Yale Physicists Measure 'Persistent Current' 68
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."
Wait... (Score:4, Interesting)
“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?
Could this be used for memory? (Score:3, Interesting)
n/t
Re:I'm no EE (Score:1, Interesting)
we already do something similar [wikipedia.org] and the problem is that it is not sufficient for 3D. Now if we could stack individual components of motherboard on top of each other and use lateral cooling current ...
Re:I'm no EE (Score:5, Interesting)
Is the heat carrying capacity of aluminum insufficient?
Depends on how thick you make the layer. Look at the kind of heat sink high performance chips today, for chips with just one layer. Multilayer chips need comparable cooling performance per layer.
You can of course add a few low-power layers to a high-power chip, which may be worth it at some point just to shorten interconnect wires (or in order to use inductive coupling). It's a lot of complexity for what is so far a small gain though.
Re:Direction? (Score:2, Interesting)
my right or your right? better question -- clockwise or counter clockwise and with respect to
1. the cantilever?
2. gravity?
3. earth's magnetic field?
4. solar magnetic field?
Re:It's the little things that impress (Score:5, Interesting)
I had an EE teacher who owned his own little company. His company had done some research using GA [wikipedia.org] to evolve a minimal adder circuit on an FPGA [wikipedia.org]. This adder was simpler than the theoretically optimal adder circuit, using fewer gates than should be possible.
They really thought they had something (it worked every time with no apparent variation on real hardware) and started putting it on a few other FPGAs to test the solution. It didn't work on the other FPGAs.
They did a full analysis of the solution and found out that although some inputs and outputs were mapped to a closed loop not connected to VDD or GND (they had no power and no output), if they were removed from the program on the working FPGA, the adder stopped working. They finally had to chalk it up to relying on electron migration and/or induction currents in the closed loops for a correct answer. They'd accidentally made something like a quantum adder, but it was entirely specific to the silicon they'd evolved it on, making it useful, but not interesting.
Re:It's the little things that impress (Score:1, Interesting)
Of course, this is true for logical circuits, etc... power used for example for (back)lightning can be brought down only by some level (not even close to uA), where we get close to 100% power->light output.
Re:It's the little things that impress (Score:4, Interesting)
Re:Wait... (Score:2, Interesting)
Re:Direction? (Score:3, Interesting)
Re:It's the little things that impress (Score:3, Interesting)
Well, in theory they should have been able to reproduce the process on a different FPGA, resulting in a different "optimal" adder which may be more or less optimal. Since it seemed to rely on self-interference caused by imperfections in the chip, you'd just have to evolve on other chips until you found a similarly optimal solution. The reason it was only interesting but not useful is that an FPGA is a lot bigger than an actual adder circuit. It took the whole FPGA to evolve the minimal adder and trying to simplify something that specific (and probably relying on exact distances and input voltages to produce the desired output) would be essentially impossible. Thus trying to evolve individual circuits by that method which undercut theoretical optimum designs would require far more waste, far less space and cost efficiency and far more power.
A more appropriate use of GA would be to develop actual silicon in a full simulator much the same as that evolved antenna [nasa.gov] project NASA backed. If you could come up with a design that always worked as long as fabrication succeeded, that's much more productive and far more efficient.
That the story is true there's little reason to doubt. Ever since that guy in 1997 evolved a 64x64 speech recognition chip on an FPGA using GA, people have been going batshit trying to take advantage of the magic of GA. The odds are good that an optimal solution will arise on a chip which turns out to be specific to that chip. I imagine if you used a GA to evolve something specific to those faulty Pentium chips that it would fail to operate properly on a machine with a non-broken ALU.
Whether it had anything to do with my instructor's company, on the other hand, I don't know.
Re:Could this be used for memory? (Score:2, Interesting)
I looked into the effect of persistent current a bit and it turns out that someone has figured out how to use it as a photonic memory. Check out the Wikipedia article [wikipedia.org] on Ahranov-Bohm nano-rings.
The Harris Lab website [yale.edu] has a number of papers on the persistent current effect. The Ahranov-Bohm effect is one of the weirdest observed effects in physics so reading about the persistent current effect that arises from it is (arguably) a fun read.
Re:quantum power strip (Score:1, Interesting)
Funny you should say that. I first began considering the idea of "persisstent current" when I realized your setup could actually retain current if there was no resistance.
Re:Wait... (Score:3, Interesting)
It doesn't pop in and out as such - certainly you can't just pluck particle/antiparticle pairs out of empty space without supplying energy. For a quantized field, the vacuum expectation value (crudely, the average value in empty space) for certain quantities can be non-zero, just like atoms in a ground state have a definite non-zero energy.
Even if the energy of a ground state is non-zero, you can't take that energy out - energy must be conserved and there's no lower energy state for free space to fall into.
The energy density of the vacuum is in essence undefined (in quantum theory at least - in general relativity it's a different matter, which is where problems come in). Only energy differences matter.
Well, that's my understanding anyway, but then I was an experimentalist, not a theorist. Perhaps someone will come along and correct me.
Re:I'm no EE (Score:2, Interesting)
That is assuming the processor manages to react in time. I've seen videos of processors whose heatsinks have been removed, where the processors appear to vaporize. What they actually did was apparently heat so quickly they deformed in such a way as to launch themselves from the socket at great velocity. (Too fast for the cameras to catch with any real clarity.)
So basically, the processor took off like a rocket, (albeit technically it was a projectile upon leaving the motherboard, rather than having any period of powered flight).
Really gives one an appreciation of the heat being generated by a modern CPU.
Perpetual energy, but no power. Memory apps. (Score:5, Interesting)
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.