The [state vector](State%20vector.md) [inner product](Inner%20products.md#Complex%20inner%20product) between two states $|\phi\rangle$ and $|\psi\rangle$, denoted as $\langle\phi|\psi\rangle$ is a complex inner product between two vectors of either the same or different [Hilbert Spaces](Hilbert%20Spaces%20in%20Quantum%20Mechanics.md) with the following meanings. # Overlap [[overlap]] # probability amplitude  ## wavefunction [Wavefunction](Wavefunction.md) #QuantumMechanics/MathematicalFoundations