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More on superposition. General state of a photon and spin states

  Рет қаралды 201,891

MIT OpenCourseWare

MIT OpenCourseWare

Күн бұрын

Пікірлер: 130
@justindrew7401
@justindrew7401 6 жыл бұрын
This guy is a genius teacher. As a teacher I can tell you this is the result of great intelligence, experience, and mastery of the subject.
@adrienrandall9483
@adrienrandall9483 3 жыл бұрын
i realize I'm kinda randomly asking but does anybody know a good website to stream new series online?
@jimhalpert9898
@jimhalpert9898 2 жыл бұрын
yes I do
@thehellfromthemountaint
@thehellfromthemountaint 3 ай бұрын
​​@@adrienrandall9483 idk if it helps. But in Russia we pirate everything and it usually have original in English with subtitles, you can try kinogo, zetflix, seasonvar Oh fck you asked this 3 years ago my bad
@joesmith8288
@joesmith8288 4 жыл бұрын
I like how much time he spends on clarifying the superposition principle and measurement.
@isatousarr7044
@isatousarr7044 28 күн бұрын
In quantum mechanics, the concept of superposition is fundamental, particularly when discussing the state of photons and the intrinsic spin of particles. Superposition refers to the ability of a quantum system to exist in multiple states simultaneously until a measurement is made. For photons, superposition commonly manifests in their polarization states. A photon can be in a superposition of horizontal and vertical polarization states, represented mathematically as |ψ⟩ = α|H⟩ + β|V⟩, where |H⟩ and |V⟩ denote the horizontal and vertical states, respectively, and α and β are complex coefficients that determine the probabilities of measuring each state. Similarly, spin states in particles like electrons also exhibit superposition. An electron's spin-½ state can be expressed as |ψ⟩ = a|↑⟩ + b|↓⟩, where |↑⟩ and |↓⟩ represent the "up" and "down" spin states. The coefficients a and b correspond to the likelihood of measuring the electron to be in either spin state upon observation. The fascinating aspect of superposition lies in its implications for quantum entanglement, interference, and the behavior of systems at the quantum level, fundamentally challenging our classical intuitions about the nature of reality. As a result, superposition not only plays a crucial role in the theoretical framework of quantum mechanics but also underpins many emerging technologies, including quantum computing and quantum cryptography.
@thisisFaye1
@thisisFaye1 5 жыл бұрын
he got a hair cut
@MrDroenix
@MrDroenix 4 жыл бұрын
Haha that was my first thought too
@endogenic6913
@endogenic6913 4 жыл бұрын
@@MrDroenix same
@uncountableuk
@uncountableuk Жыл бұрын
:) my first observation too
@ldanielfch
@ldanielfch Жыл бұрын
Yes
@eightysevenf
@eightysevenf Жыл бұрын
Lolol thanks i was like.. something’s different i’m confused 😅
@drdd333
@drdd333 6 ай бұрын
I thoroughly enjoy this gentle teacher. Brilliant.
@nst1058
@nst1058 4 жыл бұрын
Awesome mathod of explaining the theory, respect from India🙏
@zhaoxingdeng5264
@zhaoxingdeng5264 2 ай бұрын
Amazing quantum mechanics! Amazing professor!
@zheyuchong9477
@zheyuchong9477 2 ай бұрын
The way he explained this was very efficient.
@kaushaljain5999
@kaushaljain5999 4 жыл бұрын
4:41 to 4:57 in previous lecture L1.4 you have said that after polarization state becomes either or . There is no significance of cosAlpha or sinAlpha coefficient which is in front of them. So after polarization there should be no or One real parameter which is no. "1". Another Query_If there is one parameter then before polarization there should be three real parameter (one from real no 1 and two from complex no beta by alpha)
@brainstormingsharing1309
@brainstormingsharing1309 4 жыл бұрын
Absolutely well done and definitely keep it up!!! 👍👍👍👍👍
@sayedahmed7465
@sayedahmed7465 4 жыл бұрын
Excellent way of teaching , absolutely fascinating !
@FirstAmendmentAudits
@FirstAmendmentAudits 4 ай бұрын
❤ come back to 7:07
@kaushaljain5999
@kaushaljain5999 4 жыл бұрын
2:04 to 2:09 _ how will we get state minus A or iota A by superposition of A by itself. Since to get state 2 A is obvious by superimpose one A by another A.
@andressalvadorsartarelli6393
@andressalvadorsartarelli6393 2 жыл бұрын
Muy buen docente. Explica con mucha claridad
@georgesbegon4252
@georgesbegon4252 4 жыл бұрын
Données claires excellent professeur l écriture est très lisible ce qui est déjà révélateur le tableau est bien filmé quant à la validité des théories je reste très modeste pour ma part vu que l on a constaté tant de remise en question depuis Newton ..
@mona82
@mona82 7 жыл бұрын
Thanks MIT
@nimeshdwivedidwivedi1530
@nimeshdwivedidwivedi1530 2 жыл бұрын
Wonderful session sir proper understand thats superposition sir
@kaushaljain5999
@kaushaljain5999 4 жыл бұрын
1:47 to 1:52 Why is it physical assumption? Because i think it seems obvious.
@FirstAmendmentAudits
@FirstAmendmentAudits 4 ай бұрын
6:35 Come back to 6:44 6:44 6:44 6:45 6:45 6:45
@magnfiyerlmoro3301
@magnfiyerlmoro3301 7 жыл бұрын
i dont understand when he says, for 2 complex parameters there is 4 real parameters, thanks for explaining!!
@fcwong1
@fcwong1 5 жыл бұрын
alpha = a + bi beta = c + di. a, b, c, and d are the 4 real parameters.
@eshankvaishnavi3821
@eshankvaishnavi3821 4 жыл бұрын
fcwong1 thanks
@brandomiranda6703
@brandomiranda6703 4 жыл бұрын
how did he resolve Einstein's paradox (e.g. how do we know if half were down already before the measurement rather than this superposition)?
@akindeleoduwole1094
@akindeleoduwole1094 6 жыл бұрын
Quite enlightening and helpful. Thanks. From Nigeria
@zack_120
@zack_120 Жыл бұрын
These Superposition lectures did not explain the mechanism how a particle can be in both positions at the same time but only talked about what it is which is already known. It looks really weird, even hard to teach by experts. By comparison, the entanglement topic is taught clearer in a simple but convincing eq.
@lepidoptera9337
@lepidoptera9337 3 ай бұрын
The language of non-relativistic quantum mechanics is, unfortunately, very misleading. There are no particles here. What we have are systems that are exchanging energy, momentum, angular momentum and charges. When he talks about "spin up", then he means that the detecting system has received a small amount of angular momentum that has a (classical) angular momentum vector that is pointing up in the coordinate system of the detector. A quantum measurement is a histogram of a series of individual spin measurements, i.e. in that histogram roughly half the spins will point up, half will point down. Therefor the histogram is in superposition, NOT the individual measurement. The individual measurement is quantized and can only have one realized states of two possible states. That is no different from throwing dice. The probability distribution of fair dice is 1/6 for all six possible outcomes, but an individual dice throw can only be one of the possible values of 1, 2, 3, 4, 5 and 6.
@jorfoas
@jorfoas 2 жыл бұрын
I would really appreciate if the teacher labeled axes properly. For example, in minute 7:23, I am assuming that both X and Y axis represent electric fields, but that should be clarified.
@furkanunsal5814
@furkanunsal5814 4 жыл бұрын
11:07 Up allons y and down allons y
@p.s.design4338
@p.s.design4338 7 жыл бұрын
Really great lectures.
@saskiavanhoutert6081
@saskiavanhoutert6081 Жыл бұрын
Very clear explanation, thank you very much Einstein was right, your explanation also, kind regards, Saskia van Houtert engineer/office-manager graduaded at the Graphic Lyceum, the Netherlands 29 june 1995 as a Graphic Technical Engineer. And graduaded at 19 july 1997 as a office-manager. at the Economical Administration Education ECABO-BOVA at Breda. So I have 2 profession possibilities; engineer/office-manager.
@SaeKan-x1h
@SaeKan-x1h 5 ай бұрын
This is a great lecture. However, I didn't understand the last explanations. Why we get all the particles spinning up in x-direction after measurment in a superposition? I'm sorry if I misunderstanding it.
@lepidoptera9337
@lepidoptera9337 3 ай бұрын
If you are preparing an ensemble of spins all up in x-direction and then you make a measurement of that ensemble in y-direction, then on average 50% will be up and 50% will be down. The mix depends on the angle between the preparation and the measurement.
@joseluisrodriguez2605
@joseluisrodriguez2605 Жыл бұрын
Exelente mi profe saludos desde la fiee lima peru especialidad ing electronica de potencia
@ryanrizzo3866
@ryanrizzo3866 7 жыл бұрын
Excellent Lectures! Very helpful.
@silberlinie
@silberlinie 5 жыл бұрын
0:49 best. How he stands there, how the many contradictions expressed by others to what has been said here in his thoughts rush past. And he then stomping his foot inwardly and he defiantly arrives at an SO.
@afifakimih8823
@afifakimih8823 3 жыл бұрын
He is just not a good Professor,and an excellent teacher,he is one of the leading string theorist as well !!
@samybouzida7956
@samybouzida7956 3 жыл бұрын
Your comment could be misunderstood. Let me help you out here: ´´He is not just a good Professor, and an excellent teacher, he is also one of the leading string theorist as well !!`` The location of the word ´´just´´ in your sentence could lead to understand that you actually didn´t like the guy. We all know what you meant. Hope you won´t find me snob or anything. I 100% agree with you, this guy is beyond brilliant.
@bobbwc7011
@bobbwc7011 2 жыл бұрын
But string "theory" is scientific trash and should have been abandoned decades ago.
@Mizraab2912
@Mizraab2912 4 жыл бұрын
But you have to look in another direction-Such a nice line to convey that perspective matters
@joedarkmatter5051
@joedarkmatter5051 3 жыл бұрын
1:05 After he said "strange" , i see Dr Strange in him. Or is it just me =)
@theconstellation__
@theconstellation__ 4 жыл бұрын
If a photon is polarized in x direction by a polariser ,then what will happen when it passes through another identical polariser, as on Photon level it's not predictable, so do all the photons come out or ,they again come out in some probability
@kaushaljain5999
@kaushaljain5999 4 жыл бұрын
4:04 meaning of QM state
@jessstuart7495
@jessstuart7495 2 жыл бұрын
My gut tells me using the two measured outcome states (spin-up and spin-down) to describe the particle's state before measurement (superposition) might not be the best approach.
@mareksozolins6347
@mareksozolins6347 5 жыл бұрын
Good old days at school i have getting sleep to listen to teacher -)
@nickknight5373
@nickknight5373 4 жыл бұрын
He seems to be talking at a similar tempo whatever the playback speed.
@redberries8039
@redberries8039 3 жыл бұрын
6:50 beta/alpha .... '2 real parameters' or gamma 'one complex parameter' ...How are we getting the complex from a division of the reals? ...and I thought the alpha beta has to be complex anyhow?
@ryanjbuchanan
@ryanjbuchanan 2 жыл бұрын
How beautiful the internet is. If only Einstein and Newton had such tech.
@phononify
@phononify 7 жыл бұрын
Would the argument hold also for the Hydrogen atom (assuming a nuclear spin of zero): Would the state of the bound electron would be also N*(|up>+|down>), or is the ensemble of that H atoms a mixture of up and down electron spin variants ? :) How could somebody distinguish these two cases experimentally ? Could you ? Thanks for your opinions.
@cakeathon9983
@cakeathon9983 7 жыл бұрын
I'm not sure what you mean by "N*(|up>+|down>)", the electron of each atom will have spin up or down with 50% probability. The experiments for spin are done on the 47th electron of silver atoms, the same thing should apply for all atoms. That being said, I don't think it can be done experimentally, it is just assumed that what is true for silver atoms is true for all atoms. The problem is that orbitals cause an angular momentum which dwarfs the angular momentum of electron spin, so you need large atoms for which the angular momentum due to orbitals cancels itself out enough to detect electron spin.
@elsayed111
@elsayed111 4 жыл бұрын
Dear Sir, in case of super position u tl about polaristion in two diretion where in the previous lec. u told that only one direction is the valid and other vanished, THEN HOW COULD YOY TAL ABOUTH SUPERPOSITION OF BOTH OF THEM THANS
@tangye8243
@tangye8243 6 жыл бұрын
Mind-blowing!
@brandomiranda6703
@brandomiranda6703 7 жыл бұрын
Also I wasnt super convinced about his argument of how we really know they are in a superposition rather than apriori being 50-50 split, does he explain it better latter or did someone catch that better than me?
@mohamedakrout9742
@mohamedakrout9742 6 жыл бұрын
This lecture kzbin.info/www/bejne/oouWk4OLgNRosMU of the same course (taught during another semester) explains exactly how and more importantly why there should be a superposition.
@rai2134
@rai2134 3 жыл бұрын
How can we design a superposition state of spin with probabilitis of 40% and 60%?
@schmetterling4477
@schmetterling4477 2 жыл бұрын
We change the strength of the magnetic field.
@kaushaljain5999
@kaushaljain5999 4 жыл бұрын
8:04 why have you given thanks at this time?
@abdurrauf7525
@abdurrauf7525 2 жыл бұрын
Respected Sir, which books you used for these letters?
@jessstuart7495
@jessstuart7495 2 жыл бұрын
Zwiebach recently published a textbook _Mastering Quantum Mechanics: Essentials, Theory and Applications_ , MIT Press, 2022
@abdurrauf7525
@abdurrauf7525 2 жыл бұрын
@@jessstuart7495 thanks
@stormtrooper9404
@stormtrooper9404 4 жыл бұрын
May someone explain what is IA> ? And how possibly IA> ~ 2IA> ~ -IA> ~ iIA> How can one "state" be equal to that same state x2?
@compilationsmania451
@compilationsmania451 4 жыл бұрын
1) i is a complex number equal to square root of -1. The teacher explains that in the previous lectures. You should start from there if you haven't seen them. 2) In a superposition equation, the states refer to the possible results and their coefficients squared are proportional to the probability of getting that state. So, the coefficient just refers to the probability, not an actual physical quantity. So, if you have a single possible state, then it doesn't matter what coefficient you add in front of it, physically it doesn't make a difference. To give you an example, if you take a bag with any number of red balls in it, if you choose any random ball from the bag, the probability of that ball being red is 1 irrespective of how many balls are in the bag, because there are only red balls in the bag.
@PrivateSi
@PrivateSi 4 жыл бұрын
I don't get it, he starts by saying two photons in superposition don't add or substract from each other, yet we know they constructively or destructively interfere.
@kaushaljain5999
@kaushaljain5999 4 жыл бұрын
Explain 3:19 to 3:29
@sauravmittal538
@sauravmittal538 7 жыл бұрын
how cn i build a new quantum state by superposition of spin of two electrons
@GrandGobboBarb
@GrandGobboBarb 6 жыл бұрын
11:19
@brandomiranda6703
@brandomiranda6703 7 жыл бұрын
Does he ever explain what "physical equivalence" really means? Is the rescaling valid due to quantum probability measures adding to one?
@vwcanter
@vwcanter 4 жыл бұрын
Yeah, it’s just a consequence of the same linearity he spoke of. If A and B are solutions, then A+ B is a solution. Therefore, A + A is also a solution. So 2A or 3A or iA or -A are also solutions. I think you could think of it as a result of probabilities adding to one, because he describes it as “normalization”. But someone else can perhaps explain that better.
@guitarttimman
@guitarttimman Жыл бұрын
Look up schrodinger's equation.
@duf.l6268
@duf.l6268 3 ай бұрын
What is the professor's name?
@jamalelqars3189
@jamalelqars3189 2 ай бұрын
Sir Barton Zwibach
@not_amanullah
@not_amanullah 3 ай бұрын
Thanks ❤️🤍
@brandomiranda6703
@brandomiranda6703 4 жыл бұрын
why does scale affect the physics?
@anonymous.youtuber
@anonymous.youtuber 3 жыл бұрын
When you do an experiment in classical physics you act on trillions and trillions of atoms at the same time and you only measure some average result that is the sum of many individual results. The atoms don’t scale, there are just many of trillions of them. You can’t grow an atom the size of a football and experiment on it.
@not_amanullah
@not_amanullah 3 ай бұрын
This is helpful ❤️🤍
@mishalkiranreddy1214
@mishalkiranreddy1214 4 жыл бұрын
Sir what exactly a state is?
@surendrakverma555
@surendrakverma555 2 жыл бұрын
Very good 🙏🙏🙏🙏🙏🙏
@jamesfullwood7788
@jamesfullwood7788 4 жыл бұрын
It's amazing how long a physicist can go on talking about something without even defining it (i.e., the wave function). If I was one of the students in the class I'd be like "Ok great, but what IS |A> ?"
@flygonfiasco9751
@flygonfiasco9751 4 жыл бұрын
This is a continuation of other lectures, not the first day of class.
@jamesfullwood7788
@jamesfullwood7788 4 жыл бұрын
@@flygonfiasco9751 I watched all the lectures leading up to this one....
@flygonfiasco9751
@flygonfiasco9751 4 жыл бұрын
James Fullwood Rewatch L1.4. In the latter part of the video, he goes into depth about Dirac notation describing quantum states using a photon as an example.
@jamesfullwood7788
@jamesfullwood7788 4 жыл бұрын
@@flygonfiasco9751 He still doesn't give a precise definition of the wave function. In mathematics, a function is a relation between two sets, one called the domain (the set of inputs)and the second called the codomain (the set of outputs). It's obvious that the codomain of the wave function is the complex numbers, but he never defines the domain.
@m.s.6449
@m.s.6449 4 жыл бұрын
Defining something before you know anything about it is impossible. First you learn of the existence of some new object, investigate its properties and only then, based on acquired knowledge, you can invent a definition for it.
@haiekmohammed6548
@haiekmohammed6548 7 жыл бұрын
Thankx professor from morroco
@themasstermwahahahah
@themasstermwahahahah 4 жыл бұрын
he looks a lot more whimsical with the longer hair
@kaushaljain5999
@kaushaljain5999 4 жыл бұрын
9:27 Explain
@mp3lwgm
@mp3lwgm 4 жыл бұрын
The title is misleading. You do not discuss the spin states of the photon. Instead you Segway from the polarization of the photon to the spin states of the electron; awkward !
@timmy18135
@timmy18135 4 жыл бұрын
11:10
@davidwilkie9551
@davidwilkie9551 5 жыл бұрын
Spin, the concept, is a particular identification of probability positioning states in the context interpreted Superspin Modulation, the Conception of the infinitesimal sync-timing, of zero difference synchronicity universally distributed by the mechanism suggested by Wheeler and Feynman applying to the "One Electron Theory", an infinite-closed loop equivalent to the meaning of a Black Hole Singularity Conception of inflation-collapse singularity = Eternity-now +/-.., the actual circumstances of time duration timing, QM-TIMESPACE. (Requires a pictorial observation technique/imagination) If QM-TIMESPACE e-Pi-i in-form-ation of Time Timing is a Holographic brane, an objective of resonance imaging that "floats on nothing" (Avagadro's? No, Archimedes principle is the same positioning here-now forever Principle as Superposition-Exclusion holographic image projection drawing. Multi-phase reciprocal-resonance-> "loop" between micro-macro vanishing point
@bobbwc7011
@bobbwc7011 2 жыл бұрын
You need to stop taking drugs. Your comment is insane rubbish.
@andreeapopa9635
@andreeapopa9635 4 жыл бұрын
can he teach our online classes? he's a much better teacher than ours LOL. you should always focus on the explanation instead of reading your PDF @my prof. *cough cough*
@bustercam199
@bustercam199 4 ай бұрын
Seems like he is misquoting what Einstein said about Realism.
@lepidoptera9337
@lepidoptera9337 3 ай бұрын
He is talking a lot of nonsense in general here. This class won't help the average student to an understanding of quantum mechanics.
@brandomiranda6703
@brandomiranda6703 4 жыл бұрын
does he depend what physically equivalent means?
@elhaditalbi346
@elhaditalbi346 Жыл бұрын
🌎
@SfhjjFghjki
@SfhjjFghjki 7 ай бұрын
For sy contest sup calculate Never RE MINDED ,,QUESTION QUALITY WE HAVE ,WHERE A SUBJECT, 2()+ ing¿ Like similar EYES ARE GOING STAGE // «««««| NEW SWORDS ,IM XOING AND WHAT // Energy free ,quanta Est MYTH DES PROBS ,
@thehellfromthemountaint
@thehellfromthemountaint 3 ай бұрын
Hold up, medic from tf2?
@bustercam199
@bustercam199 6 ай бұрын
No, this is incorrect.
@elosant2061
@elosant2061 Жыл бұрын
when he says "superimpose" doesn't he mean "superpose"?
@scimad
@scimad 3 жыл бұрын
1.25x
@ken91656
@ken91656 11 ай бұрын
It looks like a circular argument to me.
@ericreiter1
@ericreiter1 Жыл бұрын
I retract my comment. I just have experiments showing qm fails.
@jpzhang8290
@jpzhang8290 5 жыл бұрын
Laudau-style teaching. I like it.
@ericreiter1
@ericreiter1 4 жыл бұрын
What a terrible professor.
@mubeendewan2287
@mubeendewan2287 Жыл бұрын
how so?
@xrfxlp
@xrfxlp 4 жыл бұрын
Utter nonsense!
@mubeendewan2287
@mubeendewan2287 Жыл бұрын
how so?
@glenmenas9424
@glenmenas9424 6 ай бұрын
Describing spin up or down along the z axis is so far from what is actually happening. You cannot describe the wave two dimensionally and then describe spin on a third dimensional axis, especially if we're talking about photons because of how the electric field interacts with the magnetic field in a light wave. If you're going to describe the wave function of the nature of light and photons specifically, you must start by describing the perpendicular electric and magnetic fields in three dimensions instead of two, which I have seen no one do ever. Stop thinking in terms of sign waves!
@lepidoptera9337
@lepidoptera9337 3 ай бұрын
There are no waves here. There are only quanta of energy, momentum and angular momentum. You are correct that up/down doesn't work for photons because of relativity and we have to talk about helicity, instead, but that's a technical detail that doesn't matter at this level.
@ericreiter1
@ericreiter1 Жыл бұрын
I retract my comment. I just have experiments showing qm fails.
@ericreiter1
@ericreiter1 Жыл бұрын
I retract my comment. I just have experiments showing qm fails.
@ericreiter1
@ericreiter1 Жыл бұрын
I retract my comment. I just have experiments showing qm fails.
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