AQP Seminar: Supremacy of incoherent sudden refrigeration cycles

Aalto Quantum Physics Seminar (Nanotalo). Speaker: Dr. George Thomas (PICO, Aalto)

It is interesting to explore the role of coherence in the performance of quantum heat engines and refrigerators.  In this regard, we investigate theoretically a four-step Otto refrigerator based on a two-level system (TLS) coupled alternately to two different heat baths. Modulation of the coupling is achieved by tuning the level spacing of the TLS by an external control, for example, by varying the magnetic flux. We find that the TLS, which avoids quantum coherences acts as a refrigerator with finite cooling power even in the limit of infinite operation frequency. On the other hand, the cycles that create quantum coherence in the sudden expansions and compressions lead to heating of both the baths. Further, to suppress the creation of coherence, we propose a driving method that keeps the energy eigenstates time-independent and thus restores the refrigeration cycle. We also discuss a possible physical realization of the cycle based on a superconducting qubit coupled to dissipative LC-resonators.

 J. P. Pekola, B. Karimi, G. Thomas, and D. V. Averin, arXiv:1812.10933 [quant-ph] (2018).