即竖直方向的单位向量。

It's the unit vector in the vertical direction.

这意味着这一项就是单位向量。

So, that means this actually should be the unit vector.

如何选择合适的单位向量来创建新的不等式。

How to choose appropriate unit vector to establish new inequalities.

通过保持量子态是单位向量，变换就都是幺正的。

By keeping quantum states as unit vectors, the transformations are all unitary.