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Quantum Logic Gate Created Using Excitons
Roland Piquepaille writes "In this article, PhysicsWeb reports that researchers in the U.S. "have taken another important step towards making a quantum computer. [They] have created a logic gate using two electron-hole pairs -- also known as "excitons" -- in a quantum dot." According to Wikipedia, "an exciton is a combination of an electron and a hole in a semiconductor or insulator in an excited state These physicists from the University of Michigan and other labs made a quantum dot by using a thin gallium arsenide layer stuck between two aluminium gallium arsenide barriers. And electrons trapped in the middle layer were excited by light to create a quantum logical gate with four states. The group says this could be useful "in other approaches to quantum computing based on the optical control of electron-spin qubits in quantum dots.." This summary contains more details."
an exciton is a combination of an electron and a hole in a semiconductor or insulator in an excited state
I love it when physicists talk dirty to me.
Please be advised that by posting this with my quantum computer, I am able to make all possible lewd comments about the above sentence simultaneously.
In Soviet Rush, today's Tom Sawyer gets high on you.
Using Excitons? Wow, exciting! :-)
This joke goes out to Niels Bohr, my fellow countryman.
zWhat would an EWOULDBLOCK block, if an EWOULDBLOCK could block would? -- me
Physicists in the US have taken another important step towards making a quantum computer. Duncan Steel of the University of Michigan and co-workers have created a logic gate using two electron-hole pairs - also known as "excitons" - in a quantum dot (X Li et al. 2003 Science 301 809).
Classical computers deal with binary logic and the bits being processed must be either "0" or "1". Quantum computers, on the other hand, exploit the ability of quantum particles to be in two or more states at the same time. A quantum bit or "qubit" can therefore be "0" or "1" or any combination of the two. This means that a quantum computer could, in principle, outperform a classical computer for certain tasks. However, all the quantum computers demonstrated so far have only contained a handful of qubits.
Although qubits have been made with trapped photons, atoms and ions, it is generally thought that it should be easier to build working devices with solid-state systems. Several teams have made significant progress with the superconducting approach to solid-state quantum computing. Now Steel and co-workers at Michigan, Michigan State, the Naval Research Laboratory and the University of California at San Diego have demonstrated the first all-optical quantum gate in a semiconductor quantum dot.
Exciton transitions
Steel and co-workers grew a thin gallium arsenide layer 4.2 nm thick between two 25 nm aluminium gallium arsenide barriers to make a quantum dot. Electrons are trapped in the dot because the gallium arsenide layer has a smaller energy band-gap than the surrounding material. When excited by light, electrons from the valence band in the dot move to higher energy levels. The excited electron and the 'hole' it leaves behind combine to form an exciton. The system has four states: a ground state containing two unexcited electrons; two states containing one exciton; and a state containing two excitons (see figure). The two single-exciton states can be distinguished from each other because the excitons have different polarizations.
The researchers showed that they can drive Rabi oscillations between the ground state and the one-exciton states, and also between the one-exciton states and the biexciton state, with lasers. In particular they showed that the quantum-dot system behaves like a controlled-NOT gate in which the value of one qubit is reversed (the NOT operation) if - and only if - the value of the other qubit is 1.
Although it will not be possible to scale up the system, the group says that many of the ideas and techniques they have developed could be useful in other approaches to quantum computing based on the optical control of electron-spin qubits in quantum dots.
Many of todays (hoge comparetively) processes suffer from metal migration and huge static power dissapation. If the molecule sized transistors are going to take off they have to solve there problems first or these products will have a lifetime of a few hours.
Mouse powered Chips, Open source Processors and Lego
those guys who managed to factor "14" into 7 and 2 with Shors algorithm on an actual quantum computer implementation?
Heard anything more from them? I googled, but couldn't find anything.
How small a thought it takes to fill a whole life
I make quantum logic gates out of excitons all the time, in my backyard. Using common household items?
--Mods giveth, Mods taketh away--
So they have a quantum gate. But is it just a transistor replacement, which you still would use to build traditional computers, chomping through processor instructions, processing binary (or base 4 or whatever) numbers? Or is for quantum computers working on a completely different paradigm?
Damn, does this mean it's the physicists who will get jobs and the electrical engineers who will be unemployed?
Oh wait, we're both unemployed right now.
It's nicely done, but not the breakthrough that means quantum computers for all. It is, after all, only a NOT gate. I barely consider NOT as a logic function...more like half a function.
...
Was I the only person who read the line
The group says this could be useful "in other approaches to quantum computing based on the optical control of electron-spin qubits in quantum dots..
and thought "I'm sure I've seen that on a Powerpoint presentation somewhere". This is clearly uber-smart stuff by uber-smart people, but they are beginning to sound like clueless PHBs dressing things up in techno-babble.
Maybe this is the fundamental essence of quantum computers, something maybe smart or idiotic depending on the reader, the actual quality of work is only resolved when viewed by multiple individuals.
I hearby copyright the phrase Quantum-Powerpoint, and the resolution process of determining presentation value which I shall call "De-spinning Qubits"
An Eye for an Eye will make the whole world blind - Gandhi
Does it run Linux?
Is this excitement caused by flashing purple lights natural or induced by taking ecstasy.
Thank you for browsing at -1
I think half the fun scientists have these days must be getting to name new particles and "excited states" and all that...
/would/ be fun actually...
Lucky guys, I think it
I know nothing about quantum computing except that it looks really hard, and I'm betting a lot of other people are in a similar situation. When traditional silicon (or other semiconductor) components have gotten as small and fast as feasibly possible, will quantum computers be anywhere near as usable as the desktops of today are? Meaning, will I be able to use a fast computer without a PhD?
-phish
Quantum logical states and governators to rule them all.
Imagine a Beowulf cluster of these... :P
Excitons - the particle formed by the collision of Porntons and GNUtrons.
Quantum computer? Where is the sense in that? It would have been cool some 20 years ago. PC hardware is getting so fast that even Quantum computer is slow compared to it (in near future that is).
- Dick Briggs
Or tryptamines.. mmm..
How small a thought it takes to fill a whole life
Although it will not be possible to scale up the system, the group says that many of the ideas and techniques they have developed could be useful in other approaches to quantum computing based on the optical control of electron-spin qubits in quantum dots.
... maybe this is useful ... maybe not. Not even the researchers know. Don't read too much into this "discovery". :)
So
If they can harness the amazing power of the Gravitron, then I and Joe Sixpack will stand up and take notice.
This space for rent.
...were excited by light to create a quantum logical gate with four states.
Quantum computer? Great, it's in all four states at once. Gotta love a computer that gives you infinitely different results depending on what universe you're in.
(First application: generating airfares.)
And electrons trapped in the middle layer were excited by light to create a quantum logical gate with four states.
Sweet! Score one for the Star Trek universe. Suck it Star Wars.
There is no gain. This is not a transistor in a conventional understanding (nice inverter curve). When you need to make a memory chip out of this, you better hope it can drive more than just one more transistor. This is the problem with all QC proposed now.
Excitons to be Bohring.
ok, i'll kick my own ass for that one.
Call me when they make NAND gates with a way to couple them together, then I'll get excited.
Since a Quantum computer can process millions of operations *simultaneously*, how much do I need to pay a million-CPU licence from SCO if I want to use Linux ?
Ok, so if we pair electrons and holes, we get excitons. But what do we get when we pair protons and neutrons? Do we get hardons?
No, it's not. Err... it's not NOT... errr... The gate was a "controlled NOT gate", also known as XOR.
I hereby place the above post in the public domain.
"The researchers showed that they can drive Rabi oscillations
Sounds like a bad joke:
How do you drive a Rabbi into excited oscillations?
Oh, wait... that's 'Rabi' not 'Rabbi'.
There are a thousand forms of subversion, but few can equal the convenience and immediacy of a cream pie -Noel Godin
As a kid my goal was to grow up and be the DJ in the middle sitting in that cool space chair. Cranking up old AC/DC songs through ragged-out speakers. Back then that seemed so cool.
Man, I can't WAIT to put together a beowulf cluster of these!
please dont hurt me!
....move along....nothing to see here....
the joke in the parent post is funny.
I'm going to go sit in a corner and weep, now.
*honk*
This is my sig. It's prescription, I swear. I need it for reading things... on the other side of things
No thanks, this will last me a while.
sic transit gloria mundi
Same reason I hope the speed of light isn't broken. There should be room for cleverness in the universe. Being able to compute anything and be anywhere at once just makes things boring.
-Libertarian secular transhumanist
After all, they say they're using "two electron-hole pairs", so doesn't that translate into 2 two-bit "registers" instead of a single four-bit one? End result is the same, mind you, but the method is different.
Have EVDO, will travel.
Wow, I never knew quantum computers would help keep flooded networks afloat!
See, qubit~=cubit.
See, like Noah's ark.
Oh, never mind.
These physicists from the University of Michigan and other labs made a quantum dot by using a thin gallium arsenide layer stuck between two aluminium gallium arsenide barriers.
A major advance in quantum computing is nice and all. But, would it kill U of M to get another college football (real / american) national championship? I mean, Ohio State's got a shiney new one. Ours is from 1997.
Sigh. Such is the mentality. (thankfully it's not a prevalent at U of M as it is at other universities)
There are some people that if they don't know, you can't tell 'em.
If it can be done, you have to do it. Otherwise you'll get killed in war. I'm just sort of hoping that the universe won't allow it. Better computing is a good thing, but I hear the most ardent supporters and technophiles arguing that all encryption could be broken. Just hoping those types are wrong.
-Libertarian secular transhumanist
Rrom what I understand it, a qbit is in all states simultaniously, even if it is only a single bit (0 and 1 instead of 0 or 1). Tou can emulate it using normal bits, but the way I've understood it's still "opposite", and so it's a completely different paradigm:
... (about 2^43 lines skipped)
Classic:
Is 0 the answer? FALSE
Is 1 the answer? TRUE
Quantum:
Qbit x = TestFor(answer) (test all states)
Read x = 1
Classic:
Is 0000000000000000000000000000000000000000000 the answer? FALSE
Is 1111111111111111111111111111111111111111111 the answer? FALSE
Quantum:
Qbit xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx = TestFor(answer) (test all states)
Read xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx = 1010010100010101010010010101001001000101011
However, noone has been able to get a large number of quantum bits operating. And for few qbits, you'd do faster by simply doing a classic search. A computer using low-qbit "transistors" wouldn't be operating like a base 4 classic computer, but it wouldn't be this wonderful supercomputer either. A cluster of qbit transistors would as I understand simply scale linearly. Two 10qbit transistors would have twice the power of one 10qbit transistor. While on the other hand one 20 qbit transistor would have the power of 2^10 10qbit transistors.
Kjella
Live today, because you never know what tomorrow brings
I thought the benefit of Quantum computing was that you could utilize Quantum interactions to make calculations and deciphering instantaneous. if all they are doing is replacing silicone with particles, does this achieve the goal?
I am the Alpha and the Omega-3
Look, it's only one QBIT NOT gate. So I'm afraid I'm going to have to say potentially. Get it up to a few million QBIT gates of all sorts, and I'm sure we can arrange a port so that it will virtually run Linux. Much more interesting, however, will be if they can port Windows to it, and then write a program that will tell you "34% BSOD" so that you can tell just how potentially unstable your system is, just by thinking about running different programs. (Ummm... MSIE, with gator? 99% dead. Ooops. Better think about Mozilla Firebird... aaah. There we go.) Also interesting will be a port of ONEKO/SCHROEDINGER where you get to guess whether the cat is dead or alive (not too unlike a lot of cats I currently know.)
Correct Horse Battery Staple: 72 bits of entropy. Enter "Correct H" into google. When it generates the phrase, that's
Just a thought here... if you use Quantum Bits to make a standard NOT switch, then it seems to me that the NOT switch is going to behave as a NOT switch, and nothing is going to be any better than a CMOS NOT gate.
To me, the advantage of going quantum is when you multiplex zillions of gates together to set up (if you will) a programmable analog computer that can calculate potential possibilities based upon your model.
To do that, it seems to me that we shouldn't be thinking "...duh, how do I program a not gate with this?..." to which the obvious answer is any existing NOT Gate already makes use of all our Quantum physics (that is does not violate the laws of Quantum physics)".
We should instead be thinking "what totally new sorts of gates can I be making with quantum physics, in order to properly multiplex these things together?"
When someone does that, and gives me a programmable laser on-and-in-and-interfere-and-answer-out coprocessor, then I'm going to be impressed.
Correct Horse Battery Staple: 72 bits of entropy. Enter "Correct H" into google. When it generates the phrase, that's
...who realized that grandparent (ie, YOU, I'm assuming) is a fucking karmawhore. Post fulltexts as AC next time.
I'll have to let Megatron know that the decepticons plans have been thwarted again!
That's great. I suppose I'll hold off on getting that 3.0 GHz machine I was looking at, then. How big is the hard drive gonna be?
"We shall party like the Greeks of old! You know the ones I mean." - HedonismBot
i liked the dinobots the best
and the insecticons
maybe we should let the department of energy know about enerjon cubes they seem to be renewable and made out of everything easily much better than fuel cells...
Was I the only one annoyed by the use of "know" instead of "no"?
qbits, when finally able to be applied in a logical computing infrastructure (read: stable) will make desktop computers more powerful than we can imagine - up to 30 EC by one estimate (Hacking Matter: Levitating Chairs, Quantum Mirages, and the Infinite Weirdness of Programmable Atoms).
An EC is equal to the entire combined computing power on Earth on January 1, 2000 - a theoretical number that is still mind-boggling when thinking that a desktop could reach 30 EC. Read the book for more details.
Another interesting fact: breaking 128 bit encryption with quantom dots and qbits would take mere milliseconds during a SINGLE PASS across the proc. Beat that.
call me when they use something like that to make a memory card that can store about 100GB, be smaller than a stamp, fit on a keychain, and have timings like RAM for reads AND writes :)
;)
Seriously though, I'd love to have some non-volatile memory technology to take the place of flash memory (perhaps MRAM?), be super dense, as fast as RAM, and be able to take the place of CD-R's, DVD-R's, DVD+R's, etc. I'd rather carry all my personal photos of family and friends, my CD collection, my DVD collection, etc, etc. on my keychain than a CD holder. I guess that's provided that it's also really durable and comes with a locator feature in case you lose it
Know, you weren't. One of his other greatest hits was "mesured".
Remeber, friends don't let drunken five year-olds type...
> Was I the only one annoyed by the use of "know" instead of "no"?
No, you weren't; not by a long shot.
"And electrons trapped in the middle layer were excited by light to create a quantum logical gate with four states."
Yeah, and those four states are Mississippi, Utah, New Jersey and North Dakota. Which make this story weird, because I can't even see an electron getting excited about being in one of those four states.
(Yeah, I know, someone had to say it)
Someone you trust is one of us.
Does this mean that the spammers are going to be able to send out e'mail to every computer on the planet at the same time?? ....I'm gonna need more bandwith....
I'm observing my head off but it's not collapsing!!
Hi, my name is Sam Beckett. You guys should have been at this point years ago. I wonder if... oh boy!
"Derp de derp."
You realize they're still going to try to use the gigahertz rating right?
My Blog
We'll be getting subpoenaed for distributing MP3's into an infinite number of other universes.
"I assumed blithely that there were no elves out there in the darkness"
What you're describing is the complexity class NP (Nondeterministic Polynomial-time) which isn't what quantum computers are about.
The relevant complexity class is QP (Quantum Polynomial-time), which is unfortunately much more tricky to describe.