Making Cesium Atoms Do a Quantum Walk

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."

Comments

I'm not drunk, offischer. I'm doing a quantum walk

[wdef]

"And that geodesic is not shtraight either. Sho's I'll just superimpose my states back in da car and be on my way ..."

Reliability of Cesium

[BadAnalogyGuy]

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:Encryption plan

[Killer Orca]

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

[slickwillie]

It could just be a lot of quantum talk.

Quantum CPU extensions?

[DigiShaman]

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?

[BadAnalogyGuy]

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?

[radtea]

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?

[radtea]

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:Encryption plan

[Anonymous Coward]

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

[fuzzyfuzzyfungus]

A massive cash advance drawn against every credit card in the world, and a castle made of pure unicorns in a country with flimsy extradition treaties?

That's my plan, anyway.

Re:Encryption plan

[TiberSeptm]

A working AND cost effective quantum computer capable of decrypting your pr0n is still a ways off.

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

[fuzzyfuzzyfungus]

It's probably less about people "getting you"(I suspect that, today, relatively few people are actually being protected from a hostile superior power by the strength of their crypto) and more with things like the breakdown of electronic commerce security, the spoofability of cryptographic signatures(Goodbye SSL) and new difficulties in secure authentication(SSH would be about as useful as telnet).

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.

Misunderstanding this, most likely

[gcnaddict]

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

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

[shermo]

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

Re:Misunderstanding this, most likely

[Anpheus]

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

[mindbrane]

If you download the 2009 intro to General Principles of Chemistry from the mit OpenCourseWare offerings you'll get some pretty good stuff on the relationship of Quantum Mechanics and Classical Physics. IIRC the wave descriptions of big league fast balls are used (lectures 4 & 5). I'll leave it there as any attempt by me to go into the particulars will go high and outside.

Note to Self:

[billybob_jcv]

Reading /. stories that include the phrase "...first proposed by physicist Richard Feynman..." make my head explode.

Re:Encryption plan

[Linker3000]

ROT13

Re:Encryption plan

[Linker3000]

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.