Bad Qubits — Learn Quantum by Doing

Multiple choice

Consider the pure superposition

|+\rangle = \frac{1}{\sqrt{2}}(|0\rangle + |1\rangle)

versus a 50/50 classical mixture of

|0\rangle

and

|1\rangle

. When each is measured along the x-axis, what happens?

$|+\rangle$ gives the + outcome with certainty, while the 50/50 mixture gives + or - with probability 1/2 each
Both give + or - with probability 1/2 each, so they are physically identical
$|+\rangle$ gives + or - with probability 1/2 each, while the mixture gives + with certainty
Both give the + outcome with certainty