Fock state (number state)

Ch 4.4, Ch 34.2 An eigenstate of the number operator: $\hat{N}|n\rangle = n|n\rangle$. For the harmonic oscillator, $|n\rangle$ has exactly $n$ quanta of excitation. In quantum field theory, $|n\rangle$ represents a state with exactly $n$ particles. *See also:* Number operator, Creation operator, An