Dong H, Xu D Z, Cai C Y, Sun C P
Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing, China.
Phys Rev E Stat Nonlin Soft Matter Phys. 2011 Jun;83(6 Pt 1):061108. doi: 10.1103/PhysRevE.83.061108. Epub 2011 Jun 8.
We study the physical mechanism of Maxwell's demon (MD), which helps do extra work in thermodynamic cycles with the heat engine. This is exemplified with one molecule confined in an infinitely deep square potential with a movable solid wall. The MD is modeled as a two-level system (TLS) for measuring and controlling the motion of the molecule. The processes in the cycle are described in a quantum fashion. It is discovered that a MD with quantum coherence or one at a temperature lower than the molecule's heat bath can enhance the ability of the whole working substance, formed by the heat engine plus the MD, to do work outside. This observation reveals that the essential role of the MD is to drive the whole working substance off equilibrium, or equivalently, to work between two heat baths with different effective temperatures. The elaborate studies with this model explicitly reveal the effect of finite size off the classical limit or thermodynamic limit, which contradicts common sense on a Szilard heat engine (SHE). The quantum SHE's efficiency is evaluated in detail to prove the validity of the second law of thermodynamics.
我们研究了麦克斯韦妖（MD）的物理机制，它有助于在热机的热力学循环中做额外的功。这通过一个分子被限制在具有可移动固体壁的无限深方势阱中来举例说明。麦克斯韦妖被建模为一个二能级系统（TLS），用于测量和控制分子的运动。循环中的过程以量子方式描述。研究发现，具有量子相干性的麦克斯韦妖或温度低于分子热库的麦克斯韦妖可以增强由热机加麦克斯韦妖组成的整个工作物质对外做功的能力。这一观察结果表明，麦克斯韦妖的本质作用是使整个工作物质偏离平衡，或者等效地，在具有不同有效温度的两个热库之间工作。对该模型的详细研究明确揭示了有限尺寸偏离经典极限或热力学极限的影响，这与关于西拉德热机（SHE）的常识相矛盾。详细评估了量子西拉德热机的效率，以证明热力学第二定律的有效性。
