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."

Comments

Spins

[inKubus]

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:Spins

[inKubus]

And a link to the wikipedia article, since I forgot to insert it before submitting ;)

Re:Spins

[klaun]

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.

Re:Spin Cycler?

[Legendre]

Stern-Gerlach apparatus, circa 1920.

Re:round round baby?

[meregistered]

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

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

**** 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

Re:round round baby?

[zevans]

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'

Re:Getting Over the Hump

[wass]

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).

Re:Charmed, I'm sure.

[Iron Condor]

at a cost of $18 unless you are a subscriber

Or get it for free at arXiv...