Please create an account to participate in the Slashdot moderation system

 



Forgot your password?
typodupeerror
Compare cell phone plans using Wirefly's innovative plan comparison tool ×

Readable Nuclear Spins Advance Quantum Computing 82

eldavojohn writes, "A University of Utah researcher and his team of German colleagues have shown that it is possible, using electronics, to read data stored as nuclear 'spins'. The lead researcher in the experiment was Dr. Christoph Boehme and his team's letter is available via Nature Physics (at a cost of $18 unless you are a subscriber). This is looking to be a large advance in quantum computing because prior to this, measuring the number of spins of a single phosphorus nucleus was very difficult." From the article: "The researchers used a piece of silicon crystal about 300 microns thick — about three times the width of a human hair — less than 3 inches long and about one-tenth of an inch wide. The silicon crystal was doped with phosphorus atoms. Phosphorus atoms were embedded in silicon because too many phosphorus atoms too close together would interact with each other so much that they couldn't store information. The concept is that the nuclear spin from one atom of phosphorus would store one qubit of information. The scientists used lithography to print two gold electrical contacts onto the doped silicon. Then they placed an extremely thin layer of silicon dioxide — about two billionths of a meter thick — onto the silicon between the gold contacts. As a result, the device's surface had tiny spots where the spins of phosphorus atoms could be detected."
This discussion has been archived. No new comments can be posted.

Readable Nuclear Spins Advance Quantum Computing

Comments Filter:
  • by Anonymous Coward
    Easy for you to say.
  • by Tackhead ( 54550 ) on Monday November 20, 2006 @06:46PM (#16922232)
    Cue the strange jokes. I'm charmed. You're Bohred. And the cat is both.
  • That explains why the black hole they found was spinning so fast.
  • by Anonymous Coward on Monday November 20, 2006 @06:51PM (#16922292)
    when we finally get one built, we'll realize that we spent vast amounts of time and resources into doing something that doesnt matter, and we will wish that we could go back and correct all our past mistakes.

    and thats how quantum leap really started.
    • by Dunbal ( 464142 )
      we spent vast amounts of time and resources into doing something that doesnt matter, and we will wish that we could go back and correct all our past mistakes.

            What, like fusion you mean? :)
  • Once they can, that will be news, especially if they get beyond a few qubits...
    • Puh, you call that jaded? You may not care about several order of magnitude improvement over previous attempts, but _I_ don't want to hear anything until I have a quantum computer wrist watch. Wake me in 2050!
    • To me, this is bad news. Not because of the technological implications -- the implications of this are great. The bad news, for me, is that I'm going to need to go back and revise parts of my last novel before it goes out. Kane quantum computers ("Kane chips") played a significant role, and I don't want it to have any technically inaccurate portions. ;)

      FYI, what the article doesn't mention -- the reasoning why this is important is twofold.

      1) Kane quantum computers have very little problem with "decoheren
  • by r_jensen11 ( 598210 ) on Monday November 20, 2006 @06:52PM (#16922308)

    The researchers used a piece of silicon crystal about 300 microns thick -- about three times the width of a human hair -- less than 3 inches long and about one-tenth of an inch wide.

    3x the width of a human hair? Maybe, for you. But me, I use *insert name brand* Volumizing Shampoo! Now, my hair is 3x stronger, smoother, and thicker than before!

  • Er... (Score:3, Funny)

    by Anonymous Coward on Monday November 20, 2006 @06:52PM (#16922314)
    The silicon crystal was doped with phosphorus atoms. ... The scientists used lithography to print two gold electrical contacts onto the doped silicon. Then they placed an extremely thin layer of silicon dioxide -- about two billionths of a meter thick -- onto the silicon between the gold contacts. As a result, the device's surface had tiny spots where the spins of phosphorus atoms could be detected.

    The seek time for that device sounds horrible.

  • Ah! (Score:4, Funny)

    by dkf ( 304284 ) <donal.k.fellows@manchester.ac.uk> on Monday November 20, 2006 @06:53PM (#16922330) Homepage
    So this is what spin doctors do all day!
  • What's the cheapest (and maybe smallest, lowest powered) device that can flip the spin of electrons? Even if lots of electrons (coulombs) at once. Flip them up and down, singly or en masse (pun intended). I know they're different machines; I want to know abuot the cheapest machine I could get. If civilians can even get them.
    • Re: (Score:2, Informative)

      by Legendre ( 634519 )
      Stern-Gerlach apparatus, circa 1920.
      • That's a pretty simple device. Does the magnetic field need to be very strong, and the duration of operation very long (eg. slow photons through small field in short space not OK) to flip the states?

        Does it take more energy to flip one way or another? Is either flip direction endothermic (to the electron, not net to the device with its power consumption)?

        I'd investigate a microscopic device etched in silicon for flipping throughput, but it looks like these devices are MRIs, which are still very large and po
        • Yeah, it's a pretty simple setup. Tiny magnetic fields will do the job, and it's almost instantaneous. Now, you asked "Does it take more energy to flip one way or another? Is either flip direction endothermic?", well that is a QM phenomena. Basically the thing doesn't have a direction per-se until you do the experiment, and when you do it, it comes out 50-50. You will always need to put in some energy to the measurement. So, you wanted to flip the spin, that's how you'd do it cheap & easy. To build a q
        • Strictly speaking the Stern-Gerlach experiment: passing a beam of electrons through a magnetic field and detecting the two resulting beams, doesn't flip the spin it sorts electrons based on their spin.

          Controlling the spin of electrons is hard, if you work with an electron beam, perhaps one you filtered to contain only one spin orientation, you have to insulate the beam from the environment to make sure the spins don't interact and change orientation later on. Furthermore the electrons within the beam the

          • That is a fascinating explanation of the engineering made possible by the physics of spintronics. I used NMR spectrographs in undergrad organic chem lab 20 years ago - there should be plenty of them, especially after they all got rebranded as "MRI" tech to avoid the marketing poison of calling themselves "nuclear" :).

            I wonder whether photons are more manageable, because they're organized along a line separated from each other, and don't directly interact (except transiently interfering at a single momentary
            • What I'm looking for is a way to "charge" spins...Then later "discharging them...

              What you are describing is precisely and NMR experiment. You use radiofrequency pulses to set the spin state, you then turn off the pulses and listen, the spin system will relax to the ground state emitting a radiofrequency pulse. There's no particular reason to prefer one particle over another, any quantum system can emulate another of equivalent size, that's one of the reasons Feynman got excited about developing a quant

  • What's the net potential energy difference between the difference between the different spin states, if any? And what does the curve look like - is there a big hump between them, or a small hump relative to any energy difference? If it's a hump, is it a trough to flip the states back?
    • by PhysicsPhil ( 880677 ) on Monday November 20, 2006 @09:10PM (#16923812)

      What's the net potential energy difference between the difference between the different spin states, if any? And what does the curve look like - is there a big hump between them, or a small hump relative to any energy difference? If it's a hump, is it a trough to flip the states back?

      I had to pull out my quantum mechanics book for this one. As a rough estimate for the energy difference between "up" and "down" spins, you can use the energy of the Zeeman effect (energy level splitting in an atom when in a magnetic field). The magnitude of that effect is (B/2.4e9 gauss) * 13.6 eV, where B is the size of the applied magnetic field. A supermagnet would produce fields on the order of 1e5 gauss, so we're not talking very much energy here. As another very crude estimate, consider that random thermal effects have enough energy to flip spins randomly, which is one of the big problems facing spintronics.

      As to the humping issue, this is quantum mechanics; there is no curve. Only discrete states are allowed, with nothing in between.

      • Thanks for the very specific answer.

        By "hump" I meant the amount of energy required to push the spin from one to another state - I understand that "quantum" mechanics don't change in continuous functions.

        So I suppose the Zeeman effect is that energy consumed by keeping the magnetic field at strength while the spin is changed. Does your book (or other source) indicate whether the spin flips back when the magfield is removed? Does it emit the energy difference? Or does an external stimulus have to force the f
        • by wass ( 72082 ) on Tuesday November 21, 2006 @12:37AM (#16925314)
          So I suppose the Zeeman effect is that energy consumed by keeping the magnetic field at strength while the spin is changed. Does your book (or other source) indicate whether the spin flips back when the magfield is removed? Does it emit the energy difference? Or does an external stimulus have to force the flip back?

          Zeeman effect is the splitting of degenerate 'atomic' states in the presence of a magnetic field. Atomic really means here hydrogen atom, because that's the only exactly solvable model.


          What this means is that there would be a number of discrete states that an electron in a hydrogen atom can be in, none can be the same due to Pauli exclusion. However, many of these have the same energy (called degenerate states). The degeneracy is split (ie, the energy levels are slightly changed) due to an applied magnetic field. When you consider other effects like the spin-orbit interaction (the electron's motion around the nucleus makes it seem like the charged nucleus is moving around it, creating a magnetic field which interacts with the electron's spin), and also to a lesser extent spin-spin interactions (magnetic dipole interaction between nucleus and electron) they also slightly split those degenerate energy levels.


          Anyway, the electron can be in a number of different discrete states. Applying a field changes those discrete states that the electron can be in. If you knew for certain the electron was in one state (eg, as per a measurement), and then applied or removed a field such that the state the electron was in is now not a valid state, the electron will be in a linear combination of the other now-valid states.


          Finally, I'm too lazy to punch numbers, but I suspect the grandparent's post is incorrect in that when calculating the magnitude of Zeeman splitting, it assumed an electron in a magnetic field when in this case it's really a proton in the magnetic field (different magnetic moment, by a factor of about 2000).

        • So I suppose the Zeeman effect is that energy consumed by keeping the magnetic field at strength while the spin is changed. Does your book (or other source) indicate whether the spin flips back when the magfield is removed? Does it emit the energy difference? Or does an external stimulus have to force the flip back?

          The energy is a one-shot deal, only required to flip the spin. In principle, the magnetic field doesn't need to stay on after the spins are flipped. In practice, once the field is removed, t

          • Well, maybe if we kept up this thread, someone could edit it into _Spintronics for Dummies_ ;).

            So I think you're saying that a calibrated device could require energy transduced first into a magnetic field of strength to flip the spin of an electron, operating just long enough to probably flip the spin. A much lower strength than the nuclear formula you cited - do you have the formula for the energy to flip an electron's spin?

            The electron spin, much more decoupled from the kinetics that transfer thermal ener
      • What's the net potential energy difference between the difference between the different spin states, if any? And what does the curve look like - is there a big hump between them, or a small hump relative to any energy difference? If it's a hump, is it a trough to flip the states back?

        I had to pull out my quantum mechanics book for this one. As a rough estimate for the energy difference between "up" and "down" spins, you can use the energy of the Zeeman effect (energy level splitting in an atom when in a m

      • by wass ( 72082 )
        I'm too lazy to look up values or calculate it, but when using the magnitude of Zeeman splitting, you'd need to use nuclear magneton, not the Bohr magneton (as the textbook for Zeeman splitting almost certainly did), since this effect is looking at nuclear spins. Since the proton is about 2000 times as massive as the electron, the nuclear magneton is about 2000 times smaller.
  • It sounds to me like this is some type of Schottky diode. The phosphorus is the N-type semiconductor that is doped in the silicon and you've got metal (gold) contacts.

    My question is, since the principle behind Schottky diode is the use of quantum tunneling, does this technique rely on how spin affects tunneling? If so, in what way?
  • What can we do with this new devolopment? Is there anything we can finally do? Will this change our views on certain things? enlighten me please!
    • Re:round round baby? (Score:5, Informative)

      by meregistered ( 895132 ) on Monday November 20, 2006 @07:55PM (#16923098) Journal
      Hmmmmm

      To the best of my knowledge storing data as spin, therefore creating transistors the size of atoms* will, at the very least, bypass the limitations of the current transistors measured in nanometers. A Nanometer is 10 to the -9th power of a meter**. An atom is approximately 10 to the -11th power of a meter***. Therefore this technology, when fully functional would theoretically allow two orders of magnitude greater number of transistors per area of measurement.
      So if a Pentium IV has approximately 42million transistors**** it could (in theory) contain 42,000,000 to the 2nd power more transistors.
      Accept the increase is far greater than this because the P IV die process is 0.18 microns which is 180 nanometers (if I'm correct). So the actual increase in available transistors per area of measurement would be more on the order of 42,000,000 to the 5th power: 5,489,031,744,000,000 transistors (well atoms).

      Now add to that the current problems with heat. I would expect (although I most definitely do not remember/know the laws of thermodynamics well enough to do more than vague speculation) that the amount of heat created by such a quantum system would be impressively small compared to the current system... although I would conjecture there are limitations to speed when measuring and changing spin... this would hugely increase the ability to clock the processor higher (an over abundance of heat is the primary limiting factor in clocking the processor system higher).

      Wow, so now I am looking forward to having my conjecture ripped to pieces by those who actually know :D.

      I hope that's at least a little helpful

      *(although I think of spin being associated with quarks, a much smaller, sub-atomic particle... obviously a hole in my knowledge)

      **Nanometer: http://whatis.techtarget.com/definition/0,,sid9_gc i514407,00.html [techtarget.com]

      ***Atom, Size of: http://trshare.triumf.ca/~safety/EHS/rpt/rpt_1/nod e7.html [triumf.ca]

      **** http://72.14.203.104/search?q=cache:foWPHOKFqoMJ:w ww.soc.staffs.ac.uk/mss1/hsn/hsn-lect9.ppt+transis tors+in+a+Pentium+IV&hl=en&gl=us&ct=clnk&cd=2&clie nt=firefox-a [72.14.203.104]
      • Re: (Score:2, Informative)

        by zevans ( 101778 )
        Interesting, but i think you missed the point. This is quantum tech, not just nanotech.

        A byte's worth of qubits can be in all 256 states *at once*, so as well as the 2d density of info you describe, you have to factor in that the thing is in many universes as a multiplier for the bit density it has merely in this one...

        *Feynman fans read 'history' for 'universe'
      • by wass ( 72082 )
        Storing data as spin has a far more interesting effect, and that is it's a specifically quantum mechanical value, meaning that it can be in a superposition of the two states, unlike a classical bit, and more importantly can be operated on and entangled with other qubits to allow for quantum computation. That's the whole quest for this research, to make workable quantum computers, which means at this point having workable qubits capable of storing a value for a 'reasonable' length of time.

      • by AnwerB ( 255422 )

        A Nanometer is 10 to the -9th power of a meter**. An atom is approximately 10 to the -11th power of a meter***. Therefore this technology, when fully functional would theoretically allow two orders of magnitude greater number of transistors per area of measurement.
        So if a Pentium IV has approximately 42million transistors**** it could (in theory) contain 42,000,000 to the 2nd power more transistors.

        A nm is 1e-9, while an atom is nominally 1e-11 (different atoms have different sized nuclei and numbers of she

  • by ndogg ( 158021 ) <the.rhornNO@SPAMgmail.com> on Monday November 20, 2006 @07:06PM (#16922464) Homepage Journal
    Please, stick to a standard when writing your articles--preferably metric. I want none of this crap of switching between the metric and English.
    • Re: (Score:1, Insightful)

      by Anonymous Coward
      We gave up using imperial measures for scientific work many years ago. Even my sixty year old engineering lecturer scolded me when I used them, and I only did that because most of my experience so far has come from working on classic cars.

      I suspect we only cling to them in day to day life because of their convenient size and divisors: a pint is a good measure of beer, and a quarter pound of ham will make a generous round of sandwiches. One has to get one's priorities in order.
      • by radtea ( 464814 )
        I suspect we only cling to them in day to day life because of their convenient size and divisors: a pint is a good measure of beer, and a quarter pound of ham will make a generous round of sandwiches.

        A litre is an even more convenient size for a beer! And a kilos can be treated as pounds times two, so 150 grams of hame will do not too badly, 200 is lots and 250 is really rather much.

        What is convenient is what you know, what you're used to. Metric measures are just as convenient as Imperial ones if you kno
      • We gave up using imperial measures for scientific work many megaseconds ago. Even my 1.89 gigasecond old engineering lecturer scolded me when I used them, and I only did that because most of my experience so far has come from working on classic cars.
        There, fixed that for you
  • Spins (Score:5, Informative)

    by inKubus ( 199753 ) on Monday November 20, 2006 @07:06PM (#16922472) Homepage Journal
    Actually, TFS is incorrect; they only measured the "net spin" of millions of phosphorous atoms. According to TFA, they took a measurement of the hair thing at room temperature (where the spins are pretty evenly 50-50), then they measured it at liquid helium cold (where spins are "down") and when heated by microwaves (where spins are "up"). It's important to note that "spin" really refers to the electrons. I'm guessing that in a nice silicon matrix the "spin" affects the surrounding silicon either making it more or less conductive around the phosphorous. They don't really get into what "spin" is, so you think they are actually talking about a spinning ball or something which couldn't be further from the facts. Since electrons are like photons and they are waves at small scales, it's more about these little probability eddies or whirlpools where the electrons hang out more. There's a wikipedia article that explains the concept, they say "spin angular momentum cannot be associated with rotation but instead refers only to the presence of angular momentum." So like I said, it appears the particles are affected by angular momentum (statistically), but they are not actually "spinning" because there's no such thing that that scale.

    • Re: (Score:3, Informative)

      by inKubus ( 199753 )
      And a link to the wikipedia article [wikipedia.org], since I forgot to insert it before submitting ;)

    • Actually, according to the fine article, they measured the net spin of ~10,000 phosphorous atoms. Previously it was only possible to measure the net spin of billions of phosphorous atoms. So it's a big improvement (but still not single atoms.) Furthermore, spin isn't a property of electrons only. The article mentions that they are trying to measure the atom nuclei's spin indirectly by measuring the electron spin, since these are connected.
    • Re:Spins (Score:4, Informative)

      by klaun ( 236494 ) on Monday November 20, 2006 @08:00PM (#16923182)
      It's important to note that "spin" really refers to the electrons.

      I'm not sure why you say this. It is clear from the article that they are talking about nuclear spin, not electron spin. In fact the basis of the experiment seems to be the nuclear magnetic moment... it is definitely not an electron artifact... There is a quote from the researcher (an assistant professor of physics) refering to nuclear spin in the second paragraph of the article.

      Your explanation of spin is a little off the mark as well... You seem to be confusing a couple of different concepts. I'd say spin is really a quanity associated with a particle more than anything else... much like charge. And it is not on off. One of the main divisions of particles is into fermions and bosons based on whether there spin is an non-integer or integer, and thus whether they obey the exclusion principle or not. The wave/particle nature of electrons is only tenously connected to the concept of spin, in as much as they are both quantum mechanical concepts.

    • by dido ( 9125 )

      Actually, if their goal really is quantum computing, the spin of atomic nuclei would have been a better bet than electron spin. The atomic nucleus is one of the best-isolated quantum mechanical systems known, and it usually takes a very long time for decoherence and similar behavior to destroy any superposition of spin states that you create (an absolute necessity for any type of useful quantum computation). The most promising methods to date (such as this [mit.edu] and this [ibm.com]) for quantum computation are largely bas

    • by wass ( 72082 )
      Umm, the latter part of your post is a bunch of incoherent rambling that may sound profound but is not really saying anything useful (like the alien as the professor in the episode of American Dad last night).

      Since electrons are like photons

      Okay, I'll just stop you there, electrons are NOTHING like photons, those two couldn't be further apart. Phonons are massless chargeless relativistic spin-1 bosons, electrons are massive spin-1/2 fermions with charge -e. Big HUGE difference, in every quantum effect.

      • by inKubus ( 199753 )
        Anyway, you have an electron rotating a nuclei, not a free electron. So the spin has a different effect because the electron is locked in the orbital (and maybe even the orbital of the surrounding silicon). It doesn't just fly off in one of two directions. It's going around in a circle. So, the electron has it's spin (which is not really spin, but some sort of momentum without rotation) and it's also orbiting in a cloud of probability. At quantum level and timespace, it's pretty much a solid sheet of v
  • Annoyingly, they don't know how fast the memory is
    • Re: (Score:3, Funny)

      by zevans ( 101778 )
      They built the first one and measured the speed exactly... but afterwards they could no longer find it...
  • by StandardDeviant ( 122674 ) on Monday November 20, 2006 @07:43PM (#16922924) Homepage Journal

    how is this really news? Every approach to qc that I'm aware of uses spin setting/reading (via NMR in every case that's coming to mind). Bringing this back to the g33k/slashdot crew, check out the work done around 2001 to implement Shor's Algorithm [wikipedia.org] at IBM (by Vandersypen et. al.) The wikipedia summary is a bit dense, but the original paper (cryptome appears to have a mirror [cryptome.org]) is a bit better.

    (NB: I'm far from being an expert in this field, it's just something I was interested in a while back when I was wrapping up my chemistry bachelors. There could also certainly be something newsworthy in the present article that I can't presently see.)

  • Then they placed an extremely thin layer of silicon dioxide -- about two billionths of a meter thick -- onto the silicon between the gold contacts.

    Holy cow! 20 angstroms? You can't get much thinner than that. The Si-O bond length is probably 3-4 angstroms. That is stunning.
    • by grrrl ( 110084 )
      20 angstroms (2 nanometers) is not difficult, especially given that SiO is generally not deposited on Si but rather grown out of it by oxidation (at least, for standard MOS that's how it's done). But depositions of films of this thickness is pretty regular in semiconductor work.

      In fact, all the dimensions outlined in the article are pretty standard, if not large, for this type of research.

  • Two billionths of a meter thick!? Come on! Just say, 2 nanometers please.
  • This made me wonder, are there any quantum virtual machines? Surely nobody is waiting for a physical implementation. Well, apparently there are a few: Linear Al, libquantum, and a Java quantum circuit simulator. Now I wonder how difficult it's going to be to program something...
    • by dido ( 9125 )

      Sure there are, the only trouble is simulating more than a handful of qubits will require a really powerful machine. If you had as few as 256 qubits your simulator would need to keep track of 2^256 states, about as many states as there are sub-atomic particles in the visible universe! It's one of the reasons why computer modeling of quantum mechanical phenomena on classical computers is so hard, and probably that this application, far more than Shor's or Grover's algorithms, will be the primary use for th

    • ...the universe?
  • > Then they placed an extremely thin layer of silicon
    > dioxide -- about two billionths of a meter thick

    Holy crap! That's about 2 trillionths of a kilometer thick!
  • This flash albeit published years ago by another inventor shows how the concept will work using ferroelectrics, silicon,etc. using phosphor as a visual data agent.

    http://colossalstorage.net/display/atomic_switch_d isplay.htm [colossalstorage.net]
  • They have developed nonprogrammable read only memory.
  • For those who aren't sure, "the width of a human hair" is based on the average width of a clump of random hairs kept under a glass Bell jar at constant tempterature and humidity in Paris, France. I've never seen it, but allegedly the clump is about the size of a hailstone.

  • Advancement in computer hardware engineering has/will really slow down. Successful development in quantum computing and storage will hopefully kick of a actual information revolution.
  • "[snip] about 300 microns thick [snip] less than 3 inches [snip] one-tenth of an inch wide [snip] about two billionths of a meter [snip]" Some consistency would be good! -S

DEC diagnostics would run on a dead whale. -- Mel Ferentz

Working...