Quantum Computing

Discussion in 'Community' started by davecuse, Jun 17, 2004.

  1. davecuse macrumors 6502

    davecuse

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    #1
    It's an amazing age we live in.
     
  2. obeygiant macrumors 68040

    obeygiant

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    totally cool
    #2
    Basically, researchers can use lab techniques to create a weird relationship between pairs of tiny particles. After that, the fate of one particle instantly affects the other; if one particle is made to take on a certain set of properties, the other immediately takes on identical or opposite properties, no matter how far away it is and without any apparent physical connection to the first particle.



    I've read about this. For those of you who are "trekkies" this is a prelude to 'subspace'. Communication over great distances instantly. Fascinating.
     
  3. jsw Moderator emeritus

    jsw

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    #3
    I've read up on this before, but my brain leaks knowledge shortly after it's acquired, so I've forgotten: is the info transmitted truly "instantly" (i.e., violation of speed-of-light max) or is it just "wicked fast"?
     
  4. davecuse thread starter macrumors 6502

    davecuse

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    #4
    I read up on this quite a bit when it was in the theory stage. I'm really amazed that it's been made a reality. It's baffling to me how a particle can be made to take on the inverse of another particle without being physically connected. I agree with Albert, it is a little spooky. The possibilities here are really endless, to view this as a way to make a computer faster is in my mind short sighted.
     
  5. Rend It macrumors 6502

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    First, there really isn't any information transmitted in the usual sense. What's observed in EPR-type (aka Entanglement) experiments is correlations between the quantum states of two particles, which had previously been intimately connected at some point. So, there is not really any violation of special relativity. By "usual sense", I mean information is a measure of what you don't know. For example, mp3 and AAC are able to compress huge music files because some of the data in the original CD recording is redundant, or simply inaudible. So, the compression algorithms extract only the pertinent information from the original recording. For more info try Googling "Claude Shannon".

    For more info about entanglement, see Bell's theorem, or just Google "EPR paradox".

    The 2nd point is that what's weird about these experiments is not the idea of superluminal (faster than light) communication (which technically isn't happening anyway). Rather, it's the fact that they force you to swallow the strangely disturbing nonlocal nature of quantum mechanics. This is the so-called "spooky action at a distance" that Einstein spoke of so many years ago. For more on nonlocal theories of QM, Google "David Bohm".
     
  6. themadchemist macrumors 68030

    themadchemist

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    #6
    I'll try to procure a copy of the nature paper and make it "available."
     
  7. Doctor Q Administrator

    Doctor Q

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    #7
    I love reading about quantum computing and particle entanglement. It makes my head hurt in such a good way.
     
  8. jsw Moderator emeritus

    jsw

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    #8
    Well - and I apologize if I'm just being dense here - if I have a number of entangled particles, and I bring a set of, say, 30+ of them with me somewhere, oh, really far away, and I leave the matching set with someone, then can't I send information instantly?

    I mean "mess with particle 1's state to indicate an 'A', mess with particle 2's state to indicate a 'B'", etc. - or more compactly, use the particles to send information along a 32-bit (say) bus. Again, I understand that I'm likely missing something here, but it seems from a very rough reading of articles (I'm at work and have limited time, of which I devout a fair portion to MacRumors) that you truly can send information instantly by agreeing beforehand what each entangled particle represents.
     
  9. MongoTheGeek macrumors 68040

    MongoTheGeek

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    #9
    Yes. Entangled particles are treated by the universe as if they are the same thing.
     
  10. telecomm macrumors 65816

    telecomm

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    #10
    Here's the problem with trying to expoit entanglement to communicate at speeds faster than light, i.e., superluminal signalling.

    If, for example, I rip in half a dollar bill, put each half in a separate envelope and mail them to distant locations, I could open one envelope to discover the left hand side of the bill and instantly know that the recepient of the other half would open theirs to discover the opposite side of the bill. Clearly, though, no information has been transmitted, since the setup is such that I don't know which half of the bill I've got until I open the envelope.

    There's sort of a similar thing going on with entanglement. I could separate two entangled particles, say p1 and p2, which were such that if I perform a measurement on p1 and see "+", I'd know immediately that the other person, when measuring that property on p2 would see "–", and vice versa (these could be though of as "spin" measurements). Let's say that a spin measurement on these particles is such that "+" and "–" each occur with 50% probability. This probability is part of the problem. Unlike the situation with the dollar bills, I want to be able to control the characteristics of the signal, so I don't want the particle in definitely one state or definitely the other at the outset, since then I wouldn't be able to send any info; I want to be able to affect the particles. Now the only way I can affect p1 (without destroying the entangled relationship) is to measure the spin, getting either "+" or "–", and ensuring, therefore, that the other observer discovers "–" or "+" respectively. The issue then, is that I can't control whether my measurement will reveal "+" or reveal "–".
     
  11. davecuse thread starter macrumors 6502

    davecuse

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    #11
    Why wouldn't it just be set up that particles 1-256 are used to transmit information in 1's and 0's out to component, and particles 257-512 are used to recieve 1's and 0's back from another source.

    Compression and transmission of information would no longer be an issue, you would be getting raw data instantly.
     
  12. jsw Moderator emeritus

    jsw

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    #12
    Gotcha. I'd thought that one could alter the spin, hence causing the entangled partner to alter its spin in a detectable way, as opposed to simply measuring it. The dollar bill analogy was useful. Thanks!
     
  13. Rend It macrumors 6502

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    #13
    This is a better explanation to the original question than I could come up with. But, don't forget that you don't have to measure the same thing at both ends of the experiment. What you're describing is when both detectors are oriented along the same axis. In spin or polarization measurements you can set the detectors at arbitrary angles. So, even if you set yours along the z-axis, and you measure spin up, if your friend sets his along the x-axis (assuming particles traveling in y-direction), you can't say anything about what he will measure. Simultaneous measurement of the spin components along two perpendicular spatial axes is forbidden. These are so-called incompatible observables.
     
  14. jefhatfield Retired

    jefhatfield

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    #14

    and it would be more amazing and move further if the scientists and engineers who built the foundation of "this or that" technology five, ten, and twenty years ago could let go of their ego and admit that science moves forward and lend their expertise

    from the early 80s, i have known students/engineers/scientists on the cutting edge of their field and pretty consistently, they feared the idea that someone would supercede their technology one day, and offer it for cheaper in the marketplace

    quantum computing will come along, but more slowly, due to those ego issues and foot dragging

    in my chosen field of computers/high tech, etc, i am glad to see talent coming from everywhere, espcially outside of the usa...most recently, last ten years at least, the best programmers i have met are from india, china, and russia...and though many of the ones i see around the academic community and around silicon valley often have master's and phd degrees, there are many times more who are not academics who are equally as good from those countries...actually the best programmers and high tech visionaries in silicon valley are self taught and not from schools nine out of ten times but that's a different thread...he he...but i can think of two and they started this comany here that makes insanely great....

    perhaps programmer jobs in america will go the way american garment workers did (east asia) but in the end, no matter where high tech gets concentrated, the world will benefit from the hard work of many techies here and abroad

    there is no time to say, "hey, we have the best engineers/programmers in america, and i will choose to ignore what others are doing elsewhere"...it is that type of american techie who ends up in the unemployment line ;)
     
  15. Rend It macrumors 6502

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    #15
    I'm not exactly sure who you're referring to by "students/engineers/scientists", but I can assure you that quantum computing is NOT being delayed by egotistical people in academia or government labs (such as NIST). There are very real practical and theoretical limitations to understanding the physics behind quantum computing. It's true that there are many technological possibilities that quantum computing will bring. But the grad students and researchers in that field aren't busting their humps right now because of a dream to have faster computers. Their motivation is the very strange and poorly understood physics that has been brought to light by recent experiments.

    Without an understanding of the basic science, no technology moves forward. Computers are so ubiquitous today because of how well we understand transistors. In turn, we could not understand the device physics of a transistor without an understanding of the electronic properties of semiconductors. You can thank quantum mechanics for that. Another point: today, you will rarely find a physicist working on semiconductors the way they did in the '50s. The torch has been passed to electrical/computer engineering departments. Similarly, in 50-60 years you will probably not find anyone in your local physics department fiddling with a "quantum computer". Scientists, especially physicists, are well aware that "science moves forward".

    Also, concerning the necessity of advanced education, sure if you want to write code or become an inventor or entrepreneur in IT, then advanced education probably won't be necessary. But don't group the rest of science and technology in the same heap. There are some things that can't be self-taught in a timely manner. A perfect example is my grad work in experimental physics. There is no way I could obtain all my working knowledge of ultra-high vacuum, cryogenics, low-noise electronics, etc. if I wasn't working in a university lab. I don't have $200,000 to throw into buying my own system. That's why supporting basic scientific research is so important. It provides opportunity for students to learn VERY advanced techniques and theory. That knowledge then contributes to the our general understanding of the world, which then enables engineers to use that knowledge base to design and manufacture the next big thing.

    Too often, people forget the long road to the techie things they take for granted every day.
     
  16. jefhatfield Retired

    jefhatfield

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    #16
    great points made

    mostly the people i have been most in contact with, in college and grad school, as well as in work have been programmers and hardware/network techies

    i do understand that some facets of science absolutely need formally educated people for the vast amount of workers and researchers such as medicine...i also wouldn't want a self taught dentist to drill my teeth...;)
     
  17. jefhatfield Retired

    jefhatfield

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    #17
    a very fascinating story in science was the genome project and how, for a short while, massive egos almost killed it, but certainly there were some stalls along the way due to personal problems and who got credit for what ;)

    nobody denies it takes a lot of confidence to become a phd scientist and devote years of work to a topic, and it does not surprise me if "egos" could get out of control from time to time and the subject/topic takes a backseat to who becomes the hero

    there were many computer science students i knew who resisted gui and said it would never take off...eek, the thought of non-geeks actually touching the computer due to the ease of use through a mouse...how terrible

    us geeks like to take ownership of something exclusive

    like the first time i jacked off...whew, that was great...i bet me daddy don't know about that one ;)
     
  18. davecuse thread starter macrumors 6502

    davecuse

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    #18
    What? And I thought this was about Quantum Computing....
     
  19. jefhatfield Retired

    jefhatfield

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    #19
    ... i thought i would throw a little richard pryor in there ;)
     

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