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Quantum Computing Using Quantum Dots
MikeM writes "Apparently a research group
has demonstrated extremely fine control of quantum dots (artificial atoms created by creating quantum wells in semiconductors and then inserting electrons one by one). Since they are at the quantum level, are controlled by optical lasers, and are built up from silicon using existing semiconductor fabrication techniques, they provide perfect quantum logic gates for optical computers. "
Well, you really can't have _Artificial_ atoms, but I suppose poetic license can be granted :-)
People have been working on this for about 10 years now. It's great stuff, really interesting physics. But please, don't confuse this with applications. Just ask the author what temperature his experiments run at. I'd be surprised if it's anything above 4.2 K (liquid Helium). Chances are, it's in the milli-Kelvin range, pretty damn close to absolute zero, and it sits down at the bottom of a dilution fridge.
If you are in academia and want to sell this to a sponsor, of course you mention quantum computers. But real life is FAR off (been there, done that).
Tesla may have been the greater physicist, but Einstein is recognizable, an icon. Like Mickey Mouse, if you will. Replace Einstein with Tesla and you'd get tons of mail asking: "Who?"
Sorry to be a pedant, but it's Einstein-Bose condensates.
Anyway, my main problem with quantum computing (other than the fact that actual applications won't be seen until the distant future) lies in external interference. Not only must thermal intererence be minimized by temperature control, but what about light? How can you "black-box" a quantum computer so effectively that a stray photon doesn't collapse the eigenstates of the whole damn system (sort of the "crystalizing" effect)?
I remember how shocked and disturbed I was to discover how far we are from the type of nanotechnology described in Drexler's book when I actually got my hands dirty in grad school. Since then, I've been somewhat cynical when I read about popularized accounts of new technology.
Brock Arnason
M.Eng. Physics
United Bank of Switzerland
The experiment was done in a He cryostat at 6-10 :-)
K. Certainly cold, but not in the milli-K range.
The samples used were GaAs/AlGaAs quantum wells
grown by molecular beam epitaxy - it's not silicon
based. Your point about applications is well
taken. This work is another piece in the puzzle
of understanding the physics of tightly confined
carriers. Don't forget that transistors couldn't
be developed until there was a good understanding
of the physics of semiconductors.
Any1 want to explain this in terms someone who is not a scientist will understand?
What a stupid arguement that is made. Popularity is never justification for anything. Let me put your arguement in context.
1.Go to the most congested part of downtown at 5:30PM and capture 200 people at random. They won't mind, anything is better than being stuck in a car moving slower than I can crawl.
2.Put them all in a room together.
3.Stand up on a box and yell, "All right! Everyone who has heard of Microsoft Windows, raise your hands! Then count.
4.Then yell, "OK you ninnies! Everyone who knows who has heard of Linux raise your hands. No you fools! Those who have heard of Microsoft put your hands down first... there we go. Gooood."
5.Compare counts.
What the hell is that suppose to prove? That Einstein was better than Tesla because more people know about him? That Windows is better than Linux because more 405Fwy commuters know about it? That Saddem is better than Blair because more people recognize the face of the terrorist in America vs. the British Prime Minister? Your arguements are dumb. Being named Albert myself, I naturally have a bias towards Einstein, but I'd sooner vote for Keely than Einstein. Tesla is the bomb in my book and your little example proved nothing.
Ah, Clear as a bell now!
Everybody knowns Richard Feynmann is the finest physicist ever. Should use a photo of him instead.
They said the quantum dots had a coherence time of 40 picoseconds, as opposed to bulk semiconductor which has a coherence time of 1 picosecond. This isn't even proof of concept, much less something useful for computation.
(coherence time is a figure of merit for a quantum computer. To oversimplify, you need to finish your quantum computation within the coherence time or your result will be lost in the noise)
The upshot is, you can't do much quantum computation in 40 ps. You can do much better today with nuclear-magnetic-resonance based quantum computating experiments.
In general, I doubt that there will ever be a quantum computer that has better than a constant-factor speedup for large problems. But I could easily be mistaken.
I have been reading a bit on some applications of quantum computing to math. Just like goedel and turing worked out many of the inherent limiations in a finite state machine before such machines were really capable of much more than basic arithmetic, it seems fruitful for mathematicians to work on the computability theory with regards to quantum computing, even if such computers won't be seen for half a century. I've read a few results, but I haven't been able to get any papers on the basic algebra of quantum computations. I'd like the equivalent of boolean algebra for quantum computers. If anyone could direct me to some introductory articles, I'd be very grateful. My math is grad level, physics is low undergraduate, computer science is mediocre undergraduate. Online resources are preferred.
(Voice of the masses)
Richard who?
OK. Let's think this one through. Does the Slashdot community consist of regular people or people with a *tad* more knowledge of science?
I say the latter, and then why not dare to steer away from mainstream? Why not have people send in their suggestions and/or icons?
Posted by HolyMackeralAndy:
Seems like not long ago these concepts as found in Tao of Physics and Dancing Wu Li Masters were borderline sci-fi. Reality is far out...
Posted by korto:
:|
i hope this means better hardware...
To be certain, quantum computing could Eventually get a big boost from this.
Perhaps long before that, this could become a super-dense dynamic ram. Imagine stuffing 12 or more bits into one logic unit.
BTW, don't look for this next year. Of course, semiconductors started out as impractical curiosities, and look where that went.
Make me Borg baby! Better yet, send 7 of 9 to do the job. Chya...
...I cleaned up the root partition and now there's LOTS of free space!
I think you missed the point mr. Fishing-For-A-Flame. Einstein revolutionized the way mundanes think about physics/science because he was a high profile scientist (and he had that hair!).
Here's a simply test you can perform at home:
I think you'll find every time that more people know who Einstein is. Forget about who your favorite is when dealing with the masses (Einstein ain't my fav either, he was damn cool, but there were other people on the verge of discovering what he discovered... must have been the hair.)
Einstein is a public figure even though he's been dead for some time. That's why his picture is used.
--Michael Esveldt
Well, Tesla was true genius: the kind of mind that perceives past the confines of possible and impossible. However, also like true genius, he was unable to codify or communicate his most interesting discoveries in any significant way. Thus, he is a footnote in history.
Tesla also had the problem in that he was going up against Edison, who was a much better self-promoter than a scientist. Self-promotion tends to win out over technical competance in the public eye.
Einstein articulated a theory that changed the way the world thinks about matter, about time, about space, about motion. It was a relatively simple shift that was due to happen, and Einstein was the first to rigorously "do the math." Nonetheless, this quite legitimately earned for him the status as celebrity scientist.
Well... not entirely. It's true that most of what Einstein wrote on was already moderately well known; some people, like Mach, had already come very close to the basic theory of Relativity. Einstine wasn't the first person to do the math, though, so much as he was the first person to not just throw out all the math the moment he realized that this all meant time wasn't constant. The few others before him that had worked on the concept had decided it was obviously wrong that time ran at different rates, and thus threw out the whole theory. Einstein's main contribution was to persevere beyond that point and see that everything made sense despite that...
-- Bryan Feir
Tesla was a tinkerer. Einstein made fundamental
contributions to science, arguably the greatest
in the 20th centuary.
-- Back to the shadows again...
This article seems to be the perfect counterpoint to those who say Moore's Law is up against the wall, particularly in the previous article on "Spiritual Machines".
Yes, I do think current chip fabrication techniques are reaching their limits, but this goes to show that new processes can be discovered and exploited.
OTOH, I don't think I want to discuss philosophy with my toaster anytime soon.
Or, to quote the toaster from *Red Dwarf*, "I toast, therefore I am."
A related paper, Localized Excitons: Probing One Quantum Dot at a Time - D. Gammon (Naval Research Laboratory), N.H. Bonadeo, J. Erland, et al, may be found at: http://www.electrochem.org/meetings/194/piab1.html . (It's available in ps/pdf.)
Computers based on chaos theory will become practical long before computers based on quantum theory.
Here at the Un-named East Coast School, a model of a chaotic computer has been shown to reproduce the effects of a NOR gate; we're working on showing that it can reproduce the effects of most two-bit sequential components.
Finding God in a Dog
You are a bit behind the times there at Un-named, huh ? We have already been developing chaotic computer for quite a few years now and they are already showing signs of evilness when we abuse them by installing certain un-named operating systems on them.
I am now pleased to announce that we at Un-Named University have gone one step beyond Chaotic Evil computing and have built computers dedicated solely to the purpose of bringing forth the rise of Our Master Who Sleeps Under The Sea, Cthulhu The Dreamer. You have only a few days left to live. Thank you.
Finding God in a Dog
Kinda like Einstein added in the cosmological constant to keep the universe from expanding ;-) Funny how preconceptions keep you from seeing the truth.
Something like that, yes... for that matter, Einstein's paper on the photoelectric effect (the one he won the Nobel prize for) was the first paper to ascribe a physical reality to the 'quanta' that Planck had assumed were just an artifact of the math. So in a very real sense, Einstein helped found Quantum Theory... a theory he spent much of his later life fighting tooth and nail against.
-- Bryan Feir
Quantum dots?
Hope one my friend is not reading this. He is finishing his Ph.D. on quantum dots. Doing, like, top of the line stuff.
I had to install Win 95 for him since he is too relaxed to be able to do it himself.
He use it, when not playing Duke Nukem, to count the number of quantum dots he managed to grow on some super-duper sample, by counting them by hand on a picture from super-duper microsoft loaded into Microsoft Paint.
You say hi-tech...
<^>_<(ô ô)>_<^>
This page is entitled Quantum Algebra, so you might find it interesting.
I have not spent any time there. I found it as a link from here.
SteveM
Why not Stephen Hawking?
--
The Internet is the Suppository of All Knowledge. You get it in the end.
Why do we have a picture of einstein for the science stories? Einstein was a moron. Someone should find and use a picture of Nikola Tesla--the One True Physicist.
:)
Well, Tesla was true genius: the kind of mind that perceives past the confines of possible and impossible. However, also like true genius, he was unable to codify or communicate his most interesting discoveries in any significant way. Thus, he is a footnote in history.
Einstein articulated a theory that changed the way the world thinks about matter, about time, about space, about motion. It was a relatively simple shift that was due to happen, and Einstein was the first to rigorously "do the math." Nonetheless, this quite legitimately earned for him the status as celebrity scientist.
In our pop-culture media-driven world, this celebrity status also made his image universally known, and a graphic representation of "Advanced Science."
So rave about Tesla all you want, pretty boy, but Tesla didn't change the world, and quantum logic will.
Um... calm down. Life is short enough as it is...
What particular discoveries are you talking about? Alternating Current? Transmission of information by radio waves? These are fundamental building blocks of modern technology, but they did not change the very ground rules of science itself. I did not mean to belittle your hero; I am a great fan of Tesla myself! Tesla had some astonishing discoveries, among them being the cordless transmission of electricity, that we have not successfully reinvented since he refused to use the US Patent office, and did not otherwise communicate his understanding.
But those discoveries that we have been able to use, while important, are just several among countless crucial steps on the road of technological advancement.
It's not Moore going down the drain, it's Turing.
Quantum computers are different, but that doesn't mean they can compute 1+1 faster (read the last paragraph of the article where they claimed to need _longer_ dephasing times?)
Chip manufacturers still have normal optical chips to go, which are significantly faster than conventional chips.
Why do you combine computational quantum power with intelligence? It's intriguing to take that into our own heads, where so many quantum states are available (exceeding the chemical states and processes by far).