A quantum register is the quantum mechanical analogue of a classical processor register. A mathematical description of a quantum register is achieved by using tensor products of qubit bra or ket vectors. For example, an n qubit quantum register is described by the element

∣Ψ⟩ = ∣ψ⟩₁ ⊗ ∣ψ⟩₂ ⊗ … ⊗ ∣ψ⟩_n in the tensor product Hilbert space

H = H₁ ⊗ H₂ ⊗ … ⊗ H_n

Category:Handbook of Quantum Information