自旋回波的一致热力学
Consistent thermodynamics for spin echoes
摘要：
自旋回波实验通常被认为是在违反热力学第二定律的具体物理系统中构成反热力学行为的瞬间。我们认为，一个适当的热力学处理的效果应该考虑到分子的自旋和平移自由度之间的相关性。为此，我们构建了一个熵功能使用玻尔兹曼宏观态，结合自旋和平移自由度。有了这个定义，自旋回波的热力学就没有什么特别之处了：退相对应于哈密顿演化，熵保持不变;耗散增加了熵。特别地，在回波中不存在熵减小的相位。我们还讨论了从基本的量子理论的宏观态的定义，我们表明，净磁化强度的衰减提供了一个忠实的测量熵变。
英文摘要：
Spin-echo experiments are often said to constitute an instant of anti-thermodynamic behavior in a concrete physical system that violates the second law of thermodynamics. We argue that a proper thermodynamic treatment of the effect should take into account the correlations between the spin and translational degrees of freedom of the molecules. To this end, we construct an entropy functional using Boltzmann macrostates that incorporates both spin and translational degrees of freedom. With this definition there is nothing special in the thermodynamics of spin echoes: dephasing corresponds to Hamiltonian evolution and leaves the entropy unchanged; dissipation increases the entropy. In particular, there is no phase of entropy decrease in the echo. We also discuss the definition of macrostates from the underlying quantum theory and we show that the decay of net magnetization provides a faithful measure of entropy change.
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