# Homework Help: Qubits probability

1. Apr 15, 2008

### t_n_p

1. The problem statement, all variables and given/known data
http://img249.imageshack.us/img249/4476/46715318ov5.jpg [Broken]

3. The attempt at a solution

I know to calculate the pr we square the number in front of the state.

e.g) for state psi 00, the pr is (1/root(2))^2

But for state psi 01, do I include the imaginary number part? That is, do I calculate the square of (1+i/2root(2))?

Thanks

Last edited by a moderator: May 3, 2017
2. Apr 15, 2008

### nrqed

The probability is the square of the magnitude of the coefficient (if the wavefunction is normalized). So the formula is that the probability of measuring E_{01} for example is

$$\vert C_{01} \vert^2 = C_{01} \times C_{01}^*$$

which is obviousy a rel number.
This should be familiar to you. Of course, when the coefficient is real, this becomes simply the ordinary square of the coefficient.

Last edited by a moderator: May 3, 2017
3. Apr 16, 2008

### t_n_p

Ah so its the complex conjugate. Makes sense!