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Scientists Find Flaw in Quantum Dot Construction

Posted by Zonk on Sun Feb 13, 2005 03:27 PM
from the you-changed-the-outcome-by-measuring-it! dept.
Science Technology
ThePolkapunk writes "Scientists have been having problems in predicting the behavior of Quantum Dots, which are considered to be the most likely material to be used to build nanocomputers. Physorg is reporting that physicists at Ohio University believe they've found the problem, and it's with a flaw in the construction of quantum dots. If their theory pans out, "It's one more step towards the holy grail of finding a better quantum bit, which hopefully will lead to a quantum computer."" We first mentioned this about six years ago.
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  • to ask this...

    The guy who wrote "the wellstone" is convinced that quantum dots can also be used to create programmable matter [wilmccarthy.com], something he came up with in one of his science fiction books.

    I am just curious. Is this (programmable matter via quantum wells/dots) something that actual work is being done on anywhere, or that actual signs of progress can be seen in, or that Mr. McCarthy has the actual capacity to encourage actual science work to be done on? Or is this just a lone science fiction author running around trying to convince people to take him seriously?

    • Re:I guess this seems as good a place as anywhere (Score:5, Insightful)

      by wass (72082) on Sunday February 13 2005, @04:47PM (#11662159)
      Is this (programmable matter via quantum wells/dots) something that actual work is being done on anywhere, or that actual signs of progress can be seen in, or that Mr. McCarthy has the actual capacity to encourage actual science work to be done on?

      First a note - All of my experience with quantum dots is at cryogenic temperatures, eg 4.2K and below, so I'm not aware of the behavior of systems at higher temperatures.

      It sounds like this author is making very generalized hand-waving explanations about these fairly complex systems. And is vague enough so that if any effect is discovered, he'll claim that he "discovered" it first. But if he did claim that, it would be somewhat disingenuous because it's very difficult to predict what kind of coherent long-range many-body "emergent" patterns would manifest themselves. Ie, the low-level physics is hard, the fabrication is hard, determining large-scale effects is hard, etc. Heck, even describing a simple helium-atom is hard enough (the quantum-mechanical 3-body problem), with three interacting coulomb forces to work with in addition to the nuclear potential. So it sounds like he's handwaving, but in an attempt to claim prediction of any future discovery based on quantum-dots.

      On a side note, though, all matter is already programmable by default. Phase transitions, for example, will happen at specific temperatures, or magnetic fields, etc, such that the macroscopic behavior of the material can be 'programmed' by pushing through the phase transition.

    • some basics of semiconductor nanocrystals (Score:5, Informative)

      by bodrell (665409) on Sunday February 13 2005, @05:29PM (#11662462) Journal
      This seems to be as good a place as any to try to clear up some misunderstandings. The company where I work is trying to hire a bunch of experts in Quantum Dots, and I've seen probably a dozen presentations from different researchers applying for jobs in the past six months.

      First, I know the terms Q-dots is a trademark, and I think "Quantum Dots" might be trademarked by the same company. So don't give them so much mindshare, since that company isn't really even on the "forefront" of the technology. Call them fluorescent semiconductor nanocrystals, because it actually describes what they are, so people won't think they're being used in quantum computing (not yet, at least).

      Second, these nanocrystals blink. Every researcher I've seen speak about these things mentions the blinking, but only recently did I hear someone give an explanation: poor surface coating allows electrons to leak out of the the crystal.

      Third, Semiconductor nanocrystals are made of several layers. The central layer is usually Cadmium Selenide (CdSe), coated by Zinc Selenide. The second coating has a higher band gap energy, so electrons get "stuck" inside the nanocrystal and then emit photons when they drop back to the ground state. Unfortunately, these nanocrystals are very sticky without more coatings. Often a PEG (polyethylene glycol) linker is stuck on the outside of the ZnSe surface to inhibit these non-specific binding events.

      Last, semiconductor nanocrystals are cool because you can excite them at many wavelengths, but the emitted photon's wavelength (color) depends on the size of the crystal being illuminated. The bigger the crystal, the redder the emission. That makes them size tunable, and easily multiplexible. Eventually, that could be really useful for quantum computing (or digital video, possibly).

      • Since "virus" is in quotes, I assume you don't mean an actual virus, but some kind of quantum device.

        Have you ever heard of Grey Goo [wikipedia.org]?

        I think it's an interesting idea, but I doubt it's possible.

          • Re:I guess this seems as good a place as anywhere (Score:4, Funny)

            by lgw (121541) on Sunday February 13 2005, @10:11PM (#11664443) Journal
            Actual real-world viruses are genuine nanotechnology. Further, they have been evolving for thousands of years to kill humans. It's believed that actual real-world viruses killed 95% of humans in North America and 90% of humans in Central America soon after the Spanish began exploring. Actual real-world viruses are the best possible human-killing nanotechnology given actual real-world material and energy limitations, the laws of physics, and the fact we don't live in a science-fiction novel.

            Anything mankind could come up with would be wimpy by comparison. If you disagree, you clearly haven't been put down by this year's flu. ;)

  • Quanta (Score:2, Funny)

    by Anonymous Coward
    I built my caravan from nanoscale quantum dots.
    It got rusty really quickly, and the seals on the doors leak.
    I would recommend other people avoid using them for building things.
  • "Scientists have been having problems in predicting the behavior of Quantum Dots"

    Couldn't they use the random number generator that sees into the future [slashdot.org] to predict the behavior of quantum dots? It was posted in Slashdot's Science section without the Funny Foot icon so it must be valid, just like the tsunami creatures [slashdot.org]. (Seriously, how can we not be sceptical about anything posted on Slashdot these days? When I read this headline the first thing I did was checking out on Google and Randi.org if quantum dots

    • from the FAQ (Score:5, Informative)

      by wud (709053) on Sunday February 13 2005, @04:03PM (#11661886) Homepage Journal
      How do you verify the accuracy of Slashdot stories? We don't. You do. :) If something seems outrageous, we might look for some corroboration, but as a rule, we regard this as the responsibility of the submitter and the audience. This is why it's important to read comments. You might find something that refutes, or supports, the story in the main. Answered by: CmdrTaco Last Modified: 10/28/00
    • Isn't there something wrong with a news source when the first thing I do is a research before I can trust anything I read? Isn't that a job of editors to verify their sources before posting stories? I just don't get it.)

      I hate to pull your soapbox out from under you bub, but, well, no. It's not the job of the editors. In fact, they explicitly tell you that in the FAQ [slashdot.org], and you'd know that if you bothered to read it. I guess you'd rather just complain about not getting something you were explicitly not off

  • ...if this will have an effect on the quantum slash dot effect?

  • There is no "University of Ohio" (Score:3, Informative)

    by illumnatLA (820383) on Sunday February 13 2005, @03:46PM (#11661786) Homepage
    It's Ohio University... Athens, Ohio not to be confused with Ohio State University an hour and a half northwest in Columbus.

  • Discount Quantum Dots (Score:5, Funny)

    by EdgeTreader (63569) on Sunday February 13 2005, @03:47PM (#11661795)
    "New & used Quantum Dots. aff Check out the huge selection now" ...ebay ad running next to TFA

    • That's the problem. In this era of budget reduction, our scientists are now forced to buy their Quantum Dots off of Ebay.

      Unfortunately, not only have many of these dots been defective, following the installation and usage instructions included with the Dot have left many of our top scientists sterile.

      It is possible that this is a plot by Al Queida to weaken the population of intellectuals in the US.

    • Don't buy them! I bought some, only to discover that they have a flaw in their construction. Probably somebody trying to unload their obsolete stock...

  • While there are many universities in Ohio, there is no U of O. In this case they mean Ohio Univ (not to be confused with OSU)

  • We have The Ohio State University and Ohio University, but no University of Ohio... at least not in Ohio. [NOTE: There are a number of other state-funded Universities: Bowling Green, Toledo, Akron, Kent, Miami, Case Western Reserve, et. al., but none of them have 'Ohio' in their name, except maybe Miami, which is often called "Miami of Ohio" to distinguish it from Miami University in Florida.]

  • Not that big an advance. (Score:5, Informative)

    by caffeinated_bunsen (179721) on Sunday February 13 2005, @03:52PM (#11661825)
    This only applies to self-assembled quantum dots. The ones created by lithography or otherwise manually constructed didn't have this problem in the first place. Don't get too excited (unless you're working with photoexcitation in self-assembled QDs, in which case this might matter to you).
    • Is there some reason why self-assembled quantum dots might be more promising, useful or easily mass produced than ones created by photolithography?

      Conversely is there some reason why lithographically constructed quantum dots might be more promising, useful or easily mass produced than "self-assembled" ones?

      What is the importance of the distinction?

      • It all comes down to ease of manufacturing. Self assembly is just that... if you prepare the mixtures in the right order, the thing creates itself (yes this is a bit dumbed down).

        However if one has to lithographically construct dots, you will run into all the problems that people are runnning into now with lithography, and the most important... throughput! If one can make 8 of these at one time in one chamber, or alternatively have people define them a piece of a wafer at a time by machine, which would y

      • Self-assembled systems can feasibly be very small (several atoms), a la DNA (a natural self-assembling system). Lithographic systems (electron beam or optical) are limited by diffraction of the corresponding electrons or photons used to expose the photoresist, as well as the surface properties of the photoresist itself. For these methods the minimum feature size producable can be of order 10 nm for e-beam lithography, and 100 to 1000 nm for optical lithography, depending on wavelength. Self-assembled sys

  • Official Press Release (Score:2, Informative)

    by Anonymous Coward
    Here is the official press release [ohiou.edu] on the Ohio University website [ohiou.edu].
  • Is there some relationship between /. and PhysOrg? If so, Commander Taco should be ashamed of it... PhysOrg is an eyeball tarpit, it NEVER credits the original article or provides a link back to it. Never. Not once. It might as well be dead trees...

    Here's the original article at Ohio University [ohiou.edu] without the PhysOrg spam.

  • Heisenberg (Score:3, Funny)

    by moof1138 (215921) on Sunday February 13 2005, @04:25PM (#11662015)
    Heisenberg was driving down the road, and a policeman pulled him over. He asked, "do you know how fast you were going?" Heisenberg replied, "no, but I can tell you where I am."
    • The cop must be Officer Newton.

      But Heisenberg still wouldnt know where he is, simply since he was 'pulled over' he can be sure hes now driving at 0mph! Which means he can be anywhere.

      The only way Officer Newton can catch him is to ticket him while driving real fast along his side... thereby knowing exactly where he is.

      But then if Einsteins a passenger, Heisenberg would be doing 0mph if Newton is driving along his side, thereby again not knowing where the heck Heisenburg is. Either way, given Einstein is

  • We first mentioned this six years ago... (Score:4, Funny)

    by jea6 (117959) on Sunday February 13 2005, @04:53PM (#11662216)

    We first mentioned this six years ago...



    How absurd and inanely pretentious. It's astounding that the search engine the editors are using allows them to say "it's a dupe from six years ago" but not be able to recognize the dupe from yesterday. Sheesh.

  • Quantum Exploit Detected (Score:3, Funny)

    by StikyPad (445176) on Sunday February 13 2005, @04:58PM (#11662250) Homepage
    Ads by Goooooogle

    ----- Technologies
    Quantum Cryptography solutions, consulting, and evaluations.
    www.-----.com

    Quantum Dots
    Article in BusinessWeek Read it online. Free Trial!
    www.-----.com

    You Like Quantum Physics?
    Have The Extreme Wealth and Success You Desire In Six Easy Steps!
    -----.com

    Now somebody's obviously banking on the idea that quantum physicists are most likely to fall for the six step scheme. Perhaps they'll get stuck on "Step 5: ???" and spend the rest of their natural lives trying to solve for ???.

  • Star Trek? (Score:5, Funny)

    by jpop32 (596022) on Sunday February 13 2005, @05:05PM (#11662297)
    Doesn't the article read just like your typical Star Trek plot?

    You have a noble experiment:
    Nanoscientists dream of developing a quantum computer, a device the size of a grain of sand that could be faster and more powerful than today's PCs.
    So, after they have
    blasted the quantum dots with light to create the quantum mechanical state
    they encounter the problem:
    they couldn't consistently control that state
    So, the science officers get the work and after some time the find out the cause of the problem:
    the wetting layer caused interference, instead of allowing the light to enter the dot and trigger the quantum state
    And, after some hard thinking Wesley Crusher...
    suggests that scientists could tweak the process by re-focusing the beam of light or changing the duration of the light pulses to negate the effects of the wetting layer!
    And the day is saved.

  • Six years ago? Is there some other Slashdot search interface available to the editors that doesn't suck like the one available to readers? With daily Google propaganda, you'd think they'd have some kind of useable search engine for all the vast stores of content that are "owned by the Poster", but lost in the haystack a few days after posting.
    • Quantum computers have the capability to break most encryption schemes. This would definitely be a revolution.
      • But that's by brute forcing. Surely having many orders of magnitude more processing power will change some things (such as cryptography, as you say), but it's still "more of the same".
      • On the other hand, a future which offers quantum computing may also provide unclonable encryption [perimeterinstitute.ca] and quantum key distribution [perimeterinstitute.ca], which I understand is more secure than current encryption methods.

        W

        • Re:Do we need quantum bits? (Score:4, Interesting)

          by necama (10131) on Sunday February 13 2005, @04:08PM (#11661909) Homepage
          Quantum key distribution is cryptographically equivalent to one time pads, but better -- it solves the key distribution problem; you don't need to take all the one-time pads with you when you leave.

          Go watch a fleet prepare for setting to sea, and you'll see them loading one time pads onto the ship by forklift.
        • Please explain how a quantum computers "breaks" AES. Please

          Caveat: I'm not an expert, and this is just my understanding.

          Basically, to crack AES using a brute force method, you have to try every potential key in the keyspace in a linear fashion-- ie, you start at the beginning and pile down the list. ("Not this one. Not this one either. Not this one.." etc.) Of course you can distribute [wikipedia.org] the effort across many computers and each does a portion, but every possible solution must be independently tested.
            • Well that's a bummer. Well, I guess I was misremembering exactly how it worked. I knew someone would correct me ;) So it's not brute forcing the keyspace itself.. but isn't the effect the same?

              W
        • And with RSA & friends no longer usable, how do you propose to distribute your AES etc. keys? It doesn't matter how strong your symetric cipher is, if you can't securly distribute the keys, you're fucked.

    • Re:Do we need quantum bits? (Score:5, Insightful)

      by wass (72082) on Sunday February 13 2005, @04:34PM (#11662067)
      That is, using quantum stuff as a new mechanics for our current paradigm, instead of coming up with a new paradigm that actually utilizes quantum properties fully.

      That pretty much is what researchers in quantum computing are trying to do, it's a whole different ballgame. For example, In classical computing, 3 bits lets you put a system into exactly one of 8 (2^3) distinct states. However a quantum computer with 3 qubits will let you put the system into a superposition of these eight states, such that the superpositiong (ie, wavefunction) is properly normalized.

      Quantum mechanics works in a whole different mathematical basis (Hilbert Space or Fock Space). The algebras of these spaces is quite different from classical computing, so yes, it's going to be a whole new way of looking at computing, at least at the lowest level.

      On a side note, it sounds like you have just read some Thomas Kuhn, as per your frequent usage of 'paradigm', along with comparing 'evolution' to 'revolution'.

      • Thanks for the first actual reply to my question :)

        I read some Kuhn a long time ago. You're right, I abused the words, but I think these are the best to express the concept I was trying to express.
    • While miracle breaktrougs are useful, we don't have to wait for them to do something useful. We can already build faster/cheaper/lower power computers than we do today.
      • These sets of posts are called a "discussion" on the topic. So what's wrong with saying "I don't know about this, I feel this, what do you think?"?

        Besides, what's up with civilized replies by registered users and STFU responses only by ACs?

    • Re:At what point is a computer powerful enough? (Score:5, Funny)

      by Carlbunn (817714) on Sunday February 13 2005, @03:46PM (#11661784)
      Bad, bad geek! There's no such thing as "too much computer power"
    • Computers will be "fast enough" when they can instant-on and operate at the speed of thought.

      I'm talking no waiting for documents to load, or save. No swapping. No WAITING.

      When the hardware/software reaches a point where it's a layer of skin over the fingers, it'll be Good Enough. We've progressed from thick woolen mittens to thick woolen gloves, but when it comes to operating transparency, we're not even to isotoner... let alone latex.

    • What the hell? (Score:5, Insightful)

      by mcc (14761) <amcclure@purdue.edu> on Sunday February 13 2005, @03:55PM (#11661836) Homepage
      They could be finding cures to cancer, or making better space shuttles, or doing a ton of things with applications that would be useful

      Uh.. wow.

      The people designing better computers aren't curing cancer because they aren't biologists. It isn't like intelligence is just something you can put in a pipe and direct it whereever you want. Some people are just better at certain things than others. Meanwhile the kinds of people who gravitate toward research fields tend to only be effective when they're doing things they find interesting and exciting. What they personally most enjoy or can best apply their talents toward may or may not be the most important thing in the world, but if it's productive and makes some sort of difference, who are we to question?

      And why target the people improving computing power, and not any other "nonuseful" field? In particular, why on earth target people like the ones from this article, who are improving computing power by expanding our understanding of and ability to harness basic physics, and working in an area where discoveries potentially have direct applicability to all kinds of other nanoscale technologies, like, I don't know, smart medicines.

      Even if your "couldn't they be doing something more useful" thing made sense, your examples are very poor. Better space shuttles aren't being built for a lack of ingenuity, they're being built for a lack of funding. And curing cancer in particular is a horrible example because much of the interesting expanding work in the medical research field at the moment is in bioinformatics. Meaning that cancer research would directly and seriously benefit from a major jump in the capacity of computing power, such as the one these nanocomputer people could make possible.
    • 40% of the US economy is dependent on applications of quantum mechanics, and all of the rest of it indirectly feels the effects.
    • How is getting a 800 ghz computer with 500 gigs or ram and a 40 gig video card going to change things?

      Such a computer would allow doctors and surgeons to take complete body scans of people at sub-millimetre resolutions and visualize them in real-time. Quite useful if you are trying to tell if someone has cancer, and if so, how far it has spread. Such a computer would also allow you to model complex protein-folding in real-time, thus helping identify which genes and chemicals could kill off the viruses/dis
    • said a Firestone engineer: "we found that using incorrectly designed quantum dots in the valve stems caused leaking when the tire pressure was not being directly observed."

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