\ket{\psi}The ket notation \ket{\psi} is used in quantum mechanics to denote a vector in a complex vector space, typically representing the state of a quantum system. It is part of the bra-ket notation introduced by Paul Dirac.
A general quantum state in a two-level quantum system (qubit) as a superposition of basis states.
\ket{\psi} = \alpha \ket{0} + \beta \ket{1}A specific quantum state known as a superposition state, often used in quantum computing.
\ket{\phi} = \frac{1}{\sqrt{2}} (\ket{0} + \ket{1})Time evolution of a quantum state under a Hamiltonian H, according to the Schrödinger equation.
\ket{\psi(t)} = e^{-iHt/\hbar} \ket{\psi(0)}