A quantum register is the quantum mechanical analogue of a classical processor register. A mathematical description of a quantum register is achieved by using a tensor product of qubit bra or ket vectors. For example, an $n$ qubit quantum register is described by an element $|\backslash Psi\backslash rangle=|\backslash psi\backslash rangle\_\{1\}\backslash otimes|\backslash psi\backslash rangle\_\{2\}\backslash otimes\backslash ldots\backslash otimes|\backslash psi\backslash rangle\_\{n\}$ in the tensor product Hilbert space $\backslash mathcal\{H\}=\backslash mathcal\{H\}\_\{1\}\backslash otimes\backslash mathcal\{H\}\_\{2\}\backslash otimes\backslash ldots\backslash otimes\backslash mathcal\{H\}\_\{n\}$