# Making Cesium Atoms Do a Quantum Walk

#### kdawson posted more than 4 years ago | from the like-a-perp-walk-only-without-the-cameras dept.

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 (1)

## XanC (644172) | more than 4 years ago | (#28765531)

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

## Re:Encryption plan (0)

## Anonymous Coward | more than 4 years ago | (#28765587)

## Re:Encryption plan (2, Funny)

## Killer Orca (1373645) | more than 4 years ago | (#28765593)

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 (4, Funny)

## Anonymous Coward | more than 4 years ago | (#28765777)

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.

## Re:Encryption plan (0, Offtopic)

## civilizedINTENSITY (45686) | more than 4 years ago | (#28765995)

## Re:Encryption plan (1)

## SEWilco (27983) | more than 4 years ago | (#28765983)

## Re:Encryption plan (2, Funny)

## slickwillie (34689) | more than 4 years ago | (#28765633)

It could just be a lot of quantum talk.

## Re:Encryption plan (1)

## tenco (773732) | more than 4 years ago | (#28767779)

## Re:Encryption plan (2, Funny)

## Linker3000 (626634) | more than 4 years ago | (#28768109)

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 (0)

## Anonymous Coward | more than 4 years ago | (#28765713)

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

Plead guilty?

## Re:Encryption plan (4, Funny)

## fuzzyfuzzyfungus (1223518) | more than 4 years ago | (#28765781)

That's my plan, anyway.

## Re:Encryption plan (1)

## Hurricane78 (562437) | more than 4 years ago | (#28768757)

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.

## Re:Encryption plan (2, Insightful)

## TiberSeptm (889423) | more than 4 years ago | (#28765805)

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+blogspot+whatever campaign calling someone a "pedophile" will drive them to hang themselves faster than stealing their identity anyways.

## Re:Encryption plan (1)

## XanC (644172) | more than 4 years ago | (#28765823)

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.

## Re:Encryption plan (2, Insightful)

## fuzzyfuzzyfungus (1223518) | more than 4 years ago | (#28765875)

If a superior power simply wishes to ruin you that is, as you say, typically easy without any codebreaking. People who don't have that kind of power, but would love to compromise your secrets, are markedly more common and crypto is pretty much what keeps them at bay right now.

## Re:Encryption plan (1)

## TiberSeptm (889423) | more than 4 years ago | (#28765973)

This is my point. Even the advent of a functioning and powerful quantum computer is not enough to warrant panic. The advent of a relatively cheap (even a couple million) and low-profile quantum computer would be something to worry about. Until these things can be used effectively by a couple guys in a warehouse, don't require a power footprint the size of a grow-house, don't require compressed low temperature gasses to run, and don't require quantum physicists to operate, you will not have to worry about people destroying the effectiveness of all encryption.

The impetus to actually use this sort of encryption cracking technology would have to either come from the desire to crack a particular high value encryption, or a scheme to pull in vast amounts of encrypted information to fish for things of value. Drudging through old laptops would be a ridiculous way to make something like that cost effective and you would have to be paranoid and delusional to think that someone would bother to bring such a complex and expensive apparatus to bear against YOUR old laptop.

So, like I said - until this is something that people sniffing wifi traffic at Panera bread or that Nigerian prince who emailed me the other day can afford and hide - it's not worth getting freaked out about.

## Re:Encryption plan (1)

## civilizedINTENSITY (45686) | more than 4 years ago | (#28766017)

## another awful, awful analogy (1)

## plnix0 (807376) | more than 4 years ago | (#28766483)

or a scheme to pull in vast amounts of encrypted information to fish for things of value.

Too bad the entities with large sums of money are the same ones who want to sort through encrypted data looking for things of interest.

## Re:Encryption plan (1)

## plnix0 (807376) | more than 4 years ago | (#28766507)

## Re:Encryption plan (1)

## sconeu (64226) | more than 4 years ago | (#28766213)

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]

## Re:Encryption plan (1)

## Kagura (843695) | more than 4 years ago | (#28766487)

such as in an aluminum pole

Another festivus

miracle!!## Re:Encryption plan (1)

## buchner.johannes (1139593) | more than 4 years ago | (#28765955)

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

## Re:Encryption plan (1)

## XanC (644172) | more than 4 years ago | (#28766001)

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

## Re:Encryption plan (1)

## trum4n (982031) | more than 4 years ago | (#28766111)

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.

## Re:Encryption plan (1)

## Engine (86689) | more than 4 years ago | (#28767929)

## Re:Encryption plan (1)

## buchner.johannes (1139593) | more than 4 years ago | (#28766131)

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).

## Re:Encryption plan (1)

## smaddox (928261) | more than 4 years ago | (#28766155)

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-strengths, if you are given enough time (all of the RSA challenge numbers have been factored). For certain applications timing is everything. For others, it is imperative that the code never be broken (thus one-time-pad's must be used). Quantum computers will still take a while to break a code, and it will be a looooong time (on a technological scale) before the average person has access to one. Thus, decrypting with a quantum computer will still take a significant amount of time, so for certain applications public key encryption will still rule. As quantum computers begin to permeate, more secure encryption will be necessary.

Finally, lets remember that quantum encryption is likely to be possible in the future. It is reasonable to assume that it will advance at a similar speed to quantum computers. Thus, strong encryption will still exist.

## Re:Encryption plan (1)

## Engine (86689) | more than 4 years ago | (#28767981)

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.

## Re:Encryption plan (1)

## bzipitidoo (647217) | more than 4 years ago | (#28766183)

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 better) means of eliminating a significant portion of any subset of less than optimal solutions. (Yes, P is a subset of NP.) Somewhere between P and NP is QP, the set of all problems solvable by a quantum computer in polynomial time. Maybe QP is equal to NP, we don't know. We know that some problems apparently not in P are in QP. The most notable of these problems is factoring. We also have problems we know are in NP but which we don't know are in QP, mainly because no one has come up with a quantum algorithm to do them. And also, no one has come up with a quantum algorithm for any of the problems known to be "NP-complete", that is, all the way at the NP end of the range between P and NP. If just one of those problems is solvable by a quantum computer in polynomial time, then they are all solvable and QP=NP, because NP-complete problems can all be converted to one another with algorithms in P. As far as we know, factoring is easier than NP-complete and harder than P. It's somewhere between P and NP, not all the way at one end. Of course if P=NP, then QP would be equal to both, and a quantum computer wouldn't be worth fooling with as it would be no more powerful than a classical computer. Even if a quantum computer can solve them all, because QP=NP and never mind P, almost certainly we can come up with new encryption schemes. Perhaps new methods will all have to exploit quantum effects to be secure, and perhaps not.

Even supposing QP=NP, we don't know that we can do quantum computing on a large enough scale to exploit this. I keep thinking it could prove impossible to manage more than a very few quantum bits. It may be physically impossible to handle more than a dozen for long enough to do useful work, and that could conceivably be a necessary consequence of QP=NP, which could be closely related to whatever reasons physicists may discover.

Or maybe it is possible to do significant quantum computation. And maybe a necessary consequence of that is that QP!=NP, in which case we would also know that P!=NP, and the exploratory users of the first significant quantum computer can collect the million dollar prize for solving that problem among the many other things they could do. Unless we should find a way to scale quantum computing up to arbitrarily large numbers of quantum bits for indefinite lengths of time, it will remain very difficult to explore these questions.

## Re:Encryption plan (1)

## CarpetShark (865376) | more than 4 years ago | (#28767503)

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

## Re:Encryption plan (1)

## Big Hairy Ian (1155547) | more than 4 years ago | (#28767567)

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

My money is on China

## Re:Encryption plan (2, Funny)

## Linker3000 (626634) | more than 4 years ago | (#28768091)

ROT13

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

## wdef (1050680) | more than 4 years ago | (#28765581)

## Reliability of Cesium (4, Interesting)

## BadAnalogyGuy (945258) | more than 4 years ago | (#28765583)

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.

## Re:Reliability of Cesium (0)

## Anonymous Coward | more than 4 years ago | (#28765685)

I doubt the clocks are composed purely of cesium since their cesium surface would ignite spontaneously in air.

## Re:Reliability of Cesium (1)

## Engine (86689) | more than 4 years ago | (#28768039)

## Re:Reliability of Cesium (1)

## Engine (86689) | more than 4 years ago | (#28768113)

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 a quantum computer would be a very sensitive device, and finding ways to get around the very high error rate in a QC is a very active area of research.

## Re:Reliability of Cesium (1)

## Hognoxious (631665) | more than 4 years ago | (#28770427)

Is one of them spelled with an a?

## Re:Reliability of Cesium (1)

## Engine (86689) | more than 4 years ago | (#28770631)

## Most probable location is the center? (0)

## Anonymous Coward | more than 4 years ago | (#28765651)

Not after an odd number of steps, in which case the probability of ending at the center is... zero.

## Re:Most probable location is the center? (1)

## buchner.johannes (1139593) | more than 4 years ago | (#28765919)

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).

## Quantum CPU extensions? (3, Interesting)

## DigiShaman (671371) | more than 4 years ago | (#28765669)

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? (5, Funny)

## BadAnalogyGuy (945258) | more than 4 years ago | (#28765701)

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.

## Re:Quantum CPU extensions? (1)

## DigiShaman (671371) | more than 4 years ago | (#28765877)

*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 ;)

## Re:Quantum CPU extensions? (1)

## TiberSeptm (889423) | more than 4 years ago | (#28766005)

## Re:Quantum CPU extensions? (1)

## weicco (645927) | more than 4 years ago | (#28766279)

What about

maybe?## Re:Quantum CPU extensions? (1)

## WarJolt (990309) | more than 4 years ago | (#28766493)

Nope.

## Re:Quantum CPU extensions? (1)

## szo (7842) | more than 4 years ago | (#28767709)

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

## Re:Quantum CPU extensions? (1)

## Skrynkelberg (910137) | more than 4 years ago | (#28767949)

## Re:Quantum CPU extensions? (1)

## szo (7842) | more than 4 years ago | (#28767995)

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

## Re:Quantum CPU extensions? (2, Informative)

## radtea (464814) | more than 4 years ago | (#28768987)

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 which the cat "really is" either OK or !OK. There are two possible states and classically they are mutually exclusive and jointly exhaustive, regardless of anything else we do to the system. We don't have to look at the cat or measure the cat, we know that it can only be "OK" or "!OK" (for some sufficiently crisp definition of "OK").

"Superposition" is a quantum concept. If a photon interacts with a double slit apparatus and you ask me, "Did it go through the left slit?" and I say, "Maybe" I've said something incoherent unless I quickly stick an apparatus for measuring which slit it went through into the photon's path, because until a measurement is made that distinguishes a photon that passed through the left slit from one that passed through the right, the photon is in a superposition of both states, which are still jointly exhaustive but no longer mutually exclusive, and there is no "fact of the matter" about which slit the photon "really" went through until we ask it with an appropriate apparatus.

The big question to me, which no one from Copenhagen to Consistent Histories or Decoherence answers, is why the classical world--that is, the world of human experience--arises from the quantum world at all. Which is to say, no one has ever answered Max Born's question, "WHY must I treat the measuring apparatus as classical? What will happen to me if I don't!?"

The standard interpretations all take for granted that there is a classical world in which superposition is unobservable, but this papers over the enormous ontological gap between the classical and quantum worlds. The classical world obeys Aristotelian limits on contradiction and causality and locality: a thing cannot both be and not be the same thing at the same time and in the same respect. The quantum world does not obey these limits: the photon can both be and not be a photon that has passed through the left slit, but the wavefunction pulls off some nonlocal legerdemain to clean up after itself when we try to catch it out.

Various interpretations make arguments about HOW this cleanup happens, but no one says anything about why the classical world exists at all: why we are unaware of all the "extra" components of wavefunctions floating around loose after a measurement has been made. Decoherence comes closest to an answer by simply declaring that interference phenomena are the only means by which we can be aware of these other components, but it still says nothing about why we are privileged to observe the effects of one component and not all the others, when the natural expectation would be that we 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.

## Re:Quantum CPU extensions? (1)

## radtea (464814) | more than 4 years ago | (#28769033)

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."

## Re:Quantum CPU extensions? (1)

## AshtangiMan (684031) | more than 4 years ago | (#28771997)

## Re:Quantum CPU extensions? (0)

## Anonymous Coward | more than 4 years ago | (#28772017)

While we're on the subject of Schrodinger's cat:

Isn't the de Broglie wavelength of a cat too small for superposition to be meaningful (less than Planck length)?

## Re:Quantum CPU extensions? (2, Insightful)

## radtea (464814) | more than 4 years ago | (#28773893)

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 we don't detect interference phenomena.

But WHY is interference the only way we can detect quantum phenomena? Why don't we just perceive the damned wavefunction? I think there is an essentially anthropic answer to this, in the form of an anthropic metaphysics: we experience a limited aspect of reality because the very fact of having such experience requires such a limitation. Kant would approve.

## Re:Quantum CPU extensions? (1)

## Engine (86689) | more than 4 years ago | (#28771297)

## Re:Quantum CPU extensions? (1)

## WarJolt (990309) | more than 4 years ago | (#28766513)

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

## Re:Quantum CPU extensions? (1)

## Vectronic (1221470) | more than 4 years ago | (#28765883)

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

42## Re:Quantum CPU extensions? (1)

## Octavarius (1141157) | more than 4 years ago | (#28770661)

"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 some Quantum algorithms we know of will work using this "probable-answer" property.

## Re:Quantum CPU extensions? (1)

## TiberSeptm (889423) | more than 4 years ago | (#28765895)

Even in a system where the primary task was something that quantum computers should be inherently great at, you would still need a powerful traditional processor to actually do anything. This really isn't all that different from the idea of the GPU based desktop supercomputers out there. The GPU's do what they're specialized to do much better than a traditional processor, but you still need to scale the computing power of the traditional CPUs in the system to actually utilize all that power. Similarly, a quantum computer would require a non-insignificant ammount of traditional processor power to keep the quantum processor busy and handle the output. It seems reasonable that specialized supercomputers will eventually consist of a mix of GPUs, traditional CPUs, some quantum processors, and possibly neuron-based processors in a mix determined by the task the supercomputer is designed to do. A super computer designed to model molecular interactions would clearly benefit from both high powered GPUs and quantum processors handling the tasks that they can handle far better than whatever traditional processors the computer used.

## Re:Quantum CPU extensions? (0)

## Anonymous Coward | more than 4 years ago | (#28766827)

It seems reasonable that specialized supercomputers will eventually consist of a mix of GPUs, traditional CPUs, some quantum processors, and possibly neuron-based processors in a mix determined by the task the supercomputer is designed to do.

Imagine a Beow... erm, never mind.

## Re:Quantum CPU extensions? (1)

## SEWilco (27983) | more than 4 years ago | (#28766019)

## Re:Quantum CPU extensions? (1)

## SEWilco (27983) | more than 4 years ago | (#28766061)

## Re:Quantum CPU extensions? (1)

## intx13 (808988) | more than 4 years ago | (#28766049)

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 Dell any time soon.

## Re:Quantum CPU extensions? (1)

## CarpetShark (865376) | more than 4 years ago | (#28767517)

See here:

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

## Re:Quantum CPU extensions? (1)

## ioshhdflwuegfh (1067182) | more than 4 years ago | (#28768373)

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--we can actually calculate eigen values using classical computers just fine. Once built, quantum computer could be an additional unit in the computer system, like QPU (Quantum Processing Unit), similar to today's GPUs.

## And other news (0)

## Anonymous Coward | more than 4 years ago | (#28765709)

## Misunderstanding this, most likely (3, Interesting)

## gcnaddict (841664) | more than 4 years ago | (#28765915)

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

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

## Re:Misunderstanding this, most likely (1)

## intx13 (808988) | more than 4 years ago | (#28766099)

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 with what we actually see. It involves complex numbers, high dimensions (that don't necessarily agree with what we consider "dimensions") and other mathematical constructions. The math works great... but you have to be careful about extrapolating too far and assuming the math is the reality.

## Re:Misunderstanding this, most likely (4, Informative)

## shermo (1284310) | more than 4 years ago | (#28766143)

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]

## Re:Misunderstanding this, most likely (1)

## Anonymous Coward | more than 4 years ago | (#28770163)

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 (3, Insightful)

## Anpheus (908711) | more than 4 years ago | (#28766195)

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.

## Re:Misunderstanding this, most likely (1)

## mea37 (1201159) | more than 4 years ago | (#28771847)

...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.

## Re:Misunderstanding this, most likely (2, Informative)

## mindbrane (1548037) | more than 4 years ago | (#28766265)

## Re:Misunderstanding this, most likely (1)

## 3waygeek (58990) | more than 4 years ago | (#28767811)

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

## Re:Misunderstanding this, most likely (1)

## JoCat (1291368) | more than 4 years ago | (#28774105)

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

## How to make German cesium atoms walk (1)

## SEWilco (27983) | more than 4 years ago | (#28765953)

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

## vjoel (945280) | more than 4 years ago | (#28765975)

## Note to Ars Technica (1)

## blueg3 (192743) | more than 4 years ago | (#28766059)

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

## Would P and NP (1)

## gorrepati (866378) | more than 4 years ago | (#28766091)

## Re:Would P and NP (1)

## JTeutenberg (1222754) | more than 4 years ago | (#28766211)

## Re:Would P and NP (1)

## AllureFX (1602331) | more than 4 years ago | (#28778681)

## Women are made of cesium?? (0)

## Anonymous Coward | more than 4 years ago | (#28766133)

Since women occupy every state at once, that is what makes me, a male, always wrong??? IS THAT RIGHT? IS IT?

## In other news (1)

## 4D6963 (933028) | more than 4 years ago | (#28766153)

## Note to Self: (2, Funny)

## billybob_jcv (967047) | more than 4 years ago | (#28766255)

## JOHN TITOR!!!! (0)

## Anonymous Coward | more than 4 years ago | (#28766285)

John Titor! His Time machine used cesium to coordinate its location in time/space.

## Quantum Computing Crackpottery Marches On (0, Flamebait)

## Louis Savain (65843) | more than 4 years ago | (#28766417)

It seems that a week does not go by unless somebody, somewhere, claims yet another major advance in quantum computing. But has anybody noticed that this has been going on for at least a decade and we still don't have a quantum computer that we can put our hands on? It's obvious that some people need a constant flow of money to keep themselves employed. I just wish it weren't the public's money.

Quantum Computing Crackpottery [blogspot.com]

You may mod me down as a troll but I'm right, goddamnit! Quantum computing is both fraud and crackpottery.

## Re:Quantum Computing Crackpottery Marches On (1)

## Engine (86689) | more than 4 years ago | (#28771865)

The link you provided questions quantum physics in general. Quantum physics is extremely well tested theory that is the foundation for all modern science och technology. It's not that no one has tried, but it has proved very difficult to provide a competing theory that explains even a small part of the known phenomena on the atomic level.

## Calling Natalie Portman (0)

## Anonymous Coward | more than 4 years ago | (#28766497)

"A quantum walk involves the use of internal states and superpositions, and results in the hypothetical person 'exploring' every possible position simultaneously."Let's take a quantum walk!

## Quantum walk? (1)

## Runaway1956 (1322357) | more than 4 years ago | (#28766515)

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

## Nuka Cola Quantum Anyone? (0)

## Anonymous Coward | more than 4 years ago | (#28766845)

http://fallout.wikia.com/wiki/Nuka-Cola_Quantum , If i remember correctly, Cesium was the isotope used in the game to "give that something extra" for the Nuka Cola Quantum :D

## Who composed the music? (1)

## Mogster (459037) | more than 4 years ago | (#28766969)

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

## MJ? (0)

## Anonymous Coward | more than 4 years ago | (#28767405)

Quantum walk - is that like the moon walk?

Good thing - 'cause we won't be seeing that anymore.

What - too soon?

## Useful? (1)

## tmkn (1520967) | more than 4 years ago | (#28767483)

## Full article (1)

## Dice Fivefold (640696) | more than 4 years ago | (#28767869)

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.

## Full Text of article (0)

## Anonymous Coward | more than 4 years ago | (#28767979)

Take a Walk on the Quantum Side By Adrian Cho ScienceNOW Daily News 10 July 2009 If you're a fan of results that make your brain hurt, read on. Compounding one challenging concept with another, a team of atomic physicists has put a new twist on the classic "random walk"--an idealized wandering that is key for explaining the diffusion of one liquid in another and myriad other real-world phenomena. This time, researchers have set a single atom ambling according to the rules of quantum mechanics and found that it covers more distance than it would without them. The advance, reported today in Science, could have uses in budding quantum information technologies, the researchers say. But the real accomplishment seems to be the marrying of two classic physics concepts. In less politically correct times, physics professors explained the random walk as follows. Suppose a drunk stands under a lamppost, staggering to the right or left with equal probability. After some number of steps, N, he is likely to have taken a few more steps to the left than to the right, or vice versa. In fact, after N steps, on average the drunk will have moved a distance proportional to the square root of N from the post. That may seem like a pointless thing to know, but such a random walk neatly describes the motion of a molecule in a sample of liquid or electrons rattling around in a metal. Now, Michal Karski, Artur Widera, and colleagues at the University of Bonn in Germany have thrown the weirdness of quantum mechanics into the mix. A drunk or any other "classical" object must move either to the left or to the right. But according to quantum mechanics, a tiny particle such as an atom can actually move in opposite directions at the same time and end up in a so-called su perposition state in which it's in two places at once. There is a catch, though: Whenever somebody measures the particle's position, the delicate quantum state will collapse so that the particle is found in one place or the other. Taking advantage of all this, the researchers have made a single cesium atom take a "quantum walk" along a chain of spots of laser light formed by two opposing laser beams. Starting with the atom in one spot, they tickle it with radio waves to make it spin in opposite directions--up and down--at once. They then fiddle with the polarizations of the laser beams in a way that pulls the "up" part of the quantum state to the right and the "down" part to the left. That puts the atom in a hard-to-imagine state in which it sits in one spot spinning up while at the same time it sits in the next spot spinning down. The researchers then repeat the process again and again so that the atom ends up in a quantum state in which it occupies many light spots at once. When the researchers measure the atom's position, the state collapses to just one spot. But by performing the experiment many times, they can sketch out that state. And they find that, after N steps in the process, an average atom has moved a distance proportional to N from its original spot--farther than it would get classically. "It is difficult to imagine a cleaner, more textbooklike demonstration of the idea of a quantum walk," says Poul Jessen, an experimental physicist at the University of Arizona in Tucson. The advance could be more than academic, adds Reinhard Werner, a theorist at the University of Hannover in Germany. In principle, he says, by putting several atoms into the chain of light spots and letting them interact, it might be possible to construct a kind of quantum computer that could crack problems that a conventional computer cannot. A full-blown computer is a long way off, Werner says, but "this is a first step toward more complicated things." Did we lose you? Let us know in the comments section if you'd like to see us cover more complex physics stories like this one. ( skip to comments for this article ) Previous Article The editors suggest the following Related Resources on Science sites: In Science Magazine REPORTS Quantum Walk in Position Space with Single Optically Trapped Atoms Michal Karski, Leonid FÃrster, Jai-Min Choi, Andreas Steffen, Wolfgang Alt, Dieter Meschede, and Artur Widera (10 July 2009) Science 325 (5937), 174. [DOI: 10.1126/science.1174436] ÂÂ Abstract Â ÂÂ Full Text Â ÂÂ PDF Â ÂÂ Supporting Online Material Â Comments Thanks for your feedback. Please keep it polite and to the point.

## You call this a walk? (0)

## Anonymous Coward | more than 4 years ago | (#28768029)

Quantum Walk? Call me back when also cesium atoms will do a moonwalk.

## oi... stats 101 ftw (0)

## Anonymous Coward | more than 4 years ago | (#28768775)

"In this case, his most probable location is the center, with the probability distribution tapering off in either direction"

Not true. His position will be sqrt(n) away from the center location, with a 50/50 chance of being either to the left or the right.

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

## Re:oi... stats 101 ftw (1)

## Engine (86689) | more than 4 years ago | (#28771667)

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

## Obligatory Python (1)

## jspenguin1 (883588) | more than 4 years ago | (#28770543)