Slashdot Mirror
More on Spintronics
segment writes "'We have discovered the equivalent of a new 'Ohm's Law' for spintronics - the emerging science of manipulating the spin of electrons for useful purposes,' says Shoucheng Zhang, a physics professor at Stanford. 'Unlike the Ohm's Law for electronics, the new 'Ohm's Law' that we've discovered says that the spin of the electron can be transported without any loss of energy, or dissipation. Furthermore, this effect occurs at room temperature in materials already widely used in the semiconductor industry, such as gallium arsenide.'"
OK, I RTFA, and it wasn't what I was expecting.
Isn't it a property of these kinds of things that you can seperate two electrons (or some subatomic particle, can't remember) and change one's spin, and the other, no matter how far away, will instantly change? I recall an experiment in which this worked over a distance of six miles. Wouldn't this be the perfect interconnect? No wires at all?
At subatomic levels, every process is 100% efficient. The basic principles that you learn in mechanics which warn you that there is no such thing as a perpetual motion machine, etc... are results of statistics and macroscopic effects. Microscopic is not miniaturized macroscopic.
Speed of sound, btw, does not have to involve actual sound waves... the speed of sound is simply the rate at which vibration or motion of molecules within a medium can propogate through the medium by affecting adjacent molecules.
File under 'M' for 'Manic ranting'
I think the word your looking for is sketchy. I read the piece and wondered how this got to slashdot. This is so obviously a piece to get funding for further research from a couple of quacks you can't even explain the process.
-You know its like the earth orbits around the sun and then spins on its access that's how it works.-
Give me a break they are trying to lure in the gullible who know nothing about electronics to give them money. I think the idea of spintronics is great but what they propose is not worth anyone's time there are plenty of others who are doing valid research in this area. If the best they can explain is a planetary analogy or some sort of half assed flash animation then check someone else out.
Not so sure about quantum computers, but i belive this is the idea behind them. Transistors used now read either High or low, +5v or 0v, which correspond to binary terms of 0 or 1. Thus we can gather data by reading the charges on the transistors. If we could use electrons, a up-spin meaning 0 and a down-spin 1 (not really up or down, but thats how we denote them), then we could use a 100% efficient replacement for transistors.
No, quantum computers aren't about efficiency; they're a whole bigger concept. In a quantum computer, each quantum bit, called a qubit, can be both 0 and 1 simultaneously. You then make them resolve into the answer you want by observing them in the correct manner. In effect, you test all possible combinations of bits for a solution to your problem at the same time. This is a whole different concept from the transistor/logic gate deal - google if you want to know more.
The real question is, what is 'spin current', and how does it relate to the conventional definition of electric current.
"Nothing exists except atoms and empty space; everything else is opinion." - Democritus
Spintronics is promising, but I doubt that it will be the NBT. Quantum-dot Cellular Automata (QCA), which encodes binary information based on electron orientation, seems to hold more promise. It is highly scalable, small, can hybridize with CMOS, and can already be fabricated at low temperatures. With the addition of clocking regions to lower inter-dot tunneling barriers, even pseudo-pipelining is realizable. Perhaps the best thing about this is that it all cells are coplanar! I just attended a conference (IWQDQC) on Quantum Computing, and believe me, spintronics faces its share of problems.
If you read the abstract for the actual paper you'll
see that they are basically talking about a more
sophisticated version of a quantum-hall effect,
i.e. they are talking about the evolution of a
correlated state, a different one from superconducting
condensate or bose condensate but another type
of correlated state. Correlated states can result
in negligible dissipation (e.g. superconductivity
or superfluidity). They will not be immune from
thermal fluctuations esp. at room temperature nor
will they be immune from dissipation at impurities
and such. But other than that having spin supercurrent
seems quite possible.
And I am a graduate student doing physics research
in the are of high-temperature superconductivity.
Mr. Zhang is quite well known in this area since
he proposed a so called SO5 theory which aimed to
explain everything about high-Tc in one elegant
formalism (his theory is oversimplified at best).
He has worked with Bob Laughlin a lot lately (Laughlin
got a Nobel prize for his theoretical work on, you
guessed it, quantum-hall effect). So these people
are legit, they know what they are talking about
but Zhang has been known to throw wild ideas out
there (and more often than not even those have
at least a grain of truth in them).
http://itss.raytheon.com/cafe/qadir/q192.html
Not true. Suppose you have two masses rotating each other like the Moon around the earth. Space time curvature is changing as this happens. One moment it's shaped like X, the next like Y. A test mass will see a lag time in the shape of its local spacetime due to this movement. That is, when the masses are eclipsed, they won't appear or "feel" that way at a distance where the test mass is because the image of the masses AND the spacetime curvature changes go at the speed of light. Einstein referred to these spacetime changes as gravity waves and they are a form of energy. If the masses are really large (like rotating neutron stars) the energy in these waves could be significant and it's hoped that gravity wave detectors may be able to detect them.
This is because in order for gravitons to create gravity, they'd have to jump between all objects in the universe constantly... it's a bunch of hogwash.
Quantum Mechanics says much the same thing about all particles. Their wave function is smeared out everywhere it's just that the probability is very small that an electron, say, is a mile from it's nucleus. Now everyone will agree that Gravity and Quantum Mechanics are not unified very well with existing theory; but your explanation doesn't give evidence that gravitons don't exist. I've illustrated that like a oscillating charge which creates electromagnetic waves, an oscillating mass can create gravity waves (oscillations is the shape of spacetime). Since we agree quanta of such energy exists (photons) why not gravitons?
In general, electons exist in a superposition of two states, "up" and "down", with oppositely directed "spin" (which obeys almost the same mathematical formalism as angular momentum, with some interesting twists). For a free system of electrons, the up and down states occur with equal measure so that the resulting wavefunction is spinless (sum of spin over all electrons is zero) which implies it is rotationally invariant (ie, rotate all electrons by some angle and the system is indistinguishable from the original).
In the presence of interactions (ie. an E/M field), the alignment of the field specifies an axis, and the coupling to the spin means that up and down spins (with respect to this axis) have different energies. Thus there is no longer rotational symmetry and you can control the direction of spin.
This has nothing to do with the motion of the electrons themselves, but only the spin. One way to think about this is to think of each quantum number as corresponding to a different particle. An electron has spin 1/2 and charge 1 so you can consider an electron to be a bound state of a pure spin particle and a pure charge particle. In fact, in one-dimensional systems (and possibly sometimes in 2D) this is not even a mathematical trick, and it is possible to prove that the spin and charge components are no longer bound to each other! The system behaves as if it was composed of two separate species of particles, "spinons" (carrying the spin) and "holons" (carrying the charge). This is called "spin-charge separation", and it is a collective effect, it doesn't work in a few-body system.
This is not to say that Zhang's result has anything to do with spin-charge separation per se, just an example.
Perhaps more relevant to us is the fact that zero dissipation means, in effect, zero heat. It also means zero loss so power requirements, so important in the portable market, would lessen exponentially. Spintronics based devices would therefore not need the elaborate cooling solutions current semiconductors do. A truly silent computer may be just over the horizon, folks...
Resistance is futile. Reactance buggers it up.