According to Heisenberg's Uncertainty Principle, it is impossible to measure the values of conjugate variables simultaneously as measuring one accurately would make the other equally corrupt.
So in QKD, there's a thing that states that Eve can't eavesdrop as the very act would change it's quantum state(Heisenberg's principle). I would like to know the measurement of which conjugate pair is being referred to here. Do answer fast as I'll need to do a seminar on this topic tomorrow :)