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."
Readable Nuclear Spins Advance Quantum Computing (Score:2, Funny)
Charmed, I'm sure. (Score:5, Funny)
Heat? (Score:3, Funny)
Re:Charmed, I'm sure. (Score:5, Informative)
Or get it for free at arXiv [arxiv.org]...
Nuclear spins - that explains it (Score:1)
quantum this quantum that (Score:3, Funny)
and thats how quantum leap really started.
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What, like fusion you mean?
They read the spin of 10,000, but can't read one (Score:1)
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Re:They read the spin of 10,000, but can't read on (Score:2)
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
3x as wide as a human hair? (Score:5, Funny)
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)
The seek time for that device sounds horrible.
Ah! (Score:4, Funny)
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Spin Cycler? (Score:2)
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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
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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
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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
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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
Getting Over the Hump (Score:2)
Re:Getting Over the Hump (Score:4, Interesting)
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.
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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
Re:Getting Over the Hump (Score:4, Informative)
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).
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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
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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
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Schottky Diode? (Score:2)
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?
round round baby? (Score:1)
Re:round round baby? (Score:5, Informative)
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
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_g
***Atom, Size of: http://trshare.triumf.ca/~safety/EHS/rpt/rpt_1/no
**** http://72.14.203.104/search?q=cache:foWPHOKFqoMJ:
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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'
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A nm is 1e-9, while an atom is nominally 1e-11 (different atoms have different sized nuclei and numbers of she
Stick to a standard (Score:5, Insightful)
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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.
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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
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In England there's only three things I can think of where we stick with Imperial measures: beer, milk, and driving distances. There is also a tendency for individuals here to measure their own weight in stones (14 lb to a stone), however the medical profession uses kg. Besides those things we're completely metric. Indeed, it's illegal to sell groceries in England in pounds and ounces, and petrol (gasoline) is leg
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So very true. This is why my heart leaps for joy whenever I find a bar that provides beer by the Imperial pint. That is really the perfect size for a glass of beer. Unfortunately, it doesn't convert so nicely to metric. Who wants to order 5.7 deciliters of lager?
Spins (Score:5, Informative)
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Re:Spins (Score:4, Informative)
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.
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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
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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.
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Rimshot (Score:2)
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haven't (can't, currently) read tfa, but... (Score:3, Insightful)
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.)
"Extremely thin" -- wow! (Score:2)
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.
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In fact, all the dimensions outlined in the article are pretty standard, if not large, for this type of research.
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Oh come on! (Score:1)
Quantum virtual machine (Score:1)
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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
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I mock theeeee (Score:2, Funny)
> dioxide -- about two billionths of a meter thick
Holy crap! That's about 2 trillionths of a kilometer thick!
http://www.bash.org/?2999 (Score:2)
That's almost 25%!
Flash Showing Animation (Score:1)
http://colossalstorage.net/display/atomic_switch_
So far (Score:1)
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Standard Units (Score:2)
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.
I really hope this is true (Score:1)
Units man (Score:1)