On Tue, Aug 13, 2019 at 9:09 AM smitra <[email protected]> wrote: > On 12-08-2019 08:29, Bruce Kellett wrote: > > > > Look at this another way. It is just an illustration of > > complementarity. Measuring which slit the photon went through is a > > position measurement at the slits. Measuring the interference pattern > > at the screen is equivalent to a momentum measurement at the slits. > > Such measurement operators do not commute -- the measurements are > > complementary and cannot be performed simultaneously. > > > > It doesn't matter for orthogonality of the states whether or not they > are measured.
Of course it does. The slits are not orthogonal states unless they are measured position eigenstates. If they are not measured, they are individually superpositions of many position eigenstates (including eigenstates that overlap both slits), so the slits themselves are no longer orthogonal. Orthogonal states cannot interfere, that is why a position measurement at the slits makes the interference pattern on the screen disappear. The fact remains, that orthogonal states cannot interfere: (<A| + <B|)(|A> + |B>) = <A|A> + <B|B> + 2 <A|B> and the interference term <A|B> vanishes if |A> and |B> are orthogonal. You can't get away from this basic fact about quantum mechanics. Bruce It's of course true that if we measure the position at the > screen we're measuring something else than the which way information and > the position eigenstates are not the original superposition. But it > remain a fact that the state of which we're measuring the position > operator on the screen is a superposition of two orthogonal states and > we're then seeing an interference effect defined as the difference in > the number of dots in the screen of the actual counts and the sum of > what would be seen if slit 1 were cloes and slit 2 open and vice versa. > > Saibal > -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/everything-list/CAFxXSLQ3Fqw0Tv7j47wB4reQCbF67AC0iVq%3Dyd-Knkm7799UtQ%40mail.gmail.com.
