Abstract
Standard heat machines (engine, heat pump, refrigerator) are composed of a system (working fluid) coupled to at least two equilibrium baths at different temperatures and periodically driven by an external device (piston or rotor) sometimes called the work reservoir. The aim of this paper is to go beyond this scheme by considering environments which are stationary but cannot be decomposed into a few baths at thermal equilibrium. Such situations are important, for example in solar cells, chemical machines in biology, various realizations of laser cooling or nanoscopic machines driven by laser radiation. We classify non-equilibrium baths depending on their thermodynamic behavior and show that the efficiency of heat machines powered by them is limited by the generalized Carnot bound.
Highlights
Quantum systems are rarely completely isolated from their environment, whose influence, positive or negative, should be considered
Those models generally assume the interaction between a system and an environment composed of several baths, each in thermal equilibrium, thereby termed heat baths
We showed that quantum machines weakly coupled to a single non-equilibrium stationary environment, and subject to fast periodic driving by work reservoirs, can be described by the thermodynamical principles and bounds which are very similar to the standard ones if only the definitions of the basic notions, which are consistent with thermodynamics, are used
Summary
Quantum systems are rarely completely isolated from their environment, whose influence, positive or negative, should be considered. The theory of open quantum system was developed [1,2,3,4,5,6,7] to achieve this goal and in particular to open the way to the study of quantum heat machines, such as engines and refrigerators [8,9,10,11,12,13,14,15,16] Those models generally assume the interaction between a system and an environment composed of several baths, each in thermal equilibrium, thereby termed heat baths. Sunlight at the Earth surface is a rather homogeneous environment, the shape of its spectrum roughly corresponds to the Planck distribution at the Sun surface temperature Ts, but the photon density is much lower than the equilibrium one, and the absorption in the atmosphere creates “holes” in the spectrum Another example is a laser radiation [18] in a continuous wave operation mode. Different examples of non-equilibrium baths are given and they are classified according to their effects on heat machine operation
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