The state vector in a specific basis. It can be seen as a covariant vector in this case. The state vector in position representation, e.g. ψ α ( x 0 ) = ⟨ x 0 | α ⟩ {\displaystyle \psi _{\alpha }(x_{0})=\langle x_{0}|\alpha \rangle } , where | x 0 ⟩ {\displaystyle |x_{0}\rangle } is the position eigenstate.