a vector a ket and denote it by |a>
This state ket is postulated to contain complete information about the physical state;
everything we are allowed to ask about the state is contained in the ket.
Hell Fast·
An observable, such as momentum and spin components, can be represented by an operator, such as A
Hell Fast·
the bra ⟨ϕ∣ tells you “how much of the direction ∣ϕ⟩” is contained in ∣ψ⟩
也就是 row vector 是用来计算两个 vectors 之间的关系