We investigate the performance of a three-qubits quantum thermal transistor using coarse-graining, global, and local master equations, respectively. Special attention is paid to the validity of the three methods in different internal coupling strengths. The effects of system and bath parameters on the amplification effect are studied. It is found that small middle qubit frequency, weak internal coupling, and symmetric configuration of system-bath coupling lead to large amplification factor. The heat current amplification mechanism is discussed and quantum coherence does not contribute to amplification. Besides, the thermal transistor is realized by tuning the temperature of the middle bath, the temperature of the left bath, or the internal coupling strength.

中文翻译：

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量子热晶体管：从弱耦合到强内部耦合的统一方法

我们分别使用粗粒度，全局和局部主方程来研究三量子位量子热晶体管的性能。要特别注意这三种方法在不同内部耦合强度下的有效性。研究了体系和浴参数对扩增效果的影响。发现较小的中量子比特频率，较弱的内部耦合以及系统-浴耦合的对称配置会导致较大的放大系数。讨论了热电流放大机制，并且量子相干对放大没有贡献。此外，通过调节中间槽的温度，左侧槽的温度或内部耦合强度来实现热晶体管。