量子是波（物质波，抽象波，理想波），一定全局相干，传统量子力学并没有强调这一点。
如果退相干导致量子性质消失，那么一定存在反过程，即相干过程coherencing，导致量子相干建立。
如果没有限制条件，波处在自由传播模式，其理想状态为平面波。
波在限制条件下会相干加强模式，即本征模式。本征模式只与频率(能量)有关。
限制条件下，相干条件不利的频率，迅速衰减(damping)。
对于微观电磁系统，本征模式即原子、分子、或者固体的各种本征态(能级)。
本征模式是限制条件下，全局相干(coherencing)建立的，特征时间是系统尺度除以波的传播速度(周期)，可能需要几个周期。此即量子相干建立时间。
相干建立过程(coherencing)在不同条件下，可以表现为干涉(interferencing), 共振(resonation)，同步(syncronization)
考虑到历史，系统可能一开始就处在本征模式上
在一个波的系统中，任何信号(扰动)具有较宽的频率构成(频谱，spectrum)，如果没有耗散机制，能量将因为色散、相干反馈，集中到本征模式上。
如果有外来能量源，本征模式是优势模式，是系统能谱的峰值点。
薛定谔方程是全局方程，边条件就是全局相干条件，被边条件筛选出来的波(频率，能量)，就是本征态。“解”薛定谔方程，就是边条件筛选，即选择出全局相干有利的频率(能量)。
量子的相干建立
此博文来自论坛版块：军事天地（Military）
The popular saying goes that a laboratory can prepare a pure state (coherent). If there is no surrounding environment, the pure state will evolve according to the Schrödinger equation and will remain a pure state. The world governed by the Schrödinger equation is an (ideal) isolated one, where the entire universe is a state vector. According to the decoherence hypothesis, as part of the universe, isolated systems do not exist. The pure state is destroyed by the environment, coherence diminishes, and the system becomes entangled with the environment. The Schrödinger equation is no longer applicable, and the time evolution is governed by the master equation. The originally prepared quantum pure state system will evolve into a classical mixed state, where each state appears with a definite probability (states are no longer coherent). The environment plays the role of an observer, selectively "measuring" those observables from classical mechanics through Darwinian-like selection (Einselection). Unlike the Schrödinger equation, the master equation is not time-reversal invariant, so coherence does not seem to establish spontaneously.