Four Principles of Quantum (Quantum pt1) - Computerphile
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- เผยแพร่เมื่อ 7 มิ.ย. 2023
- The four underlying principles of Quantum. Part one of a series on Quantum Computing, Victor V. Albert is a Theoretical physicist at University of Maryland and NIST.
Victor V. Albert: @victorvalbert on Twitter
/ computerphile
/ computer_phile
This video was filmed and edited by Sean Riley.
Computer Science at the University of Nottingham: bit.ly/nottscomputer
Computerphile is a sister project to Brady Haran's Numberphile. More at www.bradyharan.com
I watched this thinking I would not understand, but I believe he did a great job at explaining it. It's all directly related to physics, of which I have a rudimentary understand from getting a degree in geology a long time ago. I found the video very profound.
⌚Timestamps:
00:00 Introduction
00:32 1st Principle: Discreteness
04:31 2nd Principle: Superposition/Collapse
08:27 3rd Principle: Uncertainty
13:31 4th Principle: Entanglement
17:04 Conclusion
You forgot to inclue 15:30 😂 “best visual gag!”
@@mikew6644 hehehehehe top moment
What an outstanding explanation.
Is it? I don’t know...
I recognize it is a bit hard to thread the needle when describing entanglement so that you don’t lead people to think that it lets you send signals, while also not making it seem like entanglement is nothing more than classical correlation, but...
Hmm..
"behind them"
great to know whats actually wrong with things by someone who has touched them.
One thing that this made clear to me is how difficult it is to be left handed when writing and drawing. I wonder if the side of the hand is permanently stained by Sharpie ink. (Thanks for the clear - as far as it can be clear - explanation. I don’t have to look to know I’ll never completely get it.)
I'm left-handed and all throughout my elementary and middle school I used pencils (teachers didn't allow pens). My left palm, where my hand would rest on paper, would always be smeared in lead from pencils. What's worse is that I would sweat a lot, so my hands would be moist and get mixed with the lead and just completely smear the paper. I would rewrite some words that weren't legible anymore lol. I'm glad I was finally able to use a pen in high school.
I’m left handed and remember doing math right to left just because I could for that reason
Seems like languages that are written right-to-left like Arabic and Hebrew would be the perfect fit for left-handed folk.
Drawing, however, seems like it'd be equally bad no matter which hand you use. After all, you don't work on the picture systematically in one particular direction like you do with writing. You use random-access to make a tweak here, a tweak there until you get it to a state you don't hate.
@@Roxor128 maybe someone will come up with a little platform to suspend the hand slightly above the surface. Or a hoist like they use in the hospital for people with broken legs🙂 (I live about 10 miles from the U. Of Md. where this man works. I fully expect to answer a knock at the door where he says, “Knock it off!”)
@@glennstasse5698 My mother teaches art (small business, not school) and she's made a bunch of little bridges like that for when the class is doing monotype prints and needs to paint on the plate before printing. Much less tiring than trying to do it just holding you hand above the plate.
I had the pleasure to meet you in person in the Quantum Winter School. You were the best lecturer there!
Great presentation on some essentials. I think that any discussion of quantum needs to mention and emphasize that amplitudes of the wave function are complex and interfere.
Amazing, this really helped shift my perspective, nice sock5 btw. Destiny is almost as fun as State(s)! Starting to grasp diffuse states a bit more, thanks for the prompt video.
"Energy in a box is n^2"
Did you mean 2^n? The values 1, 2, 4 are 2^0, 2^1, 2^2. If it wasn't an error, how did you get to 2?
I also thought this was odd. I think the “proportional to square of number of oscillations” is correct, rather than it being 2^n ,
because the Hamiltonian (for “a particle in a (1D) box”) should be like, (in the interval) the second derivative times some constant , (and outside that interval, infinity)
and the eigenvalues for that would be proportional to the square of the frequency, because like,
Second derivative of sine(c x) = - c^2 sine(c x)
.
But, I don’t know how he got 1,2,4
@@drdca8263 You're right, it's a typo. Energy should be 1, 4, 9, etc.
@@victorvalbert Huh? 3^n doesn’t make any more sense than 2^n.
Oh, I guess you mean 2 n^2 + 1 , not 3^n .
1, 2, 4, they come in squares?
What?
think he meant "powers of two"
@@gloverelaxis the particle in a box energies come in squares and he made a mistake in the video. For what it's worth, the video has a few other mistakes
This is in so many regards an awsome video, but in my opinion the observation part "when we look at it" and the drawn eye lets it's seem as if it has something to do with the human observer and with consciousness, rather than just an interaction with another particle, like electrons or photons. Working to understand that decoherence will occur, even if we just measure the particle without looking at our instruments, without looking at them, it is not about the human observer but rather about the interaction with some other particle.
Just got a bit stuck in your 'part 2' about the super-positions. What does 'to observe' even mean? I'm sure I've read Roger Penrose telling me that the double-slit experiment always produces an interference pattern *until* you put a detector in one of the paths, which strongly implies that the detector is 'an observer'. I know I'm getting old, but I would really like to actually grok this before I'm done - call it a bucket-list thing!
There are different interpretations. I have a favorite. There are lots of ways a particle can be, but fewer ways a huge group of particles can be, because it's hard to coordinate large groups without smearing information out too thin. Things we call 'superpositions' are ways a particle can be, but they have to be information dense; if a huge group of particles (an observer) tries to interact with a superposition, the information smears out and ends up picking one position or the other. The particle is still in a superposition, but only one position made it to the whole group - you only observe one state.
Anyway, I'm not a physicist, so take all of this with a lot of salt.
Another way to think about it is that the observer (detector, eyeball, whatever) interacts with the quantum state and becomes entangled with it. Since the detector is not isolated from the environment, decoherence quickly propagates and we say the state has collapsed.
Basically, it means to interact with it in some way or another. Anything that can interact with the system can be an observer.
Simple, well done!
LED's are a prime example of a quantized state. The light given off is due to electrons moving between energy states. The discrete energy levels determine the wavelength of the light given off.
I am sure there are things wrong with this example, but it's good enough for a layperson to understand.
Very interesting. Yet so complicated. I wonder how many hours of human brain effort went into figuring out these 4 principles :D
Thanks for this.
Great video.
When he talks about how we need a way to write out the states denoting their quantum, he mentions a word at 3:25, that sounds like 'Ket'? Could someone please spell out the word. Thank you.
If you could observe all states in 'parallel', you could solve SAT (or any NP-problem) with a quantum computer, but that is not possible with the linear quantum model.
I don't like the sock analogy that was made at the end of the video. While at a surface level, it's as simple as 'getting information' about one system by measuring another, there is deep physics at play that makes things more interesting than that.
There is no perfect analogy, but also I don't think this guy is on this channel to explain the physics. He just wants to explain the useful aspects.
That sock animation was amazing
I was a bit embarassed that when Discreteness was mentioned I did not immediatelly understand what would be discussed
In the popular culture the notions of superposition, quantum leaps, quantum entanglement get highlighted a lot more
Discreteness of energy levels is a lot less catchy
But if I recall correctly then this very theorietical insight let scientists finally understand the hydrogen atom and the orbits of electrons and what light gets emitted when the electrons jump energy levels
And for that it is awesome
From programmer point of view: when debugging a deterministic computer code makes you want to bang your head to the wall, it must be fun working on a quantum computer where something like probability & superposition magic involved
Extraordinaly good
if there is intrinsic randomness and observation changes the 'data' randomly, how can we create a 'computer' with repeatable and predictable behavior?
to me this is still magic. There must be an explanation for superposition that doesn't feel like paranormal.
Superposition is pretty much just a way for us to describe all the outcome of an insolated system. There isn't realy one thing at multiple place at the same time. At this point there is only a set of probability to see the thing at one place or the other. When we do the mesure we need to interact with the system (We are part of it, like anythng in the universe) and that interaction change its state. For instance, to interact with a camera sensor, a wave need to emit a particule, by emiting it the wave just collapsed giving the particle its position. Think of it like a runner that is about to reach the finish line but get interupted by a fan to get its autograph, runner lose the race. If we mesured its velocity instead then a different interaction may occured loosing the ability to know its position. Like the fan that just took a picture of the runner, leaving him winning the race but not getting the autograph.
Yay! I love quantum computing
Shouldn't the discrete energy levels be 1, 4, and 9 if they're the squares of number of the quantum numbers?
Is he explaining this well? Seems like this could leave lots of misunderstandings about how this stuff works for what we know. Seems very loose with words and without the math some of this is confusing like “look at”
Yeah, he is doing a good job to explain it to the layman. Everything can be made more rigorous with the right math, except for the measurement/collapse. It's at the center of one of the most fundamental problems of quantum physics, the measurement problem. In practice, this doesn't lead to problems (you recognize what constitutes a measurement and what doesn't) and quantum physics is the most precise scientific theory ever conceived. However it is not very satisfying if you have the soul of a theoretical physicist. Maybe you heard about the multiverse once? It's an interpretation of the quantum physics that tries to solve the measurement problem (which still is very much open, there is no concensus)
I think as far as computer scientists might be concerned, it’s fine. Perhaps if you’re interested in the physics underlying the computations, you’d want some more specificity :P
@@NuclearCraftMod if one id a computer science who wants to understand quantum algorithms, one needs a better understanding than what can be obtained from this explanation
@@drdca8263 In my experience, there are things you don’t need to know in as much detail as a physicist might, except maybe in quantum cryptography. Usually, all measurements of qubits in a quantum computation are in the same {|0>, |1>} “computational” basis, and what the measurement “actually is” isn’t something you typically worry or care about.
@@NuclearCraftMod to me that seems like reasons to not need the physical interpretation so much, not a reason one wouldn’t need to understand the math. The computer scientist still needs to be and to understand, e.g. a quantum Fourier Transform
Like, if they are to understand Shor’s algorithm in any case.
I... I hope I won't have to understand this as a programmer one day...
16:12
That's not right, that's why local hidden variable can't explain the outcomes of a Bell test
Yeah I was confused when he said "the rule a priori determined in what state they are/will be"
Quantum entanglement still correlates the outcomes of experiments. What local hidden variables fails to do is reproduce the quantum correlations between different pairs of measurements. If there was only one possible pair of measurements, local hidden variables would be able to describe it. A classical analogue is that if I shuffle two different cards and give you one of them, you immediately know which one you didn’t pick by looking at the one you did.
@@NuclearCraftMod makes sense, exists in every possible state until collapse at time of observation, more complex question, what if a known third to limit... entangled state exists but is unknown to both actors in the game, say an unknown rule like x "card" may be played from outside the game, I understand this is may be conditional and can equate to a constant if the rule is in place but if its an unknown condition and trends to infinity wouldn't this skew the observation by adding noise into the system?
@@mus3equal I'm afraid I don't really understand the question, but in the quantum scenario, the particles don't exist in every possible state - they exist specifically in the entangled state. There is a difference between not knowing the state and not knowing the outcomes of experiments.
@@NuclearCraftMod Thanks for the clarification, assumptively this is why the results of the LHC collisions gave relevant information related to Boson mass despite the outcome of the experiment, the results would have been statistically significant despite the assumptions a priori of the experimenters calculations prior to collision observation.
Can a superposition collapse by knowledge as well as observation?
Yes, as both involve receiving information about a measurement outcome. This is related to the famous Wigner's friend thought experiment.
The superposition is collapsed by _interaction._ To observe the system you have to interact with it (for instance by shooting a bunch of photons at it so you can see it).
This is exactly where my knowledge came from. The couple quantum rules. A 1990’s CD with the little quantum effects that we know of the base universe.
so energy cannot be destroyed - but we do have destructive interference. where does the energy go?
What is a state ? What is the definition of a state?
thanks
at 3:11 i might have said something like "these quantizations are a bit like pixels on your screen, we live in extreme HD"
I understand the rules but why the rules are set up this way still feels like magic
The rules (postulates) are set up to reproduce what we see on the experiments, not the other way around
It makes way more sense if you actually do the math.
@@drdca8263 x2
@@drdca8263 how would math help understand why there is something that "collapses" after being measured?
@@locksmith6096 As for “why” it “collapses”, eh, but as for understanding what is even meant by “collapses”, it is helpful.
With experience with the math, much of it becomes very sensible-seeming.
(Of course, there’s the perspective that the collapse is partially subjective, where one becomes entangled with it,
and there’s also the whole “pointer states” idea? But, mostly, I don’t bother myself with *why* it “collapses” so much as just, *what* happens?)
His dismissal of "spooky action at a distance" doesn't work, because the sock analogy is so bad. Like a flipped coin, his socks have a definite state, you just don't know that state. Quantum superposition means that there isn't even a definite state until observed. That's the "spooky" part: neither particle has a definite state, but observing the state of one determines the state of the other.
my inner pragmatist thinks this will come in extremely useful for writing random number generators 20 years from now...
a sixty symbols video on computerphile
I would love to say I understood everything but at the end of the video my brain was picturing cats drawning in a pond of waves with people throwing pebbles at them. Without anything concrete to think about my brain can’t really picture what we are talking about. Where does this principles take place in the context of a quantum computer? What is a quantum computer made of? Is a node the rough equivalent of a transistor? How it is physically made? Do I need to own a pond to write code for quantum computers? These are the questions I have right now and I feel that without an answer to these I can’t really understand what has been said here.
Soldiered through most of a 45 page intro to quantum computing and then TH-cam shows me this a few days later, typical
Lets say a particle can’t be at 100°f because that’s not one of the quantized energy states (i know it doesn’t work like that on a macro scale, this is just a general question). Though 1 particle can’t be 100°f, is the reason my mashed potatoes are 100° because the average energy in all the particles is 100°f?
:) not sure if this is part joke, part analogy, or a vitally important scientifically significant breakthrough experiment, but either way;
....I suspect that by using the broad term "my mashed potatoes" it's intrinsically averaging all potatoes. if we use a term for a slightly more precise region of mash, say "the mash on a fork", we'd still be speaking of an average of that region, ultimately to make a comparison we'd have to measure a sample area so small it'd be measuring a single particle of mash, so we're be back to not being allowed a quantum state of exactly 100 degree for a potato particle. So... yes. But only by the virtue of the question being a truism - "my mashed potatoes" is _by implication_ an average over all the available potato mash*.
However, this potato knowledge isn't necessarily transferrable to actual theoretical quantum physics... But to be fair, very little knowledge is :) hence most analogies to "the big world out here" fall apart in the end of course. Tho in passing I must say that I'd like to see a very large potato accelerator being built, just in case.
*Note: if it weren't for Mr Higgs' Field of Potatoes, potato-particles would be mashless.
@@IngieKerr what?
@@TheGiantHog Temperature is not defined for a single particle, it's a thermodynamic property of an ensemble of particles. At "high" temperatures there is no quantum effects, the kinetic energy of your mashed potatoes is not quantized.
"the temperature of a particle" is a weird thing to say in the first place. it is literally just the speed that it currently moves at. once you multiple particles, like a whole molecule or a bowl of mashed potatoes, the particles are all just jittering about due to them having different speeds. so finally there are 2 things to note: 1. "temperature" is, by definition, the average speed of the particles in a system. 2. is speed (or momentum, or kinetic energy, or whatever) quantized?
If this presentation was for a general audience, I think that the presenter lost his audience at "really everybody should know about" at 0:22 :D
It gave me immense satisfaction to here someone use "a priori" in a sentence.
- Is there a reason why you've got energy levels 1, 2 and 4, no 3?
Well explained only thing that bugs me is the lowercase i when the rest are capitalised 😂 but that is more my flaw than his!
maybe he's of turkish descent :)
Nah, you're right. It's hard for me to take him seriously when he writes like a child.
Omg this explaination is convoluted...
The sock part was good though
Again and again the quantum computing is presented with superposition, entanglement and unsertanty principles. However, nobody wants to explain how is it different from an analg computer made of spheres (quantum bits) that you can rotate with certain precision (operators). It looks like someone is trying to explain how M2 chip works by presenting basic transistor, then finish the video with "you know, millions of them are connected together and they are all responsible for your iPhone".
Yeah, if they don’t talk about Hilbert spaces, they haven’t said much..
Ok, so each qubit by itself, if it is in a pure state, then has its state described by a unit vector in a 2D vector Hilbert space over the complex numbers.
For a collection of qubits, the Hilbert space describing the possible pure states for all of them together, is obtained by taking the tensor product of the Hilbert space for each of them.
A measurement, if it has a yes/no answer, can be regarded as an orthogonal projection (or, an orthogonal projection along with the orthogonal projection that is its complement).
The other operations, besides observations, are the unitaries acting on the Hilbert space. (Unitaries are linear operators which preserve lengths and angles)
yes
BUILT FOR NIST
Anyone else hear "no-no state" instead of "no node state"?
Learning about quantum computing from a dude who borrowed his microphone from the Edison museum.
Decoherence, not collapse. ;)
Waves in a pond are always touching something else, like his "skin" touched the coin.
La mecánica cuantica es una teoria inconsistente
Sponsored by Sharpie
layperson
First!
First
naught
These really suggest that we are living in a contrived model or simulation of some kind where our observation is fundamental.
"Observation" in this context has got nothing to do with people or consciousness; that's new-age nonsense not science. It relates to the transfer of information which happens everywhere in the universe.
how to build a package manager ?
Oh man… I’m going to have to watch this lefty struggle with a sharpie for the next 15 minutes?!? Rough 😉
Electrons move through reality, as noted by Dr. Prof. Ryan.
Why didn't this get mentioned here?
Disregard everything he is saying guys, He's a lefty. LOL J/k
wow, really funny joke
"a quantum state that you can pick from does not occupy arbitrary energy". Fascinating stuff, I just wish I could follow it lol
Could NOT care less..... FFS.