IBM Tech Detects & Changes Spin of Single Electron 334
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.
"
Not Electrons (Score:5, Informative)
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.)
Stern-Gerlach experiment (Score:5, Informative)
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 [wikipedia.org], a key stage in the discovery and understanding of quantum spin.
However, to quote from this discussion of the experiment [phys.rug.nl], 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.
Re:Innovation (Score:5, Informative)
Re:Spin doesn't come in pairs of electrons? (Score:4, Informative)
In a molecular system, this is not necessarily the case. (Otherwise things wouldn't be magnetic)
Re:Hmmmm. (Score:2, Informative)
As I recall, Heisenberg states the impossibility of measuring both the position and momentum of a particle at the same time. I don't think that affects changing its spin.
Re:Spin doesn't come in pairs of electrons? (Score:5, Informative)
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...
Spintronics, not Quantum Computing (Score:4, Informative)
Re:Innovation (Score:3, Informative)
Re:Stern-Gerlach experiment (Score:3, Informative)
No. The (traditional) SG experiment does not measure the spin of electrons bound to atoms. It measures the spin of a beam of electrons in a magnetic field.
Wrong. The SG experiment was applied to a beam of silver atoms, which have a single electron in their outer shell. It cannot be practically applied to a beam of free electrons, due to the spread of the electron wavefunctions under the action of the uncertainty principle (see my original post, and also the discussion here [cornell.edu]).
IBM's technique...some background (Score:1, Informative)
What is really interesting about this is that IBM's technique is so sensitive that the scientist learned that it takes 6 percent more energy to flip the spin of atoms positioned near the edge of an insulating patch on the surface than for atoms in the middle of the patch. Such detail will be valuable in understanding and engineering the properties of future nanoscale spintronic devices.
And in addition to this an electron's spin has two possible conditions, either "up" or "down." Aligning spins in a material creates magnetism. Most materials are non-magnetic because they have equal numbers of up and down electron spins, which cancel each other. But materials such as iron, or cobalt have an unequal numbers of up and down electron spins and are magnetic. In their new result, the IBM researchers measured the energy required to flip the spin of a single manganese atom from "up" to "down."
CmdrTaco mistake. (Score:5, Informative)
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.
--
Bush's education improvements were partly fraud [cbsnews.com]
Re:Not Electrons (Score:3, Informative)
"IBM scientists have measured a fundamental magnetic property of a single atom -- the energy required to flip its magnetic orientation."
That is what the article is about. In the course of measuring the energy, they flipped the spin of the atom (not of an electron, nor of the components of the atom). The article doesn't even mention the spin of electrons or the components of the atom.
How do you solve the impossible? (Score:5, Informative)
Nothing impossible to solve is solvable, and nothing unsolvable is possible to solve.
I think the word you are looking for is intractable.
Re:Hmmmm. (Score:5, Informative)
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.
RTFA (Score:3, Informative)
It's about a single ATOM
A-T-O-M
not
E-L-E-C-T-R-O-N
Re:You keep using that word (Score:3, Informative)
Were he still alive, Andre the Giant would have something to say about this sentence.
Yeah, like it was Inigo Montoya who said the line you're thinking of [imdb.com]
Re:CmdrTaco mistake. (Score:3, Informative)
To reverse an atom's spin, one must influence the spin of the electrons. This technique does just that.
This is not a new idea (Score:1, Informative)
Re:This does not answer the question. (Score:3, Informative)
Things change spin all the time. Bang on an iron slug enough times with an iron hammer, and you'll start to magnetize both objects, just from the impacts.
IBM is an applied science lab. They found no value in making Hydrogen reverse its spin, and nobody but a particle collider holds onto one free electron; they're always on the move. IBM found value in measuring the required energy to apply to a certain metal used in their products, to make that metal reverse its overall spin.
Re:Hmmmm. (Score:5, Informative)
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.
Re:Stupid question? (Score:3, Informative)
It doesn't. Who ever put that in the article leader was an idiot. First, there are very few truly "impossible" encryption problems. The one-time pad is one example of a cipher that is impossible to break. Quantum computing will not help us to break those types of ciphers. They truly are impossible to crack.
What QC will help with is solving nearly impossible problems. I.e., problems which can only be solved through brute force. A quantum computer can look at many possibilities simultaneously, so it can solve certain kinds of problems much faster than traditional computers. Factoring huge numbers is one example of a very difficult problem that quantum computers are (in theory) extremely good at.
Re:Stupid question? (Score:2, Informative)
Quantum computing, in this case, can provide the mother of all BF&I solutions. The idea is simple in practice. Try every damn number smaller than the number you're trying to factor with. Quantum computing changes that to try every damn number smaller than the number you're trying to factor, at once. If you're trying to factor a 128 bit number, you need at least a 128 qubit quantum computer. A quantum computer's power is measured in qubits, just like a regular computer is measured in bits. It takes just as many qubits as it does normal bits to encode some piece of data.
The problem with a 128 qubit quantum computer isn't possible as 128 1 qubit slices, as it is with regular digital computers. You have to be able to measure consistently 2^n different spin directions to be able to produce a n qubit quantum computer.
When people talk about this breaking strong encryption, its sort of like saying "Well, we've invented the horse-drawn carriage, now let's launch this bitch up to .995 c!" I'll believe it when L Ron Hubbard comes down from Heaven and starts the Rapture.