Abstract
We consider measurement based single temperature quantum heat engine without feedback control, introduced recently by Yi, Talkner and Kim [Phys. Rev. E 96, 022108 (2017)]. Taking the working medium of the engine to be a one-dimensional Heisenberg model of two spins, we calculate the efficiency of the engine undergoing a cyclic process. Starting with two spin-1/2 particles, we investigate the scenario of higher spins also. We show that, for this model of coupled working medium, efficiency can be higher than that of an uncoupled one. However, the relationship between the coupling constant and the efficiency of the engine is rather involved. We find that in the higher spin scenario efficiency can sometimes be negative (this means work has to be done to run the engine cycle) for certain range of coupling constants, in contrast to the aforesaid work of Yi, Talkner and Kim, where they showed that the extracted work is always positive in the absence of coupling. We provide arguments for this negative efficiency in higher spin scenarios. Interestingly, this happens only in the asymmetric scenarios, where the two spins are different. Given these facts, for judiciously chosen conditions, an engine with coupled working medium gives advantage for the efficiency over the uncoupled one.
Highlights
Unification of seemingly different heat engines in terms of efficiency started in the early 19th century with Sadi Carnot [1]
We investigate the effect of coupled working medium in the measurement based single temperature quantum heat engine without feedback
We show that, when the coupling constant J is nonzero, the efficiency is increased over the uncoupled scenario, i.e., J = 0 case for certain range of non-zero J
Summary
Unification of seemingly different heat engines in terms of efficiency started in the early 19th century with Sadi Carnot [1]. With the onset of the quantum effects, many interesting phenomena such as the increase of efficiency beyond Carnot’s limit [19,20,21] may occur It is not in contradiction with the second law of thermodynamics. The essential part of the engine which replaces feedback is a non-selective quantum measurement on the working medium, changing the average energy of the system, and, enabling one to extract useful work. We analyze the role of coupled working medium in this single temperature measurement driven quantum heat engine without feedback control [42].
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