MULTIPLE QUBITS

The state of two qubits can be described as a tensor product:

In simple notation, the two qubits state can be written as:

Two qubits exist as a superposition of four computational basis states (∣00〉, ∣01〉, ∣10〉, ∣11〉). Whereas, in a classical computer, eight qubits will be required to store four computational basis states.
The normalization condition for the above qubit requires that:

Similarly, to the case of a single qubit, measurements on two qubits will result in their collapse to a single two qubit state as one of the above computational basis states. The post measurement state will be one of those states. However, measurement on one of the qubits (e.g., the first qubit as “0”), the post measurement state will result in state:

.........(1)

The post measurement state is renormalized with a factor in the denominator, so that it satisfies the normalization condition. In the section on measurement (below), it will be shown how measurement results in the state shown above in Equation (1).