Quantum thermodynamic cycles and quantum heat engines

Abstract

In order to describe quantum heat engines, here we systematically study isothermal and isochoric processes for quantum thermodynamic cycles. Based on these results the quantum versions of both the Carnot heat engine and the Otto heat engine are defined without ambiguities. We also study the properties of quantum Carnot and Otto heat engines in comparison with their classical counterparts. Relations and mappings between these two quantum heat engines are also investigated by considering their respective quantum thermodynamic processes. In addition, we discuss the role of Maxwell's demon in quantum thermodynamic cycles. We find that there is no violation of the second law, even in the existence of such a demon, when the demon is included correctly as part of the working substance of the heat engine.

Implications of Coupling in Quantum Thermodynamic Machines

“…When the working medium of the Otto cycle is classical ideal gas, the efficiency of the system is written as η = 1 − (V 1 /V 2 ) γ−1 , where V 1 and V 2 are initial and final volumes (V 1 < V 2 ) of the adiabatic expansion process and γ = C p /C v , is the ratio of the specific heats [33]. Similar to the classical cycle, the quantum Otto cycle consists of two adiabatic processes and two thermalization processes [34,35]. The system exchanges heat with the bath during the thermalization processes and the work is done when the system undergoes adiabatic processes.…”

“…Otto cycle with a single harmonic oscillator (or a spin system) constituting the working medium of the engine is studied in different works [27,30,34,35,38,39]. Here we briefly review this.…”

“…Therefore, the isothermal process of the total system can be considered equivalent to the isothermal processes of two independent subsystems taken together. To understand the generality of the bounds of the efficiency observed in Otto cycle, we can consider other cycles such as Carnot cycle consisting of two isothermal processes and two adiabatic processes, and Stirling cycle consisting of two isothermal processes and two isochoric processes [35,39,44] (see Figure 3). Like the Otto cycle, in the Stirling cycle, the global efficiency is bounded by the efficiencies of independent subsystems because at any stage of the cycle, the total system can be decomposed into two independent subsystems.…”

“…Hence the efficiency of the total system lies below the efficiency of oscillator A. Now we can compare the performance in terms of work given in Equations (29) and (35). The terms on the right-hand side of these equations are positive when both the independent systems work in the engine mode.…”

Deep-subwavelength lithography via graphene plasmons

“…Quantum heat engines are typically based on implementations of quantum Carnot, Otto [15], Brayton [16,17], Diesel [16,18] or Stirling cycles [19,20], with a succession of strokes that alternatively extract work and exchange heat with the hot and cold reservoirs. As a result the generation of work is an intermittent process.…”