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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.'"
effectively allowing communication based upon movement.
The rod would move at the speed of sound through its medium (the speed of sound varies largely depending on its medium). IN any case, it would be MUCH slower than the speed of light.
Currently, the only thing confirmed to move faster than the speed of light (confirmed via the "alan aspect" experiments, if you want to google it), is the spin on a pair of electrons. Two elextrons in a pair alwats spin in reverse directions. Even if the two electrons are 1000 miles apart, if you polarize one (change the spin), then the other spin will reverse itself instaneously.
This was tested by alan aspect (who built upon the EPR thought experiment), who subjected two electrons traveling in opposite directions to a polarizer and found that the correspondency between the two electrons meant that there HAD to be some osrt of faster than light communication (it violated "bells theorum" if you want to do more googling). That is, it wasnt a coincidence, or due to 'hidden variables' as einstien thought. It truly was faster than light communication, somehow, between the electrons.
This is the main discrepancy between Einstein's relativity and Bohr's quanutm theory (Einstein's theories actually pushed quantum theory, ironically). Einstien's relativity theory states that should anything move faster than the speed of light in the spatial dimensions (x,y,z), it must move backwards in the fourth dimension (time). Basically, he argues that everything moves through the four dimensions (x,y,z,t) at the speed of light. Photons move through the spatial dimensions (x,y,z) at the speed of light, and thus do not mvoe through time at all. The photons that exist now have not aged at all since the big bang. This is how einstien explains "Time dilation." This has been confirmed a number of ways, most easily by clocks on airplanes. Clocks put on airplanes, which move through the spatial dimensions(x,y,z) through high speeds (high being relative to normal human movement) have been found to register less time than their "at-rest" counterparts. Of course, quantum theory somehow defies this concept. String theory explains this by offering multiple dimensions past the 4th (I beleive steven hawking's count is at 14 right now)...
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.
If anyone wants to correct me, please do. I havent taken a physics course in my life (yet) and am probably wrong about some (most) of what i just said.
the byproduct of years of oppression by the white man
If I recall correctly there are a few problems with this method of transmission:
... its a bit more complicated than that.)
1. Once you transmit using a particular electron pair you can't use that pair again, so you have to pre-prepair as many electron pairs as you think you will need for a transmission.
2. Creating perfectly isolated pairs is difficult. The basic problem is making sure the pairs you create aren't entangled with any other qubits (and using extra bits to do error correction because its next to impossible produce pure states) People are working on efficient ways to do this, but although it won't be prohibitive for, say, prearranged data transmission it really wouldn't be economical for circuits.
This article is talking about something else aparently: some kind of wave of spin -- like a current.
(BTW in the method you're talking about one doesn't exactly "change the spin"
your reffering to the Alan Aspect experiment, which was built on top of the EPR thought experiment(Einstein-podolsky-rosen.
the byproduct of years of oppression by the white man
Ohm's law describes the creation of a current by the application of a voltege. This new law seems to describe the creation of a, um, whatever you want to call the "movement" of the spin of an electron, by the application of an electric field. Or more accuratly, it probably describes the movement of a group of spins.
They're describing generally the same kind of action, at least viewed in a certain way, in two different kind of "substances."
This Space Intentionally Left Blank
Yes, but the receiver would get nothing but noise since you cannot control the direction of spin. You'll have only a probability of the spin being in a specific direction. So you cannot modulate the signal to send information. The receiver will only have corresponding results if you compare notes later. That is, sender and receiver will always have corresponding states of their entangled particles, but because the states are random they cannot carry information. It's presently a metaphysical question about how entangled particles always match states over long distances. This "quantum nonlocality" is one of the greatest scientific mysteries of the world.
Not all devices are linear and follow Ohm's law over wide ranges of voltages/currents. Sometimes there's an exponential relation, or others. For example, in a superconducting filament, one has bizarre quantum effects kicking in for the effectively 1-D system, and the effective Ohm's law has the voltage proportional to exp[I]. Only linear (and hence Ohmic) at small currents.
Then there's the Hall Effect where a current flowing through a wire (can be a thin foil) with a perpendicular magnetic field will cause the current carriers (either electrons or holes) to drift to one side or the other of the foil [F=q(v x B)] where the F is the force, v is the carrier velocity, and B is the magnetic field. x is a cross-product (v and B are vectors, so is F). In other words, the force acting on the carriers is perpendicular to the B-field and the current velocity, and creates a transverse voltage, often called the "Hall Voltage". So you now have a current creating a transverse voltage, which lets you apply a variant of Ohm's Law to define a Hall Resistance, sometimes called Rxy, where Rxy=Vhall/I (could be a non-linear relation too).
So in this case of spintronics, they define another variant of Ohm's Law to relate the current of the spins in relation to an applied electric field. Note that the transfer of spins across the device probably doesn't correspond to the actual transfer of electrons, but a signal propagation of spins instead.
Finally, there are other cases where one can have current flow without resistance. One case is superconductors. Another is the so-called Quantum Hall Effect. However, both of these occur at cryogenic temperatures.
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