Researchers Control the Flip of Electron Spin 157
karvind writes "According to PhysOrg, physicists in Europe, California and at Ohio University now have found a way to manipulate the spin of an electron with a jolt of voltage from a battery. In this experiment voltage was applied to Indium Arsenide based quantum dot which flipped the spin of electron inside it and emitted a photon. The scientists were able to manipulate how long it would take for the electron to flip its spin and emit a photon - from one to 20 nanoseconds. This may have possible applications in optoelectronics and quantum cryptography. Results were published in the latest issue of Physics Review Letters"
Election? (Score:4, Funny)
Re:Election? (Score:1, Offtopic)
Re:Election? (Score:2)
Re:Election? (Score:1)
Re:Election? (Score:2)
Re:Election? (Score:2)
Re:Election? (Score:1)
Re:Election? (Score:2)
As Usual (Score:5, Insightful)
1.) show the slashdot how electron flips
2.) slashdot crowd say cool
3.) show more engineers
4.) show sponsors, marketers, businessmen
5.) repeat step 4 for 29 years
6.) profit!
Re:As Usual (Score:2, Informative)
Re:As Usual (Score:2)
Re:As Usual (Score:2)
Giant magnetoresistance was first discovered in pure crystal layers in 1988 by Peter Grünberg of the Jülich Research Centre and Albert Fert of the University of Paris-Sud [...] IBM produced the first commercial device based on this effect in December 1997.
Oh, btw, it's used in every hard drive produced today and is one of the reasons HD prices have been falling even steeper than RAM and CPU.
Ooops, missing reference (Score:2)
20/20 Hindsight (Score:5, Funny)
When you put it that way, I don't know why it wasn't this simple the whole time!
Re:20/20 Hindsight (Score:1)
Update: researchers are now stunned to discover they can manipulate the spin with a jolt of voltage of electricity from any source.
Not just batteries.
Re:20/20 Hindsight (Score:2)
Ah, the old "spin-flip" ploy. I know it well. (Score:1)
Re:China & Cryptography (Score:2)
Sure, so do Tibetans, but information called dibs.
your sig (-1, Offtopic) (Score:2)
Somebody needs to be taken out back and shot! ;-)
Quantum computing? (Score:1)
Re:Quantum computing? (Score:1)
http://news.google.com/news?hl=en&ned=us&ie=UTF-8
Re:Quantum computing? (Score:2)
Re:Quantum computing? (Score:2)
Actually, the single-particle three-dimensional time-dependent Schrödinger equation does not account for spin or relativistic effects. If anything, you could use the configuration interaction method to analyze spin in a nonrelativistic Schrödinger equation.
Re:Quantum computing? (Score:5, Informative)
Not exactly I am afraid. There are still huge issues to quantum computing. Namely isolation and data retrieval.
A quantum computer (or at least it's processor) needs to be totally shielded to the outside world while it operates as any interraction or mesurement from the outside world will break the theory. Also, at this moment, you cannot retrieve the processed data without interfering, right? So as soon as you get the data from one of the virtual processors working in 'other worlds', the thing breaks and you can't get anything anymore from it. So it's in fact pretty useless I'm afraid.
I don't think we're going to see a quantum computer in the years to come, and much less under our desks. Even if they were invented I believe our governments will keep them away from us as they could be quite mean to encryption.
Re:Quantum computing? (Score:2, Interesting)
Re:Quantum computing? (Score:3, Interesting)
And don't think of that 'other world' explanation. It's not really what is happe
Re:Quantum computing? (Score:2)
Uh... sensing the charge on a capacitor doesn't destroy the charge on that capacitor. Yes, there will be some (increased) leakage by the sense amps but you're clearly stretching things here.
While my understanding of quantum theory is not as extensive as my electrical knowlege, I'm under the impression that making an observation of a quantum bit destroys its state. The two don't seem to be anything similar.
Re:Quantum computing? (Score:1)
Re:Quantum computing? (Score:2)
I realize what he's talking about, but he's not quite on the ball. Reading the charge doesn't obliterate the state, and the caps naturally decay which is what refresh is all about anyway. And as I stated, while not an expert at quantum physics, I don't believe you can refresh quantum bits the same way that you can refresh decaying charge in a cap.
Re:Quantum computing? (Score:2)
Re:Quantum computing? (Score:2)
Isn't that a rather religious statement? I mean, the many world interpretation fits the data just as does the Copenhagen interpretation (which I was taught). I personally see both interpretations as "useful" in that you can choose the most convenient one to think about the problem at hand.
As for the spookiness, I d
Re:Quantum computing? (Score:2, Informative)
Qualitatively (Score:1, Offtopic)
Seems like a step in the direction of understanding gravity.
Let's fund this kind of research, shall we?
Re:Qualitatively (Score:2)
Re:Qualitatively (Score:2)
In addition, gravity
Re:Qualitatively (Score:2)
At least not with static magnetic fields realizable on earth - you might be able to get some interesting stuff happening with magnetar level fields.
OTOH, there is some interesting stuff that happens with nuclear quadrupole moments and gamma ray emissions. The gamma ray emissions show some directionality when the thermal energy drops be
Not exactly ... (Score:5, Informative)
"Voltage Control of the Spin Dynamics of an Exciton in a Semiconductor Quantum Dot"
(Emphasis by be)
Now an exciton [wikipedia.org] is something quite different from an electron [wikipedia.org].
Re:Not exactly ... (Score:2, Informative)
Re:Not exactly ... (Score:2)
Mmmm... Dark exitons (Score:5, Funny)
Finally a practical application for decay dynamics following nongeminate excitation
Another application I can think of (Score:3, Interesting)
Pair off two electrons in a shell, flip the rotation of one and you change the rotation of another - instanteously. Even if they're no longer in the same atom and millions of miles apart.
Re:Another application I can think of (Score:2)
We now have a universe wide cell phone
I was trying to dig up the article on that particular experient and see if they had found further results.
Ah, the Orson Scott Card ansible ( Ender saga) founded on junk yard parts and we didn't even have to thieve the technology from an alien race.
Re:Another application I can think of (Score:2)
Entanglement doesn't work that way (Score:5, Informative)
In that case, your system won't work. Putting one of the electroncs in this spin-flipping device would destroy the fragile entanglement. In other words, flipping the spin of one would do nothing to the other.
This is how it always is with entanglement -- entangled particles only remain entangled as long as you leave their entangled properties alone. Once you measure or modify the properties of one, the entanglement is ruined.
Re:Entanglement doesn't work that way (Score:5, Informative)
Example: You start with the electrons having opposite (but indeterminate) spins, in the entangled state
|down, up> + |up, down>
(normalization constant ignored)
Now you flip the spin of the first electron. This puts you in the entangled state
|up, up> + |down, down>
Entanglement is preserved, however, you have not "flipped the spin" of the second electron. You have changed the sense of the correleation though. But you still haven't transmitted any information. The spin of each individual electron was indeterminate before you meddled, and was after you meddled.
When I said the measuring the relevant property of one of the pairs ruins the entanglement, well, that was still correct. And try as you might, there is no way to transmit classical information without performing a measurment.
Re:Entanglement doesn't work that way (Score:1)
Say that you create one million pairs of entangled particles with random spin. You set the spin of one hundred of the particles and then measure the other one hundred paired particle on the other end. You can then discard those one hundred pairs and repeat the process with another hundred. This would mean setting once (while in a indeterminate state) then observing once.
This seems to fit with your explaination, but I am probably
Re:Entanglement doesn't work that way (Score:2)
but what does "indeterminate" mean? (Score:2)
or does it mean the spin of the particle has not been (for lack of a better word) "set" yet?
The Wiki authors aren't clear about it: http://en.wikipedia.org/wiki/Quantum_entanglement [wikipedia.org]
Saying one thing: Although two entangled systems can interact across large spatial separations, ... ... no useful information can be transmitted in this way,
and then another:
If the particles are interacting then information is being transmi
Re:but what does "indeterminate" mean? (Score:4, Informative)
If those measured correlations mean interaction between those systems or not depends on which interpretation of quantum mechanics you prefer. Since there are interpretations where you don't need such an interaction, it's clear that you cannot use it to instantaneously transmit information with this effect (otherwise such interpretations couldn't possibly exist).
Re:but what does "indeterminate" mean? (Score:2)
These days scientists just all accept that it really well and truly is not set by the universe - it truly is in a quantum state, existing as a probability.
See:
http:/ [wikipedia.org]
Re:Entanglement doesn't work that way (Score:2)
You could argue that flipping the spin of one does "affect" the other. It changes the quantum state of the pair, and the "other" is a member of the pair. But it does NOT change the state in a way that:
a) Can be determined with measurments performed only on "the other". or
b) Can be used to transmit information.
US Government not interested or not invited? (Score:4, Interesting)
"The study was funded by EPSRC in the United Kingdom, Ohio University, Volkswagen, and the Alexander von Humboldt Foundations, with additional support by the Scottish Executive and the Royal Society of Edinburgh"
It seems to me that this is exactly one example of the type of technology the government should be promoting, for military benefit or not. What I am not sure of is wether the researches had the option to solicit US funding or if they chose rather to not bother?
I don't know, it struck me as a little odd considering that we're told repeatedly about how important it is to be a world leader in economy, technology, and security here is something that promotes all three and the pentagon's fat couffers are nowhere to be found. (well potentially compromises the third, but that's another story)
Re:US Government not interested or not invited? (Score:2, Interesting)
Just because you are part of America, it doesn't give you the right to discover everything in the Universe.
Perhaps I am reading into your post too much, but it implies that because of a lack of funding, it should have been an US group who headed this discovery?
Not any one group, organization or country can push forward the bounds of humanity on their own.
I for one relish any discovery that is made. I also realize that their is a political element to everything, especially scientific
Re:US Government not interested or not invited? (Score:2)
It was supposed to be a nose thumbing at the president's agenda and rhetoric.
I am well aware that the sun will one day set on the American empire, otherwise I don't think I would have left that comment at all.
Your points are all valid, and I agree with them.
Whether has always been a problem word for me.
Re:US Government not interested or not invited? (Score:1)
As I recall... (Score:2)
Re:As I recall... (Score:2)
Re:As I recall... (Score:1)
quantum crypto (Score:2, Informative)
Re:quantum crypto (Score:2)
I don't have examples handy and I'm too tired to find them, but they have probably even said that about things which we use directly or indirectly everyday in our lives nowadays.
Almost every non-ridiculous science is useful! And even some of the seemingly ridiculous science is useful too (and I'm not one to judge what's ridiculous or not...).
what happens when the elecron is "entangled" ... (Score:2)
An explanation for this interaction taking place has been to say that the two not connected objects are actually still connected... just not connected in space but some sort of "phase-space" ...
My question now is: are they still connected afterwards! They should be,
Re:what happens when the elecron is "entangled" .. (Score:4, Informative)
No. The measurement destroys the entanglement.
Re:what happens when the elecron is "entangled" .. (Score:2)
what about flipping the spin before measuring?
That may seem screwball, but doesn't simply flipping the spin effect the other entangled particle? Would it also flip? If so, would it give off any measurable signal (a photon)?
I don't care about determining the spins of the particles (and hope they stay undeterminable), I just care about making them repeatedly give of signals at selected time intervalls...
(I suppose that would mean that the spin shouldn't
Re:what happens when the elecron is "entangled" .. (Score:2)
Flipping the spin is measuring in the quantum mechanical sense. Perhaps you should think 'interaction' instead of 'measurement'.
Spin is angular momentum. Angular momentum is conserved. Thus, to change the angular momentum of something means interacting with it.
I don't care about determining the spins of the particles
It doesn't matter if you care or not. It doesn't matter if you look at the results or not. It doesn't matter if it's you even have a result.
Re:what happens when the elecron is "entangled" .. (Score:2)
If you start in the state (normalization constants ignored):
2 * |up, down> + |down, up>
where the first electron is more likely to be measured in the up state, and you apply a "coherent spin flip" (ie a flip performed WITHOUT measuring the spin) to the first electon, you end up in the state
Re:what happens when the elecron is "entangled" .. (Score:2)
Re:what happens when the elecron is "entangled" .. (Score:2)
Initially, I was in a superposition of |up, down> and |down, up>.
Then, I performed an operation that flips the spin of only the first electron, leaving me in state |down, down> + |up, up>
I have not flipped two spins. And what does angular momentum conservation have to do with it? In this case, the expectation value of total angular momentum is conserved, but there's no need for that to be true in general of a unitary operat
Re:what happens when the elecron is "entangled" .. (Score:2)
Ok. I don't understand this. I don't think that's not a eigenfunction of the spin-projection of a pure spin state.
Can you explain how this coherent spin-flip works in more detail?
Re:what happens when the elecron is "entangled" .. (Score:2)
However, that doesn't mean you can't apply the spin-flip operator to it. I don't know how to explain it in more detail, other than to try and give an experimental realization, which I don't think is what you're looking for.
Perhaps this will make more sense... let's work in "vector notation"...
define |up, up> = (1, 0, 0, 0)
|up, down> = (0, 1, 0, 0)
|down, up> = (0, 0, 1, 0)
|down, down> = (0, 0, 0, 1)
The spin
Re:what happens when the elecron is "entangled" .. (Score:2)
I made the mistake of assuming you were talking about stationary states.
Flipping a spin is not always a measurement (Score:2)
I suppose that would mean that the spin shouldn't be determinable from the emitted photon, otherwise that would equal a measurement...
I understand that the manipulation doesn't get to lead to a way of deducing the spin. Of course "cares" don't influence reality, it was a figure of speach. cool down.
I was assuming that the manipulation would not equal a meassurement, and it seems there are ways to do so as the my "neighbour-poster" expla
Re:Flipping a spin is not always a measurement (Score:2)
But flipping the spin of the first particle still does not flip the spin of the other particle.
Re:what happens when the elecron is "entangled" .. (Score:3)
Schrödinger showed one system could steer the (Score:2)
Re:what happens when the elecron is "entangled" .. (Score:1)
are they still connected afterwards! They should be, shouldn't they??
I think they are. I also think you make me think of Homeopathy [wikipedia.org] and stuff like that. Interesting!
Re:what happens when the elecron is "entangled" .. (Score:1)
Re:what happens when the elecron is "entangled" .. (Score:1)
An army physicist I worked with as an undergrad used entagled photon polarization as a method to make remote measurements. Because particular compounds can specifically polarize light, polarization of one photon will cause the immediate polarization of its entangled sister photon. (This means that you could, in theory, shine a laser beam at a chemical vapor a mile away,
"indeterminate" entangled photon polarization (Score:2)
I have always been boggled how "indeterminate state" was to be understood.
If it meant the particle has a state that simply has not been meassured yet?
Or if it meant the state of the particle has not been (for lack of a better word) "set" yet?
Re:"indeterminate" entangled photon polarization (Score:2)
We can take electrons and put them in a known "indeterminate" state, such as |up> + |down>. While you might say the spin is not "set", in fact the QUANTUM state of the spin is precisely set.
And if we know what the quantum state of the particle is, we can put it into a determinate state even without measuring it.
Thought experiment.
In principle, according to quantum mechanics, one can construct a device that will perform the following transformati
Re:what happens when the elecron is "entangled" .. (Score:2)
According to quantum mechanics, the interaction of the "remote photon" can not produce a measurable change on the "local photon" in the way you have described.
Re:what happens when the elecron is "entangled" .. (Score:1)
http://www.zamandayolculuk.com/cetinbal/teleport ation2.htm
Re:what happens when the elecron is "entangled" .. (Score:2)
"Also, quantum teleportation does not allow for faster-than-light communication. Although the teleported particle attains the polarization value instantly, the people at the sending station must convey the fact that teleportation was successful by making a phone call or using some other light speed or sub-light-speed means of communication."
This statement, from the link you quote, contradicts your implication that quantum entanglement ca
Re:what happens when the elecron is "entangled" .. (Score:2)
quantum telegraphy? (Score:1, Redundant)
(IANA quantum physicist, but...) What if the unsuspecting electron is one of a correlated pair? When the flip occurs, does the sibling electron (perhaps a galaxy away) simultaneously flip... and maybe squirt a photon to dazzle some Arcturians?
Re:quantum telegraphy? (Score:2)
No. Flipping the spin is performing a measurement.
flipping can be done without meassuring (Score:2)
http://slashdot.org/comments.pl?sid=151085&cid=12 6 72458 [slashdot.org]
As a simple analog it can be compared to multplying an unknown number with -1. It flips the sign but it doesn't set the sign or determine the value.
So the grandparents question remains open... what is "entanglement"? This isn't a new question/dilemma, Einstein didn't like it and called it "spooky action".
It boils down to the question what is an "indeterminate state"?
does it mean the particle has
Re:quantum telegraphy? (Score:2)
Curiously they formed a pattern:
ALL U BASES ARE BELONG TO US! W00T!
wow (Score:1)
Must be sth wrong with me... (Score:1, Redundant)
Researchers control the flip of the election spin
It took me a while to find out what is the idiom I don't know in this sentence, before I carefully read it again
Robert
(of course non-native English user)
Cities In Flight reference (Score:1)
Quantum Dots, Artificial Atoms (Score:1)
Artificial atoms, as I understand it anyway, are exhibited when these wells/quantum dots are crafted to store electrons in certain configurations (modeling "orbital shells"/energy levels?). The quantum dot has then been shown to exhibit some properties of an element corresponding to that electron configuration.
Is there a connection somewhere here with the electron spin "flip" (whatever that means)? If you take an ordinary a
Could this be used for... (Score:2)
If you can flip the spin of an electron, wouldn't that be a condensing of our current storage technology?
However, after doing a Google for the size of an electron as compared to an atom, this road bump chucked my question out the window.
http://www.newton.dep.anl.gov/askasci/phy00/phy00
Re:Could this be used for... (Score:2)
So, an atom may hold 1-100 electrons, but no more than 2 or 3 would have the "freedom of movement" to use for bits. In practice you'd do very good to have one bit pr. atom, and for redundancy at least ten atoms pr. bit sounds like a very
Re:Could this be used for... (Score:2)
Of course, retail will continue to suck the general public dry with SDRAM prices.
Even with new technology, we can expect prices to be inflated beyond reasonable.
i.e. 128Mb USB RAM should not cost $50
Can't wait till we get that storage to within humane levels.
Call me back (Score:1)
Re:year 2100 (Score:1)
Re:year 2100 (Score:1)
funny how the numbers game will go backwards by then.
Re:very interesting (Score:1)
Re:very interesting (Score:2, Informative)
Re:very interesting (Score:2)