Lawrence Krauss: Quantum Computing Explained
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Lawrence Krauss: Quantum Computing Explained

Let me briefly describe the difference between
a quantum computer and a regular computer, at some level. In a regular computer, you’ve
got ones and zeros, which you store in binary form and you manipulate them and they do calculations.
You can store them, for example, in a way that at least I can argue simply. Let’s say you have an elementary particle
that’s spinning. If it’s spinning, and we say it’s spinning, it’s pointing up or down
depending upon whether it’s spinning this way or this way, pointing up or down. And
so, I could store the information by having lots of particles and some of them spinning
up and some of them spinning down. Right? One’s and zero’s. But in the quantum world, it turns out that
particles like electrons are actually spinning in all directions at the same time, one of
the weird aspects of quantum mechanics. We may measure, by doing a measurement of an
electron, find it’s spinning this way. But before we did the measurement, it was spinning
this way and this way and that way and that way all at the same time. Sounds crazy, but
true. Now that means, if the electron’s spinning
in many different directions at the same time, if we don’t actually measure it, it can be
doing many computations at the same time. And so a quantum computer is based on manipulating
the state of particles like electrons so that during the calculation, many different calculations
are being performed at the same time, and only making a measurement at the end of the
computation. So we exploit that fact of quantum mechanics
that particles could do many things at the same time to do many computations at same
time. And that’s what would make a quantum computer so powerful. One of the reasons it’s so difficult to make
a quantum computer, and one of the reasons I’m a little skeptical at the moment, is that
– the reason the quantum world seems so strange to us is that we don’t behave quantum mechanically.
I don’t — you know, you can – not me, but you could run towards the wall behind us from
now ’til the end of the universe and bang your head in to it and you’d just get a tremendous
headache. But if you’re an electron, there’s a probability if I throw it towards the wall
that it will disappear and appear on the other side due to something called quantum tunneling,
okay. Those weird quantum behaviors are manifest
on small scales. We don’t obey them – have those behaviors ’cause we’re large classical
objects and the laws of quantum mechanics tell us, in some sense, that when you have
many particles interacting at some level those weird quantum mechanical correlations that
produce all the strange phenomena wash away. And so in order to have a quantum mechanical
state where you can distinctly utilize and exploit those weird quantum properties, in
some sense you have to isolate that system from all of its environment because, if it
interacts with the environment, the quantum mechanical weirdness sort of washes away. And that’s the problem with a quantum computer.
You want to make this macroscopic object, you want to keep it behaving quantum mechanically
which means isolating it very carefully from, within itself, all the interactions and the
outside world. And that’s the hard part, Is isolating things enough to maintain this what’s
called quantum coherence. And that’s the challenge and it’s a huge challenge. But the potential is unbelievably great. Once
you can engineer materials on a scale where quantum mechanical properties are important,
a whole new world of phenomenon open up to you. And you might be able to say – as we
say, if we created a quantum computer, and I’m not – I must admit I’m skeptical that
we’ll be able to do that in the near-term, but if we could, we’d be able to do computations
in a finite time that would take longer than the age of the universe right now. We’d be
able to do strange and wonderful things. And of course, if you ask me what’s the next big
breakthrough, I’ll tell you what I always tell people, which is if I knew, I’d be doing
it right now.


  • Greg Raynard

    NASA bought a 5 billion dollar quantum computer. Anyone read "Hitchhikers Guide to the Universe"? They used a "probability generator" ie quantum computer to jump thru hyperspace. The film was pretty good too. So why else would NASA need a quantum computer. It is just me? Anyone???

  • ufoengines

    So if I had a quantum computer in my smart phone it would be giving me answers to question I didn't ask even before I own one?! I ran a cross this old digital computer patent 3190554 that runs on compressed air instead of electricity. Could this idea be used in building a quantum computer? If Babbage had gone the compressed air route do you think that the folks who built pipe organs could have helped Babbage make his Difference Engine? Could this have ended the feud between Babbage and London's organ grinders?

  • Мики Ricky

    Aaaaah, I see, so quantum computers are bullshit fairy tales.  Thanks brofessor for making that clear.
    Now let's put that money into something actually useful, like Nintendo and enough with this quantum computer bullshit that's never going to happen.

  • Joshua Prater

    Quantum computation surpasses current computational ability in that Quantum computers do not (in a nutshell) check 1 possibility than the next until the correct result is found. Quantum Computers would have the ability to "know" all possibilities, one of which must by definition be that which is requested. The implications are such that dwarf computational ability as year imaginable.

  • Odious Brodious

    computers perform based on the operational reliability of switches. How in the hell will specific problems be solved by the uncertainties of quantum states?

  • William Garrett

    He does not explain quantum computing at all, he just points out instead of a 0 or a 1 it could be several different values at the same time. But I knew this already, he doea not explain how such properties would work in a computer.

  • Pete Salvador

    Completely irrelevant comment, but he would make a good Joker (Batman), the voice, intelligence and hand gestures… Perfect


    this has the same purpose as CERN.even they cant understand it so theorys abound.True quantum computing exist in an unseen dimension,the 4th which cern is so interested in exploiting.SUPRISE,not what they expect.

  • Curtis Doucet

    Easy explanation to quantum computing. Its like having a six sided die and no matter what, you always get every side.
    (Just thought of this, not sure it makes a lot of sense)

  • Hari Taqwan Santoso

    Using electron spin to do some calculations simultaneously before measurement? Seriously?
    I think inputting the algorithm to the electron before measurement itself is a sort of measurement…

  • Roach DoggJR

    I wonder, what will be the future of current technicians and programmers? If Quantum Computing becomes the norm, will technicians and current technicians die with the old binary system?

  • turmat01

    "we'b be able to do strange and wonderful things".

    Agreed. But we could do some VERY scrary shit aswell :S. Humans being humans, I'm not sure it's a good idea that we develop such things :S

  • Sky Sevastian

    its like, so how da fuq do we keep this atom there, we have to make some sht that makes its stay there even dou theres like nothing smaller at this point to keep it from moving. xDD so fucking hard dam

  • J TheWise

    I honestly think quantum computing isn't all it's cracked up to be. How do u build something that goes beyond our comprehension as humans?? We ourselves work like deterministic/classical computers. U wouldn't stick ur hand in a fire because u know fire is hot because of events in ur past. U don't need to sit there and weigh the possibilities of ur hand getting burned because it will in fact get burned. Yes there might be a 1 in infinite chance that ur hand will fly off ur wrist and teleport on the other side of the fire but how is that useful to real life?? Does a quantum computer weigh infinite possibilities? How will it determine anything??

    So in essence a quantum computer is a computer that can learn?? How does it determine if something is right or wrong without human input?? Basically quantum computers are not limited by computation power but our own comprehension as humans?? So quantum computing can't determine anything but only show every possibility really quick??

  • JayLeePoe

    I have a sister in-law, graduated Tufts with flying colors in Science– were it not for a glowing opportunity around Austin, TX (great school district), I doubt she'd be pursuing education.

    We simply need to pay good teachers more. We should also probably reexamine the summer break since it only benefits rich people. Pace things out better, behavior scheduling is HUGE.

  • David Tshudy

    I don't care if Krauss is an expert in the subject or not. He communicates well and this is a good 3 minute explanation.

  • Alexander Wingeskog

    Finally some sane (and really smart person) is actually skeptical… This seems too good to be true… Instead of iterating we (the quantum computer) already iterated every possible answer for you… you just need to ask the right question… that is the essence what a quantum computer could do if it was real… could it be? yes my guess it needs a couple of 100 years though…

    There are atleast 10 CPU/GPU manufacturers out there with loads of cash and either one of them would jump at the opportunity to beat them all with a computer that does not iterate the answer (it has every answer you asked for)… and yes they have a research and development center that would love to get ahead of everyone else… still they do the old "binary" stuff… strange is it not?…

    It's almost like the poor gasoline company's that secretly destroys the water fueled cars…

  • Eldain ss

    Why is it not logical that an electron can pass through a wall ??.

    Its very logical if you look closer at it…
    no magic, o weird things.

  • R Robin

    Worst explanation ever, he doesn't fully understand the process, it's not tunnelling or even entanglement, it just an old school analog computer just super cooled so it performs better. The question entered is analog and an answer of probabilities comes out nothing more

  • Jay Sullivan

    Let me just summarize what Lawrence is saying: "Because quantum bits can be 0 and 1 at the same time, quantum computers can do many computations at the same time".
    This oft-repeated narrative makes for excellent storytelling. However, the truth is that this view of how quantum computing works is so dumbed down and sensationalized (as it must be for the common idiot to understand it) that it is completely untrue and misleading.

    I leave you to read:

  • mrdave2112

    In the quantum world I am God; sounds crazy but it is true. Krauss will have you read Harry Potter and believe wizards are real. He is an awesome story teller.

  • MD Muhaimin Rahman- Sezan

    So Ironic that lawrance krauss "believes" a particle can spin in opposite directions at the same time, but doesn't believe-or WANT TO BELIEVE- in the creator of those particles!

  • Norin Radd

    I think its amazing that less than 5 years later we have quantum computer processors runnin upwards of 50-70 qubits

  • Michael Wizard

    What I want is for someone to show me step by step how to do a calculation using quantum computing. When asked, they tell you about superposition and entanglement. When pressed on the issue they say that you still need a standard computer involved. Why? In all the quantum computer videos I've watched they never demonstrate doing a math solution with quantum logic in a detailed step by step process.

  • fthis1234567

    Im no quantum expert, but this idiot needs to be corrected. The electron is not in different states at the same time….it's just transitioning super fast through the states. So yes, because it's going SUPER fast, it's easy to parallel the states.

  • Electro Man

    This is quantum nonsense. Quantum computers access demonic entities to obtain their results. This is mysticism disguised as science.

  • Gerry De naro

    Putting aside the insurmountable atheists' problem of a finite past, here is Krauss' version of "A Universe from Nothing"
    1 Nothing is“ a quantum vacuum seething with particles of matter and anti-matter
    2. "Empty space is complicated."
    3 – "strength of the energy [SIC] field has to be huge"
    4 – "Nothing is unstable"
    5 – "follows the rules of quantum mechanics"
    6 – "all these phenomena imply that under the right conditions not only nothing can become something, but it is required

    " Oxford dictionary defines "nothing" properly as "Not anything!" Having no attributes! *Nothing has
    "no space" not "empty space!"*
    Nothing has no boiling brew of virtual particles
    Nothing has no energy field. Nothing has no instability.
    Nothing has no quantum mechanics laws acting on it Nothing has no phenomena, no
    right conditions, and no requirements. The Oxford dictionary defines the word
    "Equivocation," as, "The use of ambiguous language to conceal
    the truth or to avoid committing oneself."
    Is Lawrence Krauss a celebrated physicist, or Just a (very, very) bad Philosopher whose science is dictated by his unwavering commitment the philosophy of Scientific naturalism ? (A scientific American assessment) A scathing review in the New York Times on Krauss' book and in particular his version of *nothing"

  • Arthur Hau

    Quantum computing has nothing to do with quantum mechanics! It is just a special case of using a Bayesian network to do computation in a faster manner. Instead of talking about conditional probabilities of some not-yet revealed states, quantum computing talks about those not-yet revealed states themselves. Whereas quantum mechanics contradicts our intuition of the behavior of our physical reality (possibly because of the poor design of the experiments or the unknown nature of the effects of the influence of the instruments used for measurement on the behaviors of the measured particles), a Bayesian network and the Bayesian interpretation of the probabilistic world is in line with our intuition!

  • Rick Hollmer

    I love it. A mere 6 years after this video was published, we have a quantum computer race. 1 qit, 2, qbit, 24 qbit, 49 qbit. It's not scaling to base 2 for some reason, but… the quantum world really is weird. LOL.

  • le berger des photons

    this guy is clearly full of shit. He doesn't even know that an electron is only a "particle" based on our tiny-brained point of view.

    The only difference between a particle and a complex oscillation is that doofuses call a "particle" a "particle".

    This quantum computing is a scam. This fellow is either a chump or a lying sack of shit. Like the cat in the box, who cares which?

  • Julio Jackson

    Who is to say we are not existing in Quantum realities. Where our multiple lives aka Reincarnation, are being explored simultaneously. That our "Present" life is one of infinite probable existences. The life you "experience", here and now, is made of infinite connections of probability that you choose to explore. Like seeing an atom in one position, we know that position is one of many simultaneous positions. Physical existence is therefore not linear or one dimensional but a connection of simultaneous probabilities creating an "image" of one position.

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