.

Quantum equivalent of thermodynamics' second law discovered for entanglement manipulation

Amazing stuff!

"... This second law of entanglement manipulation proves that, just like heat or energy in an idealized thermodynamics regime, entanglement can be reversibly manipulated, a statement which until now had been heavily contested. ...

Though entanglement still appears counterintuitive to our lived experience of the world, researchers have discovered striking parallels with something much more familiar: thermodynamics. In fact, many similarities have emerged between the theories of quantum entanglement and thermodynamics. For example, "entanglement entropy" is a characteristic of idealized, noiseless quantum systems that mimics the role of thermodynamical entropy. ..."

From the abstract:

"A central question since the beginning of quantum information science is how two distant parties can convert one entangled state into another. It has been conjectured that such conversions could be executed reversibly in an asymptotic regime, mirroring the reversible nature of Carnot cycles in classical thermodynamics. While a conclusive proof of this conjecture has been missing so far, earlier studies have excluded reversible entanglement manipulation in various settings.

In this Letter, we show that arbitrary mixed state entanglement transformations can be made reversible under local operations and classical communication, when assisted by an entanglement battery—an auxiliary quantum system that stores and supplies entanglement in a way that ensures no net entanglement is lost.

In particular, the rate of transformation in the asymptotic limit can be quantitatively expressed as a ratio of entanglement present within the quantum states involved. Our setting allows us to consider different entanglement quantifiers which give rise to unique principles governing state transformations, effectively constituting diverse manifestations of a “second law” of entanglement manipulation.

These findings resolve a long-standing open question on the reversible manipulation of entangled states and are also applicable to multipartite entanglement and other quantum resource theories, including quantum thermodynamics."

Quantum equivalent of thermodynamics' second law discovered for entanglement manipulation

Second Law of Entanglement Manipulation with an Entanglement Battery (no public access)

Second Law of Entanglement Manipulation with Entanglement Battery (preprint, open access)

Reversal Of The Arrow Of Time Discovered?

Posted: 1/5/2019 Amended: 1/12/2019  Updated: 3/16/2019

Update Of 3/16/2019

Just came across these new articles:

1. Arrow of time and its reversal on the IBM quantum computer (published 3/13/2019; appears to be the full article)
2. Physicists reverse time using quantum computer (published 3/13/2019; refers to above reference)

Unfortunately, I did not have the time to read both of these articles. However, I have the impression that this experiment is perhaps a bit too clever to prove the point.

“"However, Schrödinger's equation is reversible," adds Valerii Vinokur, a co-author of the paper, from the Argonne National Laboratory, U.S. "Mathematically, it means that under a certain transformation called complex conjugation, the equation will describe a 'smeared' electron localizing back into a small region of space over the same time period." Although this phenomenon is not observed in nature, it could theoretically happen due to a random fluctuation in the cosmic microwave background permeating the universe.” (New article 2; emphasis added)

“According to the authors, these errors are due to imperfections in the actual quantum computer.” (New article 2; emphasis added) Begs the question what else is due to these “imperfections”?

Original Post

If this is confirmed that would be huge! Apparently, more evidence for reversibility of time in the microscosmos has been discovered over the recent past (Source 1 lists such research).

How important are initial conditions [at the beginning of the universe?]? From chaos theory, we have already learnt that the initial conditions are critical for the path or trajectory of chaotic complex systems.

“... Here we report the experimental demonstration of the reversal of the arrow of time for two initially quantum correlated qubits (two spin-1/2 systems) prepared in local thermal states at different temperatures employing Nuclear Magnetic Resonance (NMR) techniques … For initially correlated systems, we observe a spontaneous heat current from the cold to the hot spin and show that this process is made possible by a decrease of the mutual information between the spins … It additionally establishes that the arrow of time is not an absolute but a relative concept that depends on the choice of initial conditions. ... Thus, an anomalous heat current does not seem to be restricted to extremely microscopic systems. The precise scaling of this effect with the system size is an interesting subject for future experimental and theoretical investigations.“

(Source 1; emphasis added)

One may freely speculate if the reversal of time is confirmed then e.g. the speed of light constraint is in question too and vice versa.

Sources:

1. Physicists Demonstrate How to Reverse of the Arrow of Time The extraordinary experiment opens the door to a new generation of devices and reveals a deeper relationship between time, entropy, and entanglement. (12/22/2017)
2. Reversing the thermodynamic arrow of time using quantum correlations (11/9/2017)