Bennett Kochise, Mukamel Shaul
Chemistry Department, University of California, Irvine, California 92697-2025, USA.
J Chem Phys. 2014 Jan 28;140(4):044313. doi: 10.1063/1.4862236.
The semi-classical theory of radiation-matter coupling misses local-field effects that may alter the pulse time-ordering and cascading that leads to the generation of new signals. These are then introduced macroscopically by solving Maxwell's equations. This procedure is convenient and intuitive but ad hoc. We show that both effects emerge naturally by including coupling to quantum modes of the radiation field that are initially in the vacuum state to second order. This approach is systematic and suggests a more general class of corrections that only arise in a QED framework. In the semi-classical theory, which only includes classical field modes, the susceptibility of a collection of N non-interacting molecules is additive and scales as N. Second-order coupling to a vacuum mode generates an effective retarded interaction that leads to cascading and local field effects both of which scale as N(2).
辐射与物质耦合的半经典理论忽略了可能改变脉冲时间顺序和级联的局部场效应，而这种级联会导致新信号的产生。然后通过求解麦克斯韦方程组从宏观上引入这些效应。这个过程方便且直观，但具有临时性。我们表明，通过将与最初处于真空态的辐射场的量子模式耦合到二阶，这两种效应会自然出现。这种方法是系统性的，并且暗示了一类仅在量子电动力学（QED）框架中出现的更普遍的修正。在仅包含经典场模式的半经典理论中，N个非相互作用分子集合的极化率是可加的，且与N成正比。与真空模式的二阶耦合会产生一种有效的延迟相互作用，从而导致级联和局部场效应，这两者都与N²成正比。
