In quantum computing, a quantum register is a system comprising multiple qubits. It is the quantum analogue of the classical processor register. Quantum computers perform calculations by manipulating qubits within a quantum register.

Definition

It is usually assumed that the register consists of qubits. It is also generally assumed that registers are not density matrices, but that they are pure, although the definition of "register" can be extended to density matrices.

pure qubits.

The Hilbert space is the tensor product.

The number of dimensions of the Hilbert spaces depends on what kind of quantum systems the register is composed of. Qubits are 2-dimensional complex), while qutrits), etc. For a register composed of N number of d-dimensional (or d-level

The registers quantum state-dimensional Hilbert space can in the bra-ket notation Such linear combinations are in quantum mechanics called superpositions are probability amplitudes. Because of the Born rule and the 2nd axiom of probability theory so the possible state space of the register is the surface of the unit sphere

Examples:

• The quantum state vector of a 5-qubit register is a unit vector

Quantum vs. classical register

There are both structural and functional differences between quantum and classical registers flip flops possibilities spanned by quantum pure qubits.

accordingly.

If we consider two pure qubits in superpositions it follows that it is capable of storing all the possible values (by having non-zero probability amplitude for all outcomes) spanned by two qubits simultaneously.

See also

• List of proposed quantum registers

• Quantum circuit

• Quantum logic gate

• Qudit

References

Further reading