If a qubit is in perfect superposition between the 0 and 1 state, there is an equal probability of measuring 0 and 1. Suppose we have a system of 5 qubits, all in the equal superposition state. If we measure the qubits, what is the probability to obtain 5 zero's?
If we measure one qubit in perfect superposition, the probability of obtaining a zero is 50%.
If we have 5 of these qubits, the probability of measuring all zero's is: (1/2)^5 = 1/25 = 3.125%