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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.'"
"But even if Moore's Law could continue to spawn ever-tinier chips, small electronic devices are plagued by a big problem: energy loss, or dissipation, as signals pass from one transistor to the next. Line up all the tiny wires that connect the transistors in a Pentium chip, and the total length would stretch almost a mile. A lot of useful energy is lost as heat as electrons travel that distance. Theoretical physicists at Stanford and the University of Tokyo think they've found a way to solve the dissipation problem by manipulating a neglected property of the electron - its ''spin,'' or orientation, typically described by its quantum state as ''up'' or ''down.'' "
"With lack of dissipation, spintronics may be the best mechanism for creating ever-smaller devices."
dawnlevy@stanford.edu
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Stanford University
'Spintronics' could enable a new generation of electronic devices, physicists say Moore's Law - a dictum of the electronics industry that says the number of transistors that fit on a computer chip will double every 18 months - may soon face some fundamental roadblocks. Most researchers think there'll eventually be a limit to how many transistors they can cram on a chip. But even if Moore's Law could continue to spawn ever-tinier chips, small electronic devices are plagued by a big problem: energy loss, or dissipation, as signals pass from one transistor to the next. Line up all the tiny wires that connect the transistors in a Pentium chip, and the total length would stretch almost a mile. A lot of useful energy is lost as heat as electrons travel that distance.
Theoretical physicists at Stanford and the University of Tokyo think they've found a way to solve the dissipation problem by manipulating a neglected property of the electron - its ''spin,'' or orientation, typically described by its quantum state as ''up'' or ''down.'' They report their findings in the Aug. 7 issue of Science Express, an online version of Science magazine. Electronics relies on Ohm's Law, which says application of a voltage to many materials results in the creation of a current. That's because electrons transmit their charge through the materials. But Ohm's Law also describes the inevitable conversion of electric energy into heat when electrons encounter resistance as they pass through materials.
''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. Professor Naoto Nagaosa of the University of Tokyo and his research assistant, Shuichi Murakami, are Zhang's co-authors. ''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. That's important because it could enable a new generation of computing devices.''
Zhang uses a celestial analogy to explain two important properties of electrons - their center of mass and their spin: ''The Earth has two kinds of motion. One is that its center of mass moves around the Sun. But the other is that it also spins by itself, or rotates. The way it moves around the Sun gives us the year, but the way it rotates around by itself gives us the day. The electron has similar properties.'' While electronics uses voltage to move an electron's center of mass, spintronics uses voltage to manipulate its spin.
The authors predict that application of an electric field will cause electrons' spins to flow together collectively in a current. The applied electric force, the spins and the spin current align in three different directions that are all perpendicular to each other (see film of the effect at http://news-service.stanford.edu/news/2003/august2 0/zhang-video-820.html).
''This is a remarkable thing,'' explains Zhang. ''I push you forward and you move sideways - not in the direction that I'm pushing you.''
So far, only superconductors are known to carry current without any dissipation. However, extremely low temperatures, typically -150 degree Celsius, are required for the dissipationless current to flow inside a superconductor. Unlike electronic superconductors being investigated in advanced laboratories throughout the world, whose operating temperatures are too low to be practical in commercial devices, Zhang, Nagaosa and Murakami theorize that the dissipationless spin cur
[Fuck Beta]
o0t!
Won't happen. The rod doesn't move as a rigid whole.
Nick Herbert describes this fallacy in Faster Than Light: Superluminal Loopholes in Physics.
The only reason we have the rights we have is that people just like us died to gain those rights. -- Cheerio Boy
I think you are referring to spooky action at a distance
Spin is an intrinsic, unchangeable quantity for an elementary particle. Particles with half-integer spins are called fermions, while particles with integer spins are called bosons. Fermions can only be created or destroyed in particle-antiparticle pairs, whereas bosons can be created or destroyed singly.
Whenever the offence inspires less horror than the punishment, the rigour of penal law is obliged to give way...
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
Remember, entropy always increases. Not even subatomic particles are immune, it just takes them a lot longer to feel it.
File under 'M' for 'Manic ranting'
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
Your thought is incorrect. Einstein assumed gravity is limited by the speed of light. An experiment done late last year involving Jupiter passing in front of a quasar seemed to confirm that assumption. Though some believe the expirement was flawed.
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
Well, that's in debate (as some other posters have stated) there are in fact, a couple of facilities in the US that are trying to detect gravitons/gravity waves using really long, precisely monitored tunnels and laser distance finders. A guy I went to school is now working on the problem of making real time adjustments for seismic activity, in order to aide the accuracy of the measurements. The facility is called LIGO, if you are interested (well, it's still called LIGO, even if you aren't).
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Crudely Drawn Games
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.
I infer from the general discussion that the "speed of light" being discussed WRT the article is the speed in a vacuum.
In the case of the Cerenkov phenomenon, the betas are traveling faster than the speed of light *in that medium.* That's still incredibly fast, but slower than the speed of light in a vacuum.
I recall that some experiments have managed to reduce the speed of light in a carefully medium to speeds of less than 40 mph. I think the medium was a Bose-Einstein Condensate at a few millions of a degree above 0 Kelvin. Were it possible to move a particle through that medium at 50 mph, it would be exceeding the speed of light -- but not "THE" speed of light.
Or maybe I'm completely wrong.
I had to dig but eventually found it at the following location. http://www.sciencemag.org/cgi/data/1087128/DC1/1
Hard drives use dipole orientation to read data. Not electron spin.
UgaBuga!
With a quick google search, you can find a number of references to the use of spintronics for disk drive heads. Here are just a couple.
Here is something from 1999:
And this is from 2003, or at least, last updated in 2003:
You are right; it is not possible to do computation without SOME losses even if we use completely reversible phenomena. The entropy increase comes when we "forget" information, .i.e., clearing a register.
That is different from what they are talking about in the article. Their goal is to move to essentially reversible reactions using spin rather than current-type electronic phenomena that contain Ohmic irreversibilities. The Ohmic losses dominate the heat generation in current ICs. The next on the list of energy loss for an IC is probably RF radiation. Entropy production from information loss is pretty far down the scale, but it is the one that cannot be "engineered away" so that is why it is always included in the "how big can a computer get" calculation.
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.
make world, not war
This isn't actually an "exponential" decrease. Your new power requirements would be whatever you need to manipulate the state of the electrons (spin current may have no dissipation, but creating pulses of spin current for signalling will need some energy). You'd probably use less power, but "exponential" refers to a way that two variables relate to each other, not just a "really big" decrease in power consumption, which is what you'd really get. Also, unless there's a breakthrough in non-volatile solid-state storage that makes it cheaper and faster than what we have now, you'll still have a hard drive (evil, power-sucking mechanical device). With luck, spintronics may provide us with this memory technology...