## Making Cesium Atoms Do a Quantum Walk 117 117

An anonymous reader recommends an Ars Technica account of a breakthrough in efforts toward quantum computing. German scientists have managed to get cesium atoms in a state called a "quantum walk": basically a superposition of all the possible states of a particle.

*"Quantum walks were first proposed by physicist Richard Feynman and are, in terms of probability, the opposite of a random walk. A random walk might be modeled by a person flipping a coin, and for each flip he steps left for heads and right for tails. In this case, his most probable location is the center, with the probability distribution tapering off in either direction. A quantum walk involves the use of internal states and superpositions, and results in the hypothetical person 'exploring' every possible position simultaneously."*In the abstract of the paper from*Science*(subscription needed for full-text access), the researchers say: "Our system allows the observation of the quantum-to-classical transition and paves the way for applications, such as quantum cellular automata."
## Encryption plan (Score:2)

Do we have a plan for when one day, our current methods of encryption all become breakable at once?

## Re: (Score:3, Funny)

Do we have a plan for when one day, our current methods of encryption all become breakable at once?

What a wasted opportunity, your first post is supposed to say "First post, or is it?"; well I suppose you can always wait for the next quantum computing breakthrough.

## Re:Encryption plan (Score:4, Funny)

Do we have a plan for when one day, our current methods of encryption all become breakable at once?

What a wasted opportunity, your first post is supposed to say "First post, or is it?"; well I suppose you can always wait for the next quantum computing breakthrough.

"3very p0st" would have been an acceptable alternative, in my opinion.

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What are you talking about, that's exactly what it said here. I guess you lost the quantum coin toss.

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It could just be a lot of quantum talk.

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No, you say every possible permutation of your sentences simultaneously and then when the other person hears this they instantly forget what they have heard.

## Re:Encryption plan (Score:5, Funny)

That's my plan, anyway.

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In a country? With that much cash, you can have your own country. With blackjack. And hookers!

Aaand a huge military, making the country survive in the first place.

Just be sure to transform all that money into gold. Because it will be worth shit, when nobody accepts it anymore.

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If someone wants to spend that kind of money and resources to get you, then it doesn't matter what kind of decryption they have. If they can't ruin you by decrypting your secrets then they can just make something up. Fake compromising information is going to be the easier way to go for long enough that you shouldn't have to worry about it. I mean a planted local news story or thorough facebook+myspace+bl

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What about all the backup tapes or laptops that are stolen, but we don't worry about it because the data was encrypted?

Today we don't consider that data to have been compromised. But in the not-too-distant future it could be cracked instantly.

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If a superior power simply wishes to ruin you that is, as you say, typically easy without any codebreaking. P

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## another awful, awful analogy (Score:1)

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If someone wants to spend that kind of money and resources to get you, then it doesn't matter what kind of decryption they have. If they can't ruin you by decrypting your secrets then they can just make something up.

Ob XKCD [xkcd.com]

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such as in an aluminum pole

Another festivus

miracle!!## Re: (Score:2)

I wouldn't worry. As long as there are NP problems that take extremely long unless you have a hint, we have encryption methods.

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But all the encrypted data in the wild that's considered safe because it's encrypted would have to be considered compromised, right?

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By using Plug and Play technology as it was intended, you have corrupted all your data. They invented a technology, and couldn't implement it, so it's useless, and some day they will figure it out.

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Well, if you have used encryption for several years now, you probably made a move from 128bit over 512bit to 2064bit key size. For some encryption methods quantum computing will just be another step, but a really big one.

For others, quantum computing may "solve the decryption" directly by the different approach (superposition, probabilistic calculations).

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First of all, only public key encryption algorithms based on factoring would be broken. Others would still be strong (until a quantum algorithm was written to break them).

More importantly, properly applied one-time-pad encryption would still be unbreakable. I wouldn't be surprised if certain military/intelligence organisations were already using one-time-pad's that were distributed before missions (on DVD or HDD).

It is also worth noting that public-key encryption is already breakable at typical bit-strength

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http://www.idquantique.com/

Quantum computers do still have a very long way to go before they are useful for anything else than factorizing very small numbers. The last record I heard of was 15, which was already quite a while ago, but I find it unlikely that they have managed to do any significant improvements since then.

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Don't start measuring your quantum particles just yet.

We don't know that a quantum computer will be able to break every encryption scheme we have. We have the famous open problem of whether P=NP. (I'd bet against.) For those who don't know, P is the set of all problems solvable in polynomial (that is, relatively quick) time, and NP is the set of all the problems solvable in polynomial time if only it was practical to try every possible solution in parallel, or there was some fast (polynomial time or

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I think the general plan is to lament how this could be possible, despite the fact that everyone ignored the possibility.

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The issue is more of a case of which country gets there 1st.

My money is on China

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ROT13

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## I'm not drunk, offischer. I'm doing a quantum walk (Score:5, Funny)

## Reliability of Cesium (Score:4, Interesting)

Cesium is an interesting element in that it is perfectly reliable. While some elements will differ in atomic weight due to random changes in their electron sphere radii and the number of neutrons in the nucleus, Cesium has a perfect vibration rate independent of external stimuli. It is so regular and reliable, in fact, that we base our entire measurement of time on clocks composed purely of Cesium.

If, as is demonstrated here, Cesium can be used to explore multiple quantum states in a regular and reliable fashion, the possibility to build quantum computers and automata based on Cesium goes way up. Not only would these "computers" function better than our current computers, they would always be 100% perfect (unless Intel manufactures them, lol) and not prone to error or breakage.

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The last part of your comment is just false. There are problems that quantum computers would be able to solve that you can't solve with any practical classical computer, but the

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Is one of them spelled with an a?

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## Fuck off, you dumb lardass (Score:2)

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## Quantum CPU extensions? (Score:4, Interesting)

As far as I know it, we have three main instruction sets. Integer, Floating Point, and Vector (

SSE, MMX..etc). Would it more likely be that we would end up with the forth set being Quantum? Or, would it be possible to have an entire CPU quantum based?## Re:Quantum CPU extensions? (Score:5, Funny)

To your first question: Yes. There would be a new instruction set called "Eigen". It would contain all possible values simultaneously. The interesting thing about such a value is that it could be used to determine the correct value of any problem simply by casting it to the appropriate data type. Since the other instruction sets can only contain a single value at any time, the correct value (for our universe) is automatically saved in the other data type.

For your other question: Yes and no.

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*smacks my forehead*

Of course!!! I would need a quantum CPU to get the correct answer because "Yes and No" are still undetermined. Now I understand ;)

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What about

maybe?## Re: (Score:2)

Nope.

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That's what superposition means, just less fancy :)

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No. Quantum or not, the sum of the probabilities of all possibilities still 1.

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That's what superposition means, just less fancy :)Nope, and this is a good straight line for my futile quest to explain something about quantum weirdness, because it is precisely the difference between "maybe" and "superposition" that makes life interesting for a quantum mechanic.

"Maybe" is a classical concept. If we see a cat get into a box, and then there is a sudden yowling and howling from the box, and you ask me, "Is the cat ok?" and I reply, "Maybe" we are talking about a classical situation, in whi

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Man, I sure screwed up that last sentence, which should read:

"...when the natural expectation would be that after a measurement had taken place we would be aware of the measurement apparatus as being in an incoherent superposition of orthogonal states."

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Nope. This is exactly the point I was trying to make: extremely short wavelengths explain why we don't observe interference phenomena. But they don't explain why we don't observe the cat as being in a superposition of ALIVE and DEAD.

That is, they don't explain why the world of experience differs from the quantum world, and this is the central question.

GIVEN that the only way we can detect the quantum world is via interference phenomena, then the really short wavelength of macroscopic objects explains why

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It's yes and no. We determined it to be both simultaneously.

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...the correct value (for our universe) is automat...

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"The interesting thing about such a value is that it could be used to determine the correct value of any problem simply by casting it to the appropriate data type."

This is incorrect. Determining the superposition's state won't give you the correct answer. It will give you a random answer from all of its possible states -- weighted by the chance of that being the right answer. This makes quantum computing much trickier.

http://scottaaronson.com/blog/?p=208 [scottaaronson.com] is a great article if you want to understand how s

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As far as I know it, we have three main instruction sets. Integer, Floating Point, and Vector (SSE, MMX..etc). Would it more likely be that we would end up with the forth set being Quantum? Or, would it be possible to have an entire CPU quantum based?

Quantum computation is unlikely to replace classical computation. There are certain problems at which quantum computation excels (problems that involve period-finding in some way, shape, or form) and many problems that it doesn't excel at (anything else).

A quantum encryption co-processor is most likely the first way in which quantum computation will reach the classical computing world, and for physical reasons (you need an actual quantum communication channel to attach to) I wouldn't expect it on your

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See here:

http://en.wikipedia.org/wiki/Quantum_computer [wikipedia.org]

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As far as I know it, we have three main instruction sets. Integer, Floating Point, and Vector (SSE, MMX..etc). Would it more likely be that we would end up with the forth set being Quantum? Or, would it be possible to have an entire CPU quantum based?

Sure it would. Modern processors do things with several bits at once (like 32 or 64 bits integers, floats that you mention). Quantum computer calculates with several quantum-bits (so-called q-bits) at once, using their entanglement together with quantum evolution and a measurement on the evolved q-bits. This has nothing to do with some word Eigen that other posts are mentioning, because we can simulate quantum computers classically, so Eigen is not necessarily operation that only quantum computer does--w

## Misunderstanding this, most likely (Score:4, Interesting)

wouldn't we be well on our way towards creating an improbability drive?

I'm probably hugely stretching this beyond what it means.

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Theoretically speaking, if we could get, say, an entire ship and all of its inhabitants to do this "quantum walk"...

Ah, but you can't. Quantum mechanics applies only to quantum particles, not big honking spaceships. Of course nobody has integrated quantum mechanics with classical mechanics yet, so you never know ;)

The thing is, quantum mechanics is just a mathematical system that seems to work pretty well. As in, it predicts what really tiny things will do extremely well. When a quantum particle takes on different states at a time, that is a mathematical concept that, when applied, produces a result that agrees w

## Re:Misunderstanding this, most likely (Score:5, Informative)

Quantum mechanics applies to large particles. Classical mechanics are merely an approximation of quantum mechanics when applied to large particles.

Wikipedia to the rescue

http://en.wikipedia.org/wiki/Correspondence_principle [wikipedia.org]

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Actually Quantum Mechanics applies to individual atoms regardless of size. Classical mechanics corresponds to the mathematical limits when the number of particles becomes large, i.e. you take the mathematical constructs of quantum mechanics and extrapolate to the number of particles being infinity and you come up with the mathematical construct for Classical Mechanics.

So Anpheus is correct. How do I know this? Well, I have a Ph.D. in Physical Chemistry.

## Re:Misunderstanding this, most likely (Score:4, Insightful)

From what I've read on the issue, such as Feynman's books and other novels targeted toward those of us who do not have a complete grasp of quantum mechanics, you are wrong.

Caveat emptor, this is merely what I've read:

Classical mechanics as explained by Feynman were the result of the sum of all possible histories, among other interpretations. Regardless of one's interpretation, Feynman and others found that as you crunch the math for larger and larger quantities of particles, the results closer and closer approximate what we think of as classical physics. As a result, classical physics is an approximation of quantum mechanics, which is a theory of how the universe really works.

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...well, yes, until you get to

reallylarge (or fast) scales, at which point QM comes into direct conflict with relativity.I've heard of recent attempts to reconcile the two, but last I heard there was still no universally accepted answer.

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Not quite a spaceship, but quantum tunnelling has been shown to apply to non-quantum particles [trygve.com].

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If we had a quantum pirate ship we could make people walk the Planck.

## How to make German cesium atoms walk (Score:2)

## Hey, babe, come for a quantum walk... (Score:1)

## Note to Ars Technica (Score:2)

Please do not write further articles about quantum computing. This one was both factually inaccurate and unreadable. :P

## Would P and NP (Score:1)

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## In other news (Score:2)

## Note to Self: (Score:2, Funny)

## Quantum walk? (Score:2)

At my age, I have trouble with a duck walk.

## Who composed the music? (Score:1)

I'm imagining something like a cross between Mancini's Baby Elephant Walk and the Hamster Dance

## Full article (Score:1)

You can get the full article from the arxive:

http://arxiv1.library.cornell.edu/abs/0907.1565 [cornell.edu]

It is really a beautiful experiment. I have never seen such a demonstration of how deterministic the propagation of the wavefunction is. By simply running the experiment backwards they manage to get the atom to go back to it's initial position in the walk.

## Obligatory Python (Score:1)

## Quantum programming (Score:2)

When talking about quantum computing, don't forget that someone has to write the programs. If you thing programming in a SIMD (Single Instruction Multiple Data) is difficult, try SIID (Single Instruction, Infinite Data).

Also remember that there are a few REALLY hard problems to solve before we can have a quantum computer compute anything. For example, to factor a key, you have to have two 'registers' and somehow get them to be the superposition of all primes less than the key value. That is, all non-primes

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A random walk might be modeled by a person flipping a coin, and for each flip he steps left for heads and right for tails. In this case, his most probable location is the center

IIRC, the center is only a solution in 1D and 2D, not in higher dimensions (esp. 3D).

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Do people even need to take a stats course any more?

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The link you provid

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Not it doesn't. It only questions the Copenhagen interpretation of quantum physics, especially the concept of superposition of quantum states. An interpretation is not a theory. It is just a guess. In this case, it is a very lame guess and silly on the face of it.

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This is BS and you know it. Superposition is certainly part of the Copenhagen interpretation [wikipedia.org]. The hard irrefutable truth is that nobody has ever observed superposed states. The only thing that is tested is the probabilistic nature of quantum interactions. The entire concept of a wave function collapse is just silly guess work. One could just as easily say that the property has a given state but the state can instantly change when the particle interacts with another (during observation) in order to obey cons

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You are plain wrong on all accounts:

Superposition is not a part of only the Copenhagen interpretation. You obviously didn't read the Wikipedia article you link to. It doesn't even contain the word superposition.

No, no one has ever observed superposed states, since the wavefunction collapses as soon as anyone try to observe it. It is not silly guesswork. The brightest minds in modern time have failed to come up with

anyother explanation. Einstein was only one of them. You can not say "the property has a## Re: (Score:1)

What are you, a wise guy? Bell's inequality is about entangled particles and nonlocality. That has nothing to do with superposition of states. The Copenhagen interpretation has to do with the Schrodinger wave function, which is about superposition. You don't even understand the very theory you're arguing about.

The only reason that quantum mechanics is counterintuitive and hard is that physicists are clueless as to what is really going on. This should be a clue that current interpretations are wrong and shou

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Bell's inequality says, loosely speaking, that if you have locality then you must have superpositions. Most physicists thinks we have locality, otherwise information could be transmitted faster than light. If information can be transmitted faster than light, we get problems with causality and then we are in a real mess. Then you could really start to talk about counterintuitive.

The Schroedinger equation is central to quantum physics. It describes how a state evolves with time. Again, it is not something tha

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Sorry, nonlocality does not imply fater than light communication. Those who worry about faster than light travel simply do not understand the science of nonlocality. Nonlocality means nonspatiality, i.e., distance is an illusion. There is no transmission of information between two entangled particles. They are facets of the same coin. Nonspatiality should be a wake-up call to physicists, IMO. The paradigm shifting implications threaten to revolutionize physics. Thomas Kuhn comes to mind.

My entire point is t

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Quantum physics is very logical. It is just counter intuitive. That you can't understand it, doesn't mean it is illogical. Kuhn's paradigm shift did already happen. It happened with the advent of Quantum Physics. It's just that you haven't caught up yet.

I'm sorry, but you are obviously just a tiresome crackpot. You don't understand quantum physics. You don't understand superpositions or entanglement. You give up relativity and the notion of space to save what you call logic. Your post doesn't contain any su

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I'll tell you what. As soon as you explain why bodies fall I'll provide an explanation for the double slit experiment.

In the meantime, keep on kissing ass and see if I care. And since I seem to have been drawn into a pissing contest, fuck you too. How about that?