Several Quantum Calculations Combined At NIST

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."

Comments

This may be slightly off-topic, but

[Anonymous Coward]

Seriously WTF is Quantum Computing? I've looked at the wiki articles and googled things, and I'm still lost. I did read that unless you have an education in this area you just won't get it, but help me out here.

Re:This may be slightly off-topic, but

[mrsteveman1]

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.

Re:This may be slightly off-topic, but

[jpmorgan]

To truly understand a quantum computer you need a fairly strong understanding of linear algebra, although knowing quantum mechanics isn't actually necessary. I'll repost an explanation I wrote for another site:

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

[xerent_sweden]

So basically it's quantum physics applied on computer science. Computers of today are based on semiconductors and diodes, which allows us to build electric circuits with memory. In this case, it's voltage applied or voltage off - one or zero. 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". This is a direct application of the wave/particle duality of matter (wiki: De Broglie-wavelength). Working out how a quantum computer - which behaves totally differently from anything we have today - and constructing such a device is really hard. Theoretically, such devices would be more efficient than our computers - and that's an understatement. This story means that we've taken yet another small step towards practical quantum computers, but also that it'll be reposted at least 100 times before working quantum computers are reality. (Off the top of my head, please correct me if I wrote something in error. Thanks! :)

Re:This may be slightly off-topic, but

[MichaelSmith]

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?

Re:This may be slightly off-topic, but

[jpmorgan]

Typically with these searches you know the answer you want, and you're interested in which input gives you that answer (the inverse problem). An important caveat about Grover's algorithm is that, while it's significantly faster than classical unordered search, it's still non-polynomial.

Re:This may be slightly off-topic, but

[FooAtWFU]

You might check it with a classical-computing algorithm. For NP problems, verification of the answer is often substantially faster than computing the answer itself.

Re:This may be slightly off-topic, but

[iris-n]

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.

Re:This may be slightly off-topic, but

[smallfries]

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

Re:Begs the Question

[jpmorgan]

That's a horribly misleading summary. Quantum computation is plagued with error... the same thing occurs in classical scenarios but we have error correction schemes to deal with that (for example, error correcting codes). Analagously there's quantum error correction which lets you recover your quantum information after corruption, however previously it was fairly limited in capability. The new research is a way to improve quantum error correction, so that the original information is recoverable after much more substantial corruption than was possible before.

Take cover!

[SEWilco]

Release the cat jokes!

Oblig. Bad Car Analogy

[PPH]

...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.