Bad Qubits — Learn Quantum by Doing

Multiple choice

For the singlet state, the correlation along axes differing by angle (x - y) is E(x, y) = -cos(x - y). With a=0, a'=pi/2, b=pi/4, b'=-pi/4, compute S = E(a,b) + E(a,b') + E(a',b) - E(a',b'). What is |S|?

4
2
2*sqrt(2) ≈ 2.828
1/sqrt(2) ≈ 0.707