Quantum refrigerators – the quantum thermodynamics of cooling Bose gases

This is a Perspective on "Quantized refrigerator for an atomic cloud" by Wolfgang Niedenzu, Igor Mazets, Gershon Kurizki, and Fred Jendrzejewski, published in Quantum 3, 155 (2019).

By Sebastian Deffner (University of Maryland Baltimore County).

We are living in exciting times. All around the globe national as well as international entities have founded “quantum initiatives”, whose goal is the development of practical and commercially available quantum technologies. Typically, quantum technologies are categorized into the three areas of quantum communication, quantum sensing, and quantum computing [1]. However, this categorization somewhat overlooks an even more promising and important arena for technological revolutions: quantum thermodynamic devices [2].

Although it is somewhat debatable whether quantum features are always a blessing, or whether they can be detrimental to the thermodynamic performance [3], it has long been clear that carefully designed quantum device can do things classical devices cannot, see e.g. Refs. [4,5,6,7,8,9,10,11,12,13]. A latest addition to such potential “quantum supremacy” of thermodynamic devices is the cleverly designed quantum refrigerator by Niedenzu et al., that was published recently in “Quantized refrigerator for an atomic cloud” [14].

More specifically, Niedenzu et al. [14] propose to utilize the quantum Otto cycle to cool cold atomic gases, and in particular to cool a Bose gas below the critical point to undergo a BEC phase transition. The thermal machine is suggested to be made of two atomic species that act as hot and cold bath, respectively. This is quite remarkable since more conventional means of cooling are typically not capable of easily cooling the BEC into the deeply degenerate quantum regime [14].

Admittedly, using standard thermodynamic cycles to cool two-atomic gases is not necessarily a novel idea, which can be found in many standard textbooks [15]. However, Niedenzu et al.’s work stands out, since the highly idealized situation of a quantum Otto cycle is carefully studied under experimentally relevant parameters. In particular, the authors analyze thoroughly the assumptions, approximations, and limits under which the theoretical proposal could be implemented in a real experiment. On a more theoretical side, the development of such technologies opens the avenue to experimental study of so far under explored regimes, where the Born-Markov approximations break down. This regime could harbor exciting ramifications for the thermodynamic properties of deeply quantum devices.

Such experimentally motivated studies are invaluable for the progress of research in Quantum Thermodynamics [2]. If the power of quantum thermodynamic universality shall be brought down from its lofty heights to the harsh facts of industrial reality, we will will need more work like the one by Niedenzu et al. [14]. Therefore, Ref. [14] could be considered an essential step towards the development of realistic and practical quantum refrigerators with potentially commercial applications.

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► References

[1] M. G. Raymer and C. Monroe, The US national quantum initiative, Quantum Sci. Technol. 4, 020504 (2019).

[2] S. Deffner and S. Campbell, Quantum Thermodynamics (Morgan & Claypool Publishers, 2019).

[3] G. Kurizki, E. Shahmoon, and A. Zwick, Thermal baths as quantum resources: more friends than foes? Physica Scripta 90, 128002 (2015).

[4] M. O. Scully, Quantum afterburner: Improving the efficiency of an ideal heat engine, Phys. Rev. Lett. 88, 050602 (2002).

[5] M. O. Scully, K. R. Chapin, K. E. Dorfman, M. B. Kim, and A. Svidzinsky, Quantum heat engine power can be increased by noise-induced coherence, PNAS 108, 15097 (2011).

[6] J. Roßnagel, O. Abah, F. Schmidt-Kaler, K. Singer, and E. Lutz, Nanoscale heat engine beyond the carnot limit, Phys. Rev. Lett. 112, 030602 (2014).

[7] W. Niedenzu, D. Gelbwaser-Klimovsky, A. G. Kofman, and G. Kurizki, On the operation of machines powered by quantum non-thermal baths, New J. Phys. 18, 083012 (2016).

[8] J. Jaramillo, M. Beau, and A. del Campo, Quantum supremacy of many-particle thermal machines, New J. Phys. 18, 075019 (2016).

[9] S. Deffner, Efficiency of harmonic quantum otto engines at maximal power, Entropy 20, 875 (2018).

[10] W. Niedenzu, V. Mukherjee, A. Ghosh, A. G. Kofman, and G. Kurizki, Quantum engine efficiency bound beyond the second law of thermodynamics, Nat. Comm. 9, 165 (2018).

[11] A. Ghosh, W. Niedenzu, V. Mukherjee, and G. Kurizki, Thermodynamic principles and implementations of quantum machines, in Thermodynamics in the Quantum Regime: Fundamental Aspects and New Directions, edited by F. Binder, L. A. Correa, C. Gogolin, J. Anders, and G. Adesso (Springer International Publishing, Cham, 2018) pp. 37–66.

[12] S. T. Dawkins, O. Abah, K. Singer, and S. Deffner, Single atom heat engine in a tapered ion trap, in Thermodynamics in the Quantum Regime: Fundamental Aspects and New Directions, edited by F. Binder, L. A. Correa, C. Gogolin, J. Anders, and G. Adesso (Springer International Publishing, Cham, 2018) pp. 887–896.

[13] C. Cherubim, F. Brito, and S. Deffner, Non-thermal quantum engine in transmon qubits, Entropy 21, 545 (2019).

[14] W. Niedenzu, I. Mazets, G. Kurizki, and F. Jendrzejewski, Quantized refrigerator for an atomic cloud, Quantum 3, 155 (2019).

[15] H. B. Callen, Thermodynamics and an introduction to thermostatistics (Wiley, New York, USA, 1985).

Cited by

[1] Nathan M. Myers, Obinna Abah, and Sebastian Deffner, "Quantum thermodynamic devices: From theoretical proposals to experimental reality", AVS Quantum Science 4 2, 027101 (2022).

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