The Study On Thermodynamics And Fluctuations Of Quantum Open System

Quantum heat engiens as energy converters provide an excellent platform for understanding nonequlibriium thermodynamics and statistical physics of quantum open systems where quantum effects and fluctuations are involved.In this thesis,we study the performance and flucuations of quantum Otto engines in finite time,revealing the novle thermodynamic behaviors of the quantum open systems.The quatum Otto engienes under consideration consitst of two quite different systems as the working substance:one is a spin system obeying Fermi-Dirac statistics,the other is a single-mode optical cavity statisfying Bose-Einstein statistics.For the Otto engine based on a spin system,we derive analtycial expressions of performance paramters,such as efficiency,power,and flucutuations,where the effects of quantum coherence due to finite-time operation and reservoir squeezing are included.For the finite-time quantum Otto engine working with a single-mode optical cavity,we investigate the machine performance by anlatyically derving the efficiency and power,with the emphasis on effects of quantum correlation on finite-time performance and machine operation mode.The main content of this thesis is as follows.1.We introduce briefly the physical meaning of quantum coherence and quantum discord and pointed out the organization of the rest of the thesis.2.We investigate the thermodynamics and fluctuations of a finite-time quantum Otto engine alternatively driven by a hot squeezed and a cold thermal reservoir.We show that reservoir squeezing significantly enhances the performance by increasing the thermodynamic efficiency and the power,and enables higher stability by decreasing the relative power fluctuations and speeding up the convergence of quantum efficiency to its most probable value.We also demonstrate the counterintuitive result that the efficiency can be larger than the Otto limit in the finite-time operation.These results are explained by our theoretical analysis that incorporates the effects of nonthermal reservoir and finite-time operation accounting for quantum friction and coherence on the machine performance and fluctuations.Experimental demonstration of this quantum heat engine is available,based on a single-electron spin pertaining to a trapped⁴⁰Ca⁺ion.We provide a general framework for reliably studying the finite-time quantum heat engine and derive important insights into the novel thermodynamic behaviors beyond the classical thermal machines.3.We theoretically prose and investigate a quantum Otto engine that is working with a single-mode radiation field inside an optical cavity and alternatively driven by a hot and a cold reservoir,where the hot reservoir is realized by using a beam of thermally entangled pairs of two-level atoms that resonantly interacts with the cavity,and the cold one is made of a collection of noninteracting boson modes.In terms of the quantum discord of the pair of atoms,we derive the analytical expressions for the performance parameters（power and efficiency）and stability measure（coefficient of variation for power）.We show that quantum discord boosts the performance and stability of the quantum engine,and even may change the operation mode.We also demonstrate that quantum discord improves the stability of machine by decreasing the coefficient of variation for power which satisfies the generalized thermodynamic uncertainty relation.Finally,we find that these results can be transferred to another quantum Otto engine model,where the optical cavity is alternatively coupled to a hot thermal bosonic bath and to a beam of pairs of the two correlated atoms that play the role of a cold reservoir.4.We summarizie the main conclusions and raise some open problems derserving to be studied in future.