Lecture 24: Entanglement: QComputing, EPR, and Bell's Theorem

MIT 8.04 Quantum Physics I, Spring 2013
Instructor: Allan Adams

In this lecture, Prof. Adams discusses the basic principles of quantum computing. No-cloning theorem and Deutsch-Jozsa algorithm are introduced. The last part of the lecture is devoted to the EPR experiment and Bell's inequality.

License: Creative Commons BY-NC-SA

[LydellAaron]

8:27 - Intro to quantum computing.
13:07 - observable states (translation: real and imaginary).
13:58 - a qubit represented with two complex numbers.
14:26 - N qubits requires 2^N complex numbers.
16:56 - if we could build a quantum mechanical computer.
19:14 - a basic quantum system.
1:16:01 - Einstein says "QM is incomplete." Everyone else, "No it's not."

[savior]

Great and interesting teacher. Watched every lecture of it, he is extremely knowledgeable. Worth every minute.

[masterspark]

Alain Aspect, the last name on the black board, won the Nobel Prize in Physics in 2022.

[amarbapat]

I am not from MIT, but I still felt my heart sink when he closed the session
Great teacher! Great content

[youcanknowanything]

always a blessing to have access to this material. May God bless the professor and the folks that produce Online Courseware for free to humanity. Thankyou👍😁

[davidc]

thank you Allan and MIT, just a great teacher, it helped me a lot to understand quantum physics.

[krystiantomczuk]

Lecture I: 777K views

Lecture 24: 35k views

Most have not made it this far haha

[menglongyouk]

Thank you, Prof. Adams, for teaching this course with passion, and thank you, MIT, for making this freely available.

[PondsideKraken]

Of all the videos I could find, this is the one I was looking for. You are an excellent teacher

[afifakimih]

I think This lecture is just made history...very complex subject yet he explain very simply, very clearly so elegantly...certainly Allan Adams get a standing ovation👏👏👏

[SimonMadsen]

that's beautiful, thanks for verifying that at the end, and thanks also earlier lecture saying that it's not 'our' consciousness that decides the states so far we know now, though that would be interesting

[oreas]

Very interesting, quite above my current education level but I understood some of it.

[alexanderalexander]

In the extreme case, it can be formally considered that a trail is stretched from the entanglement site behind the entangled particles, through which subsequent interaction is carried out. In a double-slit experiment, after a particle hits the screen, all fragments of probability waves must be somehow coordinatedly destroyed, and in the case of photons, they move at the speed of light.

[MrSimmies]

Thank you Dr. Adams. This entire course was terrific. Makes one want to find out more!

[ciarahendricks]

This course has become my new favorite 💕

[mississippijohnfahey]

That mic drop at the end... Thank you to MIT for allowing everyone to access these resources, and Prof Allan Adams for doing the dirty work. This is incredible. I have much further to go, but am very grateful to have watched these lectures.

I'm bout to go watch 8.05, buuuut, when's QFT gonna come up tho??? I preciate y'all putting up Real Analysis, that was dope! Also... 8.044? :-)

[standardcoder]

6:36
That makes much more sense than what I've trying to make sense out of textbooks

[qingfengwang]

I benefit from Allan's lecture and watched every episode while having dinner. Absolutely fascinating.

[dreggory]

This was very good, I am still hung up on a lot of the details of the bell inequality. But this has been a nice drop in the bucket of understanding quantum physics.

[recurrenTopology]

As someone coming from mathematics, it is frustrating how consistently inconsistent notation is in QM. For the same general two qubit state discussed there are no less then 5 different notational representations used in this lecture,
numbered kets, both concatenated and separated,
a|00⟩ + b|01⟩ + c|10⟩ + d|11⟩ & a|0⟩|0⟩ + b|0⟩|1⟩ + c|1⟩|0⟩ + d|1⟩|1⟩,
arrows,
a↓↓ + b↓↑ + c↑↓ + d↑↑,
and a column vector,
[a b c d]ᵀ.


They are all equivalent, but the frequent convention switching seems inelegant at best and confusing at worst. In particular, the separated kets seems prone to error as it appears as though one could easily start to confuse the right and left qubits if not careful (this might be helped if a tensor multiplication symbol was included instead of just implied). Personally, I find it easiest to start with the concatenated kets to define the system, show the equivalency to the vector representation, then work entirely with the vector representation. This has the advantage that every operation is then simply represented as a unitary matrix. While the Deutsch example then becomes slightly more verbose, as you apply the function by finding the appropriate unitary transformations for each of the four potential function forms (though they are just block identity and Pauli-X matrices), I find this a clearer and more elegant framework.