Barra Felipe
Departamento de Física, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Santiago Chile.
Sci Rep. 2015 Oct 8;5:14873. doi: 10.1038/srep14873.
The laws of thermodynamics put limits to the efficiencies of thermal machines. Analogues of these laws are now established for quantum engines weakly and passively coupled to the environment providing a framework to find improvements to their performance. Systems whose interaction with the environment is actively controlled do not fall in that framework. Here we consider systems actively and locally coupled to the environment, evolving with a so-called boundary-driven Lindblad equation. Starting from a unitary description of the system plus the environment we simultaneously obtain the Lindblad equation and the appropriate expressions for heat, work and entropy-production of the system extending the framework for the analysis of new, and some already proposed, quantum heat engines. We illustrate our findings in spin 1/2 chains and explain why an XX chain coupled in this way to a single heat bath relaxes to thermodynamic-equilibrium while and XY chain does not. Additionally, we show that an XX chain coupled to a left and a right heat baths behaves as a quantum engine, a heater or refrigerator depending on the parameters, with efficiencies bounded by Carnot efficiencies.
热力学定律对热机的效率加以限制。如今，针对与环境弱耦合及被动耦合的量子引擎，已确立了这些定律的类似物，这为探寻提升其性能的方法提供了一个框架。那些与环境的相互作用受到主动控制的系统并不属于该框架。在此，我们考虑与环境主动且局部耦合的系统，其依据所谓的边界驱动林德布拉德方程演化。从系统加环境的幺正描述出发，我们同时得到了林德布拉德方程以及系统热量、功和熵产生的恰当表达式，从而扩展了用于分析新型及一些已提出的量子热机的框架。我们在自旋1/2链中阐述了我们的发现，并解释了以这种方式耦合到单个热库的XX链为何会弛豫到热力学平衡，而XY链却不会。此外，我们表明，耦合到左右两个热库的XX链根据参数的不同可表现为量子引擎、加热器或制冷机，其效率受卡诺效率限制。
