Can someone please explain what is Quantum interference and how it differs from classical interference


closed as too broad by ACuriousMind Oct 15 '18 at 15:47

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  • $\begingroup$ This question currently seems far too broad. Without any more specific question indicating the level of prior knowledge you're essentially asking for a complete introduction to quantum mechanics. $\endgroup$ – ACuriousMind Oct 15 '18 at 15:48

Here's the thing. Interference in Classical Physics is shown by waves only. Since waves are spread out in spae-time they tend to propagate along the space with their respective wave vectors. When two waves of slightly different amplitude and frequencies interfere they produce what we call interference effect. That is the waves in phase produce constructive interference and out of phase waves cancel each other out producing destructive interference.

Now whats funny in quantum realm, particles in motion exhibit wave nature.

Know more about matter wave here

When the classical two slit experiment is commenced on electrons(Quantum particles) surprisingly it produced the interference pattern on the screen. This is due to the wave nature of electrons. So what happens exactly?

So what is it waving? Does the electron spread out in the spatial space and interact with itself? Well no. It's not the physical spread of material particle but the distribution of probability over space and time. The wave of material particle is actually its probability of finding that particle in that space. The electron interferes with its probability distribution only. That is what happens in quantum interference. The new question arises that from which slit the electron went? To answer this if we install a measuring device at the slits, surprisingly the interference pattern vanish. That means the wave nature is suppressed.

So what do we conclude from it?

Prior to the measurement, the electron goes through every possible way it can to get to the screen, that is, throgh both the slits simultaneously, thus interfering with it's own probability distribution. That is the wave nature and particle nature is suppressed.

After installing the measurement device we measure that either the electron passed through one slit or the other. That is the particle nature and the wave nature is suppressed. So interference pattern vanishes. This is what we call the collapse of wave function.

That is why it is totally different from the classical wave interference. Hope it hepled :)


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