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IBM Tech Detects & Changes Spin of Single Electron
An anonymous reader writes "Looks like we have another step forward in Quantum Computing - IBM has discovered how to detect and change the spin of a single electron. Won't be long before we're all solving impossible encryption problems.
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Whew, okay. After I RTFA I realized they hadn't done the impossible, just the really hard. IBM can measured the energy required to change the spin of a single atom not a single electron. (A prerequisite of this, of course, is detecting the spin of a single atom; but that's not that difficult with electron microscopes.)
IBM has discovered how to detect and change the spin of a single electron.
Measuring the spin of electrons bound to atoms was first achieved in the famous 1922 Stern-Gerlach experiment, a key stage in the discovery and understanding of quantum spin.
However, to quote from this discussion of the experiment, the Stern-Gerlach technique cannot be used to measure free electron spin because 'The spreading of the electron wave packet washes out the separation effect due to the electron spin'. Therefore, it appears that IBM's discovery is significant.
Tubal-Cain smokes the white owl.
Yeah IBM do some really good stuff. The IBM research has taken over from bell labs as being one of the best research labs around. It is such a shame bell labs went from being amazing to depressing but that is a different story. At IBM they have invented copper interconnects (seen in a lot of CPUs these days). They invented Silicon on Insulator transistors (seen in a lot of modern CPUs as well). They have done some nice work on carbon nanotubes (those have a long way to go though), and now spintronics (this has a really long way to go as well). They do a lot of really good stuff at IBM.
That is the degenerate or lowest energy state. If the only thing in the universe is two electrons, that is.
Materials are grouped according to how they respond to external magnetic fields as follows:
paramagnetic materials tend (usually strongly) to line up such that their spins are opposing the existing magnetic field, and therefore attracted to it. In classical terms, magnetic field lines permeate this material and cause attraction.
diamagnetic materials tend (usually extremely weakly) to line up such that their spins are aligned to the existing magnetic field, and therefore opposed to it. This effect is so small it usually can't be measured without very strong magnets or a carefully balanced system. Water is one of the most diamagnetic materials; if you're careful you can see the effect in one of those glitter lamps; let it settle down and still and hold a very strong magnet to the side, you can see the flow as the glitter moves away.
ferromagnetic materials tend, like paramagnetic materials, to line up such that their spins are opposed to external magnetic fields. However, they also tend to retain that orientation when the magnetic field is removed.
EVERY single material is one of the above. There's a proof (I forget who wrote it) saying that no static combination of electric, magnetic, and gravitational fields can be stable; that is, there is no combination of the above forces where something can be seen to levitate and balance the forces perfectly. The proof is almost correct; he didn't know there was such a thing as materials with a negative magnetic permeability (even though the permeability is slight it's enough in extreme circumstances)
Couple cool tricks:
1. If you've got a hugely strong electromagnet, you can float low size organic material in it. I once saw a video of a frog in a bubble of water levitating in apparent microgravity.
2. Certain kinds of graphite are strongly diamagnetic. The dust isn't, but the graphite layers are. You can shave flat little disks off and watch them float over an array of magnets.
3. Using bismuth and a couple neodymium magnets with a clever little gadget to help in positioning, you can make a frictionless bearing. Google if curious.
For those curious in playing around with strong magnets... forcefield.com is your friend...
I am disrespectful to dirt! Can you see that I am serious?!
This is a big step forward in spintronics, not in quantum computing. Quantum computing is predicated on the idea that solutions to the Schrödinger equation can be a linear combination of several single-state equations; this is the case with any higher order differential equation. By detecting or explicitly setting the spin, you force the solution to be only one of these equations, and the quantum magic goes away. Great news for spintronics (using spin, not charge transporation to carry information), not news at all for quantum computing.
`which fortune`
Okay, one answer is that CmdrTaco got it wrong. He said, "IBM Tech Detects & Changes Spin of Single Electron". He should have said, "IBM Tech Detects & Changes Spin of Single Atom". Huge difference.
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Bush's education improvements were partly fraud
Won't be long before we're all solving impossible encryption problems.
Nothing impossible to solve is solvable, and nothing unsolvable is possible to solve.
I think the word you are looking for is intractable.
just = (My)Opinion.toCents();
Yes, but it's more general.
In QM, you measure a property of an object by applying an "operator" (you put in a function, and it spits out another function) to its wavefunction. Heisenberg said[*] that certain pairs of operators don't commute (meaning order is important - AB != BA), and so some pairs of properties can't be measured together.
"Position and momentum" is a particular example of a pair, as is "different components of angular momentum" (L_x and L_z, say). I can't remember how 'spin' fits into things, though ...
[*]Pedantry: Yes, I know Heisenberg talked about matrices, Schrodinger about operators.
Spin is basically a quantized angular momentum intrinsic to many particles (electrons are spin 1/2, photons are spin 1).
From classical mechanics (and quantum mechanics as well), linear momentum is the generator of translations and angular momentum is the generator of rotations. So linear distance and linear momentum would be canonical variables for Hamiltonian dynamics, just as well as angle and angular momentum would be.
There are some differences, though, by noting that translations in different directions are Abelian, while rotations are non-Abelian (Abelian operations are independent of the order of the operators). You can easily see this by taking any object and rotating along the X axis and then the Y axis. You'll get a different resulting configuration than if you rotated along Y first, then X. However, if you translate in the X direction first and then the Y direction, you are in the same place as if you translated Y first, then X.
Anyway, the generalized uncertainty principle relates the minimum uncertainty one can have through a combination of two non-commuting operators. The commutator for operators A and B is defined as [A,B]=AB-BA. The generalized uncertainty relation states that if [A,B]=i C for Hermitian operators A,B, and C (the i=sqrt(-1) is necessary for making everything Hermitian work out properly), then the product deltaA×deltaB=1/2|deltaC |(where deltaA is the uncertainty of that operator on the wavefunction (ie, deltaA=sqrt(A^2-A^2). The expectation value X is the normalized integral of the operator acting on all values of the wavefunction, giving an effective average value expected if infinitely many observations were measured.
For example, one of the primary consequences of quantum mechanics in one dimension state that [x,p]=ihbar (I might be off by a sign here). Plug this into the generalized uncertainty relation, and you get the well-known result deltax×deltap=hbar/2. Note, this is only true if x and p are acting in the same direction. If they're in orthogonal directions, the operators commute, and the total uncertainty product can be as small as zero.
Angular momentum operators, on the other hand, have the commutation relation [Lx,Ly]=ihbarLz, where Lx is the angular momentum operator in the x direction, and so on. What this means is that you cannot simultaneously know the x, y, and z components of the spin vector. In other words, you don't know exactly where the vector is pointing in space. For a single particle, you would be able to simultaneously know it's x, y, and z positions, but not its angular momentum. And you can see deltaLx×deltaLy=hbar/2Lz.
So while you cannot know exactly the angular momentum of a particle, you can know a little more about it than hinted above. The operator L^2, which is a measure of the total angular momentum, commutes with the other angular momentum operators. Ie, [L^2,Lz]=0, and similar for Lx and Ly. So for a system with angular momentum, one CAN simultaneously know the total angular momentum as well as the z-component of the angular momentum. A vector in 3D space needs 3 independent components to know it exactly, but for angular momentum we can only know two exactly. So there is effectively a cone of uncertainty that any particle with angular momentum (or spin) points along.
For the curious (if anybody even read this far) - if you studied chemistry and remember the quantum numbers for the periodic table, you'll recall n, l, m, and I think s. The l refers to the measure of total angular momentum and the m refers to the z-component of that angular momentum.
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