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B How many state changes per second could optical computing do

  1. Jan 10, 2017 #1
    Using Optical Computing, what is the max amount of state changes that 1 transistor could theoretically have within 1 second? I once read that an electrical transistor could achieve 100 billion state changes per second, but I'm wondering what the number is for light, *and what it could theoretically be without each state change requiring any stalling before it can do the next.
     
  2. jcsd
  3. Jan 11, 2017 #2
    Anyone?
     
  4. Jan 11, 2017 #3

    mfb

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    Google searches suggest ~10-20 GHz for practical applications, but with theoretical speeds above 500 GHz (example).

    Edit: Better link
     
  5. Jan 12, 2017 #4
    20 GHz ?......... As I mentioned in my opening post, I've read about a 100 GHz electrical transistor, optical transistors (as some sources suggest) should at least be about twice as fast i.e. 200 GHz. (200 billion state changes per second)

    One incredibly major problem...
    400 million hydrogen atoms fit in an inch
    63360 inches in a mile
    25 thousand miles around Earth
    times 7
    = 4,435,200,000,000,000,000 atoms that light passes each second !
    Light at least at least at least can therefore give us 4 quadrillion state changes per second (assuming each photon is right behind the other ready to do the next state).
    And just think about how much space is in an atom, that's like 2,000 times the number I just gave us above !
     
  6. Jan 12, 2017 #5

    davenn

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    I don't see the relevance of that to your original Q ???

    photons are not like little bullets firing out of a gun
     
  7. Jan 12, 2017 #6

    f95toli

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    I am not sure the question can be answered.

    The switching speed of a transistor will -obviously- depend on the type of transistor. There is no way you could predict the speed of a transistor capable of switching signals at optical frequencies by extrapolating the speed of normal electrical transistors; the technologies will be entirely different.

    If the operational principle of the transistor was based on first converting the optical signal to an electrical current and then back again it would be much slower than an all-electrical transistor.

    Also, there are electrical circuits (simple flip-flops based on superconducting electronics) that can operate at hundreds of GHz
     
  8. Jan 12, 2017 #7

    BvU

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    Can't get the link to work. Do I need a subscription ?
     
  9. Jan 12, 2017 #8

    mfb

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    Photons do not even have a well-defined position. Your calculation has no relevance to optical computing.
    No subscription, but the link doesn't seem to work. I went there via google -> some captcha -> that PDF, apparently the direct link doesn't work, I'm not sure if the captcha link help. If not, search for "Photonic temporal integrator for all-optical computing site:eek:sapublishing.org".

    There are very fast transistors, but you need more than a very fast transistor to make a useful circuit.
     
  10. Jan 12, 2017 #9
    So, the transistor described here
    http://science.sciencemag.org/content/early/2013/07/03/science.1238169.full
    seems to be based on atomic states of cesium-133, | g 〉 = | 6S1/2,F = 3,mF = 3 〉, | d 〉 = | 6P3/2,4,4 〉, | s 〉 = | 6S1/2,4,4 〉, | e 〉 = | 6P3/2,5,5 〉
    The paper doesn't really say, but I suppose the switching frequency must be slow compared to all of the transition frequencies involved here.

    NIST atomic spectra database gives the 6S1/2 - 6P3/2 transition as 852.11 nm, which would be a frequency of 3.5182*10^14 Hz. On the other hand, the hyperfine transition of cs-133 is 9.192631770*10^9 Hz, which is much, much slower. I suspect you will have problems bleeding of the gate photons and the main path if you operate near this frequency.
     
  11. Jan 12, 2017 #10
    Because if they travel that far each second past that many atoms, while possibly doing as you said some "teleporting" i.e. doesn't take 4 Quadrillion moves, then if we send lots of photons to our target some will teleport at spots where the other didn't so you end up with 4 or more quadrillion.

    Nevertheless, in our current optical computing I don't see why we haven't yet got such happening i.e. 4 quadrillion states per second. Maybe they didn't plan for it? They should be able to go a lot higher.
     
  12. Jan 12, 2017 #11

    mfb

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    Photons don't teleport. You can transfer the quantum state of one photon to another photon, which is called teleporting, but that needs a classical information transfer and the whole process is slower than the speed of light.

    Photons do not have a position - do you understand that part? Your whole speculation is based on an incorrect assumption.
     
  13. Jan 12, 2017 #12
    So you're saying I should ignore the amount of atoms a photon passes in 1 second, and focus on what the latest foreseeable optical computing speed of states per second it is able to achieve? But then we truly won't theoretically know a definite number like I explained above...

    So 200 billion state changes will probably be possible, but possibly not any higher in the future? (consider this number [200 billion], and look at how many atoms a photon passes each second - 4 quadrillion (+atomic-space), that's a STRANGE difference)
     
  14. Jan 12, 2017 #13

    davenn

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    you are throwing out these crazy numbers and making wild assumptions with out any backing references
    you need to stop that please
     
  15. Jan 12, 2017 #14

    mfb

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    No, I say that number doesn't exist. It's like asking how many atoms an invisible unicorn is made of.
     
  16. Jan 12, 2017 #15
    How it is like asking how many atoms --- an invisible unicorn is made of, when I said the "invisible" photon is passing the (yes also fuzzy) 4 quadrillion (calculation above) atoms each second?
     
  17. Jan 12, 2017 #16

    Nugatory

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    Back in post #11 of this thread we said "Photons don't have a position". How does it make any sense to talk about something that has no position passing anything else?
     
  18. Jan 13, 2017 #17
    Because we can put a antenna at one place and another at the finish, and it has been calculated that photons reach (only) that far in 1 second, while if you're not in the way of the laser beam you're safe. This means it went a distance and a skinny-width way. The mere fact that it gives you more than 1 state change per second means something.
     
  19. Jan 13, 2017 #18

    mfb

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    An antenna does not emit single photons. A laser beam is not made out of individual photons either - it is a coherent superposition of photons, which is a completely different thing. You cannot even count the photons in a laser beam.
     
  20. Jan 13, 2017 #19
    Yes ok antennas emit many in all ways, and continuously. Lasers shoot many out. My last reply still stands...
     
  21. Jan 13, 2017 #20

    mfb

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    Not necessarily.
    No they do not.

    If you want to learn: great!
    If you want to ignore what everyone is trying to tell you, and rephrase your questions based on wrong assumptions over and over again: I don't think that is helpful. As long as you don't stop that approach, you won't make progress.
     
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