Follow Slashdot blog updates by subscribing to our blog RSS feed


Forgot your password?
Science Technology

Scientists Find Flaw in Quantum Dot Construction 180

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.
This discussion has been archived. No new comments can be posted.

Scientists Find Flaw in Quantum Dot Construction

Comments Filter:
  • by gik ( 256327 )
    After painstaking years of testing and research, Scientists have found the source of the problem with malfunctioning Firestone tires: THEY WEREN'T BUILT PROPERLY.

    Film at eleven. :)
    • 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."
    • by Anonymous Coward
      "After painstaking years of testing and research, Scientists have found the source of the problem with malfunctioning Firestone tires: THEY WEREN'T BUILT PROPERLY."

      See what happens when you outsource?
  • by mcc ( 14761 ) <> on Sunday February 13, 2005 @04:35PM (#11661701) Homepage
    to ask this...

    The guy who wrote "the wellstone" is convinced that quantum dots can also be used to create programmable matter [], 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?
    • Wouldn't this be kind of dangerous? Couldn't they make a "virus" that self replacated and use it to kill people, destroy stuff, so on and so forth.
      • 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 []?

        I think it's an interesting idea, but I doubt it's possible.
    • by wass ( 72082 ) on Sunday February 13, 2005 @05:47PM (#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.

      • All of my experience with quantum dots is at cryogenic temperatures, eg 4.2K and below

        Were you wearing a warm coat? ;)
        • I guess by clarifying I risk giving the appearance that I have absolutely no sense of humor, but I'll do it anyway ;-)

          Basically in these systems you must suppress thermal fluctuations sufficiently that you can observe the quantum phenomena. Specifically, many single-electron effects (as in single-electron transistors) would be 'washed-out' at too high temperatures. Working at 4.2K is easier than you think, you just dip your sample into a dewar of liquid helium.

    • by bodrell ( 665409 ) on Sunday February 13, 2005 @06:29PM (#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).

      • "quantum dot" is entirely generic and its use predates any commercial interest by many years.

        Does anyone have a *real* reference for this, like a paper on The popularized description doesn't make any sense to me, since the bandgap of the wetting layer is above that of the dot.
  • 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.
  • Disclaimer : I know next to nothing about quantum computing.

    However, I wonder if we really need quantum bits. Sure, we probably can reproduce the same kind of circuitry that we have now with quantum gates and whatnot, but I fear that would be missing the point, or rather grossly wasting, the capabilities opened by quantum mechanics, by forcing these into our current paradigm. That is, using quantum stuff as a new mechanics for our current paradigm, instead of coming up with a new paradigm that actually ut
    • In a word, this looks like evolution - will this cause a revolution?

      Revolution is punctuated evolution. Just because a given development isn't punctuation doesn't mean that it doesn't bring us one step closer to revolution.

    • 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".
        • The quantum computing method of breaking public key encryption isn't based on brute force, like the classical methods are. Shor's algorithm is in P, not NP.
      • On the other hand, a future which offers quantum computing may also provide unclonable encryption [] and quantum key distribution [], which I understand is more secure than current encryption methods.

        • by necama ( 10131 ) on Sunday February 13, 2005 @05:08PM (#11661909)
          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.
    • by Anonymous Coward
      Do we really need computers at all?
      I mean, really, get off your ass and go outside. ;p
    • by wass ( 72082 ) on Sunday February 13, 2005 @05:34PM (#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.
  • Solution (Score:2, Funny)

    by Pan T. Hose ( 707794 )
    "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 [] 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 []. (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 if quantum dots
    • from the FAQ (Score:5, Informative)

      by wud ( 709053 ) on Sunday February 13, 2005 @05:03PM (#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 [], 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?
    • I probably could have worked "effect" in there one more time.
  • by illumnatLA ( 820383 ) on Sunday February 13, 2005 @04:46PM (#11661786) Homepage
    It's Ohio University... Athens, Ohio not to be confused with Ohio State University an hour and a half northwest in Columbus.
  • by EdgeTreader ( 63569 ) on Sunday February 13, 2005 @04:47PM (#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)
  • by Asprin ( 545477 ) <<gsarnold> <at> <>> on Sunday February 13, 2005 @04:51PM (#11661815) Homepage Journal

    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.]
  • by caffeinated_bunsen ( 179721 ) on Sunday February 13, 2005 @04:52PM (#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
      • Is there some reason why self-assembled quantum dots might be more [...] easily mass produced

        There's a dead giveaway right there in your question, if you look hard enough...
  • by Anonymous Coward
    Here is the official press release [] on the Ohio University website [].
  • 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 [] without the PhysOrg spam.
    • What are you talking about?

      The original article was in Physical Review Letters, which PhysOrg and this press release you link to both cite. Neither provides a link to PRL. In fact, you almost never see links to original science material in any mass media.

      Since when did non-technical (sometimes wrong) summaries become original articles?
      • Neither provides a link to PRL.

        No, but the Ohio University one has to be considered the source copy, since they issued the press release. And it provides links to other material at Ohio University, including (after a couple of hops) to at least one of the author's own web-pages and both author's contact information.

        The PhysOrg one only provides links to imaginary eBay auctions for quantum dots.
        • Yeah, I guess imaginary auctions really are pretty sad. I can see the distinction there.

          However... why issue a press release when a member of the University has already written an entire article? I'm just complaining about an aspect of science culture I don't like. It seems scientests work to insulate themselves from the general public, and this is encouraged by things like vague and often wrong press releases from our handlers.
          • why issue a press release when a member of the University has already written an entire article?

            It's the whole "peer reviewed publication" business, of course. THe paper itself can't be published without the journal's permission, even by the original author, and they are reluctant to give that because they want to sell copies. And, admittedly, they need to sell copies to pay for the whole editorial and review process.
  • Heisenberg (Score:3, Funny)

    by moof1138 ( 215921 ) on Sunday February 13, 2005 @05:25PM (#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."
    • by mnmn ( 145599 )
      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
    • 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."

      Gotta love nerd humor.

      There's a little cottage in a tiny town in Germany with a plaque on the door which reads:

      "Heisenberg may have lodged here."
  • by Anonymous Coward
    Hmm, having problems with spray painting with energy on quantum dots at an atomic level because the current stabilization coating won't allow light through the "paint"? Seems like they need to look at a clear coat paint (read: possibly different energy frequencies that will not cause the overcoating effect).

    Alternately, how about doing something like sputtered thin film (a hard drive surface coating technology) on a quantum level, which might reduce the thickness of the stabilization coat and allow a enou
  • by jea6 ( 117959 ) on Sunday February 13, 2005 @05:53PM (#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.
  • by StikyPad ( 445176 ) on Sunday February 13, 2005 @05:58PM (#11662250) Homepage
    Ads by Goooooogle

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

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

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

    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 ???.
    • 1) Acquire dictionary; register template ad for every word, thereby defeating ad system's appropriacy filters and effectively drowning out other ads, garnering bulk eyeballs for vapid schemes which appeal to the gulliable people which inevitably crop up in every field, including quantum mechanics
      2) ???
      3) Profit.

      1) Predict overreaction to joke beaten into ground by moderators, trolls, replies.
      2) ???
      3) Proph... nevermind.
  • I am from Ohio, and I have never heard of an University of Ohio; maybe Ohio University.
  • Star Trek? (Score:5, Funny)

    by jpop32 ( 596022 ) on Sunday February 13, 2005 @06:05PM (#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.

    • he won't respond (you know who i mean), theres no use mentioning his character gratuitously

      it should be laforge who comes up with this technical idea, or data, if this is "typical" star trek plot stuff... wesley wasnt even a focus in the "typical" episode
  • 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 dots are one of many options for quantm computing. This is in no way saying THE END to attempts for QC. Holy grail of QC has already been predicted [].

    Quantum dot memories in transistor embodiment is still an option [].

  • The wetting layer is a by-product of the method used to grow the dots.
    I can talk about InAs dots in GaAs, which are the ones I know best. In order to grow the self-assembled dots, you first grow enough layers of GaAs so that you end up with an atomically flat layer of GaAs. Then, you start growing layers (one atomic layer at a time, such is the magic of molecular beam epitaxy!), until a certain "critical height" (I think it's around 5 monolayers). At that time, you stop the growth for a little while and the
  • I think it's important to point out that what these people are doinmg is not the whole story about quantum dots. They use a particular technique, and they found a way to improve it, but other people are using completely different techniques that have different advantages and disadvantages. Using "Scientists Find Flaw in Quantum Dot Construction" as a title is very misleading; it's like if an amelioration to firefox was reported as "Scientists find flaw in networking that could fix the internet".

All laws are simulations of reality. -- John C. Lilly