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How Does a Quantum Computer Work?

How Does a Quantum Computer Work?


A classical computer performs operations using
classical bits, which can be either zero or one. Now in contrast, a quantum computer users
quantum bits or qubits. And they can be both zero and one at the same time. And it is this
that gives a quantum computer its superior computing power. There are a number of physical objects that
can be used as a qubit. A single photon, a nucleus or an electron.
I met up with researchers who were using the outermost electron in phosphorous as a qubit.
But how does that work? Well, all electrons have magnetic fields, so they are basically
like tiny bar magnets. And this property is called spin. If you place them in a magnetic
field they will align with that field, just like a compass needle lines up with the magnetic
field of the earth. Now this is the lowest energy state, so you
could call it the zero state or we call it for the electron, spin down. Now you can put
it in a one state, or spin up, but that takes some energy.>>If you took out the glass from your compass
you could turn the needle the other way, but you would have to apply some force to it.
You have to push it to flip to the other side. And that is the highest energy state. In principle,
if you were so delicate to really put it exactly against the magnetic field, it would stay
there.>>Now so far this is basically just like
a classical bit. It has got two states, spin up and spin down, which are like the classical
one and zero. But the funny thing about quantum objects is that thy can be in both states
at once. Now when you measure the spin it will be either up or down. But before you
measure it, the electron can exist in what is called a quantum super position, where
these coefficients indicate the relative probability of finding the electron in one state or the
other. Now it is hard to imagine how this enables
this incredible computing power of quantum computers without considering two interacting
quantum bits.>>Hello.
>>Hi. Now there are four possible states of these
two electrons.>>You could think that, well, that is just
like two bits of a classical computer, right? If you have two bits you can write zero, zero;
zero, one; one, zero; one, one. Right? There is four numbers. But these are still just two bits of information.
Right? All I need to say to determine which one of the four numbers you have in your computer
code is the value of the first bit and the value of the second bit. Here, instead, quantum
mechanics allows me to make super position of each one of these four states. So I can
write a quantum mechanical state, which is perfectly legitimate, that is some coefficient
times this plus some coefficient times that plus some coefficient times that plus some
coefficient times that. So determine the state of this two spin system,
I need to give you four numbers, four coefficients, whereas in the classical example of the two
bits, I only need to give you two bits. So this is how you understand why two qubits
actually contain four bits of information. I need to give you four numbers to tell you
the state of this system, whereas here I only need two. Now if we make three spins, we would have
eight different states and it could give you eight different numbers to define the state
of those three spins, whereas classical it is just three bits.
If you keep going, what you find is that the amount of equivalent classical information
contained by N qubits is two to the power N classical bits. And, of course, the power of exponentials
tells you that once you have, let’s say, 300 of those qubits in what we call the folient
angle state, so you must be able to create these really crazy states where there is a
super position of all three angles being one way and another way and another way and so
on, then you have like two to the 300 classical bits, which is as many particles as there
are in the universe.>>But there is a catch, although the qubits
can exist in any combination of states, when they are measured they must fall into one
of the basis states. And all the other information about the state before the measurement is
lost.>>So you don’t want generally to have as
the final result of your quantum computation something that is a very complicated super
positional state, because our cannot measure a super position. You can only measure one
of these basis states.>>Like down, down, up, up.>>Yeah. So what you want is to design the
logical operations that you need to get to the final computational result in such a way
that the final result is something you are able to measure, just a unique state.>>That is not trivial.>>That is not trivial. And it is essentially
… I am kind of stretching things, but I guess it is to some degree the reason why
quantum computers are not a replacement of classical computers.>>They are not.>>No, they are not. They are not universally
faster. They are only faster for special types of calculations where you can use the fact
that you have all these quantum super positions available to you at the same time, to do some
kind of computational parallelism. If you just want to watch a video in high definition
or browse the internet or write some documenting work, they are not going to give you any particular
improvement if you need to use a classical algorithm to get the result. So you should
not think of a quantum computer as something where every operation is faster. In fact,
every operation is probably going to be slower than in the computer you have at your desk.
But it is a computer where the number of operations required to arrive at the result is exponentially
small. So the improvement is not in the speed of the individual operation. It is in the
total number of operations you need to arrive at the result.
But that is only the case in particular types of calculations, particular algorithms. It
is not universally, which is why it is not a replacement of a classical computer.

100 thoughts on “How Does a Quantum Computer Work?

  1. Superposition it means it's just so small and he spins very fast that's why I think you get super posision if you move from one posision to another that mean this electron changes this super posision from up to down and he is random of randomolinez 🙂

  2. So, what about a hard drive instead of a processor? Like a hard drive that is 500QB could theoretically hold like 250,000GB of data?

  3. Why is his t-shirt darken at both nipple areas? Was it designed by a Quantum computer..is that why?

  4. Hey Veritasium ! thanks for the awesome video again… I kinda understood how to store a bit of information using atoms and from this : https://www.youtube.com/watch?v=yy6TV9Dntlw... i got an overview of a Qcomputer would work. However, the explanations don't suffice. Can you please check that video and answer.

    1 – here's wat i understood, if i have 2^n Qbits ( 2^4 in that card analog) the answer is in ONE of the those 2^n states, correct? How does one go about "sifting" through the 2^n state to find the answer ?!?!?…

    2 – Say I have a drum whose surface area is painted with 2 different colors having equal areas, they are painted symmetrically about the diameter. Lets say if i have 2^n such drums and spin them all at the same rpm. would this be an analog of a 2^n Qcomputer ? I m trying to draw analogies… is this correct?

  5. Could teleportation be developed using this since the quantum molecules and particles can go through space and time causing them to be entangled from one place to another?I don’t really know what I’m talking about

  6. He is incorrect. It will replace the home pc. Smart homes with facial recognition software, smart locks, electronic controlled vents for proper thermal heating cooling, etc will require this. Your car would be connected to it as well to update software.

    It won't replace your cellphone, but a single brain for your cellphone, home pc, laptop, car, refrigerator to run off sounds applicable, eh?

    Or am i incorrect?

  7. When I see one that does something unique yet practical, we can talk. Until then, good luck with that.

  8. So, basically, it's good for making huge combinations in a short time period, but not for transforming information, because the position of each electron has to be measured every time. So it's good for storing data and data analysis, as I understand. Think of a grid of electrons that can go up and down, instead of the classic bit, where the electrons have to go back and forth.

  9. A simple explanation is that we are making bits nullable, and assigning a value to it, when we need it.

  10. one thing I don't understand is why he used hadamard states instead of the normal |01> and |10>

  11. This doesn't really explain how a quantum computer works. Your explanation is almost equivalent to explaining that a classic computer works with a light bulb. This only touches on extremely superficial ideas. Please, Give us some math, and explain how these states would be measured. Example, using a magnetic field to induce the spin, and then measure the radio frequency produced by the phosphorus atom(s) returning to ground to determine its spin state.  You should Explain more stuff like that, so that we actually get an idea of how a quantum computer works, rather than providing an explanation (over 6 minuets) that we could have gotten from google or Alexa in 30 seconds.

  12. I have two queries, it would be really helpful if someone may explain or point me in the right direction to understanding this.
    Please freeze at this point – https://youtu.be/g_IaVepNDT4?t=173
    1. Here four states described each along with a coefficient.
    As per my understanding of Quantum Entanglement, both up and both down position is not possible and hence the coefficients will always be zero. So Technically there will always be two bit of information for two Qbits instead of four.
    2. In the middle two states where each particle is in up down position, the state equation has a addition and subtraction symbol.
    I need to understand why is it written in this way. Any explanation or keyword to research this would be helpful.

  13. They still cant program it. Remains a theory like black holes and dark matter now being replaced with Tesla's plasma universe theory (ThunderboltsProject on yotube).

  14. I can imagine a quantum / traditional computing pairing that would perform operations along a logical path that are optimized for the computational needs of the arguments and operational requirements.

  15. I Guess Elon Musk will have to build a Quantum Computer to help realise his autonomous self driving car !

  16. I've seen several you tube vids trying to explain q-bits and quantum computing, and the crazy prof here did is so easily! plus, veritasium dressed as a phosphorus atom is hot!

  17. OK…finally I understand a little more about this…these computers…if they ever work will have insane computing power….but I have bad news…we dont have the technology to achieve one of these in a workable fashion…but I think I finally understand more of where they are going with this…just dont think it will be practical in my lifetime.

  18. A key to the "positions" comes from the atom model. "Quantum.Leap" I n atomic is just simple. the movement from a inner shell electron to the outer shell…. instantaneously with out loss of energy nor overshoot….(ie..atomic drift)…and to drop from shell outter orbit back into the inner orbit at the same time. The measurement for target site must be determined…otherwise..no true measurement! The loss of energy comes through multiple steps to capture at target point…less steps…less energy loss!. YOU RETAIN MORE ENERGY ..sometimes you cannot gain time!

  19. This is the best short clip to explain how it works. I'm happy they actually went through the basics of how the hardware works.

  20. Wow, sure is a lot of energy going toward a concept that can only be useful in specific or special situations and is definitely not a replacement for classical computers! Well, at least this guy was honest and straight forward about it! It seems like Quantum Computers were never intended to replace classical computers, unfortunately that was the impression I had gotten when these concepts went more mainstream. Hey, maybe one day Quantum Computing will be built into classical computers as a functional option for special operations and applications!

  21. Actually, this isn't hard to understand, but it is hard to get your head around. Quantum states exist in probabilities. However, to be observed, they must be in a fixed state. When not being observed, they are "probably" in one state or the other. The act of observation fixes the state of the particle, according to its probability of being in that state. Look up, "quantum gates" to see an explanation based on unitary matrices for an idea of how the math works.

  22. I had problem in sleep i.e. I didn't get sleepy. Then I started this video and slept halfway,though it costed me my daily Internet Limit 🤣😂🤣😂🤣😂🤣😂

  23. Sure but how can you construct such logic gates that generate a measurable result without measuring an electron's initial state? An electron's spin is in superposition as long as its not observed, afterwards it collapses to either 1 or 0. Those logical gates must somehow observe the electron to measure its state then pass that data to you. Isnt that counterintuitive?

  24. Praggo Thanks for trying. Why o why must every video about quantum anything be beset by superpositions of wacky sound effect life cheese music-oid sound my liege?

  25. Let me get this right. So you input the calculations, the quantum computer does the calculation in a few steps, then does the computer identify the qubit by choosing whether the qubit is closer to 1 or 0, or does it choose randomly but the closer the qubit is to 0 or 1, the more likely the qubit will be identified as a 1 or a 0?

  26. A team of Russian and American scientists recently used a quantum computer to essentially reverse time by decreasing entropy on the atomic level.

  27. Veritasium's other video about quantum entanglement is a good setup for this video, and his explanations of insane concepts is quite easy to grasp.

  28. I have watched 3 videos about quantum computing in order to get idea what it is.
    And they have convinced me, that it is one huge hoax.

  29. so it’s just the reason that it’s better is that you don’t know if it’s up or down which literally means nothing

  30. if you havent measured it how do you know its even doing what youre describing?

    saying its "both probabilities at once" and then saying you have never actually observed that property is like saying you know something is true just because you think its true

  31. if nobody has ever observed the phenomena of superposition due to its physical property of collapsing into a binary state upon observance, then how can you say it exists?

  32. Quantum computing is a .90 probability hoax and .10 probability real deal. Yes, at the same time. Because, you know, a bit can only be either 1 or 0 and a qubit can be either both at once, or 1 with one probability and 0 with another (is that a particular probability random number generator then?), or an infinity of values between 0 and 1 at the same time or just freaking 42, but only once!

  33. SERIOUS QUESTION:
    SInce the coefficient Mr. Morello showed were complex numbers, the actual number of corresponding classical bits shouldn't be double?

  34. Should have written something about qubit in Quran. So that "they" can "wrongly" interpret something about Quantum world, at least.

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