纠缠态的定义是不能表示成直积的状态. 而一些量子系统中，描述系统的纠缠态可近似等于直积态. 本文对这一类近似等式做概念性讨论，说明这是单个粒子相干叠加态的一种来源，很可能是唯一来源.

The definition of entangled state is that it cannot be expressed in a product state，however，in some quantum systems，the entangled states which are used to describe them could be approximately equal to the product states. Conceptual discussion for the approximate equations of such type can be used to explain that this is a source of producing coherent superposition of states of single particle，and it is very possibly the only source.