David Quintero on Nostr: Something I learnt recently in the online course on quantum foundations I'm following ...

Something I learnt recently in the online course on quantum foundations I'm following is that, in the double slit experiment, you can put in one slit a vertical polarizer, in the other an horizontal. You'll get two bands, as expected, since you're measuring.

But you can introduce, after the two slits with polarizers, diagonal polarizers, and you'll get the interference pattern! With the diagonal polarizers you don't know where the photons come from, you lose information, you have "undone" your measurement, so to say.

Curiously, you can explain everything with classical physics: a vertical and horizontal rays of light can't interfere, so two bands on the screen. And the diagonal polarizer allows interference again.