Slashdot Mirror
Readable Nuclear Spins Advance Quantum Computing
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."
Easy for you to say.
Cue the strange jokes. I'm charmed. You're Bohred. And the cat is both.
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.
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!
The seek time for that device sounds horrible.
So this is what spin doctors do all day!
"Little does he know, but there is no 'I' in 'Idiot'!"
Please, stick to a standard when writing your articles--preferably metric. I want none of this crap of switching between the metric and English.
// file: mice.h
#include "frickin_lasers.h"
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.
Cool! Amazing Toys.
Stern-Gerlach apparatus, circa 1920.
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 at IBM (by Vandersypen et. al.) The wikipedia summary is a bit dense, but the original paper (cryptome appears to have a mirror) 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.)
News for Geeks in Austin, TX
Hmmmmm
:D.
c i514407,00.html
d e7.html
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
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:
They built the first one and measured the speed exactly... but afterwards they could no longer find it...
"... and more and more now there are all kinds of electronic goodies available" -- Pink Floyd 1972
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'
"... and more and more now there are all kinds of electronic goodies available" -- Pink Floyd 1972
My blog
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.
> 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!
(-1: Post disagrees with my already-settled worldview) is not a valid mod option.
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).
make world, not war