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Quantum many-body thermal machines enabled by atom-atom correlations
by R. S. Watson, K. V. Kheruntsyan
Submission summary
| Authors (as registered SciPost users): | Karen Kheruntsyan |
| Submission information | |
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| Preprint Link: | https://arxiv.org/abs/2308.05266v3 (pdf) |
| Date submitted: | 2024-07-12 03:49 |
| Submitted by: | Kheruntsyan, Karen |
| Submitted to: | SciPost Physics |
| Ontological classification | |
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| Academic field: | Physics |
| Specialties: |
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| Approach: | Theoretical |
Abstract
Particle-particle correlations, characterized by Glauber's second-order correlation function,play an important role in the understanding of various phenomena in radio and optical astronomy, quantum and atom optics, particle physics, condensed matter physics, and quantum many-body theory. However, the relevance of such correlations to quantum thermodynamics has so far remained illusive. Here, we propose and investigate a class of quantum many-body thermal machines whose operation is directly enabled by second-order atom-atom correlations in an ultracold atomic gas. More specifically, we study quantum thermal machines that operate in a sudden interaction-quench Otto cycle and utilize a one-dimensional Lieb-Liniger gas of repulsively interacting bosons as the working fluid. The atom-atom correlations in such a gas are different to those of a classical ideal gas, and are a result of the interplay between interparticle interactions, quantum statistics, and thermal fluctuations. We show that operating these thermal machines in the intended regimes, such as a heat engine, refrigerator, thermal accelerator, or heater, would be impossible without such atom-atom correlations. Our results constitute a step forward in the design of conceptually new quantum thermodynamic devices which take advantage of uniquely quantum resources such as quantum coherence, correlations, and entanglement.
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- Provide a novel and synergetic link between different research areas.
- Open a new pathway in an existing or a new research direction, with clear potential for multi-pronged follow-up work
- Detail a groundbreaking theoretical/experimental/computational discovery
- Present a breakthrough on a previously-identified and long-standing research stumbling block
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The work by Watson and Kheruntsyan focuses on a quantum Otto cycle which taps on a working fluid which is an interacting gas.
In my opinion this paper is fairly well written and attempts to tackle a very interesting issue, which is the investigation of the effect of quantum correlations in engine cycles.
While I like this work, I have some reservations about some of the points which I will describe here. Hopefully this would help the authors make the paper clearer when they resubmit it.
1) one fundamental question which confuses me is this: are the correlations necessary? what is the true role of correlations? To be clearer, engines should not need quantum mechanics to work, as classical engines are possible. Of course one could tap on quantum effects to have a truly quantum engine, however are the correlations that you probe in your engine necessary for the functioning of the engine, or are they more simply a consequence of the interactions in the system? What I am trying to clarify is causation and not "just" co-existence because of a common origin (the interactions). My, possibly wrong thinking, is that one could think of an interacting classical gas and could probe similar physics to what you describe, and classical correlations could develop in the system too.
2) the engine is highly non-reversible. The "work-strokes" are quenches, and the "heat-strokes" are done with a single temperature bath, instead of slowly change the temperature of the system. This leads me to three comments:
- the first law of thermodynamics deals systems at equilibrium while here the system is at equilibrium only at points B and D. Thus Fig.1, with continuous lines, may be misleading/confusing. This is not a "typical" engine cycle.
- despite the non-reversible approach, the evaluation of W is actually consistent with the use of the two-time measurement approach (see XXX) because the thermal states are diagonal in the energy basis and the average energy after the quench is also correctly evaluated. But what can be misleading in the presentation is that Work seems to be an observable, or something that can be typically evaluated "simply" from energy difference. It would be good that the authors spend some lines discussing this.
- it would be good to show how far away are these performance from that of an ideal Otto cycle run between the same maximum and minimum temperatures and same changes of \chi.
3) I think that in Fig.3(d) the authors may have meant |Q_1|>|Q_2|
4) Some references which could be considered are:
For introduction to quantum thermodynamics, there is a recent article which could be good to cite https://arxiv.org/abs/2406.19206
For experiment, I would consider citing also some other early quantum engine experiments https://www.nature.com/articles/s41534-020-0264-6 and https://www.nature.com/articles/s41467-018-08090-0
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