Abstract
Nanoscale heat engines are subject to large fluctuations which affect their precision. The thermodynamic uncertainty relation (TUR) provides a trade-off between output power, fluctuations, and entropic cost. This trade-off may be overcome by systems exhibiting quantum coherence. This Letter provides a study of the TUR in a prototypical quantum heat engine, the Scovil-Schulz-DuBois maser. Comparison with a classical reference system allows us to determine the effect of quantum coherence on the performance of the heat engine. We identify analytically regions where coherence suppresses fluctuations, implying a quantum advantage, as well as regions where fluctuations are enhanced by coherence. This quantum effect cannot be anticipated from the off-diagonal elements of the density matrix. Because the fluctuations are not encoded in the steady state alone, TUR violations are a consequence of coherence that goes beyond steady-state coherence. While the system violates the conventional TUR, it adheres to a recent formulation of a quantum TUR. We further show that parameters where the engine operates close to the conventional limit are prevalent and TUR violations in the quantum model are not uncommon.
Highlights
Nanoscale heat engines [1] have become a topic of wide interest in recent years
In this work we study the thermodynamic uncertainty in the SSDB maser in detail, finding thermodynamic uncertainty relation (TUR) violations induced by coherence, in analogy to Ref. [43]
In this Letter we studied the performance of the Scovil–Schulz-DuBois heat engine in terms of the thermodynamic uncertainty Q
Summary
Nanoscale heat engines [1] have become a topic of wide interest in recent years In such devices quantum effects become relevant and radically alter the dynamical and thermodynamic properties [2,3,4,5,6,7,8]. A comparison to a classical model which obeys the TUR allows us to identify regions of operation where quantum dynamics results in improved operation as quantified by a lower value of Q. Such a quantum advantage cannot be anticipated from the off-diagonal elements of the density matrix because the fluctuations are not encoded in the steady state alone. We probe the thermodynamic uncertainty of the SSDB maser Q and compare it with the uncertainty of an equivalent classical system Qcl, where the coherent transition between u and l is replaced by a classical rate (see Fig. 2)
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