[HN Gopher] PHYS771 Lecture 9: Quantum
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PHYS771 Lecture 9: Quantum
Author : dustingetz
Score : 52 points
Date : 2023-08-20 12:57 UTC (10 hours ago)
(HTM) web link (scottaaronson.com)
(TXT) w3m dump (scottaaronson.com)
| sampo wrote:
| > For example, I've had experts in quantum field theory -- people
| who've spent years calculating path integrals of mind-boggling
| complexity -- ask me to explain the Bell inequality to them.
|
| My favourite quantum mechanics textbook is Griffiths:
| Introduction to Quantum Mechanics. It is popular as a textbook
| for the first quantum mechanics course, which is typically in the
| second or third year of a physics curriculum. It has sections on
| EPR paradox and Bell's Theorem. First edition was published in
| 1994.
| tux3 wrote:
| The cat book again! It seems everyone recommends Griffiths. I
| finally gave in and my copy should be arriving in a couple
| weeks.
|
| I've looked through the Feynman lectures a bit, and although
| it's very nice for a free resource, it doesn't seem to be used
| very much at all in curriculums.
| whimsicalism wrote:
| Feynman is not sufficient as a physics textbook.
|
| Afaik the main games in town are Griffiths, Townsend, and
| Sakurai if you are a tryhard
|
| iirc I prefer Sakurai & Townsends treatment over Griffiths
| but I might be misremembering
|
| e: oh yes, i think griffiths intentionally avoids dirac
| notation which imo screws you later on down the line
| dustingetz wrote:
| what are the challengers? there are a few twitter scientists
| who have written QM textbooks that haven't made their way into
| university curriculum yet
| whimsicalism wrote:
| sakurai & townsend are the traditional challengers, when i
| was taking it i didn't really think the modern challengers
| were up to snuff but that might have changed
| adamnemecek wrote:
| To be honest, the quantum groups are my fav formalism in that
| general field http://sporadic.stanford.edu/quantum/
| dustingetz wrote:
| read it, cool idea to present starting with negative probability,
| didn't love it as an intro, liked ivan_ah's treatment better.
| also didn't like that Scott pushed complex numbers to the end
| given their intimate connection to waves and phase and
| interference which was not discussed and is core to my personal
| intuition so far.
| vietvu wrote:
| I met quantum by the first way, it is natural. However I agree
| the latter approach, quantum is more math than physics to me.
| With the age of quantum is about to come, I will read this
| lecture.
| ivan_ah wrote:
| If anyone is interested to learn more about quantum mechanics and
| the Dirac ket notation, check this out:
| https://minireference.com/static/excerpts/noBSLA_quantum_cha...
| (79pp; includes exercises and problems with solutions)
|
| It's the last chapter from my linear algebra book. The book is
| not free, but I'm happy to make this chapter free because QM is
| cool stuff.
| Corsome wrote:
| Your books are indeed excellent!
|
| I was wondering... what's your opinion on Geometric Algebra?
| (If you have one)
| dustingetz wrote:
| i read your book cover to cover it was amazing
|
| edit: https://www.amazon.com/No-bullshit-guide-linear-
| algebra/dp/0...
| torcete wrote:
| I was checking out the kindle version preview on amazon. You
| know, when you click "Read Sample".
|
| The mathematical formulas seem to be badly formatted and hard
| to read. I reckon this is just a problem with the html
| conversion for the preview.
|
| Can somebody confirm that it looks fine on the kindle?
| dustingetz wrote:
| sorry, i read this printed. It is textbook length, studying
| requires lots of flipping around. everything else kindle
| tho
| ivan_ah wrote:
| Please do not buy the Kindle version form amazon; it's not
| mine ... someone pirated it! Funny enough I can't report
| because the amazon page is broken:
| https://www.amazon.com/report/infringement/ (show a blank
| page for me, no form to fill out)
|
| I would recommend you get a print copy since it's much
| better for learning, but if you prefer digital-only copy
| you can get it through gumraod: https://gum.co/noBSLA It
| comes in PDF, ePub, and mobi formats. Here is an ePub
| preview (of another book) so you can see the math
| rendering: https://minireference.com/static/excerpts/noBSma
| th_v5_previe... I worked for 2+ years to get this to look
| decent, see https://minireference.com/blog/generating-epub-
| from-latex/
| ivan_ah wrote:
| Hey thx man! Always good to hear from readers.
| abdullahkhalids wrote:
| This is very well written. I checked for a couple of common
| issues that arise in introductory presentations of quantum
| mechanics, and found that you navigated most of them correctly.
|
| For example, in the entanglement section, you did discuss that
| entanglement is a basis independent property, which is a
| critical point to make - basis dependent "entanglement" exists
| in classical systems; it is just correlation.
|
| However, I disagree with the inclusion of the paragraph
| starting "There is something strange about the EPR state." The
| emphasis on 'immediately' in conjunction with the large
| distance between Alice and Bob is particularly problematic. The
| setting of EPR experiments is necessarily in a relativistic
| world, and in that world time is only a local property. Saying
| things happen simultaneously (= immediately) implies the
| presence of a privileged frame of reference, which is exactly
| what we don't want to do. There are ways of saying these things
| correctly, but that requires a lot more setup.
|
| I also have a minor nitpick in the sentence below" "We have
| complete certainty about the state of the composite system
| |\psi_-\rangle^{AB} , and complete uncertainty about the states
| of the individual subsystems controlled by Alice and Bob"
| Since, entanglement exists on a scale, it is better to delete
| the second "complete" in the sentence, as we can have only
| partial uncertainty (in the sense of some entanglement measure)
| about Alice and Bob's systems.
| hackandthink wrote:
| "The second way to teach quantum mechanics leaves a blow-by-blow
| account of its discovery to the historians, and instead starts
| directly from the conceptual core -- namely, a certain
| generalization of probability theory to allow minus signs"
|
| In my opinion, this is not the most natural and easiest way to
| get into quantum mechanics.
|
| And there are also (undergraduate) physics books that tackle the
| quantum mechanical concepts directly, e.g:
|
| https://www.feynmanlectures.caltech.edu/III_toc.html
|
| especially:
|
| https://www.feynmanlectures.caltech.edu/III_03.html (Probability
| Amplitudes)
|
| Negative probabilities (Wigner Functions) are more advanced:
|
| https://en.wikipedia.org/wiki/Wigner_quasiprobability_distri...
|
| Lucien Hardy "Reconstructing quantum theory" is really
| conceptional, but I think it is not the best way to start.
|
| https://arxiv.org/abs/1303.1538
| eigenket wrote:
| Wigner Functions are great and all, but they work quite badly
| for finite dimensional systems. Specifically they are a bit
| complicated for odd dimensional systems and don't work at all
| for even dimensional systems (see e.g. [1]). Given their
| limited applicability I don't see why we should treat them as
| particuarly fundamental when introducing quantum mechanics to
| students.
|
| [1] https://arxiv.org/pdf/quant-ph/0507094.pdf
| akjssdk wrote:
| I am not sure if this is how it is a correct representation. I
| believe a common approach is to do a short history of quantum
| in the first year, and then do a from the ground up approach in
| the second and third year. Depending on who teaches it, this is
| either starting from a particle in a box or the approach stated
| here. The historical story is useful, because it tells a little
| bit of the why.
| francasso wrote:
| Love this, I agree that for someone new to QM the historical
| approach is probably not the best idea (though I can imagine many
| physicists would be upset by the qbistic vibes of the article).
|
| But, if you have the prerequisites already (classical mechanics,
| electrodynamics and thermodynamics), it does make for a
| fascinating story. Malcolm Longair's couple of books titled
| "Concepts in Physics" are a great place where you can learn the
| history in detail.
| archgoon wrote:
| [dead]
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