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

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

[Pseudonym]

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.

Having said that, the "many universes" model is, according to most quantum mechanics, not an accurate picture. It's better to think of quantum algorithms as being probabilistic algorithms that works with quantum probability theory rather than classical probability theory.