SciPost Submission Page
Proposal for an autonomous quantum heat engine
by Miika Rasola, Vasilii Vadimov, Tuomas Uusnäkki, Mikko Möttönen
Submission summary
| Authors (as registered SciPost users): | Miika Rasola · Vasilii Vadimov |
| Submission information | |
|---|---|
| Preprint Link: | https://arxiv.org/abs/2502.08359v2 (pdf) |
| Date submitted: | May 3, 2025, 9:18 a.m. |
| Submitted by: | Rasola, Miika |
| Submitted to: | SciPost Physics |
| Ontological classification | |
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| Academic field: | Physics |
| Specialties: |
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| Approaches: | Theoretical, Computational |
Abstract
We propose and theoretically analyse a superconducting electric circuit which can be used to experimentally realize an autonomous quantum heat engine. Using a quasiclassical, non-Markovian theoretical model, we demonstrate that coherent microwave power generation can emerge solely from the heat flow through the circuit determined by non-linear circuit quantum electrodynamics. The predicted energy generation rate is sufficiently high for its experimental observation with contemporary techniques, rendering this work a significant step toward the first experimental realization of an autonomous quantum heat engine based on Otto cycles.
Author indications on fulfilling journal expectations
- 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
Current status:
Reports on this Submission
Strengths
- Plausible experimental feasibility
Weaknesses
- Unclear discussion of the quantum vs. classical effects in the system
Report
Technically the work contains a device proposal and the solution of classical equations of motion of a superconducting circuit, driven by noise from resistors. This appears fine in itself, and probably is reasonable model for the proposed system at temperatures high enough. However, I have some comments below which should be clarified.
Although a classical model is not really a "single quantum" heat engine, for realizing the system it's regardless useful to understand the classical behavior. In the manuscript it is also suggested with some justifications that the principle would scale to low temperatures.
As such, the work is probably a useful step toward realizing this type of heat engines on cQED platform, and may be suitable for publication after open questions are clarified.
Requested changes
1 - In Eq. (8) and below symmetrized correlator is used, so in a sense emission and absorption are summed together. If they are different, omega > T considered in the manuscript, one could expect it may have some importance for the heat engine physics studied here.
Implications on the difference to fully classical limit is discussed in Sec. 4.3., mostly stating that the numerical results change quantitatively, and in the introduction noting that linear equations are same in quantum case. Can the final results be understood in terms of quanta emitted from the hot reservoir and absorbed in the cold or in the driven resonator? Do the equations obtained reflect such physics? The exponential dependence in Fig. 4(cd) at low T may be reasonable, but this is found from numerical results so the origin is not unambiguous. I don't find the discussion of the semiclassical approximation very clear in the present version.
2 - The Otto cycle as discussed in Sec. 4.4 is somewhat hard to see and understand from Fig. 8. From the discussion, I would guess what is implied is that (x,y)=(omega_a', <phi^2>) forms a loop with nonzero interior. This could be contrasted to proposals [45] and others, after converting between field amplitude and photon counts.
3 - The negative dissipation occurs only at nonzero resonator amplitude when there is internal dissipation, unless quality factor is very high. What can be said about the threshold where the resonator B starts to oscillate if it starts at rest?
4 - The results are calculated by time-scale separation arguments. Are these assumptions self-consistent with the results for the parameters used, i.e do the slow equations produce slow dynamics? This is not explicitly discussed in the manuscript, but probably would be useful to note it.
Recommendation
Ask for minor revision
Report
To start with, I miss a more intuitive explanation of the mechanism which drives the engine, i.e. on the origin of the self-sustained oscillations in phi_b. Is there a simple qualitative condition for their appearance? Perhaps a simple schematic figure would help more than the rather involved numerical approach described in the manuscript.
On the other hand, I wonder about the need of such a complex circuit with so many parameters. If this work is motivated by an actual experiméntal device this should be clearly stated. The choice of parameters in table 1 should also be more clearly justified.
Finally, it would be interesting that the authors comment how they plan to approach a complete quantum description of their device.
Recommendation
Ask for minor revision