Quantum register

A quantum register (also known as a qregister) is the quantum mechanical analogue of a classical processor register.

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