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Yale Physicists Measure 'Persistent Current'
eldavojohn writes "Modern processors rely on wires mere nanometers wide, and now Yale physicists have successfully measured a theoretical 'persistent current' that flows through them when they are formed into rings. The researchers predict this will help us understand how electrons behave in metals — more specifically, the quantum mechanical effect that influences how these electrons move through the metals. Hopefully, this work will shed new light on what dangers (or uses) quantum effects could have on classical processors as the inner workings shrink in size. The breakthrough involved rethinking how to measure this theoretical effect, as they previously relied on superconducting quantum interference devices to measure the magnetic field such a current would create — complicated devices that gave incorrect and inconsistent measurements. Instead, they turned to nothing but mechanical devices, known as cantilevers ('little floppy diving boards with the nanometer rings sitting on top'), that yielded measurements with a full order of magnitude more precision."
I'm not quite sure what the application would be for persistent current, although my wife might have some ideas on the subject. In any case, I'm always amazed at folks who can work and innovate at such a small scale. It's like they could build a model ship in a bottle wearing boxing gloves.
As one of the few mechanical engineers on Slashdot, I approve of this experiment.
One of our competitors trademarked the term "hypothesis". From now on, we will call them "boneheaded ideas".
“Yet these currents will flow forever, even in the absence of an applied voltage.” is this some form of perpetual energy or am I a fool?
n/t
Warning: this article may contain humor, sarcasm, parody, and perhaps even irony. Read at your own risk.
I'm no electronics engineer or chip designer, but couldn't they make things more compact by going vertical? Chips are always planar. Wouldn't you get a faster IC if you stacked the components instead? Make a sandwich; silicon, insulator, aluminum, insulator, silicon, insulator, aluminum, etc. (The aluminum would be for heat sink purposes.) Build it up 16, or 32, or even 64 layers thick. Each layer could be a processor core.
When our name is on the back of your car, we're behind you all the way!
Sounds like perpetual motion!
Know your pads. One time pad: good for cryptography. Two timing pad: where to take your mistress.
"Modern processors rely on wires mere nanometers wide." -Nothing to see here, move along.
Left to right or right to left?
But what does it all mean, Basil?
"When life gives you lemons, don't make lemonade. Make life take the lemons back!" -- Cave Johnson
The problem is not heat dissipation: it is the inefficiency of our computational machinery.
Logic devices have almost zero efficiency in that for each watt going in, nothing or almost nothing is used to deliver the logic movement. Almost everything is converted into heat, or physical motion.
So... 500 watts into a server is 500 watts of heat to dissipate... and zero watts of computing (whatever that would be).
What we need is a more efficient computing design.
wait, did they just say theoretical?
granted, it's all a theory, but is it really theoretical if they've measured it?
They're using their grammar skills there.
This reminds me of people who plug power strips back into themselves, and then wonder why it doesn't power their devices.
I'm a good cook. I'm a fantastic eater. - Steven Brust
As long as you're not taking energy out of it, no, it's not. Well, actually, energy is perpetual; it's power that's not. Perpetual motion exists in a vacuum. It just doesn't on earth with all that friction that requires perpetual power to counteract.
You can also maintain a perpetual current in a supraconductor, as long as you're not messing with the magnetic field it generates. But just like a hard vacuum, it's not a natural state down here.
they form rings and have current passing through them.... Weird stuff....
On CMOS devices static power is an order of magnitude less than dynamic power(logic movement).
I am a solid state physics Ph.d. student. There seems to be a lot of confusion on how these things work, which is unsurprising given the lack of details in this slightly sensationalist story published by Yale about work done at Yale. Hopefully this helps a bit.
First, these currents don't spontaneously arise out of the blue. There is an external applied magnetic field, so every metal ring has at least 1 flux line passing through it. As most should know, a changing magnetic field induces an electric current. Normally, in non-superconducting metals, inelastic scattering of electrons causes the current to dissipate (ie there is resistance).
The unique thing about these metal rings is that they are smaller than the electron's phase coherence length, or the distance the electron travels before it is scattered inelastically. Electrons will scatter elastically off of impurities, but those collisions are not dissipative.
This Yale group by no means discovered this phenomenon, nor are they the first to measure it. What they did was measure it with greater accuracy. The things that have been unclear for awhile are the direction the current travels in and the magnitude. Hopefully these new measurements will shed some light on the matter.
P.S. I hate Slashdot's comment system. Every time I clicked off this typing box, it refused to accept any input until I clicked randomly around the screen for at least 15 seconds.
the currents were in the physicists, not some wires. I had a crazy mental image of some guys in lab coats grabbing their ankles and/or applying ammeters to their heads and feet.
Check out Reversible Computing for some info on where this isn't the case - the idea is to have it so that the results of a computation doesn't result in the waste of energy as heat.
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Do not be discouraged. Look on this as a challenge. Keep clicking randomly and this will confuse it enough for it to start working again.
I don't read your sig. Why are you reading mine?
3-d is the past, upwards and onwards!
(Actually, I'm not kidding. The brain is a 4-dimensional circuit/computer. In addition to being spatially extended in three dimensions, computations are also temporally extended (thus adding a fourth). What might be an atomic instruction on a modern "2-d" CPU could require all four dimensions of the brain. Think in terms of remembering a word, or the lines to a poem. You get the first part, and some aspect of that influences the trajectory of the system to move to a state that represents the next part, and so on. There is a dynamic feedback loop which is extended over (and reliant on) time. Cf. dynamical systems theory.)
The energy is perpetual, so you aren't a fool. Congratulations. However, for as long as it lasts, no-one gets any power out of it. It is just a tiny, fixed current going in a circle giving a small, static magnetic field.
On a smaller scale, consider electrons circling a nucleus. They are waves, and not like little planets orbiting a sun, but some of them are going in circles endlessly. They aren't losing energy because they have to be in one quantum state, or emit or absorb a whole chunk of energy to go to another. They can't slowly leak their orbital energy away and spiral into the nucleus, which is good thing for us as matter as we know it would rapidly cease to exist.
What we have here in our little ring is the same sort of thing, but on a larger scale. You have lots of electrons, all in a stable state. Instead of a few electrons orbiting a single nucleus, you have a lot of outer electrons spread out amongst a lot of nucleii. If you have a stable state, then the loop will enclose an integer number of magnetic flux quanta. The most likely state, and the lowest energy state if there is no applied is to have no persistent current, and zero flux quanta. However, at a finite temperature, it is likely that the system is not in its lowest energy state. Why doesn't the loop let the flux quanta out and drop to the lowest energy state? Well, the quantum maths is a bit tricky, but a rough explanation goes like this...To let the flux go, one part of the ring has to stop conducting at one point and put up a resistance. This will let out the flux quantum and absorb the energy as it goes. While this makes sense from energy terms, there is no reason why one bit of the loop should do it rather than another. The superconducting SQUID devices mentioned in the article are a superconducting loop with a weak point so you can have all sorts of elegant fun with the physics as flux quanta go in and out.
So, this is no use as an energy source, but it could be very useful as a form of memory. Suppose you have a loop of 18 carbon atoms with one hydrogen to each - a bit like benzene but bigger. Like benzine, it has a loop of pi electrons above and beneath, and these electrons can do the same thing. The first energy state (one flux quantum in the loop) is about 0.5 eV above the ground state, so it should be stable at room temperature. You can read the energy state non-destructively by approaching a similar loop with a weak point (a bit like a SQUID, again), or you can destructively blank the state by twisting the ring, destroying the pi delocalization. This is not a new idea - I know it was talked about in the eighties.
The original paper was posted in June http://lanl.arxiv.org/abs/0906.4780
In the quantum world the question is how long it takes to make a transition. Only with a transition do we have exchange of energy and therefore dissipation.
"persistent current" just means the authors of the paper did not observe a transition. For superconducting rings the theoretically estimated time to see a change is longer then the age of the universe, a good definition for "impossible".
I'm not an electronics expert so tell me if you've heard of this question before. Is "capacitance" the reason the screen image improved when I touched the "rabbit ear" antennas of my old analog TV? Now that Digital TV is here this question loses its relevance, but its old question I never had an answer for.