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Violation of Heisenberg's Uncertainty Principle

Soulskill posted about 2 years ago | from the kinda-sorta dept.

Encryption 155

mbone writes "A very interesting paper (PDF) has just hit the streets (or, at least, Physics Review Letters) about the Heisenberg uncertainty relationship as it was originally formulated about measurements. The researchers find that they can exceed the uncertainty limit in measurements (although the uncertainty limit in quantum states is still followed, so the foundations of quantum mechanics still appear to be sound.) This is really an attack on quantum entanglement (the correlations imposed between two related particles), and so may have immediate applications in cracking quantum cryptography systems. It may also be easier to read quantum communications without being detected than people originally thought."

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155 comments

Insert Breaking Bad Joke Here (5, Funny)

Anonymous Coward | about 2 years ago | (#41272881)

Let's just get all the Walter White jokes out of the way...

Re:Insert Breaking Bad Joke Here (2)

MrEdofCourse (2670081) | about 2 years ago | (#41275361)

I came here for this. Come on people, where are they?

Re:Insert Breaking Bad Joke Here (0)

Anonymous Coward | about 2 years ago | (#41275413)

Yeah Science! http://www.youtube.com/watch?v=2uMBbkSMppM

I have the fix (5, Funny)

Anonymous Coward | about 2 years ago | (#41272885)

I learned about it on the factual science TV show (currently honored on Google.com), Star Trek. They need a Heisenberg compensator.

Re:I have the fix (0)

Anonymous Coward | about 2 years ago | (#41272897)

I learned about it on the factual science TV show (currently honored on Google.com), Star Trek. They need a Heisenberg compensator.

Well, why not? Heisenberg did say it was incertain.

Re:I have the fix (3, Funny)

Bradmont (513167) | about 2 years ago | (#41273475)

No, they need to *uncouple* the heisenberg compensator. *Everybody* knows that.

Re:I have the fix (5, Informative)

feepness (543479) | about 2 years ago | (#41274047)

It's *decouple*. And now I'm disgusted by both of us.

Re:I have the fix (0)

Anonymous Coward | about 2 years ago | (#41274161)

I sentence you both to Bussard collector cleaning duty. Make those things shine.

Hogwash! Bring back the bible! (-1, Troll)

Anonymous Coward | about 2 years ago | (#41272907)

And simpler, wholesome times. You know what you really need to do, so do it!

Here we go again (4, Funny)

cvtan (752695) | about 2 years ago | (#41272927)

"Microsoft issues yet another patch to its quantum communications system to prevent hackers from eavesdropping on encrypted signals. The updates will be issued on Tuesday, but they might not be..."

Walter White (1, Funny)

XPeter (1429763) | about 2 years ago | (#41272929)

He's not only a fantastic meth cook, but a stellar physicist as well

Re:Walter White (1)

Anonymous Coward | about 2 years ago | (#41272971)

If you can find him.

Re:Walter White (2)

Razgorov Prikazka (1699498) | about 2 years ago | (#41273393)

Shouldn't be hard, just dont focus on his speed.
Besides, if guns kill people, then meth will ruin your teeth... no... ehhhh... never mind...
Just dont focus on his speed ok!?!

Magic (1, Insightful)

ilguido (1704434) | about 2 years ago | (#41272935)

Quantum entanglement is the equivalent of magic.

Re:Magic (0)

Anonymous Coward | about 2 years ago | (#41272959)

I don't even know what's going on anymore!

Re:Magic (5, Interesting)

Seumas (6865) | about 2 years ago | (#41272963)

This is exactly how I feel when it comes to quantum-anything. Especially quantum-computing, which leaves me looking at papers on it the way my cat looks at me when I ask him to do my taxes. It's one of the best examples I've encountered of anything sufficiently advanced enough being indistinguishable from magic.

Re:Magic (5, Funny)

rossdee (243626) | about 2 years ago | (#41273081)

Back in the day we didn't have Quantum Computers, but we did have Quantum hard drives. You were never certain when they were going to fail

Re:Magic (0)

Jorl17 (1716772) | about 2 years ago | (#41274499)

You made my day!

Re:Magic (3, Funny)

HungWeiLo (250320) | about 2 years ago | (#41275089)

I have a lemon 20MB Quantum hard drive in an ancient box. It's a lemon because it still reads and writes!

Not magic (3, Interesting)

aNonnyMouseCowered (2693969) | about 2 years ago | (#41273251)

Most people won't consider quantum physics magic simply because it involves things that aren't experienced in everyday life. If I see a chair float in the air, I'd say it's magic because a chair suddenly floating up is contrary to my everyday experience of chairs. Familiar things behaving in unfamiliar ways, that's magic. A person being cut up and put back together is a magic trick. A medieval person might consider the Amazon Kindle magic because it resembles a book or at least a biblical tablet and yet contains the contents of thousands of books.

I'd consider quantum states magical only in so far as they produce macroscopic effects, a real-life cat that's both alive and dead. Quantum entanglement would be magical if it would allow us to develop instantaneous communication devices or, even more magical, Star Trek-style teleportation.

Re:Not magic (3, Informative)

TapeCutter (624760) | about 2 years ago | (#41273477)

Some things in Physics are "magical", or "miraculous" if you prefer. The most obvious are the fundamental forces, space, and time. Currently Physics gives us a very useful description of how these things behave and interact, but it is more or less clueless as to why they exist in the first place [youtube.com] .

Re:Magic (0)

Anonymous Coward | about 2 years ago | (#41274089)

Okay, how about your flash memory drive? It uses quantum tunnelling to write data, so is it a magic stick?

Re:the way my cat looks at me (1)

TaoPhoenix (980487) | about 2 years ago | (#41276021)

Is your cat named Schrodinger? And are you quite certain of how he was looking at you? (Ba-dump-duush!)

Re:Magic (3, Informative)

History's Coming To (1059484) | about 2 years ago | (#41273015)

Actually, it's the equivalent of finding socks in the dark. If two photons are produced by an interaction of spin zero then the two photons will have spin up and spin down, although you can't know which is which without measuring one. What you DO know is that they have opposite spin, so by measuring one you instantly receive information about the other, however far away it is. There are several "pairs" of information which each particle/photon can have, such as momentum/location, the more accurately you measure one the less accurately you know the other, what these guys are proposing (as far as I can tell, it's at the limit of my understanding) is that they can use entanglement properties to discover information beyond Heisenberg's original limit.

Re:Magic (5, Informative)

N7DR (536428) | about 2 years ago | (#41273557)

Bearing in mind that it's generally an error to try to summarise anything about quantum mechanics in a paragraph or two:

Actually, it's the equivalent of finding socks in the dark. If two photons are produced by an interaction of spin zero then the two photons will have spin up and spin down, although you can't know which is which without measuring one. .

I'm sorry,. but the way you write that makes it seem that they have spin up and spin down, and then you measure them to find out which is which. If that's indeed what you meant, I'm afraid that's fundamentally incorrect.

The whole point about the weirdness of quantum entanglement is that the quanta are NOT in a state where one is up and one is down prior to the measurement. Only when you make the measurement does this happen. Prior to the measurement, quantum mechanics says that they are both in a state that is BOTH up and down at the same time.

In other words, quanta are not like socks. We can be reasonably sure that socks' measurable properties are fixed before we actually look at them. Not so with quanta.

You can think of this in this way: when you make a measurement on one of the quanta, it flips a coin that tells it whether to be up or down. Its twin quantum is then bound to give the opposite result. But prior to the coin toss, neither quantum knows how it will respond to a measurement. The most that can be said is that whatever the result of measuring one, the other will give the opposite result.

Re:Magic (1)

grumbel (592662) | about 2 years ago | (#41273665)

Only when you make the measurement does this happen.

How do we know that? Is there any way to figure out if a quanta has bean measured or not? Don't think so, as otherwise we could use it to transmit information via quantum teleportation, which we can't.

Re:Magic (5, Informative)

aBaldrich (1692238) | about 2 years ago | (#41273711)

This has been tested experimentally. http://en.wikipedia.org/wiki/Bell_test_experiments [wikipedia.org]

Re:Magic (1)

RightSaidFred99 (874576) | about 2 years ago | (#41276623)

By definition it can't be tested experimentally. You don't know until you measure, and the only way to know is therefore to measure. So it's not science as it can't be tested.

It's the old "if a tree falls in the forest and there's nobody around to hear it, does it make a sound" question in another form. I would assert they do have a spin, now disprove this assertion.

Re:Magic (1)

Old Wolf (56093) | about 2 years ago | (#41276845)

By definition it can't be tested experimentally. You don't know until you measure, and the only way to know is therefore to measure. So it's not science as it can't be tested.

You have it backwards. Science is about predicting the results of measurements. If a theory correctly predicts the results of experiments then we consider the theory to be correct. The meaning of words like "truth", "knowledge" and "reality" in this context is best left to the philosophers.

Re:Magic (1)

RightSaidFred99 (874576) | about 2 years ago | (#41276975)

That's my point. You can not test the theory that photons (or other particles) don't assume a given state until they are measured. Because this theory can't be tested by any kind of measurement, it is not science. It's philosophy. A wrong one at that.

Entanglement is just like having two billiard balls in the middle of the table next to each other. You hit the cue ball right in the middle - one spins left, one spins right. Ooooh, magic!!! The only difference is it's more then just simple spin and you can't predict which will spin one way and which the other.

Re:Magic (1)

Americium (1343605) | about 2 years ago | (#41274277)

Quantum cryptography does error checking to assure no one else is measuring said quanta. Other measurements would introduce error if they don't commute with your measurements.

Re:Magic (2)

History's Coming To (1059484) | about 2 years ago | (#41274021)

Yes, sorry, I over-simplified. What I should have said is that the two photons have a combined spin of zero, both have an indeterminate state so that indeterminate state A + indeterminate state B = spin zero. When one particle or the other is measured the two wavefunctions collapse (Copenhagen) or we find out which of the possible universes we are in (Everett).

Does this experiment have any bearing on Bell's Inequality? (And on that thread, would Bell's Theorem be satisfied by an infinite number of hidden variables?)

Re:Magic (2)

Americium (1343605) | about 2 years ago | (#41274249)

To prove Bell's Theorem you simply assume a single other hidden variable exists, perhaps signifying if the particle is actually spin up or spin down before you measure it. This assumption contradicts quantum mechanics and therefore cannot be true, so there is nothing else you can know about the system if quantum mechanics is the correct description.

If simply one more variable produced this result, I do not see how adding infinitely many more variables would help, or be of any practical use as a theory of nature.

Re:Magic (1)

History's Coming To (1059484) | about 2 years ago | (#41275045)

Just wondering about the Feynman's path integrals, and whether a very high number of hidden variables would still produce Bell's results.

Re:Magic (3, Interesting)

Americium (1343605) | about 2 years ago | (#41275105)

Feynman's path integrals are over all space, or all paths, but are of the wave function. Bell's proof showed that any hidden variables would produce different results when measurements are taken, or Feynman's path integrals calculated. So no, hidden variables do not exist. Thinking about whether the particle is actually spin up or spin down before measurements are taken is meaningless, as quantum mechanics only give probabilities of the outcome of a measurement using the wave function to calculate these probabilities. It actually says nothing at all about the particle before measurements are taken.

Re:Magic (1)

Anonymous Coward | about 2 years ago | (#41274121)

"Prior to the measurement, quantum mechanics says that they are both in a state that is BOTH up and down at the same time"

Prior to measurement by whom or what? - You, me, some physical process somewhere that no-one is aware of? Surely it's just a status of lack of knowledge - not an actual physical status.

Say someone elsewhere in the universe does the measurement - what state are they in for you? Can they have both a defined state and an undefined state simultaneously?

Clearly they are always in a definite state - but either a state you do know or a state you don't know.

Re:Magic (2)

Old Wolf (56093) | about 2 years ago | (#41276875)

Prior to measurement by whom or what? - You, me, some physical process somewhere that no-one is aware of? Surely it's just a status of lack of knowledge - not an actual physical status.

This has been troubling philosophers for the last 100 years or so, but the majority viewpoint now is that when something "measures" a system, what's happening is that the measurer interacts with the system, and they become entangled together. The result of this entanglement turns out to be that "me-seeing-down + it-being-down" and "me-seeing-up + it-being-up" dominate the possible outcomes.

Look up 'interpretation of quantum mechanics' on wikipedia for much more detailed info

The 'lack of knowledge' theory is fairly easily debunked (see Bell inequailities). There's no way you can explain the results of the experiment in terms of there being a concrete physical status that we just don't know about yet.

Re:Magic (0)

Anonymous Coward | about 2 years ago | (#41274571)

You can't prove it works that way because it cannot be measured before it's measured. You're talking about philosophy and pretending like it's science. But wise and intelligent people know better.

Re:Magic (0)

Anonymous Coward | about 2 years ago | (#41275861)

But I said measured by whom. If one measurement is enough to determine it's state, then it's interaction with the universe from the moment of it's creation should be enough.

Everything else is simply down to "your" state of knowledge about it - not it's intrinsic state.

Re:Magic (0)

Anonymous Coward | about 2 years ago | (#41275143)

seems to me that nature is calculated backwords in time. Both particles have exact state and then , going back in time, measuring disturbs it and puts both particles to undefined state.

Re:Magic (0)

Anonymous Coward | about 2 years ago | (#41275833)

"You can think of this in this way: when you make a measurement on one of the quanta, it flips a coin that tells it whether to be up or down. Its twin quantum is then bound to give the opposite result. But prior to the coin toss, neither quantum knows how it will respond to a measurement. The most that can be said is that whatever the result of measuring one, the other will give the opposite result."

What you say is totally illogical, so you cannot be understanding the situation correctly.

" it flips a coin that tells it whether to be up or down" - No - it is either up or down - your measurement simply finds out which.

" The most that can be said is that whatever the result of measuring one, the other will give the opposite result." - Yes that is absolutely the most that can be said.

Re:Magic (1)

Old Wolf (56093) | about 2 years ago | (#41276819)

The whole point about the weirdness of quantum entanglement is that the quanta are NOT in a state where one is up and one is down prior to the measurement. Only when you make the measurement does this happen. Prior to the measurement, quantum mechanics says that they are both in a state that is BOTH up and down at the same time

It's even cooler than that. If you measure the spin of one of the particles in *any direction* -- say, northwest, then the other one will be found to be spinning the opposite way , southeast in this example.

(In the language of linear algebra, the space of possible spin states is a two-dimensional complex vector space. Opposite directions are considered orthogonal, and since any pair of two orthogonal unit vectors forms a basis that spans a two-dimensional space; the state can be represented in any of these bases).

Re:Magic (1)

Hatta (162192) | about 2 years ago | (#41273733)

Actually, it's the equivalent of finding socks in the dark.

Actually, it's not at all like finding socks in the dark. What you are suggesting here is hidden variable theory. The state of the sock(or quantum particle) is determined at the beginning of the experiment and hidden until the observation is made.

This is a convenient way to think about it, but inaccurate. It's a bit much to go into here, but Bell's theorem [wikipedia.org] prohibits this possibility. Basically, if you angle the detectors you get an observed correlation between spins that differs from what is expected if the spins are predetermined.

Re:Magic (1)

bjs555 (889176) | about 2 years ago | (#41273927)

Help me to understand what entanglement really means. As it's explained above, I don't see how it's different than this scenario:

Take two playing cards, the king of hearts and the king of spades, and place them face down on a table. Mix them up until you don't know which is which. Have a friend pick one card without looking at it and drive away with it in his car. When he's gone 100 miles have him call you up. Tell him you will now perform magic and tell him what card he has. Look at the card that's remained with you. If it's the king of hearts, tell him he has the king of spades. If it's the king of spades, tell him he has the king of hearts.

I'm sure I'm missing something about what entanglement actually is but I don't know where I've gone wrong.

Re:Magic (1)

History's Coming To (1059484) | about 2 years ago | (#41274045)

That's pretty much it, with the caveat that while you're not looking at the cards they are both still in a state of flux. In the real world each card is most definitely either/or, but if you did the QM equivalent of the experiment the cards would both be in a state of "both" until measured. My original post was over-simplified, see corrective posts above.

Re:Magic (1)

Americium (1343605) | about 2 years ago | (#41274315)

Your idea supposes the card is actually a heart before you look at it and it couldn't be something else when you look at it. This supposes the particle is actually spin up or spin down before you make a measurement and that quantum mechanics must be missing this "hidden variable", i.e. it's not a complete theoretical description of reality. See Bell's Theorem for details as to why this is incorrect. There is no way to tell if it's spin up or spin down before you make the measurement and if there was a "hidden variable", quantum mechanics wouldn't work the way it does. You can also spin flip the particles several times before taking measurement without affecting the entanglement.

Re:Magic (1)

colinrichardday (768814) | about 2 years ago | (#41275049)

Isn't having his friend state that the card is the king of spades a measurement?

Re:Magic (2)

Americium (1343605) | about 2 years ago | (#41275139)

But could it have been hearts? No, it was actually a spades card the whole time, you just didn't know. It had the property of being a spades the entire time (a hidden variable). Could you spin flip his card to a hearts and have yours change to a spade faster than light? No. Quantum mechanics however works this way, although you still cannot transfer information faster than light, and there is no property (hidden variable) that tells you what it was before the measurement was made. Measuring the spin on a different axis will also give you non classical results in these entangled states.

Re:Magic (4, Insightful)

mbone (558574) | about 2 years ago | (#41274421)

That is a good description of classical entanglement - what, in this context, would be called a hidden variable theory (the cards have a certain face value, even if you can't see them).

Let's see if I can expand this analogy. Suppose you had two decks of cards, each with only two cards - say the king of hearts and the king of spades. Off-stage, I shuffle them, so that there is either one deck of 2 hearts, and one of two spades, or one deck of both, and another of both. Say that the chances of either shuffle are the same.

Now, repeat your experiment, except you and your friend only get to pull 1 card each, each from your own deck. Classically, the chances are

- 50%, you pull from 1 spade and 1 heart
- 25%, you pull from 2 spades
- 25%, you pull from 2 hearts.

And, of course, ditto for your friend.

Now, if you pull a spade, then the classical chances are

2/3 the other card is a heart
1/3 the other card is a spade

and the classical chances for your friend are thus

2/3 he has a spade and a heart
1/3 he has 2 hearts

so his (classical) chances on his card are

2/3 he pulls a heart
1/3 he pulls a spade.

(If you pull a spade, you CANNOT have two hearts, while he can.)

So, if you pull a Spade, you can tell your friend he is likely to have a heart. Do this a lot of times, and you should be correct 2/3 of the time. The cards are indeed entangled, but classically. Experimental error (maybe you can't always see your cards well) will lower this, but (for a long enough term average) cannot raise this.

In Quantum Mechanics, however, you can get correlations that you cannot get in classical physics, i.e., greater than 2/3 in this case. That is the essence of Bell's Theorem - you have correlations that you just can't "get there from here," classically. This is a consequence of having a complex amplitude. Again, it's not just having a correlation, it's that you can get correlations you just can't classically.

I saw a lecture from Dick Feynman once where he showed that you could explain all of this by allowing for negative probabilities for intermediate results, and that this was mathematically the same as the normal (i.e., complex) formulation of QM. (Since you cannot actually measure the intermediate results, you never actually measure a negative probability.) In some ways, I find that helps to grasp the weirdness. YMMV.

Re:Magic (1)

Old Wolf (56093) | about 2 years ago | (#41276895)

Help me to understand what entanglement really means. As it's explained above, I don't see how it's different than this scenario:

Take two playing cards, the king of hearts and the king of spades, and place them face down on a table. Mix them up until you don't know which is which. Have a friend pick one card without looking at it and drive away with it in his car. When he's gone 100 miles have him call you up. Tell him you will now perform magic and tell him what card he has. Look at the card that's remained with you. If it's the king of hearts, tell him he has the king of spades. If it's the king of spades, tell him he has the king of hearts.

OK, but imagine that you can also rotate your card by 90 degrees, and when you turn it over you get the jack of diamonds. If you tell your friend to rotate his card by 90 degrees before turning it over, then he must always find the jack of clubs.

Further, if you don't rotate your card (and you see the king of spades), but your friend does rotate his card by 90 degrees. What happens then? The theory predicts that there's a 50% chance he sees the king of spades, and 50% he sees the king of hearts.

Now, try to make cards that works that way. Once you're done, mail it to the Nobel Prize committee :)

Re:Magic (1)

Old Wolf (56093) | about 2 years ago | (#41276905)

Heh, I munged up my own example. He has 50% chance of seeing jack of clubs and 50% of seeing jack of diamonds.

Has no one pointed out... (0)

Anonymous Coward | about 2 years ago | (#41275851)

...that socks aren't different for left and right feet?

Re:Magic (0)

Anonymous Coward | about 2 years ago | (#41273047)

Note the main difference: quantum entanglement works

Clarke (0)

Anonymous Coward | about 2 years ago | (#41273075)

"Any sufficiently advanced technology is indistinguishable from magic." -- Arthur C. Clarke

Re:Magic (0)

Anonymous Coward | about 2 years ago | (#41273201)

Well I don't know about the presence of magic, but I for one would definitely like to see some Equivalent Exchange

Nig6a (-1)

Anonymous Coward | about 2 years ago | (#41272937)

Like I even tried to resist... (2, Funny)

hyades1 (1149581) | about 2 years ago | (#41272939)

"...so the foundations of quantum mechanics still appear to be sound..."

Are they sure about that? I think they fe-line to us.

So this means (2, Funny)

microcars (708223) | about 2 years ago | (#41272977)

that Walt Jr. can have BOTH pancakes AND cereal for breakfast?

Uncertain uncertainty limit (1)

ultrasawblade (2105922) | about 2 years ago | (#41273005)

So basically this "uncertainty limit" is itself uncertain.

I don't know much about quantum physics but isn't that how it's supposed to work?

Is there more truth to recursive opensource software algorithims than we previously thought?

(-1 Completely Ignorant)

Re:Uncertain uncertainty limit (0)

Anonymous Coward | about 2 years ago | (#41273043)

(-1 Completely Ignorant)

Ignorance is not a sin, denying it is.
Admitting to one's ignorance is a virtue.

Re:Uncertain uncertainty limit (0)

Anonymous Coward | about 2 years ago | (#41273103)

So basically this "uncertainty limit" is itself uncertain.

I don't know much about quantum physics but isn't that how it's supposed to work?

Is there more truth to recursive opensource software algorithims than we previously thought?

(-1 Completely Ignorant)

no, uncertainty limit is certain :P

Re:Uncertain uncertainty limit (1)

bmo (77928) | about 2 years ago | (#41273229)

>(-1 Completely Ignorant)

"The trouble with the world is that the stupid are cocksure and the intelligent are full of doubt." --Bertrand Russell

--
BMO

Re:Uncertain uncertainty limit (1)

M0j0_j0j0 (1250800) | about 2 years ago | (#41273337)

"Quoting dead people all the time is the trouble of the world" - Abraham Lincoln (The Vampire Slayer )

Re:Uncertain uncertainty limit (1)

bmo (77928) | about 2 years ago | (#41273355)

"All quotes on the internet are true" -- Andrew Jackson

--
BMO

Re:Uncertain uncertainty limit (1)

sgt_doom (655561) | about 2 years ago | (#41274833)

Are you sure about that?

Re:Uncertain uncertainty limit (1)

funwithBSD (245349) | about 2 years ago | (#41276693)

I know, the results could just be dead cat bounce.

Old news (-1)

Anonymous Coward | about 2 years ago | (#41273011)

http://arstechnica.com/science/2010/08/quantum-memory-may-topple-heisenbergs-uncertainty-principle/
as much as I understand it (which is not much) !

Nobody with a clue is surprised (4, Informative)

gweihir (88907) | about 2 years ago | (#41273013)

Quantum "encryption" was never that. It is only quantum "modulation" and its "security" is pure conjecture, not anything actually provable in the mathematical sense as you get with real encryption. That does not hinder a log of gullible fools to hail it as the new thing. (It does have a lot of other fundamental and unsolved problems, even if it should be secure.)

Re:Nobody with a clue is surprised (1)

Hentes (2461350) | about 2 years ago | (#41273097)

The security of "real" encryption hasn't been proved mathematically.

Re:Nobody with a clue is surprised (3, Informative)

doshell (757915) | about 2 years ago | (#41273195)

Except for the one-time pad [wikipedia.org] .

Re:Nobody with a clue is surprised (1)

Americium (1343605) | about 2 years ago | (#41274365)

That's what quantum encryption is used to exchange.

Re:Nobody with a clue is surprised (1)

TexVex (669445) | about 2 years ago | (#41274703)

More like the quantum encryption is.

Re:Nobody with a clue is surprised (1)

gweihir (88907) | about 2 years ago | (#41273375)

There is quite a bit more. Some proofs need assumptions and an attacker model is always required. But your knowledge is outdated.

Re:Nobody with a clue is surprised (1)

Americium (1343605) | about 2 years ago | (#41274329)

The whole basis of quantum encryption was mathematical and the error checking routines have been prove mathematically. It's only used to exchange keys.

Re:Nobody with a clue is surprised (1)

osu-neko (2604) | about 2 years ago | (#41274533)

...not anything actually provable in the mathematical sense as you get with real encryption. That does not hinder a log of gullible fools to hail it as the new thing.

Almost every technological breakthrough that has made life better and some people quite rich was based on things not actually "provable in the mathematical sense" (which is nearly everything we think we know, including the whole of empirical science).

Re:Nobody with a clue is surprised (1)

sgt_doom (655561) | about 2 years ago | (#41274789)

Well said...

conformational Bias (0)

Anonymous Coward | about 2 years ago | (#41273017)

the arguements are, if i measure something, it changes that something, somehow. So i measure that something weakly, which changes that something weakly, and note the changes, that i didn't?
Seems to me he confirmed that if i measure something, that i changed it. Re-enforcing the principle, and Quantifying that it occured. Wrong premmis to start with, just a reconfirmation of the principal and the affect/effect at weak levels.

Maybe yes, maybe no (1)

PopeRatzo (965947) | about 2 years ago | (#41273107)

They thought they found a violation of Heisenberg's Uncertainty Principle but they weren't sure.

Re:Maybe yes, maybe no (3, Funny)

Shark (78448) | about 2 years ago | (#41273835)

I'm waiting for the undead cat.

Interesting but... (0)

thesandtiger (819476) | about 2 years ago | (#41273133)

I'm not really sure how to feel about this.

Uncertainty (2)

puddingebola (2036796) | about 2 years ago | (#41273139)

The uncertainty on my understanding of this article is very large, that mean the uncertainty on someone else's understanding is very small. That person needs to explain it.

Obligatory (2)

K. S. Kyosuke (729550) | about 2 years ago | (#41273141)

Q: "So, how do your Heisenberg compensators work?"

The researchers: "They work just fine, thank you."

I can only hope (2)

Hentes (2461350) | about 2 years ago | (#41273179)

that they checked heir cables before publishing this.

Argh science journalism. (5, Insightful)

Phanatic1a (413374) | about 2 years ago | (#41273423)

This article is horrible.

"The Heisenberg uncertainty principle is in part an embodiment of the idea that in the quantum world, the mere act of observing an event changes it."

That's not the Heisenberg uncertainty principle. That's just the observer effect, and it's not something peculiar to quantum mechanics. You want to measure the temperature of a system, so you stick a thermometer in there. Okay, the mercury in the thermometer absorbs a bit of heat from the system, providing you with a temperature measurement at the same time it changes the temperature of the system. If you want to measure the parameters of a particle, you stick a bubble chamber in the way, and as the particle flies through the chamber it smacks into hydrogen molecules, showing you what it's doing but also taking a different path than it would have if none of those hydrogen molecules were in the way. Big fat hairy deal.

The HUP doesn't just say that you can't simultaneously measure the position and momentum of a particle, it says that a particle *does not simultaneously possess* a well-defined position and momentum. If the particle's doing something in a system and is interacting in such a way that you can define its position to arbitrary precision, then it *does not have* a well-defined momentum for you to measure, and vice versa. Position and momentum are what are called quantum conjugate variables, and the HUP says that when you have a pair of those variables, then the product of their uncertainties is greater than or equal to a constant. There is *no state* in which that particle is even *allowed* to exist in which it possesses both a well-defined position and well-defined momentum.

A signal processing analogy, for any analog people. A particle's wavefunction carries information about its position and its momentum. Where the wave exists is where the particle actually is, and the wavelength is the particle's momentum. Take a particle whose momentum you know to the utmost precision, and graph that. Range of momentums on the x axis, probability of the particle having that momentum on the y axis. You'll get a graph that looks like a Dirac function, a value of 0 everywhere except for a single spike corresponding to the particle momentum, area under the curve of 1.

Now switch domains, change from the momentum to the position domain, this is mathmatically the same thing as changing from a time domain to a frequency domain, which means you can use your old friend the Fourier Transform.

What do you get when you do an FT of a Dirac function? You get a constant value everywhere, from -infinity to +infinity. If you know exactly where that particle is, you have no idea *where* it is, and it's not because you disturbed it in measuring it, it's because *it* has no idea where it is, a well-defined position does not exist; since the uncertainty in the momentum measurement approaches zero than the uncertainty in the position measurement has to approach infinity so that the product of those uncertainties remains greater than a constant.

The "you change the system by measuring it" is an analogy, and it's one that Heisenberg himself used to explain the HUP, but *that is not what it says*. The HUP is not a statement about the process of measuring things, it is a statement about the nature of the universe, and finding a way to improve a measuring system to reduce the disturbance it creates in the system it's measuring has nothing to do with the HUP.

Re:Argh science journalism. (3, Insightful)

Celarent Darii (1561999) | about 2 years ago | (#41273635)

Only on Slashdot can you find a comment better than the article. Someone give him a modpoint.

Re:Argh science journalism. (3, Interesting)

osu-neko (2604) | about 2 years ago | (#41274591)

Only on Slashdot can you find a comment better than the article. Someone give him a modpoint.

With the proviso that the comment would be utterly incomprehensible to the target audience of the original article. "Better" is thus a relative term, and an assessment the BBC would rightfully disagree with in this case.

Re:Argh science journalism. (1)

houghi (78078) | about 2 years ago | (#41275463)

Only on Slashdot? You must not look at anything produced by any news outlet. (Not even talking about Fox 'News')

Re:Argh science journalism. (1)

Celarent Darii (1561999) | about 2 years ago | (#41275753)

Well, on most quality news sites the comments are of much lower quality than the comments. I was just saying that Slashdot is an exception - well, at least in this case.

Re:Argh science journalism. (1)

Celarent Darii (1561999) | about 2 years ago | (#41275761)

Errm I meant to say that the comments are of much lower quality than the articles. Time to stop commenting before I ruin Slashdot. Goodnight.

Re:Argh science journalism. (0)

Anonymous Coward | about 2 years ago | (#41274205)

It's always seemed self-evident to me - if a particle is changing it's position, then it has a momentum but no fixed position - if it has no momentum then it is not changing it's position, so it has a fixed position. In other words, the quality of each depends on a changing value for the other.

No (1)

Anonymous Coward | about 2 years ago | (#41274659)

It's always seemed self-evident to me - if a particle is changing it's position, then it has a momentum but no fixed position

No. If it was that simple then this issue would arise already in Newtonian mechanics. A Newtonian particle with a well-defined momentum is constantly changing its position, but at any given instant in time it does have a particular position. This is just not the case in quantum mechanics; one has only a probability of finding a particle at a given point, and if it has a definite momentum then that probability is uniform over space, so it's position is completely indeterminate (in a 1D example, anyway).

if it has no momentum then it is not changing it's position, so it has a fixed position. In other words, the quality of each depends on a changing value for the other.

Again, no. Classically, a particle with a fixed momentum zero has a fixed position, but in quantum mechanics this is not possible. The best one can do is localize a particle to some region of space (i.e., "trap" it with some imposed potential, be it electric or whatever), in which case it will have a mean momentum of zero, and a mean position, but both its momentum and position are statistically distributed about this mean values (i.e., are "fluctuating" if you like, but this is also a dangerous way to think about it, because their values aren't fluctuating with time, they are in fact fundamentally uncertain at any instant of time), and the product of the widths of these distributions must be greater than some fundamental finite value, and that is the uncertainty principle.

Re:No (0)

Anonymous Coward | about 2 years ago | (#41275951)

"Classically, a particle with a fixed momentum zero has a fixed position"

Maybe it would if such a state was even classically possible. Surely even "classically" nothing has a fixed position or a fixed momentum - everything is in motion, in a varying field, which has forces acting on it to continually change it's velocity (and so momentum).

" A Newtonian particle with a well-defined momentum is constantly changing its position, but at any given instant in time it does have a particular position"

Instant in time ?? Surely there is no such thing - only a smallest possible unit - or as you put it - some fundamental finite value.

Re:Argh science journalism. (1)

ABoerma (941672) | about 2 years ago | (#41274613)

The 'you change the system by measuring it' is called the observer effect, and it has to do with wave function collapse and not with uncertainty.

Regarding the HUP: you can derive that without referring to measurement apparatuses, by just looking at the momentum and position operators. Let position x and momentum p each have standard deviation dx and dp, respectively, then by the Cauchy-Schwarz inequality

        dx dp >= |cov(x,p)|.

The covariance of x and p is

        cov(x,p) = E[(x-E[x])(p-E[p])],

where E[A] is the expected value of operator A, and as the commutator of operators x and p is [x,p]=i hbar,

        dx dp >= |E[(x-E[x])(p-E[p])]| = |E[xp]-E[px]|/2 = hbar/2,

which is the Heisenberg uncertainty principle.
 

Re:Argh science journalism. (5, Informative)

SoftwareArtist (1472499) | about 2 years ago | (#41274707)

While the article is terrible, the actual paper is very clear about this. There are two different things that are commonly referred to as "the Heisenberg uncertainty principle". One refers to the intrinsic properties of a wavefunction and the impossibility of being in an eigenstate of two noncommuting observables. The other - which is what Heisenberg originally proposed - refers to the fact that performing a measurement alters the state of the thing being measured. Many people, including the authors of quantum mechanics textbooks, frequently talk about these as if they were equivalent, but they aren't.

Here's the first paragraph of the paper, which lays all this out very clearly:

The Heisenberg Uncertainty Principle is one of the cornerstones of quantum mechanics. In his original paper on the subject, Heisenberg wrote “At the instant of time when the position is determined, that is, at the instant when the photon is scattered by the electron, the electron undergoes a discontinuous change in momentum. This change is the greater the smaller the wavelength of the light employed, i.e., the more exact the determination of the position” [1]. Here Heisenberg was following Einstein’s example and attempting to base a new physical theory only on observable quantities, that is, on the results of measurements. The modern version of the uncertainty principle proved in our textbooks today, however, deals not with the precision of a measurement and the disturbance it introduces, but with the intrinsic uncertainty any quantum state must possess, regardless of what measurement (if any) is performed [2–4]. These two readings of the uncertainty principle are typically taught side-by-side, although only the modern one is given rigorous proof. It has been shown that the original formulation is not only less general than the modern one – it is in fact mathematically incorrect [5]. Recently, Ozawa proved a revised, universally valid, relationship between precision and disturbance [6], which was indirectly validated in [7]. Here, using tools developed for linear-optical quantum computing to implement a proposal due to Lund and Wiseman [8], we provide the first direct experimental characterization of the precision and disturbance arising from a measurement, violating Heisenberg’s original relationship.

Uncertainty (5, Funny)

Nkwe (604125) | about 2 years ago | (#41273449)

So the paper says we are not sure about the uncertainty principle?

Re:Uncertainty (0)

Anonymous Coward | about 2 years ago | (#41274515)

So the paper says we are not sure about the uncertainty principle?

Maybe. I'm not sure.

Quantum Entangelment/Mechanics Lectures (1)

Anonymous Coward | about 2 years ago | (#41273593)

http://www.youtube.com/watch?v=0Eeuqh9QfNI : Quantum Entanglement Lectures from Leonard Susskind. It really isn't that complicated, there are a lot of people here making statements that should instead be asking questions. This series along with his series on Quantum Mechanics should help answer those questions.

DEAD OR ALIVE CATS QUANTUM MAGIC bleuicgailaap (0)

Anonymous Coward | about 2 years ago | (#41274555)

> While there is a rigorously proven relationship about uncertainties intrinsic to any quantum system, often referred to as “Heisenberg’s Uncertainty Principle,” Heisenberg originally formulated his ideas in terms of a relationship between the precision of a measurement and the disturbance it must create. Although this latter relationship is not rigorously proven, it is commonly believed (and taught) as an aspect of the broader uncertainty principle. Here, we experimentally observe a violation of Heisenberg’s “measurement-disturbance relationship”

So the actual Heisenberg’s Uncertainty Principle is still as valid as ever (and of course it is because it's a mathematical consquence of the axioms of quantum mechanics), just some erroneous formulation he started out with has been shown wrong.

Fantasy Physics still confuses (1)

sgt_doom (655561) | about 2 years ago | (#41274777)

Pierre-Simon Laplace was correct. Prof. Taleb, in his book, The Black Swann, clearly demolishes the Uncertainty Principle and too few people still don't understand Bell's Theorem and therefore are confused on "quantum entanglement" and the EPR.
(Read that fellow who's a prof in quantum mechanics at MIT, Seth Lloyd.)

It's about universal balance --- too many people are still unfamiliar with GFB Riemann, most unfortunately. In the present we are saddled with Fantasy Finance and Fantasy Physics, I fear.....

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