## Several Quantum Calculations Combined At NIST 91 91

Al writes

*"Researchers at the National Institute of Standards and Technology (NIST) have demonstrated a crucial step toward building a practical quantum computer: multiple computing operations on quantum bits. The NIST team performed five quantum logic operations and 10 transport operations (meaning they moved the qubit from one part of the system to another) in series, while reliably maintaining the states of their ions — a tricky task because the ions can easily be knocked out of their prepared state. The researchers used beryllium ions stored within so-called ion traps and added magnesium ions to keep the beryllium ones cool and prevent them from losing their quantum state."*In related news, another reader links to an Australian study indicating that quantum computers "can continue to work perfectly even if half their components, or qubits, are missing."
## This may be slightly off-topic, but (Score:3, Interesting)

## Re:This may be slightly off-topic, but (Score:5, Funny)

They are computers that leap from datacenter to datacenter, solving previously unsolvable problems, and hoping each time that the next leap will be the leap home.

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Well, at the tiny smallscale - aka, the quantum level - small particles are being buffeted between different states so quickly, that to us it can look like they're in 2 states at once (like being in 2 different places at the same time - like that Superman comic)

If you're

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Nearly, but not quite. With Superman switching places really fast, Superman is really ever only in one place at a time. Qubits are not - they

really can bein two different states at the same time.The bit about state operations isn't really true. You can't do twice as many operations, but with quantum mechanics you can do some new, really funky operations that you can't do with classical bits. Like entanglement.

It's possible to figure out ways to use these multiple states and funky operations to solve probl

## Re:This may be slightly off-topic, but (Score:4, Funny)

Ziggy computes a 98.3% chance that is the correct definition for Quantum Computing.

## Re:This may be slightly off-topic, but (Score:4, Informative)

Not 100% accurate, but here's a rough way to understand a quantum computer: If you've ever heard of the concept that whenever there's some chance, the universe 'splits' and both events occur, that's what's going on. When the quantum computer makes a qubit 1 and 0 at the same time, it basically uses a truly random event to determine which value the bit will be. The universe 'splits' and down one path there is a 1, and down the other there is a 0. Except the quantum computer 'splits' the universe in such a way that the two universes can interact with each other. It is even possible to have the quantum computer compute something on every input at once and then search through all the different universes to find an answer; this is known as Gover's algorithm.

The critical part is coherence: making sure that the only difference between the different universes is inside the quantum computer itself. So long as coherence is maintained, the universes can merge back together and all you're left with is the right answer (99.99999% of the time). If coherence isn't maintained then the universes can't remerge, and you don't get a correct answer. Decoherence is actually extremely hard to deal with, and the biggest engineering challenge in designing a quantum computer.

## Re:This may be slightly off-topic, but (Score:5, Insightful)

The critical part is coherence: making sure that the only difference between the different universes is inside the quantum computer itself. So long as coherence is maintained, the universes can merge back together and all you're left with is the right answer (99.99999% of the time).

How does the observer in the universe with the right answer know their answer is right?

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## Re:This may be slightly off-topic, but (Score:5, Informative)

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42?

I just tried to run Shor's algorithm on that number. The factors turned out to be 6 and 9.

## Re:This may be slightly off-topic, but (Score:5, Informative)

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And if it turns out that P != NP then verification of the answer will always be substantially faster than computing the answer itself.

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Example: decomposition of a number into its prime factors.

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Usually the answer is one that's difficult to compute but easy to check, such as any problem in NP. Checking that you have a factor of a number is much easier than producing a factor, and checking that a proof is correct is much easier than producing a correct proof.

The other option is to simply run it more than once. If you have an algorithm which is wrong 1% of the time (and that 1% is uncorrelated to the "input"), then if you run it ten times, the chance that all of them are wrong is extremely small.

Ha

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It's not really better (or worse). One of the basic postulates of Quantum Mechanics is that several interpretations seem to fit equally well, and there's no mathematical reason to pick one of them and decide it's superior to the others.

Psychologically, it's definitely less mind blowing for most people to treat a lot of quantum processes as something happening to probabilities rather than objectified things. It's probably much less mind numbing for the average person, to claim, for exam

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Well, in some sense it is so. It's just not Lucifer who destroys the quantum heaven, but decoherence.

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the quantum realm is somehow superior to the classical one

The quantum realm is superior to the classical one, all classical stuff is just a subset of quantum stuff. A ball bouncing off a wall not only obeys the laws of classical physics it also follows those of quantum mechanics.

whereas in the classical universe, we find real things instead

There is only one

universe, there are different 'realms/domains' but fundamentally everything obeys the laws of quantum mechanics and the classical universe is just you see on the surface, the "real things" are quantum objects. It happens that for stuff we experience in everyday life stuff## Re: (Score:2)

I'm not sure that I agree. The multi-universe interpretation suffers from a very serious, IMO fatal, problem in lay-explanatory power, which is that it's difficult to picture several split universes "interfering" to cancel each other out.

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You have to be aware that any result a regular computer computes is also correct only within a certain probability. Once the quantum computers success probability is higher than the probability of flipping a bit inside a regular CPU, you are done. You are not only as good as it probably gets, you are as good as regular computers.

If you don't trust the Quantum computer then, you have to stop using any computer.

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Quantum computers are good for problems where the reverse problem is easy. Take factorization: It is hard to factorize a large number, but if someone gives you two numbers and claims those are the factors, it's easy to check if they multiply to your number.

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When the answer is 42.

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The analogy isn't great, and all responses to do with it being easy to verify the answer are wrong. if the QC just gives you a wrong answer as often as a guess would, which is implied in the responses, then there is no point using a QC!

Imagine a game where you have to guess the correct input to get an output (one of these games is called factorisation), QC is a way of cheating at these games, instead of actually trying all the inputs the QC tries them all the ones that give the wrong answer cancel! The inte

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Can they also eliminate lots of latency by doing the computation BEFORE reading the file?

## Re: (Score:3, Informative)

f you've ever heard of the concept that whenever there's some chance, the universe 'splits' and both events occur, that's what's going on. When the quantum computer makes a qubit 1 and 0 at the same time, it basically uses a truly random event to determine which value the bit will be. The universe 'splits' and down one path there is a 1, and down the other there is a 0. Except the quantum computer 'splits' the universe in such a way that the two universes can interact with each other. It is even possible to## Re: (Score:2)

You could couch the argument as not regarding whole universes, but rather regarding only the quantum system (computer) involved. It's basically the same argument: the system splits into many states, they must be kept in coherence, and then they recombine at the end when you perform the measurement and get your answer.

Copenhagen just has that extra measurement step which disconnects the observer and the system (which IMHO is a bit arbitrary), but otherwise it's very similar. And you can simply generalise the

## Re:This may be slightly off-topic, but (Score:5, Interesting)

You just couldn't resist using Everett's interpretation, could you?

I don't think it is a good idea using it to explain something to laymen. They usually end up thinking that quantum mechanics is some kind of inaccessible black magic.

Just to be clear here, it is possible (and it is what's done most of the times) to describe quantum mechanics without ever talking about splitting universes.

Let's see: the qubit can hold some combination of 0 and 1 (NOT 0 and 1). By the same reason (superposition), the quantum computer can perform multiples paths of computation at the same time, which can be used to accelerate the computation of some algorithms.

Quantum computers are quite sensible to noise; it causes decoherence, which can be understood as a loss of quantumness. In other words, a qubit that suffered too much decoherence can't hold a superposition of 0 and 1 anymore.

See? It wasn't that difficult.

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Before or after the sacrifice of a naked virgin in the full moon with a quicksilver spoon?

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Which is like.....99.99999% of Slashdot?

The other .00001% had arranged marriages.

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/.ers go out in the *full* moonlight? Don't you just shrivel up 500,000 times slower?

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Not if you have taco sauce on your head....

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I consider that a very bad explanation of quantum computers (and yes, I work in the field of quantum information, so I know quite well about it). Nothing against many-worlds, but using it to explain a quantum computer is IMHO misplaced. The working of quantum computers is "interpretation-invariant" and adding many-worlds here only muddles the waters.

Even the usual statement that a qubit is "at the same time 0 and 1", while in some sense true, isn't really helpful. Indeed, a

singlequbit can be modeled by di## Re:This may be slightly off-topic, but (Score:4, Interesting)

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Quantum computing is a whole new world of computing; because it's based on the principles of quantum physics. This means that a quantum computer does not resemble the computers of today at all. In a quantum computer, information is stored in "qubits", which is 0, 1 or "undetermined / both".

Yeah, I'm still not buying it. Quantum computing has yet to do anything that lives up to even its basic promise. If it's possible to harness these states, we should have been able to demonstrate, at the very least, the capacity for computation on the scale of, say, the average pocket calculator. And yet, we've still gotten nowhere. Why? Well, there are many possible reasons, but I tend to favor the simplest: quantum mechanics is a field that is built on some very nice math and as many intersections with rea

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but fundamentally we don't really understand what's going on at the level of the atom, much less at the level of its constituent parts.

The problem with most atoms is they deal with a lot of objects (e.g n-body problems), we do however grok hydrogen and have a thorough understanding of the rules of the game. While we probably will get a huge discovery on how the insides of an atom work (and perhaps an other on how the insides of however whatever we find in that works), we know how electrons and photons interact with eachother well enough to construct QC that use these as building blocks.

The Bernoulli principle was know about since 1738 but

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If we can learn something from the history of computing (transistors, silicone chips, disk space), we know that we are good at aggressive exponential growth. I think they had 1 qubit calculation experiments running 2-3 years ago, and 4 qubit or so last year. Now you can calculate when they will crack AES.

What wasn't mentioned yet is that due to the superposition of states (instead of 0/1), you can define requirements to the state, ideally so that it must be definite. Then you measure it and retrieve the (on

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Ya know, alot of these 'summaries' are not really helpful, so I'll take a shot :).

QC for the most part can be thought of in the same fashion as convenetion computer ... etc.

science, qbits == bits, 'transistors', memory

The really cool part, and the part that makes it very interesting to many, is a certain property

of the qbits. Normal bits are independent, each being calculated and contributing to further

calculations on its own. In a QC, then qbits are 'entangled', which can result in one qbit

being effecte

## works with half their components missing (Score:2)

imagine half a beowulf cluster of these things!

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## Begs the Question (Score:2)

Uhhhh....Hmmmmm....

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Uhhhh....Hmmmmm....

I wonder if it keeps working when all of its components are missing?

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Only half the time.

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</misinterpreting the summary for fun and profit>

## Re:Begs the Question (Score:5, Informative)

## Entangled Backups (Score:2)

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## Take cover! (Score:3, Funny)

## Cat joke no. 1 (Score:2)

I can has measurement?

## Now then... (Score:1)

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The scientists may have a bit more work ahead, though, as they don't yet have a qubit state for FILE_NOT_FOUND.

That's only because it is a redundant state. When you search for file X you now get - "At least 50% of file X found in folder Y with at least 90% of its contents intact." Although, immediately after the search, the office assistant still taunts at you when you are not looking.

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## Inadequate and stupid (Score:1)

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Probably a step up from how you'd feel if a discussion of women and relationships came up. ;)

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## Oblig. Bad Car Analogy (Score:4, Funny)

...quantum computers "can continue to work perfectly even if half their components, or qubits, are missing."

Based on the number of spare parts I end up with after every time I tinker with it, so can my car.

## Quick Quantum Computing Explanation (Score:1, Informative)

In the quantum universe, you can take a fundamental property like "position" and put a particle into a superposition state. A particle can be at position a with some probability and position b with some probability. Amazing, huh?

Now, the second component is that you can use quantum entanglement to create superposition states of multiple particles. Einstein had this great idea where measuring the state of one particle tells you what the state of another entangled particle is. This is fundamentally what allow

## Good Lord (Score:2)

Thanks is so *fucking* amazing. It's becoming clearer every day that quantum computing is in the state silicon computing was back in the 50's.

Things are going to get very weird!

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## Applicaton (Score:1)