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Physicists Watch Individual Electrons Flow

Posted by ryuzaki0 on from the going-with-the-flow dept.

SG writes "Physicists at the Tokyo Institute of Technology have developed the world's most sensitive ammeter yet. The device allows current to be measured at the attoampere level and is expected to be of use in nanoelectronics, calibration devices, quantum computation and biology."

35 of 120 comments (clear)

  1. Picture by Anonymous Coward · · Score: 5, Funny

    Here's a picture of the ammeter in action.

  2. Re:WHY!? by MyLongNickName · · Score: 2, Informative

    RTFA.

    The device could be used for a wide variety of applications, including nanoelectronics, calibration devices, quantum computation and biology (Science 312 1634).

    And that was in the first paragraph. It took you longer to type your post than it would have to actually read the first paragraph. And you even forgot to yell 'frist post.

    --
    See my journal for slashdot ID's by year. Mine created in 2005. http://slashdot.org/journal/289875/slashdot-ids-by-year
  3. Re:WHY!? by Ant+P. · · Score: 3, Funny

    For the likes of Intel, this is the hardware equivalent of gdb.

  4. So... by RyanFenton · · Score: 4, Interesting

    Would it have to change the flow by measuring it? How much by pure quantum "observation" effects?

    As a non-phyisics grad (Computer science), I'm wondering.

    Ryan Fenton

    1. Re:So... by MindStalker · · Score: 4, Insightful

      If you read this is simply a device that channels electrons into a single file channel then measures the movement through the channel. Akin to putting a dam in water then putting a very small pipe in the dam and putting a meter on that. What you are ultimatly changing is the amount of electrons that get through, so I'm guessing to measure a current of any size you would have to have millions or more of these???

    2. Re:So... by agentcdog · · Score: 5, Informative

      Apparantly, it uses quantum effects to do its measurements. There are two very small electron "cages" and the electron must tunnel across from one "quantum dot" (their words) to the other. In answer to your question ALL ammeters affect the systems that they measure. Mostly it isn't a big deal because they have very low resistance. There are some situations where it is very difficult to measure current. One scenario is when the resistance of the circuit is very small. The other is when the current is very small. The reason it is so hard to measure small currents is that there is thermal movements of electrons in the metal. When you amplify the current it amplifies the noise. There are various ways of getting around this. According to TFA this technique introduces very little noise, which allows it to measure very small currents. The whole heisenberg effect is more a matter of indeterminacy for individual particles. The scale of the measurements appear to be big enough that the sum of the individual particles should be an accurate representation of the flow. If anyone reading the article can add clarity, I would welcome it.

      --
      If I understand Dirac correctly, his meaning is this: there is no God, and Dirac is his Prophet. -Pauli
  5. Cool! by Crazyscottie · · Score: 5, Funny

    So now ol' Ben Franklin can finally see which direction electrons really flow!

    --
    Just because it can't be explained doesn't mean it isn't true. Science fits into reality... not the other way around.
    1. Re:Cool! by ookabooka · · Score: 2, Informative

      Electrons do move from negative to positive, but the "current" as defined by Ohm's Law does "flow" from positive to negative. Way back when they didnt know which direction stuff moved, so they defined it as moving from positive to negative for the sake of their mathematical calculations. Right hand rule, left hand rule. . bah semantics.

      --
      If you are about to mod me down, keep in mind that this post was most likely sarcastic.
  6. Current, tunneling ? by karvind · · Score: 5, Interesting
    I RTFA and it employs two quantum dots to distinguish the direction of the flow. As the article mentions: scientists already know how count single electrons travelling through an individual quantum dot

    My question is if I want to measure current (assume an ideal current source) then I will hook it up to this new invention. The mechanism of current in this new measuring device is quantum tunneling. Is there any reason that the current source in question employs the same mechanism. It may still be conventional drift-diffusion with very very low fields (and probably very low mobility). Now when I interface it with this double-quantum device, does the change in mechanism ensures current quantity ? If answer yes, what is the intutive answer. I can understand current continuity when it is drift and diffusion.

    1. Re:Current, tunneling ? by yincrash · · Score: 4, Funny

      what?

    2. Re:Current, tunneling ? by XchristX · · Score: 2, Interesting

      There would have to be some sort of "effective quantum impedance" (for want of a better phrase) of the contact which can be adjusted such that the device sees a very small input impedance so that the device does not measurably affect the source.

      --
      l'Homme n'est Rien l'Oeuvre Tout: Gustave Flaubert to George Sand
  7. Re:WHY!? by Anonymous Coward · · Score: 4, Funny

    It's alright. I'm sure there is no electrical activity in your brain. You're safe. :-)

  8. Look at that one go! by vldragon · · Score: 5, Funny

    Before you read any of the article and just say the headline: "Physicists Watch Individual Electrons Flow" did anyone think of a bunch of guys in white lab coats looking down at a table with money in their fists betting on electron races? Because I did... And boy was it disturbing... Gambling physicists can be very rude. (At least the ones in my head are)

    --
    Eating the brains of your enemies does not make you smarter. But it's still fun.
    1. Re:Look at that one go! by Cheapy · · Score: 5, Funny

      "Damnit Jones! You altered the race event by observing it!"

      --
      Would you kindly mod me +1 insightful?
    2. Re:Look at that one go! by Ignominious+Cow+Herd · · Score: 5, Funny

      "Who won the race!?"

      "I dunno, but there's a dead cat in this box over here."

      --
      Lump lingered last in line for brains, and the ones she got were sorta rotten and insane.
  9. Re:WHY!? by gone_bush · · Score: 3, Insightful
    I agree.

    Just because it _may not_ be of any use today does not mean that it will always be "useless". The parabola was known to the ancient Greeks but it only saw its first "practical" use in the hands of Galileo Galilei who used it to predict the trajectory of cannon balls.

    --
    Two roads diverged in a wood, and I - I took the one less travelled by. (Robert Frost, 1916)
  10. Re:Shweet by CODiNE · · Score: 2, Insightful

    A ghost detector? Amazing new technology comes around and all you can think of is a ghost detector?? Sheesh...

    dowsers already do that just fine. :)

    --
    Cwm, fjord-bank glyphs vext quiz
  11. So does this mean... by Audent · · Score: 2, Interesting

    that we can finally see just what happens with that light box experiment with waves/particles of light?

    Someone with a clue help me out here. Does this mean we'll get a definitive answer on how a single particle of light can actually be in two places at once?

    --
    I am a leaf on the wind
    1. Re:So does this mean... by Maelwryth · · Score: 2, Informative

      Try this http://www.vega.org.uk/video/subseries/8. If you don't have the bandwidth you can buy them from the University of Auckland.

      --
      I reserve the write to mangle english.
    2. Re:So does this mean... by Savantissimo · · Score: 5, Insightful

      We already know the answer to that. "Wave propagation" and "particle interaction" are redundant expressions; "wave interaction" and "particle propagation" are oxymoronic. "Waves" and "particles" are not entities or properties but rather behaviors - wave propagation is the constant or increasing lack of information about the quantum relative to the observer/instrument/indicator and particle interaction is the creation or transmission of information relative to the observer/instrument/indicator.

      Single particle interactions are never in two places at once. The information that originally was one quantum may be distributed across space as it propagates as a wave or distributed across ensembles of different quanta in entangled states, but the interactions (particles) themselves are always strictly local.

      --
      "Is life so dear, or peace so sweet, as to be purchased at the price of chains and slavery?" - Patrick Henry
    3. Re:So does this mean... by fulvioc · · Score: 5, Informative

      You're talking about the double-slit experiment or two-slit experiment consisting of letting light diffract through two slits producing fringes on a screen. These fringes or interference patterns have light and dark regions corresponding to where the light waves have constructively and destructively interfered. The experiment can also be performed with a beam of electrons or atoms, showing similar interference patterns; this is taken as evidence of the "wave-particle duality" predicted by quantum physics. Note, however, that a double-slit experiment can also be performed with water waves in a ripple tank; the explanation of the observed wave phenomena does not require quantum mechanics in any way. The phenomenon is quantum mechanical only when quantum particles - such as atoms, electrons, or photons - manifest as waves. I doubt the machine will be able to distinguish whether one electron goes through one slit and/or vice/versa. Remember, observing the behavior of these particles causes the wave pattern to collapse. They're almost there, but they're very far off at the same time.

    4. Re:So does this mean... by Memnos · · Score: 5, Interesting

      I think that a plausible explanation (or at least one that deserves more research) is the Pilot Wave theory proposed by de Broglie-Bohm. See http://plato.stanford.edu/entries/qm-bohm/ and other numerous sites for a discusion of this proposition. (Disclaimer: I have never been a big fan of the Copenhagen Interpetation.) Nonetheless, I feel that an explanation which obviates the "observer problem" and explains decoherence merits looking at.

      --
      I don't trust atoms -- they make up stuff.
    5. Re:So does this mean... by Bob+Gelumph · · Score: 3, Informative

      You misunderstand what the double slit experiment involves.
      In the double slit experiment, the light or particle source that is used is turned down so low that at any given time, there is no more than 1 particle going through the barrier.
      This cannot be replicated in a ripple tank. A ripple tank, or any kind of macro scale wave inherently cannot produce the same result as the double slit experiment because it can not be proven that any individual particle is the wave is interfering with itself.

      --
      I'm gonna need a spec.
    6. Re:So does this mean... by moosesocks · · Score: 2, Interesting

      My education on these matters is sadly limited (for now), but I'm not quite so sure they're "almost there", or if they'll ever be "there" for that matter.

      Any observation of a quantum particle requires some sort of interaction with that particle. Once you interact with the particle, the wave function collapses.

      Unless I'm horribly mistaken, this breakthrough only allows us to observe particles with less interaction to them. Regardless of this fact, any observation imlies a collapse of the wave function. Einstein proved this IIRC.

      From what I understand, until *any* given phenomena is observed, it is occupying all possible states of being. Once it is observed, the probability function collapses, and it settles on one state of being. This manifests itself particularly well in the double slit experiment, because, the particle has a 50% chance of hitting one slit or the other, and as long as you don't make any observations before the particle hits the slit(s), it seems to pass through *both*. Of course, the definition of "observation" is pretty broadly defined as any interaction with just about anything.

      Perhaps someone with more knowledge can comment. (It's not like any of this is even relevant anymore anyhow..... Bistromathematics will soon replace quantum physics. )

      --
      -- If you try to fail and succeed, which have you done? - Uli's moose
    7. Re:So does this mean... by hawkfish · · Score: 2, Informative

      You link looks broken, but this description (where it is called the "Guide Wave Interpretation") points out that it is incompatible with Bell's inequality.

      For a pretty thorough discussion of various interpretations, have a look at the containing article.

      --
      You will not drink with us, but you would taste our steel? - Walter Matthau, The Pirates
  12. more info by Anonymous Coward · · Score: 3, Informative

    http://www.analogzone.com/tmt_0912.pdf

  13. For an unknow reason by this+great+guy · · Score: 4, Funny

    For an unknow reason, their device automatically falls into sleep mode after having counted too many electrons.

  14. Re:Shweet by kfg · · Score: 3, Funny

    Can't dowse for shit with one of those.

    KFG

  15. Re:WHY!? by Savantissimo · · Score: 4, Insightful

    The big one, I think, will be allowing the SI definition of current to be changed from the present unwieldly method of "an ampere is the steady current that when flowing in straight parallel wires of infinite length and negligible cross section, separated by a distance of one meter in free space, produces a force between the wires of 2 × 10-7 newtons per meter of length", then defining the Coulomb as "the charge delivered by a current of 1 ampere in 1 second".

    The new, accurate electron counting capability alows the quantum of electrical charge to become the base unit, as it should be, and then to define current as the number of charges per second.

    --
    "Is life so dear, or peace so sweet, as to be purchased at the price of chains and slavery?" - Patrick Henry
  16. Comment removed by account_deleted · · Score: 2, Funny

    Comment removed based on user account deletion

  17. god damn! by x2A · · Score: 2, Funny

    You changed the results my measuring it!

    --
    The revolution will not be televised... but it will have a page on Wikipedia
  18. Re:To: MODS -- next time click the link by karnal · · Score: 2, Funny

    You must be new here.

    --
    Karnal
  19. Exciting as watching... by fahrbot-bot · · Score: 4, Funny
    Physicists Watch Individual Electrons Flow

    ...paint dry.

    Ahh, the wayward electron...

    An Electron's Longings
    The electron
    at the edge of the valence band
    said:

    I stand upon the edge
    Condemned by fate's cruel hand
    To lie in a state of perpetual freeze
    With energy lacking to do a trapeze
    Across to freedom's higher land

    There are many who have risen beyond
    Coulombic forces. They blisfully exist
    Unshelled. Their orbitals know no bond.
    With carefree abandon they diffuse and drift.

    Will no photon shine a light ?
    Will no dopant lend a hand ?
    To conquer Fermi's improbable height
    To leap into the conduction band !
    --
    It must have been something you assimilated. . . .
  20. Re:still can not validate US electronic elections by KDR_11k · · Score: 2, Funny

    No but it can accurately calculate your power bill.

    --
    Justice is the sheep getting arrested while an impartial judge declares the vote void.
  21. Re:WHY!? by vigour · · Score: 3, Insightful

    Because you can study the physics of smaller and smaller systems. There are only a few areas that this device will be useful, but researchers are always fighting against noise while trying to increase the sensitivity of their devices.

    Up until now the record for smallest current was about 100 attoamps with a dc squid. The great thing about them is that you can detect currents from 100 attoamps (if you're very, very careful) all the way up to milliamps, all in the same device in the same setup.

    This new device with coupled quantum dots will only work on the attoamp scale, so is not as versatile, but the years of work that went into designing, fabricating, and measuring this device is astounding.

    Think about it, they are measuring individual electrons, they are fighting against a huge number of electrons surrounding their devices, which experience random thermal noise. The thermal noise in the shielding around their device can generate eddy currents of the order of what they are detecting so they had to account for that too, and design special shielding.

    Not only that, they have to think about the coupling of the quantum dots. You only want charge transfer from resonant tunneling, if the dots are too strongly coupled to their surroundings the quantum coherence is swamped, the linewidths of the levels being populated would be broadened too much. And if they are not coupled strong enough, you won't get enough resonant tunneling.

    Of course there are a lot more considerations, going from concept, design parameters, actual method of fabrication and preparation, detection methods, and noise and data analysis.

    All in all it's a great technical achievement to do what they've done.