## Double Slit IV: Quantum Eraser: Home Version

Interesting physics explained with many thought experiments and little math.
SsDd
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### Double Slit IV: Quantum Eraser: Home Version

The lecture video is embedded below.

Additionally, slides used in the lecture are embedded below, or can also be downloaded directly from here.

Questions after the lecture? Please feel free to post them in the same thread.

Click to play embedded YouTube video.

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Double-slit experiment
Wave–particle duality

SsDd
Science Officer
Posts: 113
Joined: Sat Dec 05, 2009 1:06 am
AKA: Abhi
Location: Michigan Tech

### Re: Double Slit IV: Quantum Eraser: Home Version

However, the photon is now ENTANGLED with the which-path apparatus. The state of the photon cannot be specified without reference to the states of the polarizers. This kind of distinction becomes very apparent when you look at the math. I’m not suggesting that getting into the math is a good idea for this kind of course. What I am suggesting is that such distinctions are CRUCIAL. I think they have everything to do with why we all struggle with QM.

maplebayou1
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### Re: Double Slit IV: Quantum Eraser: Home Version

I continue to struggle with basic concepts. On the one hand, I have been watching some of Leonard Susskind's lectures on QM, in which he essentially equates measurement with entanglement between an isolated system and another system. This is confusing to me. Measurement in the QM sense seems to involve the acquisition of a particular value for an observable at a particular time. Entanglement, on the other hand, does not seem to occur at a particular time in the experiment, but is merely introduced as part of the framework for calculating the time evolution of the system, given the experimental apparatus. Perhaps there is some ultimate equivalence but it is beyond me at the moment

The issue of time seems to be at the heart of varying interpretations of QM. Whether a system is in a particular state at a particular time, whether it is in multiple states, or whether it exists merely as potentialities until it interacts with some other system. What exactly causes it to exhibit certain behavior, and when exactly these causal relationships come into play in the course of an experiment. These are very unresolved questions in my mind, and perhaps they can't be resolved under current paradigms.

owlice
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### Re: Double Slit IV: Quantum Eraser: Home Version

An interesting question on this lecture came in email from Alvydas Jakeliunas: