A coherent state is a right eigenstate of the annihilation operator, a ^ ^ | α α ⟩ ⟩ = α α | α α ⟩ ⟩ , which may be represented in terms of Fock states as | α α ⟩ ⟩ = e − − | α α | 2 2 ∑ ∑ n = 0 ∞ ∞ α α n n ! | n ⟩ ⟩