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Researchers Control the Flip of Electron Spin

Zonk posted more than 9 years ago | from the wheeee dept.

Technology 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"

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157 comments

Election? (4, Funny)

Anonymous Coward | more than 9 years ago | (#12672042)

Was I the only one who thought this read "Researchers Control the Flip of Election Spin"?

Re:Election? (-1, Troll)

ZeroExistenZ (721849) | more than 9 years ago | (#12672057)

You're French?

Re:Election? (0)

Anonymous Coward | more than 9 years ago | (#12672112)

That'd be referendum [bbc.co.uk] spin (French voters rejected the new EU constitution). Not particularly nerdy but the same goes for most of what ends up in the politics section here.

Re:Election? (0)

Anonymous Coward | more than 9 years ago | (#12672155)

Nah (0)

Anonymous Coward | more than 9 years ago | (#12672174)

it was diebold who did that in the last election.

Re:Election? (0, Offtopic)

ScrewMaster (602015) | more than 9 years ago | (#12672316)

I'm like to know who moderated the first post as redundant.

Re:Election? (0)

Anonymous Coward | more than 9 years ago | (#12672429)

I'd like to know who moderated the first post as redundant.

How much would you pay to find out?

Re:Election? (0)

Anonymous Coward | more than 9 years ago | (#12672469)

why whats wrong with the mod ? I think when I meta-moderate it, I will consider it fair.

Re:Election? (0)

Anonymous Coward | more than 9 years ago | (#12673139)

I agree. +4 Funny is a fair rating.

Re:Election? (0)

Anonymous Coward | more than 9 years ago | (#12672589)

No, but I read it as: "Republicans Control the Flip of Election Spin"

Re:Election? (1)

spammacus (805242) | more than 9 years ago | (#12672988)

No. Nice to know I'm not the only tin hat man here.

Re:Election? (1)

-kertrats- (718219) | more than 9 years ago | (#12673077)

Wow, I read it that way and thought to myself, "Yes! A certain +5 post!", then I come on and find it in the first post :(

Flip? (-1, Offtopic)

Bananatree3 (872975) | more than 9 years ago | (#12672052)

I think I am going to flip if I don't get an extra JOLT of caffene!

year 2100 (0)

jlebrech (810586) | more than 9 years ago | (#12672054)

AMD release the 20 nanosecond electron flip chip.
Quickly followed by the 19 nanosecond electron flip chip (with less electrons)

Re:year 2100 (1)

1nt3lx (124618) | more than 9 years ago | (#12672071)

fewer electrons.

Re:year 2100 (1)

jlebrech (810586) | more than 9 years ago | (#12672074)

yeh from Intel.

funny how the numbers game will go backwards by then.

As Usual (5, Insightful)

superpulpsicle (533373) | more than 9 years ago | (#12672058)

All universities new findings take 30 years before they are applied to the corporate world.

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 (2, Informative)

whimsy (24742) | more than 9 years ago | (#12672270)

PCR [wikipedia.org] is 20 years old and ubiquitous in industry.

Re:As Usual (1)

cnettel (836611) | more than 9 years ago | (#12672277)

Yeah, just like the transistor and the IC took 30 years from invention to commercial impact. It's like being an inventor that's 6 years older than before and now waiting for his Nobel prize, it may arrive tomorrow, or next year, in thirty years, or never. For the Nobel prize case, though, you might expect the actual prize to be handed over in December, in Sweden. Not generally so with corporate success.

Re:As Usual (0)

Anonymous Coward | more than 9 years ago | (#12672540)

This charming but strange solution has me juming up and down from top to bottom in excitement.

Ehem...Can I mod myself -1 pathetic

Re:As Usual (0)

Anonymous Coward | more than 9 years ago | (#12672560)

I seem to recal the Underpants Gnomes having a similar strategy. Hell it worked for them!

20/20 Hindsight (4, Funny)

yotto (590067) | more than 9 years ago | (#12672061)

*...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.*

When you put it that way, I don't know why it wasn't this simple the whole time!

Re:20/20 Hindsight (0)

Anonymous Coward | more than 9 years ago | (#12672399)

I've been doing this for years. No wait, are my nipples made of Indium Arsenide?

Re:20/20 Hindsight (1)

sentientbeing (688713) | more than 9 years ago | (#12672706)

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

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 (1)

spagetti_code (773137) | more than 9 years ago | (#12673003)

And then again, lets remove the dumbing-down and try to figure out what they *really* did...
"...We report the observation of a spin-flip process in a quantum dot whereby a dark exciton with total angular momentum L=2 becomes a bright exciton with L=1. The spin-flip process is revealed in the decay dynamics following nongeminate excitation. We are able to control the spin-flip rate by more than an order of magnitude simply with a dc voltage. The spin-flip mechanism involves a spin exchange with the Fermi sea in the back contact of our device and corresponds to the high temperature Kondo regime. We use the Anderson Hamiltonian to calculate a spin-flip rate, and we find excellent agreement with the experimental results...

ummmm.....

Quantum computing? (1)

Fermatprime (883412) | more than 9 years ago | (#12672066)

Does this development get us any closer to the development of a quantum computer? I don't even remember the last I heard about that branch of science...

Re:Quantum computing? (1)

Cyclotron_Boy (708254) | more than 9 years ago | (#12672178)

It could definitely have implications in quantum computing. It is interesting that TFA didn't mention any application here, though. Also, I'll have to look back into the time-dependent Schrodinger equation to remind myself how this plays in quantum mechanics. Seems that the precise timing of the electron spin flip could have some interesting quantum effects... -F

Re:Quantum computing? (5, Informative)

heelios (887437) | more than 9 years ago | (#12672183)

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? (2, Interesting)

jfern (115937) | more than 9 years ago | (#12672218)

Quantum error correction can be used to fix quantum errors. If the errors are independent, local, then there is a fault tolerant threshold, below which you will be able to correct enough errors to do arbitrary quantum computation. Error correction will typically add polylog (polynomial in log n) overhead in the number of qubits and the running time. So Shor's factoring algorithm becomes O(n^3 log^a n) instead of O(n^3).

Re:Quantum computing? (2, Interesting)

kmac06 (608921) | more than 9 years ago | (#12672705)

No, it doesn't need to be completely sheilded. As far as 'reading' the information simultaneously detroying the quantum state, that is true...just like reading a memory cell that uses a capacitor destroys the information, yet we miraculously still build computers with them :P. Also, the application of quantum computers is quite limited (factoring numbers is one thing they can do well), don't expect to be playing Doom 6 on them.

And don't think of that 'other world' explanation. It's not really what is happening according to current theory, just a convenient/spooky way to explain it to some lay people. And yes, IAAP

Re:Quantum computing? (2, Informative)

jfern (115937) | more than 9 years ago | (#12672203)

This advance deals with manipulating the spin of a single electron (a single qubit) The hard part of quantum computing is reliably maniuplating two qubits. With single qubit operations and measurements, and a two qubit CNOT, one can perform arbitrary quantum computation.

Qualitatively (0, Offtopic)

smitty_one_each (243267) | more than 9 years ago | (#12672078)

It seems like this is just a small-scale example of effects like this [spacedaily.com] , where the whole planet does a whoopsie.
Seems like a step in the direction of understanding gravity.
Let's fund this kind of research, shall we?

Re:Qualitatively (1)

TheKidWho (705796) | more than 9 years ago | (#12672106)

No, I don't think the two effects are related at all...

Re:Qualitatively (0)

Anonymous Coward | more than 9 years ago | (#12672165)

Excuse me, and I don't mean to be rude or anything, but what the fuck are you talking about?

Re:Qualitatively (1)

cnettel (836611) | more than 9 years ago | (#12672304)

No, the Earth magnetic spin is a non-quantum effect, that is, the explanation is probably modelled by classical mechanics, just assuming that certain things are surrounded by magnetic fields. This is quite different, there's a single particle that you can get to enter different energy configurations by exposing it to energy. It's more related to nuclear-magnetic spin excitation, which is employed in magnetic radiology and also in "pure" NMR chemical applications, than the planet magnet.

In addition, gravity is not related to particle spin and magnetism. Oh, well, at least not any more than we already knew, that gravity is a bastard among forces that wrecks just about any perfectly good unifying theory in one way or another.

Now, let me walk out onto the "imagine things and make physicists laugh at you" plank (especially before I RTFA) -- I've wondered a little, in the NMR case, if it would be possible to induce nuclear fission or at least some kind of nuclear decay through heavy RF excitation of nuclei. It seems slightly reasonable that the added energy would make crossing the barrier between temporary stability and decay a little lower. Now, why you would prefer this over bombarding the stuff with neutrons, well, that's another matter...

'Spin' is something the Jews know very well indeed (-1, Troll)

Anonymous Coward | more than 9 years ago | (#12672086)

Any news item that can be spun to be positive to the Jews, or negative to their enemies, is so spun.

One day, I swear by Allah, they will pay for their transgressions.

Allahu Akbar!

muhammed jihad! (-1, Offtopic)

Anonymous Coward | more than 9 years ago | (#12672147)

muhammed jihad muhammed jihad

Re:muhammed jihad! (0)

Anonymous Coward | more than 9 years ago | (#12672503)

derka derka akalaka muhammad jihad!

Re:'Spin' is something the Jews know very well ind (-1, Offtopic)

Anonymous Coward | more than 9 years ago | (#12672152)

According to ancient Chinese folk lore you're very complimentary toward Jews. The reasoning is, hatred being self consuming, pays the compliment to the focus of your hatred as being worthy of consumming your life. I think in return they don't think you're worth the cost.

very interesting (0)

dkode (517172) | more than 9 years ago | (#12672087)

I have been reading alot on quantum mechanics (or at least trying to read it I should state).

This is interesting because it gives us a large leap in attaining more knowledge, and in turn will get us much further to unlocking the full potential of the universe as a whole.

is everyone ready? now the part comes where we attain the ultimate question, or destory ourselves in the process. hang onto your hats!

Re:very interesting (0)

Anonymous Coward | more than 9 years ago | (#12672104)

My 65 year old professor (David Mermin, Cornell University) said that he still doesn't understand quantum mechanics (or atleast why it works).

Re:very interesting (0)

Anonymous Coward | more than 9 years ago | (#12672175)

Quantum mechanics is well described as an algorithm. Like a recipe, if you follow the injunctions, it just works. Beyond that, as far as I've been able to ascertain, no one understands Quantum mechanics.

Re:very interesting (1)

cocoamix (560647) | more than 9 years ago | (#12672195)

Neither did Einstein. He didn't accept parts of it, anyway, which is why he pretty much wasted the last decades of his life searching for a GUT that would never work.

Re:very interesting (2, Informative)

Anonymous Coward | more than 9 years ago | (#12672226)

I don't think Einstein wasted his life on arguing against QM. If it was not him, the subtleness of QM wouldn't have been exposed. And the issue raised by him isn't resolved completely. You can refer to J Bell's paper to understand why it is not a trivial problem. Currently QM is accepted because it works and there had been various non-intutive way to explain them (hidden variables, parallel universe etc). And again if you think nothing useful came out of GUT, you are only reading popular science articles and not Phy Rev papers.

Re:very interesting (1)

Tri0de (182282) | more than 9 years ago | (#12673104)

The great Richard Fenyman said that "anyone who was NOT confused by and annoyed at quantum mechanics did not understand it"!

Re:very interesting (0)

Anonymous Coward | more than 9 years ago | (#12672189)

"...in turn will get us much further to unlocking the full potential of the universe as a whole."

I'm pretty sure the universe, by definition, is at it's full potential. ..."as a whole." is redundant.

Practical bifurcation transmitters? (0)

Anonymous Coward | more than 9 years ago | (#12672088)

My understanding of the problem with communication via bifurcation (seperate two particles, change the spin of one and the other will change!), is the problems of being able to manipulate and detect the spin of a single particle with convenient equipment. Could this solve that problem?

Oh great (0)

Anonymous Coward | more than 9 years ago | (#12672094)

You just know that this "electronics" is going to become the new buzzword and people will insist every single computer sold have it

Not exactly ... (5, Informative)

maxwell demon (590494) | more than 9 years ago | (#12672105)

The title of the linked-to article in Physical Review Letters is:
"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 ... (2, Informative)

Anonymous Coward | more than 9 years ago | (#12672144)

Technically yes. But in semiconductors you cannot get isolated electron. You excite an electron from the valence band to conduction band and leave behind a hole (sorry for the technical details). The work manipulates this excited electron and flips the spin. PhysOrg is not a site for hardcore physcists.

Re:Not exactly ... (1)

imsabbel (611519) | more than 9 years ago | (#12672415)

Well, but excitons arent "normal" electron/hole pairs, but bound systems, which behave quite differently than the "free" positive and negatic charge carriers.

Re:Not exactly ... (0)

Anonymous Coward | more than 9 years ago | (#12672279)

An exciton is a bound state of an electron and a hole in an insulator (or semiconductor), or in other words, a Coulomb correlated electron/hole pair. It is an elementary excitation of a solid.

Oh! Well, that just clears everything up then!

fp (-1, Offtopic)

Anonymous Coward | more than 9 years ago | (#12672109)

fp - ha

Mmmm... Dark exitons (5, Funny)

gerbalblaste (882682) | more than 9 years ago | (#12672111)

"A dark exciton with total angular momentum L=2 ecomes a bright exciton with L=1."
Finally a practical application for decay dynamics following nongeminate excitation

i agree (-1, Troll)

Anonymous Coward | more than 9 years ago | (#12672123)

why don't you palpate my testicles with your tongue while the head of my penis rests upon your tonsils

YAY CAPTCHA

Re:Mmmm... Dark exitons (0)

Anonymous Coward | more than 9 years ago | (#12672148)

I can't tell you how long I've been waiting for this. Now I can die happy.

Electron spin resonance (0)

Anonymous Coward | more than 9 years ago | (#12672118)

OK, not that I've RTFA, but as I understand it, we can flip electron spins rather easily. Look up 'electron spin resonance', or 'electron paramagnetic resonance'. It's a common experimental technique used to study electron energy levels in materials and therefore identify their composition.

Basically, a magnetic field is put across a sample containing unpaired electrons, which causes their spins to align either 'with' or 'against' the field.

Then the sample is illuminated with EM radiation, that is, a beam of photons is shone upon it. The energy of the beam --- the frequency of the photons --- is varied, until we see the electron spins flip from the 'with' state to the 'against' state or vice-versa. This energy is therefore absorbed by the electron.

The spectrum of EM frequency vs. absorbance can tell us what types of atoms are present in the sample.

NOW I'll go read the article...

Another application I can think of (2, Interesting)

proverbialcow (177020) | more than 9 years ago | (#12672120)

How about an ansible?

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 (0)

Anonymous Coward | more than 9 years ago | (#12672141)

You forgot the more important part of maintaining spin coherence over the distance. It's easier with photons.

Re:Another application I can think of (1)

Cylix (55374) | more than 9 years ago | (#12672160)

That is precisely what I was thinking of.

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 (1)

TexVex (669445) | more than 9 years ago | (#12672204)

Yes, and eventually we'll figure out subspace and warp fields, too.

Entanglement doesn't work that way (4, Informative)

Asparfame (96993) | more than 9 years ago | (#12672311)

By "Pair off two electrons", I presume you mean put them in an entangled state where the spins of the two electrons are correlated? (For example, in the state |up, down> + |down, up>).

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 (0)

Anonymous Coward | more than 9 years ago | (#12672362)

Once you measure or modify the properties of one, the entanglement is ruined.

But that's exactly what is desired. Your "entanglement is ruined" point actually corresponds to collapse of the entanglement wave function, and that occurs in a correlated manner until the end state is reached.

Therefore flipping one does very much affect the other!

Re:Entanglement doesn't work that way (1)

Asparfame (96993) | more than 9 years ago | (#12672401)

What do you mean by "occurs in a correlated manner until the end state is reached."?

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.

Re:Entanglement doesn't work that way (4, Informative)

Asparfame (96993) | more than 9 years ago | (#12672375)

Proviso: When I said that modifying the properties of one member of the pair ruins the entanglement, that was not completely correct. If you managed to come up with a scheme to flip the spin of one without measuring the spin, then entanglement would be maintained. However, this would still not flip the spin of the other electron -- the entanglement would not have a different character.

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 (1)

logicerror (228525) | more than 9 years ago | (#12672570)

Could you not then use statistics as a means of gathering some information?

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 missing something.

Re:Entanglement doesn't work that way (1)

Asparfame (96993) | more than 9 years ago | (#12672623)

To "set the spin" (ie put it in a known state) is equivalent to performing a measurment, and spoils the entanglement.

but what does "indeterminate" mean? (1)

xlurker (253257) | more than 9 years ago | (#12672772)

does it mean the particle has a spin that simply has not been meassured yet?
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, ...
and then another: ... no useful information can be transmitted in this way,

If the particles are interacting then information is being transmitted. To say that it's not usefull is more of a copout. It is just maybe not yet possible for us to meassure some kind information while keeping the particles in an indeterminate state (e.g. without meassuring the spin state).

(Of course what Wiki authors write has no bearing on reality, it could be that the spin states are set, which is also the simplest explanation.)

Re:but what does "indeterminate" mean? (3, Informative)

maxwell demon (590494) | more than 9 years ago | (#12672904)

It means the spin does not yet have a determined value. And this can indeed be checked. There are probability inequalities (the so-called Bell inequalities, named after Bell who found them) which must hold if the result of measurement should be pre-determined for each particle. The laws of quantum mechanics violate those inequalities, and experiments by Aspect have shown that nature obeys quantum mechanics also in this respect (the violation of the Bell inequalities has been measured).

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).

US Government not interested or not invited? (3, Interesting)

1nt3lx (124618) | more than 9 years ago | (#12672128)

I found myself reading this article quite mindful of the frequency of stories recently that suggest the US is headed down a dangerous path of neglect and ignorance. Not only in the arena of biological research (stem cell, et al) but in technological developments as well. This is not a matter of observation but rather official administrative policy http://science.slashdot.org/article.pl?sid=05/04/0 2/183230&tid=98&tid=103&tid=190&tid=215&tid=231&ti d=14 [slashdot.org] .

"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? (2, Interesting)

memoriesofgreen (784598) | more than 9 years ago | (#12672556)

A couple of points;

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 discoveries.

It is up to every civilization to grow, prosper and then fall. I, as one of Her Majesties Subjects (UK), understand that empires are fleeting.

PS

Their is an H in whether ("I am not sure of is wether the researches"), if you are going to proclaim yourself as a spelling Nazi (
http://slashdot.org/~1nt3lx/journal/7289 [slashdot.org] ) then at least don't be hypocritical. Also a few commas wouldn't go amiss.

Re:US Government not interested or not invited? (1)

Beetle B. (516615) | more than 9 years ago | (#12673126)

They are funding it. I know, because my graduate advisor is working on it (here in the US, supported by DARPA). In fact, a lot of money in the US is going into this...

As I recall... (1)

MagicDude (727944) | more than 9 years ago | (#12672134)

As I recall, there was an episode of Deep Space Nine that played with this idea about controlling an electron's spin. There was a device which would randomly make an unusual proportion of electrons spin in one direction, the the result was that a person's luck would be changed to either unusually good or unusually bad. I thought it was an intersting idea on what might happen if you change one of the fundamental aspects of matter in that spins are always balanced, some kind of quantum conservation of momentum.

Re:As I recall... (1)

maxwell demon (590494) | more than 9 years ago | (#12672153)

Ok, which way must I hold my ferromagnet to get good luck? Because a ferromagnet actually works through a strong bias of spins in one direction ...

Re:As I recall... (1)

simcop2387 (703011) | more than 9 years ago | (#12672542)

it wasn't with electrons it was with neutrinos. and it wasn't exactly to one person, just a field around that person, which is why when the stations computers/replicators were used to make a larger variation of the device the larger ones caused problems all over the station with their larger field.

Re:As I recall... (0)

Anonymous Coward | more than 9 years ago | (#12672657)

You've got it backwards. The manipulation of the spins was just a side effect of the luck-altering device whose magical mechanism was never explained.

They used the fact that the spin disparity increased with proximity to track down the device's location. Also, it was neutrino spins, not electron spins.

quantum crypto (2, Informative)

cryptoz (878581) | more than 9 years ago | (#12672151)

Cryptography is in a desperate state right now. Virtually every product that needs to include it has in implemented in such a way that it's basically useless. And so quantum crypto is rolling in more and more these days with newer and better discoveries (like the one here) coming out periodically. However, yeah, it's great, w00t, applications for quantum crypto, etc, but that doesn't really mean much. We already have messages that are unbreakable through brute-force. All that needs improvement through our crypto is more secure ways of entering information into computers and sending it without screwing up by keeping the message in RAM, storing it in a temp file, etc.

So sure, the ability to flip the electron spin is great for quantum cryptography itself, but...how does that help anyone, really?

slashdot is so damn slow (-1, Troll)

Anonymous Coward | more than 9 years ago | (#12672167)

i read about this well over a year ago, in a computing magazine at that, and slashdot is just now showing the story? must not be enough "omg water is wet" stories out there today

what happens when the elecron is "entangled" ... (1)

xlurker (253257) | more than 9 years ago | (#12672186)

as I understand it, the entanglement effect only concerns the yet undecided spin before/during the first measurement which leads to the spin of the *other* entangled electron being determined at the same time. ("same time" can be tricky...)

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, shouldn't they??

If the spin can be willyfully changed that could mean instantaneous transmission of data...

Since there is no free lunch this problably will not work... either because the entanglement is only valid for one measurement or it was never there. I wouldn't be surprised if the entanglment effect is just a theoretical construct to make modelling reality easier...

Re:what happens when the elecron is "entangled" .. (3, Informative)

maxwell demon (590494) | more than 9 years ago | (#12672225)

My question now is: are they still connected afterwards!

No. The measurement destroys the entanglement.

Re:what happens when the elecron is "entangled" .. (1)

xlurker (253257) | more than 9 years ago | (#12672280)

No. The measurement destroys the entanglement.

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 be determinable from the emitted photon, otherwise that would equal a measurement...)

Re:what happens when the elecron is "entangled" .. (1)

k98sven (324383) | more than 9 years ago | (#12672336)

what about flipping the spin before measuring?

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. What matters is that an interaction happened, where you could, in theory have received information about the spin state.

Re:what happens when the elecron is "entangled" .. (1)

Asparfame (96993) | more than 9 years ago | (#12672458)

What you said it mostly correct. However, it is theoretically possible (and has been done in practice as well, in fact) to flip a spin without performing a measurment. Flipping a spin is not always a measurment.

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

2 * |down, down> + |up, up>

This is still an entangled state, and the spin of each electron is still indeterminate. Contrary to the desires of the parent to your comment, however, you still have not managed to flip the spin of the second electron.

Flipping a spin is not always a measurement (1)

xlurker (253257) | more than 9 years ago | (#12672584)

in a way you're repeating the last sentence of my previous post:

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" explained.

Re:Flipping a spin is not always a measurement (1)

Asparfame (96993) | more than 9 years ago | (#12672637)

Yes.

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" .. (2)

TexVex (669445) | more than 9 years ago | (#12672264)

Entangled quantum things aren't connected in any way except mathematically. It's nothing more than saying that if you have two electrons entangled with opposite spin, then measuring one of them tells you the spin of the other, without you having to measure it. When you measure the spin of the first one, you've disturbed it as a result, and it no longer has any relationship to the other electron at all. However, the cool and useful thing is that you have gained information about another electron without measuring it.

Schrödinger showed one system could steer the (1)

xlurker (253257) | more than 9 years ago | (#12672448)

other. Google search "Quantum Entanglement" yielded this: (from http://plato.stanford.edu/entries/qt-entangle/ [stanford.edu] )
In the second part of the paper, Schrödinger showed that, in general, a sophisticated experimenter can, by a suitable choice of operations carried out on one system, steer the second system into any 'mixture' of quantum states he chooses, i.e., not steer the system into any one particular state, but constrain the state into which the system evolves to lie in a given set, and at the same time fix the probabilities with which the system evolves into the states from the given set. He found this conclusion sufficiently unsettling to suggest that the entanglement between two separating systems would persist only for distances small enough that the time taken by light to travel from one system to the other could be neglected, compared with the characteristic time periods associated with other changes in the composite system. He speculated that for longer distances each of the two systems might in fact be in a state associated with a certain mixture, determined by the precise form of the entangled state.

What you're saying is that the spin is already determined and *not* yet undetermined? I've never quite known what to think about that. I would, as you suggest, also prefer the theoretical construct notion. But it seems this is not yet clear...?

The author of the Wiki page actually begs to differ:http://en.wikipedia.org/wiki/Quantum_entang lement [wikipedia.org] and implies that the entangled particles do interact :

Although two entangled systems can interact across large spatial separations, ...
but goes on to say:
... no useful information can be transmitted in this way, ...

Re:what happens when the elecron is "entangled" .. (1)

whathappenedtomonday (581634) | more than 9 years ago | (#12672521)

instantaneous transmission of data...
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" .. (1)

teratogenicbenzene (887723) | more than 9 years ago | (#12672892)

While electron spin entaglement is quite difficult, entangled photon polarization (as an information "protocol") is quite straightforward.

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, and by reading the polarization states of trapped entagled photons, remotely measure the vapor's composition)

The facinating thing is that this "information" transferral happens instantly. A polarization change in one photon immediately results in the polarization of its sister, regardless of the distance between them.

"indeterminate" entangled photon polarization (1)

xlurker (253257) | more than 9 years ago | (#12672947)

so what you're saying is the "indeterminate state" in the case of the entangled photons means that their states had not been "set" yet?

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 (1)

Asparfame (96993) | more than 9 years ago | (#12673153)

Closer to "not yet set". But even that is misleading.

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 transformation on an electron spin:

|up> -> |up> + |down>

|down> -> |up> - |down>

This can be done WITHOUT measuring the electron's spin, because what I have described, in math jargon, is a "unitary transformation". This basically means "reversible" or "information preserving".

Now, imagine that I have a bunch of electrons in the state |up> + |down>, and I put them through my device. What state do they end up in? We use the superposition principle to find out...

|up> + |down> -> ( |up> + |down> ) + ( |up> - |down> ) = |up>

(as usual, I am ignoring all of the normilization constants)

Long story short, the indeterminate state of my input electroncs ends up in a determinite |up> state. But the device does not perform a measurment to do this.

The indeterminate state is transformed into a determinate state without measuring (ie "setting") the spin. Thus, it is a little problematic to think that indeterminate states are just states that haven't been "set" yet, because they can be transformed to determinate states without setting (measuring) them.

Further weirdness:

If I measure the spins of the particles only after they come out of my device, then I get all ups.

If I measure the spins before the device AND after the device, I get a mixture of ups and downs on both sides of the device. (why? because measuring before the device forces the electron into state |up> or state |down>, and both of these states are then transformed by my device back into indeterminate states).

Re:what happens when the elecron is "entangled" .. (1)

Asparfame (96993) | more than 9 years ago | (#12672994)

Perhaps you don't realize that you've made an extremely controversial statement. What you claim this army physicist did is contrary to accepted quantum mechanics since circa 1930. Do you have any evidence to back up this claim?

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.

quantum telegraphy? (0, Redundant)

moviepig.com (745183) | more than 9 years ago | (#12672196)

...flipped the spin of electron inside it and emitted a photon...

(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? (1)

k98sven (324383) | more than 9 years ago | (#12672292)

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

No. Flipping the spin is performing a measurement.

flipping can be done without meassuring (1)

xlurker (253257) | more than 9 years ago | (#12672899)

as one guy here has posted a few times:

http://slashdot.org/comments.pl?sid=151085&cid=126 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 a spin that simply has not been meassured yet?
or does it mean the spin of the particle has not been (for lack of a better word) "set" yet?

wow (1)

MaroonWarrior71 (886386) | more than 9 years ago | (#12672339)

absolutely riveting.

Misread (0, Redundant)

duffer_01 (184844) | more than 9 years ago | (#12672578)

Ha, I first read this as "Researchers Control the Flip of Election Spin". I thought back to John Kerry and thought, hmmm, not a bad idea.

Must be sth wrong with me... (0, Redundant)

Gadzinka (256729) | more than 9 years ago | (#12672857)

Must be something very wrong with my faith in politics and politicians, since I've misread the title of the article as:

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)
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